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//===- ScalarEvolution.cpp - Scalar Evolution Analysis --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the scalar evolution analysis
// engine, which is used primarily to analyze expressions involving induction
// variables in loops.
//
// There are several aspects to this library. First is the representation of
// scalar expressions, which are represented as subclasses of the SCEV class.
// These classes are used to represent certain types of subexpressions that we
// can handle. We only create one SCEV of a particular shape, so
// pointer-comparisons for equality are legal.
//
// One important aspect of the SCEV objects is that they are never cyclic, even
// if there is a cycle in the dataflow for an expression (ie, a PHI node). If
// the PHI node is one of the idioms that we can represent (e.g., a polynomial
// recurrence) then we represent it directly as a recurrence node, otherwise we
// represent it as a SCEVUnknown node.
//
// In addition to being able to represent expressions of various types, we also
// have folders that are used to build the *canonical* representation for a
// particular expression. These folders are capable of using a variety of
// rewrite rules to simplify the expressions.
//
// Once the folders are defined, we can implement the more interesting
// higher-level code, such as the code that recognizes PHI nodes of various
// types, computes the execution count of a loop, etc.
//
// TODO: We should use these routines and value representations to implement
// dependence analysis!
//
//===----------------------------------------------------------------------===//
//
// There are several good references for the techniques used in this analysis.
//
// Chains of recurrences -- a method to expedite the evaluation
// of closed-form functions
// Olaf Bachmann, Paul S. Wang, Eugene V. Zima
//
// On computational properties of chains of recurrences
// Eugene V. Zima
//
// Symbolic Evaluation of Chains of Recurrences for Loop Optimization
// Robert A. van Engelen
//
// Efficient Symbolic Analysis for Optimizing Compilers
// Robert A. van Engelen
//
// Using the chains of recurrences algebra for data dependence testing and
// induction variable substitution
// MS Thesis, Johnie Birch
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionPatternMatch.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/Verifier.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/SaveAndRestore.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <map>
#include <memory>
#include <numeric>
#include <optional>
#include <tuple>
#include <utility>
#include <vector>
using namespace llvm;
using namespace PatternMatch;
using namespace SCEVPatternMatch;
#define DEBUG_TYPE "scalar-evolution"
STATISTIC(NumExitCountsComputed,
"Number of loop exits with predictable exit counts");
STATISTIC(NumExitCountsNotComputed,
"Number of loop exits without predictable exit counts");
STATISTIC(NumBruteForceTripCountsComputed,
"Number of loops with trip counts computed by force");
#ifdef EXPENSIVE_CHECKS
bool llvm::VerifySCEV = true;
#else
bool llvm::VerifySCEV = false;
#endif
static cl::opt<unsigned>
MaxBruteForceIterations("scalar-evolution-max-iterations", cl::ReallyHidden,
cl::desc("Maximum number of iterations SCEV will "
"symbolically execute a constant "
"derived loop"),
cl::init(100));
static cl::opt<bool, true> VerifySCEVOpt(
"verify-scev", cl::Hidden, cl::location(VerifySCEV),
cl::desc("Verify ScalarEvolution's backedge taken counts (slow)"));
static cl::opt<bool> VerifySCEVStrict(
"verify-scev-strict", cl::Hidden,
cl::desc("Enable stricter verification with -verify-scev is passed"));
static cl::opt<bool> VerifyIR(
"scev-verify-ir", cl::Hidden,
cl::desc("Verify IR correctness when making sensitive SCEV queries (slow)"),
cl::init(false));
static cl::opt<unsigned> MulOpsInlineThreshold(
"scev-mulops-inline-threshold", cl::Hidden,
cl::desc("Threshold for inlining multiplication operands into a SCEV"),
cl::init(32));
static cl::opt<unsigned> AddOpsInlineThreshold(
"scev-addops-inline-threshold", cl::Hidden,
cl::desc("Threshold for inlining addition operands into a SCEV"),
cl::init(500));
static cl::opt<unsigned> MaxSCEVCompareDepth(
"scalar-evolution-max-scev-compare-depth", cl::Hidden,
cl::desc("Maximum depth of recursive SCEV complexity comparisons"),
cl::init(32));
static cl::opt<unsigned> MaxSCEVOperationsImplicationDepth(
"scalar-evolution-max-scev-operations-implication-depth", cl::Hidden,
cl::desc("Maximum depth of recursive SCEV operations implication analysis"),
cl::init(2));
static cl::opt<unsigned> MaxValueCompareDepth(
"scalar-evolution-max-value-compare-depth", cl::Hidden,
cl::desc("Maximum depth of recursive value complexity comparisons"),
cl::init(2));
static cl::opt<unsigned>
MaxArithDepth("scalar-evolution-max-arith-depth", cl::Hidden,
cl::desc("Maximum depth of recursive arithmetics"),
cl::init(32));
static cl::opt<unsigned> MaxConstantEvolvingDepth(
"scalar-evolution-max-constant-evolving-depth", cl::Hidden,
cl::desc("Maximum depth of recursive constant evolving"), cl::init(32));
static cl::opt<unsigned>
MaxCastDepth("scalar-evolution-max-cast-depth", cl::Hidden,
cl::desc("Maximum depth of recursive SExt/ZExt/Trunc"),
cl::init(8));
static cl::opt<unsigned>
MaxAddRecSize("scalar-evolution-max-add-rec-size", cl::Hidden,
cl::desc("Max coefficients in AddRec during evolving"),
cl::init(8));
static cl::opt<unsigned>
HugeExprThreshold("scalar-evolution-huge-expr-threshold", cl::Hidden,
cl::desc("Size of the expression which is considered huge"),
cl::init(4096));
static cl::opt<unsigned> RangeIterThreshold(
"scev-range-iter-threshold", cl::Hidden,
cl::desc("Threshold for switching to iteratively computing SCEV ranges"),
cl::init(32));
static cl::opt<unsigned> MaxLoopGuardCollectionDepth(
"scalar-evolution-max-loop-guard-collection-depth", cl::Hidden,
cl::desc("Maximum depth for recursive loop guard collection"), cl::init(1));
static cl::opt<bool>
ClassifyExpressions("scalar-evolution-classify-expressions",
cl::Hidden, cl::init(true),
cl::desc("When printing analysis, include information on every instruction"));
static cl::opt<bool> UseExpensiveRangeSharpening(
"scalar-evolution-use-expensive-range-sharpening", cl::Hidden,
cl::init(false),
cl::desc("Use more powerful methods of sharpening expression ranges. May "
"be costly in terms of compile time"));
static cl::opt<unsigned> MaxPhiSCCAnalysisSize(
"scalar-evolution-max-scc-analysis-depth", cl::Hidden,
cl::desc("Maximum amount of nodes to process while searching SCEVUnknown "
"Phi strongly connected components"),
cl::init(8));
static cl::opt<bool>
EnableFiniteLoopControl("scalar-evolution-finite-loop", cl::Hidden,
cl::desc("Handle <= and >= in finite loops"),
cl::init(true));
static cl::opt<bool> UseContextForNoWrapFlagInference(
"scalar-evolution-use-context-for-no-wrap-flag-strenghening", cl::Hidden,
cl::desc("Infer nuw/nsw flags using context where suitable"),
cl::init(true));
//===----------------------------------------------------------------------===//
// SCEV class definitions
//===----------------------------------------------------------------------===//
//===----------------------------------------------------------------------===//
// Implementation of the SCEV class.
//
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void SCEV::dump() const {
print(dbgs());
dbgs() << '\n';
}
#endif
void SCEV::print(raw_ostream &OS) const {
switch (getSCEVType()) {
case scConstant:
cast<SCEVConstant>(this)->getValue()->printAsOperand(OS, false);
return;
case scVScale:
OS << "vscale";
return;
case scPtrToInt: {
const SCEVPtrToIntExpr *PtrToInt = cast<SCEVPtrToIntExpr>(this);
const SCEV *Op = PtrToInt->getOperand();
OS << "(ptrtoint " << *Op->getType() << " " << *Op << " to "
<< *PtrToInt->getType() << ")";
return;
}
case scTruncate: {
const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(this);
const SCEV *Op = Trunc->getOperand();
OS << "(trunc " << *Op->getType() << " " << *Op << " to "
<< *Trunc->getType() << ")";
return;
}
case scZeroExtend: {
const SCEVZeroExtendExpr *ZExt = cast<SCEVZeroExtendExpr>(this);
const SCEV *Op = ZExt->getOperand();
OS << "(zext " << *Op->getType() << " " << *Op << " to "
<< *ZExt->getType() << ")";
return;
}
case scSignExtend: {
const SCEVSignExtendExpr *SExt = cast<SCEVSignExtendExpr>(this);
const SCEV *Op = SExt->getOperand();
OS << "(sext " << *Op->getType() << " " << *Op << " to "
<< *SExt->getType() << ")";
return;
}
case scAddRecExpr: {
const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(this);
OS << "{" << *AR->getOperand(0);
for (unsigned i = 1, e = AR->getNumOperands(); i != e; ++i)
OS << ",+," << *AR->getOperand(i);
OS << "}<";
if (AR->hasNoUnsignedWrap())
OS << "nuw><";
if (AR->hasNoSignedWrap())
OS << "nsw><";
if (AR->hasNoSelfWrap() &&
!AR->getNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW)))
OS << "nw><";
AR->getLoop()->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ">";
return;
}
case scAddExpr:
case scMulExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr: {
const SCEVNAryExpr *NAry = cast<SCEVNAryExpr>(this);
const char *OpStr = nullptr;
switch (NAry->getSCEVType()) {
case scAddExpr: OpStr = " + "; break;
case scMulExpr: OpStr = " * "; break;
case scUMaxExpr: OpStr = " umax "; break;
case scSMaxExpr: OpStr = " smax "; break;
case scUMinExpr:
OpStr = " umin ";
break;
case scSMinExpr:
OpStr = " smin ";
break;
case scSequentialUMinExpr:
OpStr = " umin_seq ";
break;
default:
llvm_unreachable("There are no other nary expression types.");
}
OS << "(";
ListSeparator LS(OpStr);
for (const SCEV *Op : NAry->operands())
OS << LS << *Op;
OS << ")";
switch (NAry->getSCEVType()) {
case scAddExpr:
case scMulExpr:
if (NAry->hasNoUnsignedWrap())
OS << "<nuw>";
if (NAry->hasNoSignedWrap())
OS << "<nsw>";
break;
default:
// Nothing to print for other nary expressions.
break;
}
return;
}
case scUDivExpr: {
const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(this);
OS << "(" << *UDiv->getLHS() << " /u " << *UDiv->getRHS() << ")";
return;
}
case scUnknown:
cast<SCEVUnknown>(this)->getValue()->printAsOperand(OS, false);
return;
case scCouldNotCompute:
OS << "***COULDNOTCOMPUTE***";
return;
}
llvm_unreachable("Unknown SCEV kind!");
}
Type *SCEV::getType() const {
switch (getSCEVType()) {
case scConstant:
return cast<SCEVConstant>(this)->getType();
case scVScale:
return cast<SCEVVScale>(this)->getType();
case scPtrToInt:
case scTruncate:
case scZeroExtend:
case scSignExtend:
return cast<SCEVCastExpr>(this)->getType();
case scAddRecExpr:
return cast<SCEVAddRecExpr>(this)->getType();
case scMulExpr:
return cast<SCEVMulExpr>(this)->getType();
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
return cast<SCEVMinMaxExpr>(this)->getType();
case scSequentialUMinExpr:
return cast<SCEVSequentialMinMaxExpr>(this)->getType();
case scAddExpr:
return cast<SCEVAddExpr>(this)->getType();
case scUDivExpr:
return cast<SCEVUDivExpr>(this)->getType();
case scUnknown:
return cast<SCEVUnknown>(this)->getType();
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
ArrayRef<const SCEV *> SCEV::operands() const {
switch (getSCEVType()) {
case scConstant:
case scVScale:
case scUnknown:
return {};
case scPtrToInt:
case scTruncate:
case scZeroExtend:
case scSignExtend:
return cast<SCEVCastExpr>(this)->operands();
case scAddRecExpr:
case scAddExpr:
case scMulExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr:
return cast<SCEVNAryExpr>(this)->operands();
case scUDivExpr:
return cast<SCEVUDivExpr>(this)->operands();
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
bool SCEV::isZero() const { return match(this, m_scev_Zero()); }
bool SCEV::isOne() const { return match(this, m_scev_One()); }
bool SCEV::isAllOnesValue() const { return match(this, m_scev_AllOnes()); }
bool SCEV::isNonConstantNegative() const {
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(this);
if (!Mul) return false;
// If there is a constant factor, it will be first.
const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
if (!SC) return false;
// Return true if the value is negative, this matches things like (-42 * V).
return SC->getAPInt().isNegative();
}
SCEVCouldNotCompute::SCEVCouldNotCompute() :
SCEV(FoldingSetNodeIDRef(), scCouldNotCompute, 0) {}
bool SCEVCouldNotCompute::classof(const SCEV *S) {
return S->getSCEVType() == scCouldNotCompute;
}
const SCEV *ScalarEvolution::getConstant(ConstantInt *V) {
FoldingSetNodeID ID;
ID.AddInteger(scConstant);
ID.AddPointer(V);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
SCEV *S = new (SCEVAllocator) SCEVConstant(ID.Intern(SCEVAllocator), V);
UniqueSCEVs.InsertNode(S, IP);
return S;
}
const SCEV *ScalarEvolution::getConstant(const APInt &Val) {
return getConstant(ConstantInt::get(getContext(), Val));
}
const SCEV *
ScalarEvolution::getConstant(Type *Ty, uint64_t V, bool isSigned) {
IntegerType *ITy = cast<IntegerType>(getEffectiveSCEVType(Ty));
return getConstant(ConstantInt::get(ITy, V, isSigned));
}
const SCEV *ScalarEvolution::getVScale(Type *Ty) {
FoldingSetNodeID ID;
ID.AddInteger(scVScale);
ID.AddPointer(Ty);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
return S;
SCEV *S = new (SCEVAllocator) SCEVVScale(ID.Intern(SCEVAllocator), Ty);
UniqueSCEVs.InsertNode(S, IP);
return S;
}
const SCEV *ScalarEvolution::getElementCount(Type *Ty, ElementCount EC) {
const SCEV *Res = getConstant(Ty, EC.getKnownMinValue());
if (EC.isScalable())
Res = getMulExpr(Res, getVScale(Ty));
return Res;
}
SCEVCastExpr::SCEVCastExpr(const FoldingSetNodeIDRef ID, SCEVTypes SCEVTy,
const SCEV *op, Type *ty)
: SCEV(ID, SCEVTy, computeExpressionSize(op)), Op(op), Ty(ty) {}
SCEVPtrToIntExpr::SCEVPtrToIntExpr(const FoldingSetNodeIDRef ID, const SCEV *Op,
Type *ITy)
: SCEVCastExpr(ID, scPtrToInt, Op, ITy) {
assert(getOperand()->getType()->isPointerTy() && Ty->isIntegerTy() &&
"Must be a non-bit-width-changing pointer-to-integer cast!");
}
SCEVIntegralCastExpr::SCEVIntegralCastExpr(const FoldingSetNodeIDRef ID,
SCEVTypes SCEVTy, const SCEV *op,
Type *ty)
: SCEVCastExpr(ID, SCEVTy, op, ty) {}
SCEVTruncateExpr::SCEVTruncateExpr(const FoldingSetNodeIDRef ID, const SCEV *op,
Type *ty)
: SCEVIntegralCastExpr(ID, scTruncate, op, ty) {
assert(getOperand()->getType()->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot truncate non-integer value!");
}
SCEVZeroExtendExpr::SCEVZeroExtendExpr(const FoldingSetNodeIDRef ID,
const SCEV *op, Type *ty)
: SCEVIntegralCastExpr(ID, scZeroExtend, op, ty) {
assert(getOperand()->getType()->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot zero extend non-integer value!");
}
SCEVSignExtendExpr::SCEVSignExtendExpr(const FoldingSetNodeIDRef ID,
const SCEV *op, Type *ty)
: SCEVIntegralCastExpr(ID, scSignExtend, op, ty) {
assert(getOperand()->getType()->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot sign extend non-integer value!");
}
void SCEVUnknown::deleted() {
// Clear this SCEVUnknown from various maps.
SE->forgetMemoizedResults(this);
// Remove this SCEVUnknown from the uniquing map.
SE->UniqueSCEVs.RemoveNode(this);
// Release the value.
setValPtr(nullptr);
}
void SCEVUnknown::allUsesReplacedWith(Value *New) {
// Clear this SCEVUnknown from various maps.
SE->forgetMemoizedResults(this);
// Remove this SCEVUnknown from the uniquing map.
SE->UniqueSCEVs.RemoveNode(this);
// Replace the value pointer in case someone is still using this SCEVUnknown.
setValPtr(New);
}
//===----------------------------------------------------------------------===//
// SCEV Utilities
//===----------------------------------------------------------------------===//
/// Compare the two values \p LV and \p RV in terms of their "complexity" where
/// "complexity" is a partial (and somewhat ad-hoc) relation used to order
/// operands in SCEV expressions.
static int CompareValueComplexity(const LoopInfo *const LI, Value *LV,
Value *RV, unsigned Depth) {
if (Depth > MaxValueCompareDepth)
return 0;
// Order pointer values after integer values. This helps SCEVExpander form
// GEPs.
bool LIsPointer = LV->getType()->isPointerTy(),
RIsPointer = RV->getType()->isPointerTy();
if (LIsPointer != RIsPointer)
return (int)LIsPointer - (int)RIsPointer;
// Compare getValueID values.
unsigned LID = LV->getValueID(), RID = RV->getValueID();
if (LID != RID)
return (int)LID - (int)RID;
// Sort arguments by their position.
if (const auto *LA = dyn_cast<Argument>(LV)) {
const auto *RA = cast<Argument>(RV);
unsigned LArgNo = LA->getArgNo(), RArgNo = RA->getArgNo();
return (int)LArgNo - (int)RArgNo;
}
if (const auto *LGV = dyn_cast<GlobalValue>(LV)) {
const auto *RGV = cast<GlobalValue>(RV);
const auto IsGVNameSemantic = [&](const GlobalValue *GV) {
auto LT = GV->getLinkage();
return !(GlobalValue::isPrivateLinkage(LT) ||
GlobalValue::isInternalLinkage(LT));
};
// Use the names to distinguish the two values, but only if the
// names are semantically important.
if (IsGVNameSemantic(LGV) && IsGVNameSemantic(RGV))
return LGV->getName().compare(RGV->getName());
}
// For instructions, compare their loop depth, and their operand count. This
// is pretty loose.
if (const auto *LInst = dyn_cast<Instruction>(LV)) {
const auto *RInst = cast<Instruction>(RV);
// Compare loop depths.
const BasicBlock *LParent = LInst->getParent(),
*RParent = RInst->getParent();
if (LParent != RParent) {
unsigned LDepth = LI->getLoopDepth(LParent),
RDepth = LI->getLoopDepth(RParent);
if (LDepth != RDepth)
return (int)LDepth - (int)RDepth;
}
// Compare the number of operands.
unsigned LNumOps = LInst->getNumOperands(),
RNumOps = RInst->getNumOperands();
if (LNumOps != RNumOps)
return (int)LNumOps - (int)RNumOps;
for (unsigned Idx : seq(LNumOps)) {
int Result = CompareValueComplexity(LI, LInst->getOperand(Idx),
RInst->getOperand(Idx), Depth + 1);
if (Result != 0)
return Result;
}
}
return 0;
}
// Return negative, zero, or positive, if LHS is less than, equal to, or greater
// than RHS, respectively. A three-way result allows recursive comparisons to be
// more efficient.
// If the max analysis depth was reached, return std::nullopt, assuming we do
// not know if they are equivalent for sure.
static std::optional<int>
CompareSCEVComplexity(const LoopInfo *const LI, const SCEV *LHS,
const SCEV *RHS, DominatorTree &DT, unsigned Depth = 0) {
// Fast-path: SCEVs are uniqued so we can do a quick equality check.
if (LHS == RHS)
return 0;
// Primarily, sort the SCEVs by their getSCEVType().
SCEVTypes LType = LHS->getSCEVType(), RType = RHS->getSCEVType();
if (LType != RType)
return (int)LType - (int)RType;
if (Depth > MaxSCEVCompareDepth)
return std::nullopt;
// Aside from the getSCEVType() ordering, the particular ordering
// isn't very important except that it's beneficial to be consistent,
// so that (a + b) and (b + a) don't end up as different expressions.
switch (LType) {
case scUnknown: {
const SCEVUnknown *LU = cast<SCEVUnknown>(LHS);
const SCEVUnknown *RU = cast<SCEVUnknown>(RHS);
int X =
CompareValueComplexity(LI, LU->getValue(), RU->getValue(), Depth + 1);
return X;
}
case scConstant: {
const SCEVConstant *LC = cast<SCEVConstant>(LHS);
const SCEVConstant *RC = cast<SCEVConstant>(RHS);
// Compare constant values.
const APInt &LA = LC->getAPInt();
const APInt &RA = RC->getAPInt();
unsigned LBitWidth = LA.getBitWidth(), RBitWidth = RA.getBitWidth();
if (LBitWidth != RBitWidth)
return (int)LBitWidth - (int)RBitWidth;
return LA.ult(RA) ? -1 : 1;
}
case scVScale: {
const auto *LTy = cast<IntegerType>(cast<SCEVVScale>(LHS)->getType());
const auto *RTy = cast<IntegerType>(cast<SCEVVScale>(RHS)->getType());
return LTy->getBitWidth() - RTy->getBitWidth();
}
case scAddRecExpr: {
const SCEVAddRecExpr *LA = cast<SCEVAddRecExpr>(LHS);
const SCEVAddRecExpr *RA = cast<SCEVAddRecExpr>(RHS);
// There is always a dominance between two recs that are used by one SCEV,
// so we can safely sort recs by loop header dominance. We require such
// order in getAddExpr.
const Loop *LLoop = LA->getLoop(), *RLoop = RA->getLoop();
if (LLoop != RLoop) {
const BasicBlock *LHead = LLoop->getHeader(), *RHead = RLoop->getHeader();
assert(LHead != RHead && "Two loops share the same header?");
if (DT.dominates(LHead, RHead))
return 1;
assert(DT.dominates(RHead, LHead) &&
"No dominance between recurrences used by one SCEV?");
return -1;
}
[[fallthrough]];
}
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scSMaxExpr:
case scUMaxExpr:
case scSMinExpr:
case scUMinExpr:
case scSequentialUMinExpr: {
ArrayRef<const SCEV *> LOps = LHS->operands();
ArrayRef<const SCEV *> ROps = RHS->operands();
// Lexicographically compare n-ary-like expressions.
unsigned LNumOps = LOps.size(), RNumOps = ROps.size();
if (LNumOps != RNumOps)
return (int)LNumOps - (int)RNumOps;
for (unsigned i = 0; i != LNumOps; ++i) {
auto X = CompareSCEVComplexity(LI, LOps[i], ROps[i], DT, Depth + 1);
if (X != 0)
return X;
}
return 0;
}
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
/// Given a list of SCEV objects, order them by their complexity, and group
/// objects of the same complexity together by value. When this routine is
/// finished, we know that any duplicates in the vector are consecutive and that
/// complexity is monotonically increasing.
///
/// Note that we go take special precautions to ensure that we get deterministic
/// results from this routine. In other words, we don't want the results of
/// this to depend on where the addresses of various SCEV objects happened to
/// land in memory.
static void GroupByComplexity(SmallVectorImpl<const SCEV *> &Ops,
LoopInfo *LI, DominatorTree &DT) {
if (Ops.size() < 2) return; // Noop
// Whether LHS has provably less complexity than RHS.
auto IsLessComplex = [&](const SCEV *LHS, const SCEV *RHS) {
auto Complexity = CompareSCEVComplexity(LI, LHS, RHS, DT);
return Complexity && *Complexity < 0;
};
if (Ops.size() == 2) {
// This is the common case, which also happens to be trivially simple.
// Special case it.
const SCEV *&LHS = Ops[0], *&RHS = Ops[1];
if (IsLessComplex(RHS, LHS))
std::swap(LHS, RHS);
return;
}
// Do the rough sort by complexity.
llvm::stable_sort(Ops, [&](const SCEV *LHS, const SCEV *RHS) {
return IsLessComplex(LHS, RHS);
});
// Now that we are sorted by complexity, group elements of the same
// complexity. Note that this is, at worst, N^2, but the vector is likely to
// be extremely short in practice. Note that we take this approach because we
// do not want to depend on the addresses of the objects we are grouping.
for (unsigned i = 0, e = Ops.size(); i != e-2; ++i) {
const SCEV *S = Ops[i];
unsigned Complexity = S->getSCEVType();
// If there are any objects of the same complexity and same value as this
// one, group them.
for (unsigned j = i+1; j != e && Ops[j]->getSCEVType() == Complexity; ++j) {
if (Ops[j] == S) { // Found a duplicate.
// Move it to immediately after i'th element.
std::swap(Ops[i+1], Ops[j]);
++i; // no need to rescan it.
if (i == e-2) return; // Done!
}
}
}
}
/// Returns true if \p Ops contains a huge SCEV (the subtree of S contains at
/// least HugeExprThreshold nodes).
static bool hasHugeExpression(ArrayRef<const SCEV *> Ops) {
return any_of(Ops, [](const SCEV *S) {
return S->getExpressionSize() >= HugeExprThreshold;
});
}
/// Performs a number of common optimizations on the passed \p Ops. If the
/// whole expression reduces down to a single operand, it will be returned.
///
/// The following optimizations are performed:
/// * Fold constants using the \p Fold function.
/// * Remove identity constants satisfying \p IsIdentity.
/// * If a constant satisfies \p IsAbsorber, return it.
/// * Sort operands by complexity.
template <typename FoldT, typename IsIdentityT, typename IsAbsorberT>
static const SCEV *
constantFoldAndGroupOps(ScalarEvolution &SE, LoopInfo &LI, DominatorTree &DT,
SmallVectorImpl<const SCEV *> &Ops, FoldT Fold,
IsIdentityT IsIdentity, IsAbsorberT IsAbsorber) {
const SCEVConstant *Folded = nullptr;
for (unsigned Idx = 0; Idx < Ops.size();) {
const SCEV *Op = Ops[Idx];
if (const auto *C = dyn_cast<SCEVConstant>(Op)) {
if (!Folded)
Folded = C;
else
Folded = cast<SCEVConstant>(
SE.getConstant(Fold(Folded->getAPInt(), C->getAPInt())));
Ops.erase(Ops.begin() + Idx);
continue;
}
++Idx;
}
if (Ops.empty()) {
assert(Folded && "Must have folded value");
return Folded;
}
if (Folded && IsAbsorber(Folded->getAPInt()))
return Folded;
GroupByComplexity(Ops, &LI, DT);
if (Folded && !IsIdentity(Folded->getAPInt()))
Ops.insert(Ops.begin(), Folded);
return Ops.size() == 1 ? Ops[0] : nullptr;
}
//===----------------------------------------------------------------------===//
// Simple SCEV method implementations
//===----------------------------------------------------------------------===//
/// Compute BC(It, K). The result has width W. Assume, K > 0.
static const SCEV *BinomialCoefficient(const SCEV *It, unsigned K,
ScalarEvolution &SE,
Type *ResultTy) {
// Handle the simplest case efficiently.
if (K == 1)
return SE.getTruncateOrZeroExtend(It, ResultTy);
// We are using the following formula for BC(It, K):
//
// BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / K!
//
// Suppose, W is the bitwidth of the return value. We must be prepared for
// overflow. Hence, we must assure that the result of our computation is
// equal to the accurate one modulo 2^W. Unfortunately, division isn't
// safe in modular arithmetic.
//
// However, this code doesn't use exactly that formula; the formula it uses
// is something like the following, where T is the number of factors of 2 in
// K! (i.e. trailing zeros in the binary representation of K!), and ^ is
// exponentiation:
//
// BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / 2^T / (K! / 2^T)
//
// This formula is trivially equivalent to the previous formula. However,
// this formula can be implemented much more efficiently. The trick is that
// K! / 2^T is odd, and exact division by an odd number *is* safe in modular
// arithmetic. To do exact division in modular arithmetic, all we have
// to do is multiply by the inverse. Therefore, this step can be done at
// width W.
//
// The next issue is how to safely do the division by 2^T. The way this
// is done is by doing the multiplication step at a width of at least W + T
// bits. This way, the bottom W+T bits of the product are accurate. Then,
// when we perform the division by 2^T (which is equivalent to a right shift
// by T), the bottom W bits are accurate. Extra bits are okay; they'll get
// truncated out after the division by 2^T.
//
// In comparison to just directly using the first formula, this technique
// is much more efficient; using the first formula requires W * K bits,
// but this formula less than W + K bits. Also, the first formula requires
// a division step, whereas this formula only requires multiplies and shifts.
//
// It doesn't matter whether the subtraction step is done in the calculation
// width or the input iteration count's width; if the subtraction overflows,
// the result must be zero anyway. We prefer here to do it in the width of
// the induction variable because it helps a lot for certain cases; CodeGen
// isn't smart enough to ignore the overflow, which leads to much less
// efficient code if the width of the subtraction is wider than the native
// register width.
//
// (It's possible to not widen at all by pulling out factors of 2 before
// the multiplication; for example, K=2 can be calculated as
// It/2*(It+(It*INT_MIN/INT_MIN)+-1). However, it requires
// extra arithmetic, so it's not an obvious win, and it gets
// much more complicated for K > 3.)
// Protection from insane SCEVs; this bound is conservative,
// but it probably doesn't matter.
if (K > 1000)
return SE.getCouldNotCompute();
unsigned W = SE.getTypeSizeInBits(ResultTy);
// Calculate K! / 2^T and T; we divide out the factors of two before
// multiplying for calculating K! / 2^T to avoid overflow.
// Other overflow doesn't matter because we only care about the bottom
// W bits of the result.
APInt OddFactorial(W, 1);
unsigned T = 1;
for (unsigned i = 3; i <= K; ++i) {
unsigned TwoFactors = countr_zero(i);
T += TwoFactors;
OddFactorial *= (i >> TwoFactors);
}
// We need at least W + T bits for the multiplication step
unsigned CalculationBits = W + T;
// Calculate 2^T, at width T+W.
APInt DivFactor = APInt::getOneBitSet(CalculationBits, T);
// Calculate the multiplicative inverse of K! / 2^T;
// this multiplication factor will perform the exact division by
// K! / 2^T.
APInt MultiplyFactor = OddFactorial.multiplicativeInverse();
// Calculate the product, at width T+W
IntegerType *CalculationTy = IntegerType::get(SE.getContext(),
CalculationBits);
const SCEV *Dividend = SE.getTruncateOrZeroExtend(It, CalculationTy);
for (unsigned i = 1; i != K; ++i) {
const SCEV *S = SE.getMinusSCEV(It, SE.getConstant(It->getType(), i));
Dividend = SE.getMulExpr(Dividend,
SE.getTruncateOrZeroExtend(S, CalculationTy));
}
// Divide by 2^T
const SCEV *DivResult = SE.getUDivExpr(Dividend, SE.getConstant(DivFactor));
// Truncate the result, and divide by K! / 2^T.
return SE.getMulExpr(SE.getConstant(MultiplyFactor),
SE.getTruncateOrZeroExtend(DivResult, ResultTy));
}
/// Return the value of this chain of recurrences at the specified iteration
/// number. We can evaluate this recurrence by multiplying each element in the
/// chain by the binomial coefficient corresponding to it. In other words, we
/// can evaluate {A,+,B,+,C,+,D} as:
///
/// A*BC(It, 0) + B*BC(It, 1) + C*BC(It, 2) + D*BC(It, 3)
///
/// where BC(It, k) stands for binomial coefficient.
const SCEV *SCEVAddRecExpr::evaluateAtIteration(const SCEV *It,
ScalarEvolution &SE) const {
return evaluateAtIteration(operands(), It, SE);
}
const SCEV *
SCEVAddRecExpr::evaluateAtIteration(ArrayRef<const SCEV *> Operands,
const SCEV *It, ScalarEvolution &SE) {
assert(Operands.size() > 0);
const SCEV *Result = Operands[0];
for (unsigned i = 1, e = Operands.size(); i != e; ++i) {
// The computation is correct in the face of overflow provided that the
// multiplication is performed _after_ the evaluation of the binomial
// coefficient.
const SCEV *Coeff = BinomialCoefficient(It, i, SE, Result->getType());
if (isa<SCEVCouldNotCompute>(Coeff))
return Coeff;
Result = SE.getAddExpr(Result, SE.getMulExpr(Operands[i], Coeff));
}
return Result;
}
//===----------------------------------------------------------------------===//
// SCEV Expression folder implementations
//===----------------------------------------------------------------------===//
const SCEV *ScalarEvolution::getLosslessPtrToIntExpr(const SCEV *Op,
unsigned Depth) {
assert(Depth <= 1 &&
"getLosslessPtrToIntExpr() should self-recurse at most once.");
// We could be called with an integer-typed operands during SCEV rewrites.
// Since the operand is an integer already, just perform zext/trunc/self cast.
if (!Op->getType()->isPointerTy())
return Op;
// What would be an ID for such a SCEV cast expression?
FoldingSetNodeID ID;
ID.AddInteger(scPtrToInt);
ID.AddPointer(Op);
void *IP = nullptr;
// Is there already an expression for such a cast?
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
return S;
// It isn't legal for optimizations to construct new ptrtoint expressions
// for non-integral pointers.
if (getDataLayout().isNonIntegralPointerType(Op->getType()))
return getCouldNotCompute();
Type *IntPtrTy = getDataLayout().getIntPtrType(Op->getType());
// We can only trivially model ptrtoint if SCEV's effective (integer) type
// is sufficiently wide to represent all possible pointer values.
// We could theoretically teach SCEV to truncate wider pointers, but
// that isn't implemented for now.
if (getDataLayout().getTypeSizeInBits(getEffectiveSCEVType(Op->getType())) !=
getDataLayout().getTypeSizeInBits(IntPtrTy))
return getCouldNotCompute();
// If not, is this expression something we can't reduce any further?
if (auto *U = dyn_cast<SCEVUnknown>(Op)) {
// Perform some basic constant folding. If the operand of the ptr2int cast
// is a null pointer, don't create a ptr2int SCEV expression (that will be
// left as-is), but produce a zero constant.
// NOTE: We could handle a more general case, but lack motivational cases.
if (isa<ConstantPointerNull>(U->getValue()))
return getZero(IntPtrTy);
// Create an explicit cast node.
// We can reuse the existing insert position since if we get here,
// we won't have made any changes which would invalidate it.
SCEV *S = new (SCEVAllocator)
SCEVPtrToIntExpr(ID.Intern(SCEVAllocator), Op, IntPtrTy);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
assert(Depth == 0 && "getLosslessPtrToIntExpr() should not self-recurse for "
"non-SCEVUnknown's.");
// Otherwise, we've got some expression that is more complex than just a
// single SCEVUnknown. But we don't want to have a SCEVPtrToIntExpr of an
// arbitrary expression, we want to have SCEVPtrToIntExpr of an SCEVUnknown
// only, and the expressions must otherwise be integer-typed.
// So sink the cast down to the SCEVUnknown's.
/// The SCEVPtrToIntSinkingRewriter takes a scalar evolution expression,
/// which computes a pointer-typed value, and rewrites the whole expression
/// tree so that *all* the computations are done on integers, and the only
/// pointer-typed operands in the expression are SCEVUnknown.
class SCEVPtrToIntSinkingRewriter
: public SCEVRewriteVisitor<SCEVPtrToIntSinkingRewriter> {
using Base = SCEVRewriteVisitor<SCEVPtrToIntSinkingRewriter>;
public:
SCEVPtrToIntSinkingRewriter(ScalarEvolution &SE) : SCEVRewriteVisitor(SE) {}
static const SCEV *rewrite(const SCEV *Scev, ScalarEvolution &SE) {
SCEVPtrToIntSinkingRewriter Rewriter(SE);
return Rewriter.visit(Scev);
}
const SCEV *visit(const SCEV *S) {
Type *STy = S->getType();
// If the expression is not pointer-typed, just keep it as-is.
if (!STy->isPointerTy())
return S;
// Else, recursively sink the cast down into it.
return Base::visit(S);
}
const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
SmallVector<const SCEV *, 2> Operands;
bool Changed = false;
for (const auto *Op : Expr->operands()) {
Operands.push_back(visit(Op));
Changed |= Op != Operands.back();
}
return !Changed ? Expr : SE.getAddExpr(Operands, Expr->getNoWrapFlags());
}
const SCEV *visitMulExpr(const SCEVMulExpr *Expr) {
SmallVector<const SCEV *, 2> Operands;
bool Changed = false;
for (const auto *Op : Expr->operands()) {
Operands.push_back(visit(Op));
Changed |= Op != Operands.back();
}
return !Changed ? Expr : SE.getMulExpr(Operands, Expr->getNoWrapFlags());
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
assert(Expr->getType()->isPointerTy() &&
"Should only reach pointer-typed SCEVUnknown's.");
return SE.getLosslessPtrToIntExpr(Expr, /*Depth=*/1);
}
};
// And actually perform the cast sinking.
const SCEV *IntOp = SCEVPtrToIntSinkingRewriter::rewrite(Op, *this);
assert(IntOp->getType()->isIntegerTy() &&
"We must have succeeded in sinking the cast, "
"and ending up with an integer-typed expression!");
return IntOp;
}
const SCEV *ScalarEvolution::getPtrToIntExpr(const SCEV *Op, Type *Ty) {
assert(Ty->isIntegerTy() && "Target type must be an integer type!");
const SCEV *IntOp = getLosslessPtrToIntExpr(Op);
if (isa<SCEVCouldNotCompute>(IntOp))
return IntOp;
return getTruncateOrZeroExtend(IntOp, Ty);
}
const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op, Type *Ty,
unsigned Depth) {
assert(getTypeSizeInBits(Op->getType()) > getTypeSizeInBits(Ty) &&
"This is not a truncating conversion!");
assert(isSCEVable(Ty) &&
"This is not a conversion to a SCEVable type!");
assert(!Op->getType()->isPointerTy() && "Can't truncate pointer!");
Ty = getEffectiveSCEVType(Ty);
FoldingSetNodeID ID;
ID.AddInteger(scTruncate);
ID.AddPointer(Op);
ID.AddPointer(Ty);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
// Fold if the operand is constant.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
return getConstant(
cast<ConstantInt>(ConstantExpr::getTrunc(SC->getValue(), Ty)));
// trunc(trunc(x)) --> trunc(x)
if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op))
return getTruncateExpr(ST->getOperand(), Ty, Depth + 1);
// trunc(sext(x)) --> sext(x) if widening or trunc(x) if narrowing
if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op))
return getTruncateOrSignExtend(SS->getOperand(), Ty, Depth + 1);
// trunc(zext(x)) --> zext(x) if widening or trunc(x) if narrowing
if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
return getTruncateOrZeroExtend(SZ->getOperand(), Ty, Depth + 1);
if (Depth > MaxCastDepth) {
SCEV *S =
new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator), Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
// trunc(x1 + ... + xN) --> trunc(x1) + ... + trunc(xN) and
// trunc(x1 * ... * xN) --> trunc(x1) * ... * trunc(xN),
// if after transforming we have at most one truncate, not counting truncates
// that replace other casts.
if (isa<SCEVAddExpr>(Op) || isa<SCEVMulExpr>(Op)) {
auto *CommOp = cast<SCEVCommutativeExpr>(Op);
SmallVector<const SCEV *, 4> Operands;
unsigned numTruncs = 0;
for (unsigned i = 0, e = CommOp->getNumOperands(); i != e && numTruncs < 2;
++i) {
const SCEV *S = getTruncateExpr(CommOp->getOperand(i), Ty, Depth + 1);
if (!isa<SCEVIntegralCastExpr>(CommOp->getOperand(i)) &&
isa<SCEVTruncateExpr>(S))
numTruncs++;
Operands.push_back(S);
}
if (numTruncs < 2) {
if (isa<SCEVAddExpr>(Op))
return getAddExpr(Operands);
if (isa<SCEVMulExpr>(Op))
return getMulExpr(Operands);
llvm_unreachable("Unexpected SCEV type for Op.");
}
// Although we checked in the beginning that ID is not in the cache, it is
// possible that during recursion and different modification ID was inserted
// into the cache. So if we find it, just return it.
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
return S;
}
// If the input value is a chrec scev, truncate the chrec's operands.
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Op)) {
SmallVector<const SCEV *, 4> Operands;
for (const SCEV *Op : AddRec->operands())
Operands.push_back(getTruncateExpr(Op, Ty, Depth + 1));
return getAddRecExpr(Operands, AddRec->getLoop(), SCEV::FlagAnyWrap);
}
// Return zero if truncating to known zeros.
uint32_t MinTrailingZeros = getMinTrailingZeros(Op);
if (MinTrailingZeros >= getTypeSizeInBits(Ty))
return getZero(Ty);
// The cast wasn't folded; create an explicit cast node. We can reuse
// the existing insert position since if we get here, we won't have
// made any changes which would invalidate it.
SCEV *S = new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator),
Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
// Get the limit of a recurrence such that incrementing by Step cannot cause
// signed overflow as long as the value of the recurrence within the
// loop does not exceed this limit before incrementing.
static const SCEV *getSignedOverflowLimitForStep(const SCEV *Step,
ICmpInst::Predicate *Pred,
ScalarEvolution *SE) {
unsigned BitWidth = SE->getTypeSizeInBits(Step->getType());
if (SE->isKnownPositive(Step)) {
*Pred = ICmpInst::ICMP_SLT;
return SE->getConstant(APInt::getSignedMinValue(BitWidth) -
SE->getSignedRangeMax(Step));
}
if (SE->isKnownNegative(Step)) {
*Pred = ICmpInst::ICMP_SGT;
return SE->getConstant(APInt::getSignedMaxValue(BitWidth) -
SE->getSignedRangeMin(Step));
}
return nullptr;
}
// Get the limit of a recurrence such that incrementing by Step cannot cause
// unsigned overflow as long as the value of the recurrence within the loop does
// not exceed this limit before incrementing.
static const SCEV *getUnsignedOverflowLimitForStep(const SCEV *Step,
ICmpInst::Predicate *Pred,
ScalarEvolution *SE) {
unsigned BitWidth = SE->getTypeSizeInBits(Step->getType());
*Pred = ICmpInst::ICMP_ULT;
return SE->getConstant(APInt::getMinValue(BitWidth) -
SE->getUnsignedRangeMax(Step));
}
namespace {
struct ExtendOpTraitsBase {
typedef const SCEV *(ScalarEvolution::*GetExtendExprTy)(const SCEV *, Type *,
unsigned);
};
// Used to make code generic over signed and unsigned overflow.
template <typename ExtendOp> struct ExtendOpTraits {
// Members present:
//
// static const SCEV::NoWrapFlags WrapType;
//
// static const ExtendOpTraitsBase::GetExtendExprTy GetExtendExpr;
//
// static const SCEV *getOverflowLimitForStep(const SCEV *Step,
// ICmpInst::Predicate *Pred,
// ScalarEvolution *SE);
};
template <>
struct ExtendOpTraits<SCEVSignExtendExpr> : public ExtendOpTraitsBase {
static const SCEV::NoWrapFlags WrapType = SCEV::FlagNSW;
static const GetExtendExprTy GetExtendExpr;
static const SCEV *getOverflowLimitForStep(const SCEV *Step,
ICmpInst::Predicate *Pred,
ScalarEvolution *SE) {
return getSignedOverflowLimitForStep(Step, Pred, SE);
}
};
const ExtendOpTraitsBase::GetExtendExprTy ExtendOpTraits<
SCEVSignExtendExpr>::GetExtendExpr = &ScalarEvolution::getSignExtendExpr;
template <>
struct ExtendOpTraits<SCEVZeroExtendExpr> : public ExtendOpTraitsBase {
static const SCEV::NoWrapFlags WrapType = SCEV::FlagNUW;
static const GetExtendExprTy GetExtendExpr;
static const SCEV *getOverflowLimitForStep(const SCEV *Step,
ICmpInst::Predicate *Pred,
ScalarEvolution *SE) {
return getUnsignedOverflowLimitForStep(Step, Pred, SE);
}
};
const ExtendOpTraitsBase::GetExtendExprTy ExtendOpTraits<
SCEVZeroExtendExpr>::GetExtendExpr = &ScalarEvolution::getZeroExtendExpr;
} // end anonymous namespace
// The recurrence AR has been shown to have no signed/unsigned wrap or something
// close to it. Typically, if we can prove NSW/NUW for AR, then we can just as
// easily prove NSW/NUW for its preincrement or postincrement sibling. This
// allows normalizing a sign/zero extended AddRec as such: {sext/zext(Step +
// Start),+,Step} => {(Step + sext/zext(Start),+,Step} As a result, the
// expression "Step + sext/zext(PreIncAR)" is congruent with
// "sext/zext(PostIncAR)"
template <typename ExtendOpTy>
static const SCEV *getPreStartForExtend(const SCEVAddRecExpr *AR, Type *Ty,
ScalarEvolution *SE, unsigned Depth) {
auto WrapType = ExtendOpTraits<ExtendOpTy>::WrapType;
auto GetExtendExpr = ExtendOpTraits<ExtendOpTy>::GetExtendExpr;
const Loop *L = AR->getLoop();
const SCEV *Start = AR->getStart();
const SCEV *Step = AR->getStepRecurrence(*SE);
// Check for a simple looking step prior to loop entry.
const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Start);
if (!SA)
return nullptr;
// Create an AddExpr for "PreStart" after subtracting Step. Full SCEV
// subtraction is expensive. For this purpose, perform a quick and dirty
// difference, by checking for Step in the operand list. Note, that
// SA might have repeated ops, like %a + %a + ..., so only remove one.
SmallVector<const SCEV *, 4> DiffOps(SA->operands());
for (auto It = DiffOps.begin(); It != DiffOps.end(); ++It)
if (*It == Step) {
DiffOps.erase(It);
break;
}
if (DiffOps.size() == SA->getNumOperands())
return nullptr;
// Try to prove `WrapType` (SCEV::FlagNSW or SCEV::FlagNUW) on `PreStart` +
// `Step`:
// 1. NSW/NUW flags on the step increment.
auto PreStartFlags =
ScalarEvolution::maskFlags(SA->getNoWrapFlags(), SCEV::FlagNUW);
const SCEV *PreStart = SE->getAddExpr(DiffOps, PreStartFlags);
const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>(
SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagAnyWrap));
// "{S,+,X} is <nsw>/<nuw>" and "the backedge is taken at least once" implies
// "S+X does not sign/unsign-overflow".
//
const SCEV *BECount = SE->getBackedgeTakenCount(L);
if (PreAR && PreAR->getNoWrapFlags(WrapType) &&
!isa<SCEVCouldNotCompute>(BECount) && SE->isKnownPositive(BECount))
return PreStart;
// 2. Direct overflow check on the step operation's expression.
unsigned BitWidth = SE->getTypeSizeInBits(AR->getType());
Type *WideTy = IntegerType::get(SE->getContext(), BitWidth * 2);
const SCEV *OperandExtendedStart =
SE->getAddExpr((SE->*GetExtendExpr)(PreStart, WideTy, Depth),
(SE->*GetExtendExpr)(Step, WideTy, Depth));
if ((SE->*GetExtendExpr)(Start, WideTy, Depth) == OperandExtendedStart) {
if (PreAR && AR->getNoWrapFlags(WrapType)) {
// If we know `AR` == {`PreStart`+`Step`,+,`Step`} is `WrapType` (FlagNSW
// or FlagNUW) and that `PreStart` + `Step` is `WrapType` too, then
// `PreAR` == {`PreStart`,+,`Step`} is also `WrapType`. Cache this fact.
SE->setNoWrapFlags(const_cast<SCEVAddRecExpr *>(PreAR), WrapType);
}
return PreStart;
}
// 3. Loop precondition.
ICmpInst::Predicate Pred;
const SCEV *OverflowLimit =
ExtendOpTraits<ExtendOpTy>::getOverflowLimitForStep(Step, &Pred, SE);
if (OverflowLimit &&
SE->isLoopEntryGuardedByCond(L, Pred, PreStart, OverflowLimit))
return PreStart;
return nullptr;
}
// Get the normalized zero or sign extended expression for this AddRec's Start.
template <typename ExtendOpTy>
static const SCEV *getExtendAddRecStart(const SCEVAddRecExpr *AR, Type *Ty,
ScalarEvolution *SE,
unsigned Depth) {
auto GetExtendExpr = ExtendOpTraits<ExtendOpTy>::GetExtendExpr;
const SCEV *PreStart = getPreStartForExtend<ExtendOpTy>(AR, Ty, SE, Depth);
if (!PreStart)
return (SE->*GetExtendExpr)(AR->getStart(), Ty, Depth);
return SE->getAddExpr((SE->*GetExtendExpr)(AR->getStepRecurrence(*SE), Ty,
Depth),
(SE->*GetExtendExpr)(PreStart, Ty, Depth));
}
// Try to prove away overflow by looking at "nearby" add recurrences. A
// motivating example for this rule: if we know `{0,+,4}` is `ult` `-1` and it
// does not itself wrap then we can conclude that `{1,+,4}` is `nuw`.
//
// Formally:
//
// {S,+,X} == {S-T,+,X} + T
// => Ext({S,+,X}) == Ext({S-T,+,X} + T)
//
// If ({S-T,+,X} + T) does not overflow ... (1)
//
// RHS == Ext({S-T,+,X} + T) == Ext({S-T,+,X}) + Ext(T)
//
// If {S-T,+,X} does not overflow ... (2)
//
// RHS == Ext({S-T,+,X}) + Ext(T) == {Ext(S-T),+,Ext(X)} + Ext(T)
// == {Ext(S-T)+Ext(T),+,Ext(X)}
//
// If (S-T)+T does not overflow ... (3)
//
// RHS == {Ext(S-T)+Ext(T),+,Ext(X)} == {Ext(S-T+T),+,Ext(X)}
// == {Ext(S),+,Ext(X)} == LHS
//
// Thus, if (1), (2) and (3) are true for some T, then
// Ext({S,+,X}) == {Ext(S),+,Ext(X)}
//
// (3) is implied by (1) -- "(S-T)+T does not overflow" is simply "({S-T,+,X}+T)
// does not overflow" restricted to the 0th iteration. Therefore we only need
// to check for (1) and (2).
//
// In the current context, S is `Start`, X is `Step`, Ext is `ExtendOpTy` and T
// is `Delta` (defined below).
template <typename ExtendOpTy>
bool ScalarEvolution::proveNoWrapByVaryingStart(const SCEV *Start,
const SCEV *Step,
const Loop *L) {
auto WrapType = ExtendOpTraits<ExtendOpTy>::WrapType;
// We restrict `Start` to a constant to prevent SCEV from spending too much
// time here. It is correct (but more expensive) to continue with a
// non-constant `Start` and do a general SCEV subtraction to compute
// `PreStart` below.
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(Start);
if (!StartC)
return false;
APInt StartAI = StartC->getAPInt();
for (unsigned Delta : {-2, -1, 1, 2}) {
const SCEV *PreStart = getConstant(StartAI - Delta);
FoldingSetNodeID ID;
ID.AddInteger(scAddRecExpr);
ID.AddPointer(PreStart);
ID.AddPointer(Step);
ID.AddPointer(L);
void *IP = nullptr;
const auto *PreAR =
static_cast<SCEVAddRecExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP));
// Give up if we don't already have the add recurrence we need because
// actually constructing an add recurrence is relatively expensive.
if (PreAR && PreAR->getNoWrapFlags(WrapType)) { // proves (2)
const SCEV *DeltaS = getConstant(StartC->getType(), Delta);
ICmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
const SCEV *Limit = ExtendOpTraits<ExtendOpTy>::getOverflowLimitForStep(
DeltaS, &Pred, this);
if (Limit && isKnownPredicate(Pred, PreAR, Limit)) // proves (1)
return true;
}
}
return false;
}
// Finds an integer D for an expression (C + x + y + ...) such that the top
// level addition in (D + (C - D + x + y + ...)) would not wrap (signed or
// unsigned) and the number of trailing zeros of (C - D + x + y + ...) is
// maximized, where C is the \p ConstantTerm, x, y, ... are arbitrary SCEVs, and
// the (C + x + y + ...) expression is \p WholeAddExpr.
static APInt extractConstantWithoutWrapping(ScalarEvolution &SE,
const SCEVConstant *ConstantTerm,
const SCEVAddExpr *WholeAddExpr) {
const APInt &C = ConstantTerm->getAPInt();
const unsigned BitWidth = C.getBitWidth();
// Find number of trailing zeros of (x + y + ...) w/o the C first:
uint32_t TZ = BitWidth;
for (unsigned I = 1, E = WholeAddExpr->getNumOperands(); I < E && TZ; ++I)
TZ = std::min(TZ, SE.getMinTrailingZeros(WholeAddExpr->getOperand(I)));
if (TZ) {
// Set D to be as many least significant bits of C as possible while still
// guaranteeing that adding D to (C - D + x + y + ...) won't cause a wrap:
return TZ < BitWidth ? C.trunc(TZ).zext(BitWidth) : C;
}
return APInt(BitWidth, 0);
}
// Finds an integer D for an affine AddRec expression {C,+,x} such that the top
// level addition in (D + {C-D,+,x}) would not wrap (signed or unsigned) and the
// number of trailing zeros of (C - D + x * n) is maximized, where C is the \p
// ConstantStart, x is an arbitrary \p Step, and n is the loop trip count.
static APInt extractConstantWithoutWrapping(ScalarEvolution &SE,
const APInt &ConstantStart,
const SCEV *Step) {
const unsigned BitWidth = ConstantStart.getBitWidth();
const uint32_t TZ = SE.getMinTrailingZeros(Step);
if (TZ)
return TZ < BitWidth ? ConstantStart.trunc(TZ).zext(BitWidth)
: ConstantStart;
return APInt(BitWidth, 0);
}
static void insertFoldCacheEntry(
const ScalarEvolution::FoldID &ID, const SCEV *S,
DenseMap<ScalarEvolution::FoldID, const SCEV *> &FoldCache,
DenseMap<const SCEV *, SmallVector<ScalarEvolution::FoldID, 2>>
&FoldCacheUser) {
auto I = FoldCache.insert({ID, S});
if (!I.second) {
// Remove FoldCacheUser entry for ID when replacing an existing FoldCache
// entry.
auto &UserIDs = FoldCacheUser[I.first->second];
assert(count(UserIDs, ID) == 1 && "unexpected duplicates in UserIDs");
for (unsigned I = 0; I != UserIDs.size(); ++I)
if (UserIDs[I] == ID) {
std::swap(UserIDs[I], UserIDs.back());
break;
}
UserIDs.pop_back();
I.first->second = S;
}
FoldCacheUser[S].push_back(ID);
}
const SCEV *
ScalarEvolution::getZeroExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth) {
assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
"This is not an extending conversion!");
assert(isSCEVable(Ty) &&
"This is not a conversion to a SCEVable type!");
assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
Ty = getEffectiveSCEVType(Ty);
FoldID ID(scZeroExtend, Op, Ty);
auto Iter = FoldCache.find(ID);
if (Iter != FoldCache.end())
return Iter->second;
const SCEV *S = getZeroExtendExprImpl(Op, Ty, Depth);
if (!isa<SCEVZeroExtendExpr>(S))
insertFoldCacheEntry(ID, S, FoldCache, FoldCacheUser);
return S;
}
const SCEV *ScalarEvolution::getZeroExtendExprImpl(const SCEV *Op, Type *Ty,
unsigned Depth) {
assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
"This is not an extending conversion!");
assert(isSCEVable(Ty) && "This is not a conversion to a SCEVable type!");
assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
// Fold if the operand is constant.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
return getConstant(SC->getAPInt().zext(getTypeSizeInBits(Ty)));
// zext(zext(x)) --> zext(x)
if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
return getZeroExtendExpr(SZ->getOperand(), Ty, Depth + 1);
// Before doing any expensive analysis, check to see if we've already
// computed a SCEV for this Op and Ty.
FoldingSetNodeID ID;
ID.AddInteger(scZeroExtend);
ID.AddPointer(Op);
ID.AddPointer(Ty);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
if (Depth > MaxCastDepth) {
SCEV *S = new (SCEVAllocator) SCEVZeroExtendExpr(ID.Intern(SCEVAllocator),
Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
// zext(trunc(x)) --> zext(x) or x or trunc(x)
if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
// It's possible the bits taken off by the truncate were all zero bits. If
// so, we should be able to simplify this further.
const SCEV *X = ST->getOperand();
ConstantRange CR = getUnsignedRange(X);
unsigned TruncBits = getTypeSizeInBits(ST->getType());
unsigned NewBits = getTypeSizeInBits(Ty);
if (CR.truncate(TruncBits).zeroExtend(NewBits).contains(
CR.zextOrTrunc(NewBits)))
return getTruncateOrZeroExtend(X, Ty, Depth);
}
// If the input value is a chrec scev, and we can prove that the value
// did not overflow the old, smaller, value, we can zero extend all of the
// operands (often constants). This allows analysis of something like
// this: for (unsigned char X = 0; X < 100; ++X) { int Y = X; }
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op))
if (AR->isAffine()) {
const SCEV *Start = AR->getStart();
const SCEV *Step = AR->getStepRecurrence(*this);
unsigned BitWidth = getTypeSizeInBits(AR->getType());
const Loop *L = AR->getLoop();
// If we have special knowledge that this addrec won't overflow,
// we don't need to do any further analysis.
if (AR->hasNoUnsignedWrap()) {
Start =
getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
Step = getZeroExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
// being called from within backedge-taken count analysis, such that
// attempting to ask for the backedge-taken count would likely result
// in infinite recursion. In the later case, the analysis code will
// cope with a conservative value, and it will take care to purge
// that value once it has finished.
const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(MaxBECount)) {
// Manually compute the final value for AR, checking for overflow.
// Check whether the backedge-taken count can be losslessly casted to
// the addrec's type. The count is always unsigned.
const SCEV *CastedMaxBECount =
getTruncateOrZeroExtend(MaxBECount, Start->getType(), Depth);
const SCEV *RecastedMaxBECount = getTruncateOrZeroExtend(
CastedMaxBECount, MaxBECount->getType(), Depth);
if (MaxBECount == RecastedMaxBECount) {
Type *WideTy = IntegerType::get(getContext(), BitWidth * 2);
// Check whether Start+Step*MaxBECount has no unsigned overflow.
const SCEV *ZMul = getMulExpr(CastedMaxBECount, Step,
SCEV::FlagAnyWrap, Depth + 1);
const SCEV *ZAdd = getZeroExtendExpr(getAddExpr(Start, ZMul,
SCEV::FlagAnyWrap,
Depth + 1),
WideTy, Depth + 1);
const SCEV *WideStart = getZeroExtendExpr(Start, WideTy, Depth + 1);
const SCEV *WideMaxBECount =
getZeroExtendExpr(CastedMaxBECount, WideTy, Depth + 1);
const SCEV *OperandExtendedAdd =
getAddExpr(WideStart,
getMulExpr(WideMaxBECount,
getZeroExtendExpr(Step, WideTy, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1);
if (ZAdd == OperandExtendedAdd) {
// Cache knowledge of AR NUW, which is propagated to this AddRec.
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNUW);
// Return the expression with the addrec on the outside.
Start = getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this,
Depth + 1);
Step = getZeroExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
// Similar to above, only this time treat the step value as signed.
// This covers loops that count down.
OperandExtendedAdd =
getAddExpr(WideStart,
getMulExpr(WideMaxBECount,
getSignExtendExpr(Step, WideTy, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1);
if (ZAdd == OperandExtendedAdd) {
// Cache knowledge of AR NW, which is propagated to this AddRec.
// Negative step causes unsigned wrap, but it still can't self-wrap.
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
// Return the expression with the addrec on the outside.
Start = getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this,
Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
}
}
// Normally, in the cases we can prove no-overflow via a
// backedge guarding condition, we can also compute a backedge
// taken count for the loop. The exceptions are assumptions and
// guards present in the loop -- SCEV is not great at exploiting
// these to compute max backedge taken counts, but can still use
// these to prove lack of overflow. Use this fact to avoid
// doing extra work that may not pay off.
if (!isa<SCEVCouldNotCompute>(MaxBECount) || HasGuards ||
!AC.assumptions().empty()) {
auto NewFlags = proveNoUnsignedWrapViaInduction(AR);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), NewFlags);
if (AR->hasNoUnsignedWrap()) {
// Same as nuw case above - duplicated here to avoid a compile time
// issue. It's not clear that the order of checks does matter, but
// it's one of two issue possible causes for a change which was
// reverted. Be conservative for the moment.
Start =
getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
Step = getZeroExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
// For a negative step, we can extend the operands iff doing so only
// traverses values in the range zext([0,UINT_MAX]).
if (isKnownNegative(Step)) {
const SCEV *N = getConstant(APInt::getMaxValue(BitWidth) -
getSignedRangeMin(Step));
if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT, AR, N) ||
isKnownOnEveryIteration(ICmpInst::ICMP_UGT, AR, N)) {
// Cache knowledge of AR NW, which is propagated to this
// AddRec. Negative step causes unsigned wrap, but it
// still can't self-wrap.
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
// Return the expression with the addrec on the outside.
Start = getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this,
Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
}
}
// zext({C,+,Step}) --> (zext(D) + zext({C-D,+,Step}))<nuw><nsw>
// if D + (C - D + Step * n) could be proven to not unsigned wrap
// where D maximizes the number of trailing zeros of (C - D + Step * n)
if (const auto *SC = dyn_cast<SCEVConstant>(Start)) {
const APInt &C = SC->getAPInt();
const APInt &D = extractConstantWithoutWrapping(*this, C, Step);
if (D != 0) {
const SCEV *SZExtD = getZeroExtendExpr(getConstant(D), Ty, Depth);
const SCEV *SResidual =
getAddRecExpr(getConstant(C - D), Step, L, AR->getNoWrapFlags());
const SCEV *SZExtR = getZeroExtendExpr(SResidual, Ty, Depth + 1);
return getAddExpr(SZExtD, SZExtR,
(SCEV::NoWrapFlags)(SCEV::FlagNSW | SCEV::FlagNUW),
Depth + 1);
}
}
if (proveNoWrapByVaryingStart<SCEVZeroExtendExpr>(Start, Step, L)) {
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNUW);
Start =
getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
Step = getZeroExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
}
// zext(A % B) --> zext(A) % zext(B)
{
const SCEV *LHS;
const SCEV *RHS;
if (matchURem(Op, LHS, RHS))
return getURemExpr(getZeroExtendExpr(LHS, Ty, Depth + 1),
getZeroExtendExpr(RHS, Ty, Depth + 1));
}
// zext(A / B) --> zext(A) / zext(B).
if (auto *Div = dyn_cast<SCEVUDivExpr>(Op))
return getUDivExpr(getZeroExtendExpr(Div->getLHS(), Ty, Depth + 1),
getZeroExtendExpr(Div->getRHS(), Ty, Depth + 1));
if (auto *SA = dyn_cast<SCEVAddExpr>(Op)) {
// zext((A + B + ...)<nuw>) --> (zext(A) + zext(B) + ...)<nuw>
if (SA->hasNoUnsignedWrap()) {
// If the addition does not unsign overflow then we can, by definition,
// commute the zero extension with the addition operation.
SmallVector<const SCEV *, 4> Ops;
for (const auto *Op : SA->operands())
Ops.push_back(getZeroExtendExpr(Op, Ty, Depth + 1));
return getAddExpr(Ops, SCEV::FlagNUW, Depth + 1);
}
// zext(C + x + y + ...) --> (zext(D) + zext((C - D) + x + y + ...))
// if D + (C - D + x + y + ...) could be proven to not unsigned wrap
// where D maximizes the number of trailing zeros of (C - D + x + y + ...)
//
// Often address arithmetics contain expressions like
// (zext (add (shl X, C1), C2)), for instance, (zext (5 + (4 * X))).
// This transformation is useful while proving that such expressions are
// equal or differ by a small constant amount, see LoadStoreVectorizer pass.
if (const auto *SC = dyn_cast<SCEVConstant>(SA->getOperand(0))) {
const APInt &D = extractConstantWithoutWrapping(*this, SC, SA);
if (D != 0) {
const SCEV *SZExtD = getZeroExtendExpr(getConstant(D), Ty, Depth);
const SCEV *SResidual =
getAddExpr(getConstant(-D), SA, SCEV::FlagAnyWrap, Depth);
const SCEV *SZExtR = getZeroExtendExpr(SResidual, Ty, Depth + 1);
return getAddExpr(SZExtD, SZExtR,
(SCEV::NoWrapFlags)(SCEV::FlagNSW | SCEV::FlagNUW),
Depth + 1);
}
}
}
if (auto *SM = dyn_cast<SCEVMulExpr>(Op)) {
// zext((A * B * ...)<nuw>) --> (zext(A) * zext(B) * ...)<nuw>
if (SM->hasNoUnsignedWrap()) {
// If the multiply does not unsign overflow then we can, by definition,
// commute the zero extension with the multiply operation.
SmallVector<const SCEV *, 4> Ops;
for (const auto *Op : SM->operands())
Ops.push_back(getZeroExtendExpr(Op, Ty, Depth + 1));
return getMulExpr(Ops, SCEV::FlagNUW, Depth + 1);
}
// zext(2^K * (trunc X to iN)) to iM ->
// 2^K * (zext(trunc X to i{N-K}) to iM)<nuw>
//
// Proof:
//
// zext(2^K * (trunc X to iN)) to iM
// = zext((trunc X to iN) << K) to iM
// = zext((trunc X to i{N-K}) << K)<nuw> to iM
// (because shl removes the top K bits)
// = zext((2^K * (trunc X to i{N-K}))<nuw>) to iM
// = (2^K * (zext(trunc X to i{N-K}) to iM))<nuw>.
//
if (SM->getNumOperands() == 2)
if (auto *MulLHS = dyn_cast<SCEVConstant>(SM->getOperand(0)))
if (MulLHS->getAPInt().isPowerOf2())
if (auto *TruncRHS = dyn_cast<SCEVTruncateExpr>(SM->getOperand(1))) {
int NewTruncBits = getTypeSizeInBits(TruncRHS->getType()) -
MulLHS->getAPInt().logBase2();
Type *NewTruncTy = IntegerType::get(getContext(), NewTruncBits);
return getMulExpr(
getZeroExtendExpr(MulLHS, Ty),
getZeroExtendExpr(
getTruncateExpr(TruncRHS->getOperand(), NewTruncTy), Ty),
SCEV::FlagNUW, Depth + 1);
}
}
// zext(umin(x, y)) -> umin(zext(x), zext(y))
// zext(umax(x, y)) -> umax(zext(x), zext(y))
if (isa<SCEVUMinExpr>(Op) || isa<SCEVUMaxExpr>(Op)) {
auto *MinMax = cast<SCEVMinMaxExpr>(Op);
SmallVector<const SCEV *, 4> Operands;
for (auto *Operand : MinMax->operands())
Operands.push_back(getZeroExtendExpr(Operand, Ty));
if (isa<SCEVUMinExpr>(MinMax))
return getUMinExpr(Operands);
return getUMaxExpr(Operands);
}
// zext(umin_seq(x, y)) -> umin_seq(zext(x), zext(y))
if (auto *MinMax = dyn_cast<SCEVSequentialMinMaxExpr>(Op)) {
assert(isa<SCEVSequentialUMinExpr>(MinMax) && "Not supported!");
SmallVector<const SCEV *, 4> Operands;
for (auto *Operand : MinMax->operands())
Operands.push_back(getZeroExtendExpr(Operand, Ty));
return getUMinExpr(Operands, /*Sequential*/ true);
}
// The cast wasn't folded; create an explicit cast node.
// Recompute the insert position, as it may have been invalidated.
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
SCEV *S = new (SCEVAllocator) SCEVZeroExtendExpr(ID.Intern(SCEVAllocator),
Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
const SCEV *
ScalarEvolution::getSignExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth) {
assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
"This is not an extending conversion!");
assert(isSCEVable(Ty) &&
"This is not a conversion to a SCEVable type!");
assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
Ty = getEffectiveSCEVType(Ty);
FoldID ID(scSignExtend, Op, Ty);
auto Iter = FoldCache.find(ID);
if (Iter != FoldCache.end())
return Iter->second;
const SCEV *S = getSignExtendExprImpl(Op, Ty, Depth);
if (!isa<SCEVSignExtendExpr>(S))
insertFoldCacheEntry(ID, S, FoldCache, FoldCacheUser);
return S;
}
const SCEV *ScalarEvolution::getSignExtendExprImpl(const SCEV *Op, Type *Ty,
unsigned Depth) {
assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
"This is not an extending conversion!");
assert(isSCEVable(Ty) && "This is not a conversion to a SCEVable type!");
assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
Ty = getEffectiveSCEVType(Ty);
// Fold if the operand is constant.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
return getConstant(SC->getAPInt().sext(getTypeSizeInBits(Ty)));
// sext(sext(x)) --> sext(x)
if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op))
return getSignExtendExpr(SS->getOperand(), Ty, Depth + 1);
// sext(zext(x)) --> zext(x)
if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
return getZeroExtendExpr(SZ->getOperand(), Ty, Depth + 1);
// Before doing any expensive analysis, check to see if we've already
// computed a SCEV for this Op and Ty.
FoldingSetNodeID ID;
ID.AddInteger(scSignExtend);
ID.AddPointer(Op);
ID.AddPointer(Ty);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
// Limit recursion depth.
if (Depth > MaxCastDepth) {
SCEV *S = new (SCEVAllocator) SCEVSignExtendExpr(ID.Intern(SCEVAllocator),
Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
// sext(trunc(x)) --> sext(x) or x or trunc(x)
if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
// It's possible the bits taken off by the truncate were all sign bits. If
// so, we should be able to simplify this further.
const SCEV *X = ST->getOperand();
ConstantRange CR = getSignedRange(X);
unsigned TruncBits = getTypeSizeInBits(ST->getType());
unsigned NewBits = getTypeSizeInBits(Ty);
if (CR.truncate(TruncBits).signExtend(NewBits).contains(
CR.sextOrTrunc(NewBits)))
return getTruncateOrSignExtend(X, Ty, Depth);
}
if (auto *SA = dyn_cast<SCEVAddExpr>(Op)) {
// sext((A + B + ...)<nsw>) --> (sext(A) + sext(B) + ...)<nsw>
if (SA->hasNoSignedWrap()) {
// If the addition does not sign overflow then we can, by definition,
// commute the sign extension with the addition operation.
SmallVector<const SCEV *, 4> Ops;
for (const auto *Op : SA->operands())
Ops.push_back(getSignExtendExpr(Op, Ty, Depth + 1));
return getAddExpr(Ops, SCEV::FlagNSW, Depth + 1);
}
// sext(C + x + y + ...) --> (sext(D) + sext((C - D) + x + y + ...))
// if D + (C - D + x + y + ...) could be proven to not signed wrap
// where D maximizes the number of trailing zeros of (C - D + x + y + ...)
//
// For instance, this will bring two seemingly different expressions:
// 1 + sext(5 + 20 * %x + 24 * %y) and
// sext(6 + 20 * %x + 24 * %y)
// to the same form:
// 2 + sext(4 + 20 * %x + 24 * %y)
if (const auto *SC = dyn_cast<SCEVConstant>(SA->getOperand(0))) {
const APInt &D = extractConstantWithoutWrapping(*this, SC, SA);
if (D != 0) {
const SCEV *SSExtD = getSignExtendExpr(getConstant(D), Ty, Depth);
const SCEV *SResidual =
getAddExpr(getConstant(-D), SA, SCEV::FlagAnyWrap, Depth);
const SCEV *SSExtR = getSignExtendExpr(SResidual, Ty, Depth + 1);
return getAddExpr(SSExtD, SSExtR,
(SCEV::NoWrapFlags)(SCEV::FlagNSW | SCEV::FlagNUW),
Depth + 1);
}
}
}
// If the input value is a chrec scev, and we can prove that the value
// did not overflow the old, smaller, value, we can sign extend all of the
// operands (often constants). This allows analysis of something like
// this: for (signed char X = 0; X < 100; ++X) { int Y = X; }
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op))
if (AR->isAffine()) {
const SCEV *Start = AR->getStart();
const SCEV *Step = AR->getStepRecurrence(*this);
unsigned BitWidth = getTypeSizeInBits(AR->getType());
const Loop *L = AR->getLoop();
// If we have special knowledge that this addrec won't overflow,
// we don't need to do any further analysis.
if (AR->hasNoSignedWrap()) {
Start =
getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, SCEV::FlagNSW);
}
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
// being called from within backedge-taken count analysis, such that
// attempting to ask for the backedge-taken count would likely result
// in infinite recursion. In the later case, the analysis code will
// cope with a conservative value, and it will take care to purge
// that value once it has finished.
const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(MaxBECount)) {
// Manually compute the final value for AR, checking for
// overflow.
// Check whether the backedge-taken count can be losslessly casted to
// the addrec's type. The count is always unsigned.
const SCEV *CastedMaxBECount =
getTruncateOrZeroExtend(MaxBECount, Start->getType(), Depth);
const SCEV *RecastedMaxBECount = getTruncateOrZeroExtend(
CastedMaxBECount, MaxBECount->getType(), Depth);
if (MaxBECount == RecastedMaxBECount) {
Type *WideTy = IntegerType::get(getContext(), BitWidth * 2);
// Check whether Start+Step*MaxBECount has no signed overflow.
const SCEV *SMul = getMulExpr(CastedMaxBECount, Step,
SCEV::FlagAnyWrap, Depth + 1);
const SCEV *SAdd = getSignExtendExpr(getAddExpr(Start, SMul,
SCEV::FlagAnyWrap,
Depth + 1),
WideTy, Depth + 1);
const SCEV *WideStart = getSignExtendExpr(Start, WideTy, Depth + 1);
const SCEV *WideMaxBECount =
getZeroExtendExpr(CastedMaxBECount, WideTy, Depth + 1);
const SCEV *OperandExtendedAdd =
getAddExpr(WideStart,
getMulExpr(WideMaxBECount,
getSignExtendExpr(Step, WideTy, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1);
if (SAdd == OperandExtendedAdd) {
// Cache knowledge of AR NSW, which is propagated to this AddRec.
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNSW);
// Return the expression with the addrec on the outside.
Start = getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this,
Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
// Similar to above, only this time treat the step value as unsigned.
// This covers loops that count up with an unsigned step.
OperandExtendedAdd =
getAddExpr(WideStart,
getMulExpr(WideMaxBECount,
getZeroExtendExpr(Step, WideTy, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1);
if (SAdd == OperandExtendedAdd) {
// If AR wraps around then
//
// abs(Step) * MaxBECount > unsigned-max(AR->getType())
// => SAdd != OperandExtendedAdd
//
// Thus (AR is not NW => SAdd != OperandExtendedAdd) <=>
// (SAdd == OperandExtendedAdd => AR is NW)
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
// Return the expression with the addrec on the outside.
Start = getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this,
Depth + 1);
Step = getZeroExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
}
}
auto NewFlags = proveNoSignedWrapViaInduction(AR);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), NewFlags);
if (AR->hasNoSignedWrap()) {
// Same as nsw case above - duplicated here to avoid a compile time
// issue. It's not clear that the order of checks does matter, but
// it's one of two issue possible causes for a change which was
// reverted. Be conservative for the moment.
Start =
getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
// sext({C,+,Step}) --> (sext(D) + sext({C-D,+,Step}))<nuw><nsw>
// if D + (C - D + Step * n) could be proven to not signed wrap
// where D maximizes the number of trailing zeros of (C - D + Step * n)
if (const auto *SC = dyn_cast<SCEVConstant>(Start)) {
const APInt &C = SC->getAPInt();
const APInt &D = extractConstantWithoutWrapping(*this, C, Step);
if (D != 0) {
const SCEV *SSExtD = getSignExtendExpr(getConstant(D), Ty, Depth);
const SCEV *SResidual =
getAddRecExpr(getConstant(C - D), Step, L, AR->getNoWrapFlags());
const SCEV *SSExtR = getSignExtendExpr(SResidual, Ty, Depth + 1);
return getAddExpr(SSExtD, SSExtR,
(SCEV::NoWrapFlags)(SCEV::FlagNSW | SCEV::FlagNUW),
Depth + 1);
}
}
if (proveNoWrapByVaryingStart<SCEVSignExtendExpr>(Start, Step, L)) {
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNSW);
Start =
getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
Step = getSignExtendExpr(Step, Ty, Depth + 1);
return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
}
}
// If the input value is provably positive and we could not simplify
// away the sext build a zext instead.
if (isKnownNonNegative(Op))
return getZeroExtendExpr(Op, Ty, Depth + 1);
// sext(smin(x, y)) -> smin(sext(x), sext(y))
// sext(smax(x, y)) -> smax(sext(x), sext(y))
if (isa<SCEVSMinExpr>(Op) || isa<SCEVSMaxExpr>(Op)) {
auto *MinMax = cast<SCEVMinMaxExpr>(Op);
SmallVector<const SCEV *, 4> Operands;
for (auto *Operand : MinMax->operands())
Operands.push_back(getSignExtendExpr(Operand, Ty));
if (isa<SCEVSMinExpr>(MinMax))
return getSMinExpr(Operands);
return getSMaxExpr(Operands);
}
// The cast wasn't folded; create an explicit cast node.
// Recompute the insert position, as it may have been invalidated.
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
SCEV *S = new (SCEVAllocator) SCEVSignExtendExpr(ID.Intern(SCEVAllocator),
Op, Ty);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, { Op });
return S;
}
const SCEV *ScalarEvolution::getCastExpr(SCEVTypes Kind, const SCEV *Op,
Type *Ty) {
switch (Kind) {
case scTruncate:
return getTruncateExpr(Op, Ty);
case scZeroExtend:
return getZeroExtendExpr(Op, Ty);
case scSignExtend:
return getSignExtendExpr(Op, Ty);
case scPtrToInt:
return getPtrToIntExpr(Op, Ty);
default:
llvm_unreachable("Not a SCEV cast expression!");
}
}
/// getAnyExtendExpr - Return a SCEV for the given operand extended with
/// unspecified bits out to the given type.
const SCEV *ScalarEvolution::getAnyExtendExpr(const SCEV *Op,
Type *Ty) {
assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
"This is not an extending conversion!");
assert(isSCEVable(Ty) &&
"This is not a conversion to a SCEVable type!");
Ty = getEffectiveSCEVType(Ty);
// Sign-extend negative constants.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
if (SC->getAPInt().isNegative())
return getSignExtendExpr(Op, Ty);
// Peel off a truncate cast.
if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Op)) {
const SCEV *NewOp = T->getOperand();
if (getTypeSizeInBits(NewOp->getType()) < getTypeSizeInBits(Ty))
return getAnyExtendExpr(NewOp, Ty);
return getTruncateOrNoop(NewOp, Ty);
}
// Next try a zext cast. If the cast is folded, use it.
const SCEV *ZExt = getZeroExtendExpr(Op, Ty);
if (!isa<SCEVZeroExtendExpr>(ZExt))
return ZExt;
// Next try a sext cast. If the cast is folded, use it.
const SCEV *SExt = getSignExtendExpr(Op, Ty);
if (!isa<SCEVSignExtendExpr>(SExt))
return SExt;
// Force the cast to be folded into the operands of an addrec.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op)) {
SmallVector<const SCEV *, 4> Ops;
for (const SCEV *Op : AR->operands())
Ops.push_back(getAnyExtendExpr(Op, Ty));
return getAddRecExpr(Ops, AR->getLoop(), SCEV::FlagNW);
}
// If the expression is obviously signed, use the sext cast value.
if (isa<SCEVSMaxExpr>(Op))
return SExt;
// Absent any other information, use the zext cast value.
return ZExt;
}
/// Process the given Ops list, which is a list of operands to be added under
/// the given scale, update the given map. This is a helper function for
/// getAddRecExpr. As an example of what it does, given a sequence of operands
/// that would form an add expression like this:
///
/// m + n + 13 + (A * (o + p + (B * (q + m + 29)))) + r + (-1 * r)
///
/// where A and B are constants, update the map with these values:
///
/// (m, 1+A*B), (n, 1), (o, A), (p, A), (q, A*B), (r, 0)
///
/// and add 13 + A*B*29 to AccumulatedConstant.
/// This will allow getAddRecExpr to produce this:
///
/// 13+A*B*29 + n + (m * (1+A*B)) + ((o + p) * A) + (q * A*B)
///
/// This form often exposes folding opportunities that are hidden in
/// the original operand list.
///
/// Return true iff it appears that any interesting folding opportunities
/// may be exposed. This helps getAddRecExpr short-circuit extra work in
/// the common case where no interesting opportunities are present, and
/// is also used as a check to avoid infinite recursion.
static bool
CollectAddOperandsWithScales(SmallDenseMap<const SCEV *, APInt, 16> &M,
SmallVectorImpl<const SCEV *> &NewOps,
APInt &AccumulatedConstant,
ArrayRef<const SCEV *> Ops, const APInt &Scale,
ScalarEvolution &SE) {
bool Interesting = false;
// Iterate over the add operands. They are sorted, with constants first.
unsigned i = 0;
while (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i])) {
++i;
// Pull a buried constant out to the outside.
if (Scale != 1 || AccumulatedConstant != 0 || C->getValue()->isZero())
Interesting = true;
AccumulatedConstant += Scale * C->getAPInt();
}
// Next comes everything else. We're especially interested in multiplies
// here, but they're in the middle, so just visit the rest with one loop.
for (; i != Ops.size(); ++i) {
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[i]);
if (Mul && isa<SCEVConstant>(Mul->getOperand(0))) {
APInt NewScale =
Scale * cast<SCEVConstant>(Mul->getOperand(0))->getAPInt();
if (Mul->getNumOperands() == 2 && isa<SCEVAddExpr>(Mul->getOperand(1))) {
// A multiplication of a constant with another add; recurse.
const SCEVAddExpr *Add = cast<SCEVAddExpr>(Mul->getOperand(1));
Interesting |=
CollectAddOperandsWithScales(M, NewOps, AccumulatedConstant,
Add->operands(), NewScale, SE);
} else {
// A multiplication of a constant with some other value. Update
// the map.
SmallVector<const SCEV *, 4> MulOps(drop_begin(Mul->operands()));
const SCEV *Key = SE.getMulExpr(MulOps);
auto Pair = M.insert({Key, NewScale});
if (Pair.second) {
NewOps.push_back(Pair.first->first);
} else {
Pair.first->second += NewScale;
// The map already had an entry for this value, which may indicate
// a folding opportunity.
Interesting = true;
}
}
} else {
// An ordinary operand. Update the map.
std::pair<DenseMap<const SCEV *, APInt>::iterator, bool> Pair =
M.insert({Ops[i], Scale});
if (Pair.second) {
NewOps.push_back(Pair.first->first);
} else {
Pair.first->second += Scale;
// The map already had an entry for this value, which may indicate
// a folding opportunity.
Interesting = true;
}
}
}
return Interesting;
}
bool ScalarEvolution::willNotOverflow(Instruction::BinaryOps BinOp, bool Signed,
const SCEV *LHS, const SCEV *RHS,
const Instruction *CtxI) {
const SCEV *(ScalarEvolution::*Operation)(const SCEV *, const SCEV *,
SCEV::NoWrapFlags, unsigned);
switch (BinOp) {
default:
llvm_unreachable("Unsupported binary op");
case Instruction::Add:
Operation = &ScalarEvolution::getAddExpr;
break;
case Instruction::Sub:
Operation = &ScalarEvolution::getMinusSCEV;
break;
case Instruction::Mul:
Operation = &ScalarEvolution::getMulExpr;
break;
}
const SCEV *(ScalarEvolution::*Extension)(const SCEV *, Type *, unsigned) =
Signed ? &ScalarEvolution::getSignExtendExpr
: &ScalarEvolution::getZeroExtendExpr;
// Check ext(LHS op RHS) == ext(LHS) op ext(RHS)
auto *NarrowTy = cast<IntegerType>(LHS->getType());
auto *WideTy =
IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);
const SCEV *A = (this->*Extension)(
(this->*Operation)(LHS, RHS, SCEV::FlagAnyWrap, 0), WideTy, 0);
const SCEV *LHSB = (this->*Extension)(LHS, WideTy, 0);
const SCEV *RHSB = (this->*Extension)(RHS, WideTy, 0);
const SCEV *B = (this->*Operation)(LHSB, RHSB, SCEV::FlagAnyWrap, 0);
if (A == B)
return true;
// Can we use context to prove the fact we need?
if (!CtxI)
return false;
// TODO: Support mul.
if (BinOp == Instruction::Mul)
return false;
auto *RHSC = dyn_cast<SCEVConstant>(RHS);
// TODO: Lift this limitation.
if (!RHSC)
return false;
APInt C = RHSC->getAPInt();
unsigned NumBits = C.getBitWidth();
bool IsSub = (BinOp == Instruction::Sub);
bool IsNegativeConst = (Signed && C.isNegative());
// Compute the direction and magnitude by which we need to check overflow.
bool OverflowDown = IsSub ^ IsNegativeConst;
APInt Magnitude = C;
if (IsNegativeConst) {
if (C == APInt::getSignedMinValue(NumBits))
// TODO: SINT_MIN on inversion gives the same negative value, we don't
// want to deal with that.
return false;
Magnitude = -C;
}
ICmpInst::Predicate Pred = Signed ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
if (OverflowDown) {
// To avoid overflow down, we need to make sure that MIN + Magnitude <= LHS.
APInt Min = Signed ? APInt::getSignedMinValue(NumBits)
: APInt::getMinValue(NumBits);
APInt Limit = Min + Magnitude;
return isKnownPredicateAt(Pred, getConstant(Limit), LHS, CtxI);
} else {
// To avoid overflow up, we need to make sure that LHS <= MAX - Magnitude.
APInt Max = Signed ? APInt::getSignedMaxValue(NumBits)
: APInt::getMaxValue(NumBits);
APInt Limit = Max - Magnitude;
return isKnownPredicateAt(Pred, LHS, getConstant(Limit), CtxI);
}
}
std::optional<SCEV::NoWrapFlags>
ScalarEvolution::getStrengthenedNoWrapFlagsFromBinOp(
const OverflowingBinaryOperator *OBO) {
// It cannot be done any better.
if (OBO->hasNoUnsignedWrap() && OBO->hasNoSignedWrap())
return std::nullopt;
SCEV::NoWrapFlags Flags = SCEV::NoWrapFlags::FlagAnyWrap;
if (OBO->hasNoUnsignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
if (OBO->hasNoSignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
bool Deduced = false;
if (OBO->getOpcode() != Instruction::Add &&
OBO->getOpcode() != Instruction::Sub &&
OBO->getOpcode() != Instruction::Mul)
return std::nullopt;
const SCEV *LHS = getSCEV(OBO->getOperand(0));
const SCEV *RHS = getSCEV(OBO->getOperand(1));
const Instruction *CtxI =
UseContextForNoWrapFlagInference ? dyn_cast<Instruction>(OBO) : nullptr;
if (!OBO->hasNoUnsignedWrap() &&
willNotOverflow((Instruction::BinaryOps)OBO->getOpcode(),
/* Signed */ false, LHS, RHS, CtxI)) {
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
Deduced = true;
}
if (!OBO->hasNoSignedWrap() &&
willNotOverflow((Instruction::BinaryOps)OBO->getOpcode(),
/* Signed */ true, LHS, RHS, CtxI)) {
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
Deduced = true;
}
if (Deduced)
return Flags;
return std::nullopt;
}
// We're trying to construct a SCEV of type `Type' with `Ops' as operands and
// `OldFlags' as can't-wrap behavior. Infer a more aggressive set of
// can't-overflow flags for the operation if possible.
static SCEV::NoWrapFlags
StrengthenNoWrapFlags(ScalarEvolution *SE, SCEVTypes Type,
const ArrayRef<const SCEV *> Ops,
SCEV::NoWrapFlags Flags) {
using namespace std::placeholders;
using OBO = OverflowingBinaryOperator;
bool CanAnalyze =
Type == scAddExpr || Type == scAddRecExpr || Type == scMulExpr;
(void)CanAnalyze;
assert(CanAnalyze && "don't call from other places!");
int SignOrUnsignMask = SCEV::FlagNUW | SCEV::FlagNSW;
SCEV::NoWrapFlags SignOrUnsignWrap =
ScalarEvolution::maskFlags(Flags, SignOrUnsignMask);
// If FlagNSW is true and all the operands are non-negative, infer FlagNUW.
auto IsKnownNonNegative = [&](const SCEV *S) {
return SE->isKnownNonNegative(S);
};
if (SignOrUnsignWrap == SCEV::FlagNSW && all_of(Ops, IsKnownNonNegative))
Flags =
ScalarEvolution::setFlags(Flags, (SCEV::NoWrapFlags)SignOrUnsignMask);
SignOrUnsignWrap = ScalarEvolution::maskFlags(Flags, SignOrUnsignMask);
if (SignOrUnsignWrap != SignOrUnsignMask &&
(Type == scAddExpr || Type == scMulExpr) && Ops.size() == 2 &&
isa<SCEVConstant>(Ops[0])) {
auto Opcode = [&] {
switch (Type) {
case scAddExpr:
return Instruction::Add;
case scMulExpr:
return Instruction::Mul;
default:
llvm_unreachable("Unexpected SCEV op.");
}
}();
const APInt &C = cast<SCEVConstant>(Ops[0])->getAPInt();
// (A <opcode> C) --> (A <opcode> C)<nsw> if the op doesn't sign overflow.
if (!(SignOrUnsignWrap & SCEV::FlagNSW)) {
auto NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
Opcode, C, OBO::NoSignedWrap);
if (NSWRegion.contains(SE->getSignedRange(Ops[1])))
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
}
// (A <opcode> C) --> (A <opcode> C)<nuw> if the op doesn't unsign overflow.
if (!(SignOrUnsignWrap & SCEV::FlagNUW)) {
auto NUWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
Opcode, C, OBO::NoUnsignedWrap);
if (NUWRegion.contains(SE->getUnsignedRange(Ops[1])))
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
}
}
// <0,+,nonnegative><nw> is also nuw
// TODO: Add corresponding nsw case
if (Type == scAddRecExpr && ScalarEvolution::hasFlags(Flags, SCEV::FlagNW) &&
!ScalarEvolution::hasFlags(Flags, SCEV::FlagNUW) && Ops.size() == 2 &&
Ops[0]->isZero() && IsKnownNonNegative(Ops[1]))
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
// both (udiv X, Y) * Y and Y * (udiv X, Y) are always NUW
if (Type == scMulExpr && !ScalarEvolution::hasFlags(Flags, SCEV::FlagNUW) &&
Ops.size() == 2) {
if (auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[0]))
if (UDiv->getOperand(1) == Ops[1])
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
if (auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[1]))
if (UDiv->getOperand(1) == Ops[0])
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
}
return Flags;
}
bool ScalarEvolution::isAvailableAtLoopEntry(const SCEV *S, const Loop *L) {
return isLoopInvariant(S, L) && properlyDominates(S, L->getHeader());
}
/// Get a canonical add expression, or something simpler if possible.
const SCEV *ScalarEvolution::getAddExpr(SmallVectorImpl<const SCEV *> &Ops,
SCEV::NoWrapFlags OrigFlags,
unsigned Depth) {
assert(!(OrigFlags & ~(SCEV::FlagNUW | SCEV::FlagNSW)) &&
"only nuw or nsw allowed");
assert(!Ops.empty() && "Cannot get empty add!");
if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
for (unsigned i = 1, e = Ops.size(); i != e; ++i)
assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
"SCEVAddExpr operand types don't match!");
unsigned NumPtrs = count_if(
Ops, [](const SCEV *Op) { return Op->getType()->isPointerTy(); });
assert(NumPtrs <= 1 && "add has at most one pointer operand");
#endif
const SCEV *Folded = constantFoldAndGroupOps(
*this, LI, DT, Ops,
[](const APInt &C1, const APInt &C2) { return C1 + C2; },
[](const APInt &C) { return C.isZero(); }, // identity
[](const APInt &C) { return false; }); // absorber
if (Folded)
return Folded;
unsigned Idx = isa<SCEVConstant>(Ops[0]) ? 1 : 0;
// Delay expensive flag strengthening until necessary.
auto ComputeFlags = [this, OrigFlags](const ArrayRef<const SCEV *> Ops) {
return StrengthenNoWrapFlags(this, scAddExpr, Ops, OrigFlags);
};
// Limit recursion calls depth.
if (Depth > MaxArithDepth || hasHugeExpression(Ops))
return getOrCreateAddExpr(Ops, ComputeFlags(Ops));
if (SCEV *S = findExistingSCEVInCache(scAddExpr, Ops)) {
// Don't strengthen flags if we have no new information.
SCEVAddExpr *Add = static_cast<SCEVAddExpr *>(S);
if (Add->getNoWrapFlags(OrigFlags) != OrigFlags)
Add->setNoWrapFlags(ComputeFlags(Ops));
return S;
}
// Okay, check to see if the same value occurs in the operand list more than
// once. If so, merge them together into an multiply expression. Since we
// sorted the list, these values are required to be adjacent.
Type *Ty = Ops[0]->getType();
bool FoundMatch = false;
for (unsigned i = 0, e = Ops.size(); i != e-1; ++i)
if (Ops[i] == Ops[i+1]) { // X + Y + Y --> X + Y*2
// Scan ahead to count how many equal operands there are.
unsigned Count = 2;
while (i+Count != e && Ops[i+Count] == Ops[i])
++Count;
// Merge the values into a multiply.
const SCEV *Scale = getConstant(Ty, Count);
const SCEV *Mul = getMulExpr(Scale, Ops[i], SCEV::FlagAnyWrap, Depth + 1);
if (Ops.size() == Count)
return Mul;
Ops[i] = Mul;
Ops.erase(Ops.begin()+i+1, Ops.begin()+i+Count);
--i; e -= Count - 1;
FoundMatch = true;
}
if (FoundMatch)
return getAddExpr(Ops, OrigFlags, Depth + 1);
// Check for truncates. If all the operands are truncated from the same
// type, see if factoring out the truncate would permit the result to be
// folded. eg., n*trunc(x) + m*trunc(y) --> trunc(trunc(m)*x + trunc(n)*y)
// if the contents of the resulting outer trunc fold to something simple.
auto FindTruncSrcType = [&]() -> Type * {
// We're ultimately looking to fold an addrec of truncs and muls of only
// constants and truncs, so if we find any other types of SCEV
// as operands of the addrec then we bail and return nullptr here.
// Otherwise, we return the type of the operand of a trunc that we find.
if (auto *T = dyn_cast<SCEVTruncateExpr>(Ops[Idx]))
return T->getOperand()->getType();
if (const auto *Mul = dyn_cast<SCEVMulExpr>(Ops[Idx])) {
const auto *LastOp = Mul->getOperand(Mul->getNumOperands() - 1);
if (const auto *T = dyn_cast<SCEVTruncateExpr>(LastOp))
return T->getOperand()->getType();
}
return nullptr;
};
if (auto *SrcType = FindTruncSrcType()) {
SmallVector<const SCEV *, 8> LargeOps;
bool Ok = true;
// Check all the operands to see if they can be represented in the
// source type of the truncate.
for (const SCEV *Op : Ops) {
if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Op)) {
if (T->getOperand()->getType() != SrcType) {
Ok = false;
break;
}
LargeOps.push_back(T->getOperand());
} else if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Op)) {
LargeOps.push_back(getAnyExtendExpr(C, SrcType));
} else if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(Op)) {
SmallVector<const SCEV *, 8> LargeMulOps;
for (unsigned j = 0, f = M->getNumOperands(); j != f && Ok; ++j) {
if (const SCEVTruncateExpr *T =
dyn_cast<SCEVTruncateExpr>(M->getOperand(j))) {
if (T->getOperand()->getType() != SrcType) {
Ok = false;
break;
}
LargeMulOps.push_back(T->getOperand());
} else if (const auto *C = dyn_cast<SCEVConstant>(M->getOperand(j))) {
LargeMulOps.push_back(getAnyExtendExpr(C, SrcType));
} else {
Ok = false;
break;
}
}
if (Ok)
LargeOps.push_back(getMulExpr(LargeMulOps, SCEV::FlagAnyWrap, Depth + 1));
} else {
Ok = false;
break;
}
}
if (Ok) {
// Evaluate the expression in the larger type.
const SCEV *Fold = getAddExpr(LargeOps, SCEV::FlagAnyWrap, Depth + 1);
// If it folds to something simple, use it. Otherwise, don't.
if (isa<SCEVConstant>(Fold) || isa<SCEVUnknown>(Fold))
return getTruncateExpr(Fold, Ty);
}
}
if (Ops.size() == 2) {
// Check if we have an expression of the form ((X + C1) - C2), where C1 and
// C2 can be folded in a way that allows retaining wrapping flags of (X +
// C1).
const SCEV *A = Ops[0];
const SCEV *B = Ops[1];
auto *AddExpr = dyn_cast<SCEVAddExpr>(B);
auto *C = dyn_cast<SCEVConstant>(A);
if (AddExpr && C && isa<SCEVConstant>(AddExpr->getOperand(0))) {
auto C1 = cast<SCEVConstant>(AddExpr->getOperand(0))->getAPInt();
auto C2 = C->getAPInt();
SCEV::NoWrapFlags PreservedFlags = SCEV::FlagAnyWrap;
APInt ConstAdd = C1 + C2;
auto AddFlags = AddExpr->getNoWrapFlags();
// Adding a smaller constant is NUW if the original AddExpr was NUW.
if (ScalarEvolution::hasFlags(AddFlags, SCEV::FlagNUW) &&
ConstAdd.ule(C1)) {
PreservedFlags =
ScalarEvolution::setFlags(PreservedFlags, SCEV::FlagNUW);
}
// Adding a constant with the same sign and small magnitude is NSW, if the
// original AddExpr was NSW.
if (ScalarEvolution::hasFlags(AddFlags, SCEV::FlagNSW) &&
C1.isSignBitSet() == ConstAdd.isSignBitSet() &&
ConstAdd.abs().ule(C1.abs())) {
PreservedFlags =
ScalarEvolution::setFlags(PreservedFlags, SCEV::FlagNSW);
}
if (PreservedFlags != SCEV::FlagAnyWrap) {
SmallVector<const SCEV *, 4> NewOps(AddExpr->operands());
NewOps[0] = getConstant(ConstAdd);
return getAddExpr(NewOps, PreservedFlags);
}
}
}
// Canonicalize (-1 * urem X, Y) + X --> (Y * X/Y)
if (Ops.size() == 2) {
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[0]);
if (Mul && Mul->getNumOperands() == 2 &&
Mul->getOperand(0)->isAllOnesValue()) {
const SCEV *X;
const SCEV *Y;
if (matchURem(Mul->getOperand(1), X, Y) && X == Ops[1]) {
return getMulExpr(Y, getUDivExpr(X, Y));
}
}
}
// Skip past any other cast SCEVs.
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddExpr)
++Idx;
// If there are add operands they would be next.
if (Idx < Ops.size()) {
bool DeletedAdd = false;
// If the original flags and all inlined SCEVAddExprs are NUW, use the
// common NUW flag for expression after inlining. Other flags cannot be
// preserved, because they may depend on the original order of operations.
SCEV::NoWrapFlags CommonFlags = maskFlags(OrigFlags, SCEV::FlagNUW);
while (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[Idx])) {
if (Ops.size() > AddOpsInlineThreshold ||
Add->getNumOperands() > AddOpsInlineThreshold)
break;
// If we have an add, expand the add operands onto the end of the operands
// list.
Ops.erase(Ops.begin()+Idx);
append_range(Ops, Add->operands());
DeletedAdd = true;
CommonFlags = maskFlags(CommonFlags, Add->getNoWrapFlags());
}
// If we deleted at least one add, we added operands to the end of the list,
// and they are not necessarily sorted. Recurse to resort and resimplify
// any operands we just acquired.
if (DeletedAdd)
return getAddExpr(Ops, CommonFlags, Depth + 1);
}
// Skip over the add expression until we get to a multiply.
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr)
++Idx;
// Check to see if there are any folding opportunities present with
// operands multiplied by constant values.
if (Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx])) {
uint64_t BitWidth = getTypeSizeInBits(Ty);
SmallDenseMap<const SCEV *, APInt, 16> M;
SmallVector<const SCEV *, 8> NewOps;
APInt AccumulatedConstant(BitWidth, 0);
if (CollectAddOperandsWithScales(M, NewOps, AccumulatedConstant,
Ops, APInt(BitWidth, 1), *this)) {
struct APIntCompare {
bool operator()(const APInt &LHS, const APInt &RHS) const {
return LHS.ult(RHS);
}
};
// Some interesting folding opportunity is present, so its worthwhile to
// re-generate the operands list. Group the operands by constant scale,
// to avoid multiplying by the same constant scale multiple times.
std::map<APInt, SmallVector<const SCEV *, 4>, APIntCompare> MulOpLists;
for (const SCEV *NewOp : NewOps)
MulOpLists[M.find(NewOp)->second].push_back(NewOp);
// Re-generate the operands list.
Ops.clear();
if (AccumulatedConstant != 0)
Ops.push_back(getConstant(AccumulatedConstant));
for (auto &MulOp : MulOpLists) {
if (MulOp.first == 1) {
Ops.push_back(getAddExpr(MulOp.second, SCEV::FlagAnyWrap, Depth + 1));
} else if (MulOp.first != 0) {
Ops.push_back(getMulExpr(
getConstant(MulOp.first),
getAddExpr(MulOp.second, SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1));
}
}
if (Ops.empty())
return getZero(Ty);
if (Ops.size() == 1)
return Ops[0];
return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
}
// If we are adding something to a multiply expression, make sure the
// something is not already an operand of the multiply. If so, merge it into
// the multiply.
for (; Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx]); ++Idx) {
const SCEVMulExpr *Mul = cast<SCEVMulExpr>(Ops[Idx]);
for (unsigned MulOp = 0, e = Mul->getNumOperands(); MulOp != e; ++MulOp) {
const SCEV *MulOpSCEV = Mul->getOperand(MulOp);
if (isa<SCEVConstant>(MulOpSCEV))
continue;
for (unsigned AddOp = 0, e = Ops.size(); AddOp != e; ++AddOp)
if (MulOpSCEV == Ops[AddOp]) {
// Fold W + X + (X * Y * Z) --> W + (X * ((Y*Z)+1))
const SCEV *InnerMul = Mul->getOperand(MulOp == 0);
if (Mul->getNumOperands() != 2) {
// If the multiply has more than two operands, we must get the
// Y*Z term.
SmallVector<const SCEV *, 4> MulOps(
Mul->operands().take_front(MulOp));
append_range(MulOps, Mul->operands().drop_front(MulOp + 1));
InnerMul = getMulExpr(MulOps, SCEV::FlagAnyWrap, Depth + 1);
}
SmallVector<const SCEV *, 2> TwoOps = {getOne(Ty), InnerMul};
const SCEV *AddOne = getAddExpr(TwoOps, SCEV::FlagAnyWrap, Depth + 1);
const SCEV *OuterMul = getMulExpr(AddOne, MulOpSCEV,
SCEV::FlagAnyWrap, Depth + 1);
if (Ops.size() == 2) return OuterMul;
if (AddOp < Idx) {
Ops.erase(Ops.begin()+AddOp);
Ops.erase(Ops.begin()+Idx-1);
} else {
Ops.erase(Ops.begin()+Idx);
Ops.erase(Ops.begin()+AddOp-1);
}
Ops.push_back(OuterMul);
return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
// Check this multiply against other multiplies being added together.
for (unsigned OtherMulIdx = Idx+1;
OtherMulIdx < Ops.size() && isa<SCEVMulExpr>(Ops[OtherMulIdx]);
++OtherMulIdx) {
const SCEVMulExpr *OtherMul = cast<SCEVMulExpr>(Ops[OtherMulIdx]);
// If MulOp occurs in OtherMul, we can fold the two multiplies
// together.
for (unsigned OMulOp = 0, e = OtherMul->getNumOperands();
OMulOp != e; ++OMulOp)
if (OtherMul->getOperand(OMulOp) == MulOpSCEV) {
// Fold X + (A*B*C) + (A*D*E) --> X + (A*(B*C+D*E))
const SCEV *InnerMul1 = Mul->getOperand(MulOp == 0);
if (Mul->getNumOperands() != 2) {
SmallVector<const SCEV *, 4> MulOps(
Mul->operands().take_front(MulOp));
append_range(MulOps, Mul->operands().drop_front(MulOp+1));
InnerMul1 = getMulExpr(MulOps, SCEV::FlagAnyWrap, Depth + 1);
}
const SCEV *InnerMul2 = OtherMul->getOperand(OMulOp == 0);
if (OtherMul->getNumOperands() != 2) {
SmallVector<const SCEV *, 4> MulOps(
OtherMul->operands().take_front(OMulOp));
append_range(MulOps, OtherMul->operands().drop_front(OMulOp+1));
InnerMul2 = getMulExpr(MulOps, SCEV::FlagAnyWrap, Depth + 1);
}
SmallVector<const SCEV *, 2> TwoOps = {InnerMul1, InnerMul2};
const SCEV *InnerMulSum =
getAddExpr(TwoOps, SCEV::FlagAnyWrap, Depth + 1);
const SCEV *OuterMul = getMulExpr(MulOpSCEV, InnerMulSum,
SCEV::FlagAnyWrap, Depth + 1);
if (Ops.size() == 2) return OuterMul;
Ops.erase(Ops.begin()+Idx);
Ops.erase(Ops.begin()+OtherMulIdx-1);
Ops.push_back(OuterMul);
return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
}
}
}
// If there are any add recurrences in the operands list, see if any other
// added values are loop invariant. If so, we can fold them into the
// recurrence.
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr)
++Idx;
// Scan over all recurrences, trying to fold loop invariants into them.
for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) {
// Scan all of the other operands to this add and add them to the vector if
// they are loop invariant w.r.t. the recurrence.
SmallVector<const SCEV *, 8> LIOps;
const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]);
const Loop *AddRecLoop = AddRec->getLoop();
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
if (isAvailableAtLoopEntry(Ops[i], AddRecLoop)) {
LIOps.push_back(Ops[i]);
Ops.erase(Ops.begin()+i);
--i; --e;
}
// If we found some loop invariants, fold them into the recurrence.
if (!LIOps.empty()) {
// Compute nowrap flags for the addition of the loop-invariant ops and
// the addrec. Temporarily push it as an operand for that purpose. These
// flags are valid in the scope of the addrec only.
LIOps.push_back(AddRec);
SCEV::NoWrapFlags Flags = ComputeFlags(LIOps);
LIOps.pop_back();
// NLI + LI + {Start,+,Step} --> NLI + {LI+Start,+,Step}
LIOps.push_back(AddRec->getStart());
SmallVector<const SCEV *, 4> AddRecOps(AddRec->operands());
// It is not in general safe to propagate flags valid on an add within
// the addrec scope to one outside it. We must prove that the inner
// scope is guaranteed to execute if the outer one does to be able to
// safely propagate. We know the program is undefined if poison is
// produced on the inner scoped addrec. We also know that *for this use*
// the outer scoped add can't overflow (because of the flags we just
// computed for the inner scoped add) without the program being undefined.
// Proving that entry to the outer scope neccesitates entry to the inner
// scope, thus proves the program undefined if the flags would be violated
// in the outer scope.
SCEV::NoWrapFlags AddFlags = Flags;
if (AddFlags != SCEV::FlagAnyWrap) {
auto *DefI = getDefiningScopeBound(LIOps);
auto *ReachI = &*AddRecLoop->getHeader()->begin();
if (!isGuaranteedToTransferExecutionTo(DefI, ReachI))
AddFlags = SCEV::FlagAnyWrap;
}
AddRecOps[0] = getAddExpr(LIOps, AddFlags, Depth + 1);
// Build the new addrec. Propagate the NUW and NSW flags if both the
// outer add and the inner addrec are guaranteed to have no overflow.
// Always propagate NW.
Flags = AddRec->getNoWrapFlags(setFlags(Flags, SCEV::FlagNW));
const SCEV *NewRec = getAddRecExpr(AddRecOps, AddRecLoop, Flags);
// If all of the other operands were loop invariant, we are done.
if (Ops.size() == 1) return NewRec;
// Otherwise, add the folded AddRec by the non-invariant parts.
for (unsigned i = 0;; ++i)
if (Ops[i] == AddRec) {
Ops[i] = NewRec;
break;
}
return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
// Okay, if there weren't any loop invariants to be folded, check to see if
// there are multiple AddRec's with the same loop induction variable being
// added together. If so, we can fold them.
for (unsigned OtherIdx = Idx+1;
OtherIdx < Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
++OtherIdx) {
// We expect the AddRecExpr's to be sorted in reverse dominance order,
// so that the 1st found AddRecExpr is dominated by all others.
assert(DT.dominates(
cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()->getHeader(),
AddRec->getLoop()->getHeader()) &&
"AddRecExprs are not sorted in reverse dominance order?");
if (AddRecLoop == cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) {
// Other + {A,+,B}<L> + {C,+,D}<L> --> Other + {A+C,+,B+D}<L>
SmallVector<const SCEV *, 4> AddRecOps(AddRec->operands());
for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
++OtherIdx) {
const auto *OtherAddRec = cast<SCEVAddRecExpr>(Ops[OtherIdx]);
if (OtherAddRec->getLoop() == AddRecLoop) {
for (unsigned i = 0, e = OtherAddRec->getNumOperands();
i != e; ++i) {
if (i >= AddRecOps.size()) {
append_range(AddRecOps, OtherAddRec->operands().drop_front(i));
break;
}
SmallVector<const SCEV *, 2> TwoOps = {
AddRecOps[i], OtherAddRec->getOperand(i)};
AddRecOps[i] = getAddExpr(TwoOps, SCEV::FlagAnyWrap, Depth + 1);
}
Ops.erase(Ops.begin() + OtherIdx); --OtherIdx;
}
}
// Step size has changed, so we cannot guarantee no self-wraparound.
Ops[Idx] = getAddRecExpr(AddRecOps, AddRecLoop, SCEV::FlagAnyWrap);
return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
}
// Otherwise couldn't fold anything into this recurrence. Move onto the
// next one.
}
// Okay, it looks like we really DO need an add expr. Check to see if we
// already have one, otherwise create a new one.
return getOrCreateAddExpr(Ops, ComputeFlags(Ops));
}
const SCEV *
ScalarEvolution::getOrCreateAddExpr(ArrayRef<const SCEV *> Ops,
SCEV::NoWrapFlags Flags) {
FoldingSetNodeID ID;
ID.AddInteger(scAddExpr);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
void *IP = nullptr;
SCEVAddExpr *S =
static_cast<SCEVAddExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP));
if (!S) {
const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size());
std::uninitialized_copy(Ops.begin(), Ops.end(), O);
S = new (SCEVAllocator)
SCEVAddExpr(ID.Intern(SCEVAllocator), O, Ops.size());
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Ops);
}
S->setNoWrapFlags(Flags);
return S;
}
const SCEV *
ScalarEvolution::getOrCreateAddRecExpr(ArrayRef<const SCEV *> Ops,
const Loop *L, SCEV::NoWrapFlags Flags) {
FoldingSetNodeID ID;
ID.AddInteger(scAddRecExpr);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
ID.AddPointer(L);
void *IP = nullptr;
SCEVAddRecExpr *S =
static_cast<SCEVAddRecExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP));
if (!S) {
const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size());
std::uninitialized_copy(Ops.begin(), Ops.end(), O);
S = new (SCEVAllocator)
SCEVAddRecExpr(ID.Intern(SCEVAllocator), O, Ops.size(), L);
UniqueSCEVs.InsertNode(S, IP);
LoopUsers[L].push_back(S);
registerUser(S, Ops);
}
setNoWrapFlags(S, Flags);
return S;
}
const SCEV *
ScalarEvolution::getOrCreateMulExpr(ArrayRef<const SCEV *> Ops,
SCEV::NoWrapFlags Flags) {
FoldingSetNodeID ID;
ID.AddInteger(scMulExpr);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
void *IP = nullptr;
SCEVMulExpr *S =
static_cast<SCEVMulExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP));
if (!S) {
const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size());
std::uninitialized_copy(Ops.begin(), Ops.end(), O);
S = new (SCEVAllocator) SCEVMulExpr(ID.Intern(SCEVAllocator),
O, Ops.size());
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Ops);
}
S->setNoWrapFlags(Flags);
return S;
}
static uint64_t umul_ov(uint64_t i, uint64_t j, bool &Overflow) {
uint64_t k = i*j;
if (j > 1 && k / j != i) Overflow = true;
return k;
}
/// Compute the result of "n choose k", the binomial coefficient. If an
/// intermediate computation overflows, Overflow will be set and the return will
/// be garbage. Overflow is not cleared on absence of overflow.
static uint64_t Choose(uint64_t n, uint64_t k, bool &Overflow) {
// We use the multiplicative formula:
// n(n-1)(n-2)...(n-(k-1)) / k(k-1)(k-2)...1 .
// At each iteration, we take the n-th term of the numeral and divide by the
// (k-n)th term of the denominator. This division will always produce an
// integral result, and helps reduce the chance of overflow in the
// intermediate computations. However, we can still overflow even when the
// final result would fit.
if (n == 0 || n == k) return 1;
if (k > n) return 0;
if (k > n/2)
k = n-k;
uint64_t r = 1;
for (uint64_t i = 1; i <= k; ++i) {
r = umul_ov(r, n-(i-1), Overflow);
r /= i;
}
return r;
}
/// Determine if any of the operands in this SCEV are a constant or if
/// any of the add or multiply expressions in this SCEV contain a constant.
static bool containsConstantInAddMulChain(const SCEV *StartExpr) {
struct FindConstantInAddMulChain {
bool FoundConstant = false;
bool follow(const SCEV *S) {
FoundConstant |= isa<SCEVConstant>(S);
return isa<SCEVAddExpr>(S) || isa<SCEVMulExpr>(S);
}
bool isDone() const {
return FoundConstant;
}
};
FindConstantInAddMulChain F;
SCEVTraversal<FindConstantInAddMulChain> ST(F);
ST.visitAll(StartExpr);
return F.FoundConstant;
}
/// Get a canonical multiply expression, or something simpler if possible.
const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
SCEV::NoWrapFlags OrigFlags,
unsigned Depth) {
assert(OrigFlags == maskFlags(OrigFlags, SCEV::FlagNUW | SCEV::FlagNSW) &&
"only nuw or nsw allowed");
assert(!Ops.empty() && "Cannot get empty mul!");
if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
Type *ETy = Ops[0]->getType();
assert(!ETy->isPointerTy());
for (unsigned i = 1, e = Ops.size(); i != e; ++i)
assert(Ops[i]->getType() == ETy &&
"SCEVMulExpr operand types don't match!");
#endif
const SCEV *Folded = constantFoldAndGroupOps(
*this, LI, DT, Ops,
[](const APInt &C1, const APInt &C2) { return C1 * C2; },
[](const APInt &C) { return C.isOne(); }, // identity
[](const APInt &C) { return C.isZero(); }); // absorber
if (Folded)
return Folded;
// Delay expensive flag strengthening until necessary.
auto ComputeFlags = [this, OrigFlags](const ArrayRef<const SCEV *> Ops) {
return StrengthenNoWrapFlags(this, scMulExpr, Ops, OrigFlags);
};
// Limit recursion calls depth.
if (Depth > MaxArithDepth || hasHugeExpression(Ops))
return getOrCreateMulExpr(Ops, ComputeFlags(Ops));
if (SCEV *S = findExistingSCEVInCache(scMulExpr, Ops)) {
// Don't strengthen flags if we have no new information.
SCEVMulExpr *Mul = static_cast<SCEVMulExpr *>(S);
if (Mul->getNoWrapFlags(OrigFlags) != OrigFlags)
Mul->setNoWrapFlags(ComputeFlags(Ops));
return S;
}
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) {
if (Ops.size() == 2) {
// C1*(C2+V) -> C1*C2 + C1*V
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1]))
// If any of Add's ops are Adds or Muls with a constant, apply this
// transformation as well.
//
// TODO: There are some cases where this transformation is not
// profitable; for example, Add = (C0 + X) * Y + Z. Maybe the scope of
// this transformation should be narrowed down.
if (Add->getNumOperands() == 2 && containsConstantInAddMulChain(Add)) {
const SCEV *LHS = getMulExpr(LHSC, Add->getOperand(0),
SCEV::FlagAnyWrap, Depth + 1);
const SCEV *RHS = getMulExpr(LHSC, Add->getOperand(1),
SCEV::FlagAnyWrap, Depth + 1);
return getAddExpr(LHS, RHS, SCEV::FlagAnyWrap, Depth + 1);
}
if (Ops[0]->isAllOnesValue()) {
// If we have a mul by -1 of an add, try distributing the -1 among the
// add operands.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1])) {
SmallVector<const SCEV *, 4> NewOps;
bool AnyFolded = false;
for (const SCEV *AddOp : Add->operands()) {
const SCEV *Mul = getMulExpr(Ops[0], AddOp, SCEV::FlagAnyWrap,
Depth + 1);
if (!isa<SCEVMulExpr>(Mul)) AnyFolded = true;
NewOps.push_back(Mul);
}
if (AnyFolded)
return getAddExpr(NewOps, SCEV::FlagAnyWrap, Depth + 1);
} else if (const auto *AddRec = dyn_cast<SCEVAddRecExpr>(Ops[1])) {
// Negation preserves a recurrence's no self-wrap property.
SmallVector<const SCEV *, 4> Operands;
for (const SCEV *AddRecOp : AddRec->operands())
Operands.push_back(getMulExpr(Ops[0], AddRecOp, SCEV::FlagAnyWrap,
Depth + 1));
// Let M be the minimum representable signed value. AddRec with nsw
// multiplied by -1 can have signed overflow if and only if it takes a
// value of M: M * (-1) would stay M and (M + 1) * (-1) would be the
// maximum signed value. In all other cases signed overflow is
// impossible.
auto FlagsMask = SCEV::FlagNW;
if (hasFlags(AddRec->getNoWrapFlags(), SCEV::FlagNSW)) {
auto MinInt =
APInt::getSignedMinValue(getTypeSizeInBits(AddRec->getType()));
if (getSignedRangeMin(AddRec) != MinInt)
FlagsMask = setFlags(FlagsMask, SCEV::FlagNSW);
}
return getAddRecExpr(Operands, AddRec->getLoop(),
AddRec->getNoWrapFlags(FlagsMask));
}
}
}
}
// Skip over the add expression until we get to a multiply.
unsigned Idx = 0;
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr)
++Idx;
// If there are mul operands inline them all into this expression.
if (Idx < Ops.size()) {
bool DeletedMul = false;
while (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[Idx])) {
if (Ops.size() > MulOpsInlineThreshold)
break;
// If we have an mul, expand the mul operands onto the end of the
// operands list.
Ops.erase(Ops.begin()+Idx);
append_range(Ops, Mul->operands());
DeletedMul = true;
}
// If we deleted at least one mul, we added operands to the end of the
// list, and they are not necessarily sorted. Recurse to resort and
// resimplify any operands we just acquired.
if (DeletedMul)
return getMulExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
// If there are any add recurrences in the operands list, see if any other
// added values are loop invariant. If so, we can fold them into the
// recurrence.
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr)
++Idx;
// Scan over all recurrences, trying to fold loop invariants into them.
for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) {
// Scan all of the other operands to this mul and add them to the vector
// if they are loop invariant w.r.t. the recurrence.
SmallVector<const SCEV *, 8> LIOps;
const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]);
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
if (isAvailableAtLoopEntry(Ops[i], AddRec->getLoop())) {
LIOps.push_back(Ops[i]);
Ops.erase(Ops.begin()+i);
--i; --e;
}
// If we found some loop invariants, fold them into the recurrence.
if (!LIOps.empty()) {
// NLI * LI * {Start,+,Step} --> NLI * {LI*Start,+,LI*Step}
SmallVector<const SCEV *, 4> NewOps;
NewOps.reserve(AddRec->getNumOperands());
const SCEV *Scale = getMulExpr(LIOps, SCEV::FlagAnyWrap, Depth + 1);
// If both the mul and addrec are nuw, we can preserve nuw.
// If both the mul and addrec are nsw, we can only preserve nsw if either
// a) they are also nuw, or
// b) all multiplications of addrec operands with scale are nsw.
SCEV::NoWrapFlags Flags =
AddRec->getNoWrapFlags(ComputeFlags({Scale, AddRec}));
for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
NewOps.push_back(getMulExpr(Scale, AddRec->getOperand(i),
SCEV::FlagAnyWrap, Depth + 1));
if (hasFlags(Flags, SCEV::FlagNSW) && !hasFlags(Flags, SCEV::FlagNUW)) {
ConstantRange NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
Instruction::Mul, getSignedRange(Scale),
OverflowingBinaryOperator::NoSignedWrap);
if (!NSWRegion.contains(getSignedRange(AddRec->getOperand(i))))
Flags = clearFlags(Flags, SCEV::FlagNSW);
}
}
const SCEV *NewRec = getAddRecExpr(NewOps, AddRec->getLoop(), Flags);
// If all of the other operands were loop invariant, we are done.
if (Ops.size() == 1) return NewRec;
// Otherwise, multiply the folded AddRec by the non-invariant parts.
for (unsigned i = 0;; ++i)
if (Ops[i] == AddRec) {
Ops[i] = NewRec;
break;
}
return getMulExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
}
// Okay, if there weren't any loop invariants to be folded, check to see
// if there are multiple AddRec's with the same loop induction variable
// being multiplied together. If so, we can fold them.
// {A1,+,A2,+,...,+,An}<L> * {B1,+,B2,+,...,+,Bn}<L>
// = {x=1 in [ sum y=x..2x [ sum z=max(y-x, y-n)..min(x,n) [
// choose(x, 2x)*choose(2x-y, x-z)*A_{y-z}*B_z
// ]]],+,...up to x=2n}.
// Note that the arguments to choose() are always integers with values
// known at compile time, never SCEV objects.
//
// The implementation avoids pointless extra computations when the two
// addrec's are of different length (mathematically, it's equivalent to
// an infinite stream of zeros on the right).
bool OpsModified = false;
for (unsigned OtherIdx = Idx+1;
OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
++OtherIdx) {
const SCEVAddRecExpr *OtherAddRec =
dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx]);
if (!OtherAddRec || OtherAddRec->getLoop() != AddRec->getLoop())
continue;
// Limit max number of arguments to avoid creation of unreasonably big
// SCEVAddRecs with very complex operands.
if (AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 >
MaxAddRecSize || hasHugeExpression({AddRec, OtherAddRec}))
continue;
bool Overflow = false;
Type *Ty = AddRec->getType();
bool LargerThan64Bits = getTypeSizeInBits(Ty) > 64;
SmallVector<const SCEV*, 7> AddRecOps;
for (int x = 0, xe = AddRec->getNumOperands() +
OtherAddRec->getNumOperands() - 1; x != xe && !Overflow; ++x) {
SmallVector <const SCEV *, 7> SumOps;
for (int y = x, ye = 2*x+1; y != ye && !Overflow; ++y) {
uint64_t Coeff1 = Choose(x, 2*x - y, Overflow);
for (int z = std::max(y-x, y-(int)AddRec->getNumOperands()+1),
ze = std::min(x+1, (int)OtherAddRec->getNumOperands());
z < ze && !Overflow; ++z) {
uint64_t Coeff2 = Choose(2*x - y, x-z, Overflow);
uint64_t Coeff;
if (LargerThan64Bits)
Coeff = umul_ov(Coeff1, Coeff2, Overflow);
else
Coeff = Coeff1*Coeff2;
const SCEV *CoeffTerm = getConstant(Ty, Coeff);
const SCEV *Term1 = AddRec->getOperand(y-z);
const SCEV *Term2 = OtherAddRec->getOperand(z);
SumOps.push_back(getMulExpr(CoeffTerm, Term1, Term2,
SCEV::FlagAnyWrap, Depth + 1));
}
}
if (SumOps.empty())
SumOps.push_back(getZero(Ty));
AddRecOps.push_back(getAddExpr(SumOps, SCEV::FlagAnyWrap, Depth + 1));
}
if (!Overflow) {
const SCEV *NewAddRec = getAddRecExpr(AddRecOps, AddRec->getLoop(),
SCEV::FlagAnyWrap);
if (Ops.size() == 2) return NewAddRec;
Ops[Idx] = NewAddRec;
Ops.erase(Ops.begin() + OtherIdx); --OtherIdx;
OpsModified = true;
AddRec = dyn_cast<SCEVAddRecExpr>(NewAddRec);
if (!AddRec)
break;
}
}
if (OpsModified)
return getMulExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
// Otherwise couldn't fold anything into this recurrence. Move onto the
// next one.
}
// Okay, it looks like we really DO need an mul expr. Check to see if we
// already have one, otherwise create a new one.
return getOrCreateMulExpr(Ops, ComputeFlags(Ops));
}
/// Represents an unsigned remainder expression based on unsigned division.
const SCEV *ScalarEvolution::getURemExpr(const SCEV *LHS,
const SCEV *RHS) {
assert(getEffectiveSCEVType(LHS->getType()) ==
getEffectiveSCEVType(RHS->getType()) &&
"SCEVURemExpr operand types don't match!");
// Short-circuit easy cases
if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
// If constant is one, the result is trivial
if (RHSC->getValue()->isOne())
return getZero(LHS->getType()); // X urem 1 --> 0
// If constant is a power of two, fold into a zext(trunc(LHS)).
if (RHSC->getAPInt().isPowerOf2()) {
Type *FullTy = LHS->getType();
Type *TruncTy =
IntegerType::get(getContext(), RHSC->getAPInt().logBase2());
return getZeroExtendExpr(getTruncateExpr(LHS, TruncTy), FullTy);
}
}
// Fallback to %a == %x urem %y == %x -<nuw> ((%x udiv %y) *<nuw> %y)
const SCEV *UDiv = getUDivExpr(LHS, RHS);
const SCEV *Mult = getMulExpr(UDiv, RHS, SCEV::FlagNUW);
return getMinusSCEV(LHS, Mult, SCEV::FlagNUW);
}
/// Get a canonical unsigned division expression, or something simpler if
/// possible.
const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
const SCEV *RHS) {
assert(!LHS->getType()->isPointerTy() &&
"SCEVUDivExpr operand can't be pointer!");
assert(LHS->getType() == RHS->getType() &&
"SCEVUDivExpr operand types don't match!");
FoldingSetNodeID ID;
ID.AddInteger(scUDivExpr);
ID.AddPointer(LHS);
ID.AddPointer(RHS);
void *IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
return S;
// 0 udiv Y == 0
if (match(LHS, m_scev_Zero()))
return LHS;
if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
if (RHSC->getValue()->isOne())
return LHS; // X udiv 1 --> x
// If the denominator is zero, the result of the udiv is undefined. Don't
// try to analyze it, because the resolution chosen here may differ from
// the resolution chosen in other parts of the compiler.
if (!RHSC->getValue()->isZero()) {
// Determine if the division can be folded into the operands of
// its operands.
// TODO: Generalize this to non-constants by using known-bits information.
Type *Ty = LHS->getType();
unsigned LZ = RHSC->getAPInt().countl_zero();
unsigned MaxShiftAmt = getTypeSizeInBits(Ty) - LZ - 1;
// For non-power-of-two values, effectively round the value up to the
// nearest power of two.
if (!RHSC->getAPInt().isPowerOf2())
++MaxShiftAmt;
IntegerType *ExtTy =
IntegerType::get(getContext(), getTypeSizeInBits(Ty) + MaxShiftAmt);
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS))
if (const SCEVConstant *Step =
dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this))) {
// {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
const APInt &StepInt = Step->getAPInt();
const APInt &DivInt = RHSC->getAPInt();
if (!StepInt.urem(DivInt) &&
getZeroExtendExpr(AR, ExtTy) ==
getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
getZeroExtendExpr(Step, ExtTy),
AR->getLoop(), SCEV::FlagAnyWrap)) {
SmallVector<const SCEV *, 4> Operands;
for (const SCEV *Op : AR->operands())
Operands.push_back(getUDivExpr(Op, RHS));
return getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagNW);
}
/// Get a canonical UDivExpr for a recurrence.
/// {X,+,N}/C => {Y,+,N}/C where Y=X-(X%N). Safe when C%N=0.
// We can currently only fold X%N if X is constant.
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart());
if (StartC && !DivInt.urem(StepInt) &&
getZeroExtendExpr(AR, ExtTy) ==
getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
getZeroExtendExpr(Step, ExtTy),
AR->getLoop(), SCEV::FlagAnyWrap)) {
const APInt &StartInt = StartC->getAPInt();
const APInt &StartRem = StartInt.urem(StepInt);
if (StartRem != 0) {
const SCEV *NewLHS =
getAddRecExpr(getConstant(StartInt - StartRem), Step,
AR->getLoop(), SCEV::FlagNW);
if (LHS != NewLHS) {
LHS = NewLHS;
// Reset the ID to include the new LHS, and check if it is
// already cached.
ID.clear();
ID.AddInteger(scUDivExpr);
ID.AddPointer(LHS);
ID.AddPointer(RHS);
IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
return S;
}
}
}
}
// (A*B)/C --> A*(B/C) if safe and B/C can be folded.
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS)) {
SmallVector<const SCEV *, 4> Operands;
for (const SCEV *Op : M->operands())
Operands.push_back(getZeroExtendExpr(Op, ExtTy));
if (getZeroExtendExpr(M, ExtTy) == getMulExpr(Operands))
// Find an operand that's safely divisible.
for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) {
const SCEV *Op = M->getOperand(i);
const SCEV *Div = getUDivExpr(Op, RHSC);
if (!isa<SCEVUDivExpr>(Div) && getMulExpr(Div, RHSC) == Op) {
Operands = SmallVector<const SCEV *, 4>(M->operands());
Operands[i] = Div;
return getMulExpr(Operands);
}
}
}
// (A/B)/C --> A/(B*C) if safe and B*C can be folded.
if (const SCEVUDivExpr *OtherDiv = dyn_cast<SCEVUDivExpr>(LHS)) {
if (auto *DivisorConstant =
dyn_cast<SCEVConstant>(OtherDiv->getRHS())) {
bool Overflow = false;
APInt NewRHS =
DivisorConstant->getAPInt().umul_ov(RHSC->getAPInt(), Overflow);
if (Overflow) {
return getConstant(RHSC->getType(), 0, false);
}
return getUDivExpr(OtherDiv->getLHS(), getConstant(NewRHS));
}
}
// (A+B)/C --> (A/C + B/C) if safe and A/C and B/C can be folded.
if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(LHS)) {
SmallVector<const SCEV *, 4> Operands;
for (const SCEV *Op : A->operands())
Operands.push_back(getZeroExtendExpr(Op, ExtTy));
if (getZeroExtendExpr(A, ExtTy) == getAddExpr(Operands)) {
Operands.clear();
for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i) {
const SCEV *Op = getUDivExpr(A->getOperand(i), RHS);
if (isa<SCEVUDivExpr>(Op) ||
getMulExpr(Op, RHS) != A->getOperand(i))
break;
Operands.push_back(Op);
}
if (Operands.size() == A->getNumOperands())
return getAddExpr(Operands);
}
}
// Fold if both operands are constant.
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS))
return getConstant(LHSC->getAPInt().udiv(RHSC->getAPInt()));
}
}
// ((-C + (C smax %x)) /u %x) evaluates to zero, for any positive constant C.
if (const auto *AE = dyn_cast<SCEVAddExpr>(LHS);
AE && AE->getNumOperands() == 2) {
if (const auto *VC = dyn_cast<SCEVConstant>(AE->getOperand(0))) {
const APInt &NegC = VC->getAPInt();
if (NegC.isNegative() && !NegC.isMinSignedValue()) {
const auto *MME = dyn_cast<SCEVSMaxExpr>(AE->getOperand(1));
if (MME && MME->getNumOperands() == 2 &&
isa<SCEVConstant>(MME->getOperand(0)) &&
cast<SCEVConstant>(MME->getOperand(0))->getAPInt() == -NegC &&
MME->getOperand(1) == RHS)
return getZero(LHS->getType());
}
}
}
// The Insertion Point (IP) might be invalid by now (due to UniqueSCEVs
// changes). Make sure we get a new one.
IP = nullptr;
if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
SCEV *S = new (SCEVAllocator) SCEVUDivExpr(ID.Intern(SCEVAllocator),
LHS, RHS);
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, {LHS, RHS});
return S;
}
APInt gcd(const SCEVConstant *C1, const SCEVConstant *C2) {
APInt A = C1->getAPInt().abs();
APInt B = C2->getAPInt().abs();
uint32_t ABW = A.getBitWidth();
uint32_t BBW = B.getBitWidth();
if (ABW > BBW)
B = B.zext(ABW);
else if (ABW < BBW)
A = A.zext(BBW);
return APIntOps::GreatestCommonDivisor(std::move(A), std::move(B));
}
/// Get a canonical unsigned division expression, or something simpler if
/// possible. There is no representation for an exact udiv in SCEV IR, but we
/// can attempt to remove factors from the LHS and RHS. We can't do this when
/// it's not exact because the udiv may be clearing bits.
const SCEV *ScalarEvolution::getUDivExactExpr(const SCEV *LHS,
const SCEV *RHS) {
// TODO: we could try to find factors in all sorts of things, but for now we
// just deal with u/exact (multiply, constant). See SCEVDivision towards the
// end of this file for inspiration.
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS);
if (!Mul || !Mul->hasNoUnsignedWrap())
return getUDivExpr(LHS, RHS);
if (const SCEVConstant *RHSCst = dyn_cast<SCEVConstant>(RHS)) {
// If the mulexpr multiplies by a constant, then that constant must be the
// first element of the mulexpr.
if (const auto *LHSCst = dyn_cast<SCEVConstant>(Mul->getOperand(0))) {
if (LHSCst == RHSCst) {
SmallVector<const SCEV *, 2> Operands(drop_begin(Mul->operands()));
return getMulExpr(Operands);
}
// We can't just assume that LHSCst divides RHSCst cleanly, it could be
// that there's a factor provided by one of the other terms. We need to
// check.
APInt Factor = gcd(LHSCst, RHSCst);
if (!Factor.isIntN(1)) {
LHSCst =
cast<SCEVConstant>(getConstant(LHSCst->getAPInt().udiv(Factor)));
RHSCst =
cast<SCEVConstant>(getConstant(RHSCst->getAPInt().udiv(Factor)));
SmallVector<const SCEV *, 2> Operands;
Operands.push_back(LHSCst);
append_range(Operands, Mul->operands().drop_front());
LHS = getMulExpr(Operands);
RHS = RHSCst;
Mul = dyn_cast<SCEVMulExpr>(LHS);
if (!Mul)
return getUDivExactExpr(LHS, RHS);
}
}
}
for (int i = 0, e = Mul->getNumOperands(); i != e; ++i) {
if (Mul->getOperand(i) == RHS) {
SmallVector<const SCEV *, 2> Operands;
append_range(Operands, Mul->operands().take_front(i));
append_range(Operands, Mul->operands().drop_front(i + 1));
return getMulExpr(Operands);
}
}
return getUDivExpr(LHS, RHS);
}
/// Get an add recurrence expression for the specified loop. Simplify the
/// expression as much as possible.
const SCEV *ScalarEvolution::getAddRecExpr(const SCEV *Start, const SCEV *Step,
const Loop *L,
SCEV::NoWrapFlags Flags) {
SmallVector<const SCEV *, 4> Operands;
Operands.push_back(Start);
if (const SCEVAddRecExpr *StepChrec = dyn_cast<SCEVAddRecExpr>(Step))
if (StepChrec->getLoop() == L) {
append_range(Operands, StepChrec->operands());
return getAddRecExpr(Operands, L, maskFlags(Flags, SCEV::FlagNW));
}
Operands.push_back(Step);
return getAddRecExpr(Operands, L, Flags);
}
/// Get an add recurrence expression for the specified loop. Simplify the
/// expression as much as possible.
const SCEV *
ScalarEvolution::getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands,
const Loop *L, SCEV::NoWrapFlags Flags) {
if (Operands.size() == 1) return Operands[0];
#ifndef NDEBUG
Type *ETy = getEffectiveSCEVType(Operands[0]->getType());
for (const SCEV *Op : llvm::drop_begin(Operands)) {
assert(getEffectiveSCEVType(Op->getType()) == ETy &&
"SCEVAddRecExpr operand types don't match!");
assert(!Op->getType()->isPointerTy() && "Step must be integer");
}
for (const SCEV *Op : Operands)
assert(isAvailableAtLoopEntry(Op, L) &&
"SCEVAddRecExpr operand is not available at loop entry!");
#endif
if (Operands.back()->isZero()) {
Operands.pop_back();
return getAddRecExpr(Operands, L, SCEV::FlagAnyWrap); // {X,+,0} --> X
}
// It's tempting to want to call getConstantMaxBackedgeTakenCount count here and
// use that information to infer NUW and NSW flags. However, computing a
// BE count requires calling getAddRecExpr, so we may not yet have a
// meaningful BE count at this point (and if we don't, we'd be stuck
// with a SCEVCouldNotCompute as the cached BE count).
Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
// Canonicalize nested AddRecs in by nesting them in order of loop depth.
if (const SCEVAddRecExpr *NestedAR = dyn_cast<SCEVAddRecExpr>(Operands[0])) {
const Loop *NestedLoop = NestedAR->getLoop();
if (L->contains(NestedLoop)
? (L->getLoopDepth() < NestedLoop->getLoopDepth())
: (!NestedLoop->contains(L) &&
DT.dominates(L->getHeader(), NestedLoop->getHeader()))) {
SmallVector<const SCEV *, 4> NestedOperands(NestedAR->operands());
Operands[0] = NestedAR->getStart();
// AddRecs require their operands be loop-invariant with respect to their
// loops. Don't perform this transformation if it would break this
// requirement.
bool AllInvariant = all_of(
Operands, [&](const SCEV *Op) { return isLoopInvariant(Op, L); });
if (AllInvariant) {
// Create a recurrence for the outer loop with the same step size.
//
// The outer recurrence keeps its NW flag but only keeps NUW/NSW if the
// inner recurrence has the same property.
SCEV::NoWrapFlags OuterFlags =
maskFlags(Flags, SCEV::FlagNW | NestedAR->getNoWrapFlags());
NestedOperands[0] = getAddRecExpr(Operands, L, OuterFlags);
AllInvariant = all_of(NestedOperands, [&](const SCEV *Op) {
return isLoopInvariant(Op, NestedLoop);
});
if (AllInvariant) {
// Ok, both add recurrences are valid after the transformation.
//
// The inner recurrence keeps its NW flag but only keeps NUW/NSW if
// the outer recurrence has the same property.
SCEV::NoWrapFlags InnerFlags =
maskFlags(NestedAR->getNoWrapFlags(), SCEV::FlagNW | Flags);
return getAddRecExpr(NestedOperands, NestedLoop, InnerFlags);
}
}
// Reset Operands to its original state.
Operands[0] = NestedAR;
}
}
// Okay, it looks like we really DO need an addrec expr. Check to see if we
// already have one, otherwise create a new one.
return getOrCreateAddRecExpr(Operands, L, Flags);
}
const SCEV *
ScalarEvolution::getGEPExpr(GEPOperator *GEP,
const SmallVectorImpl<const SCEV *> &IndexExprs) {
const SCEV *BaseExpr = getSCEV(GEP->getPointerOperand());
// getSCEV(Base)->getType() has the same address space as Base->getType()
// because SCEV::getType() preserves the address space.
Type *IntIdxTy = getEffectiveSCEVType(BaseExpr->getType());
GEPNoWrapFlags NW = GEP->getNoWrapFlags();
if (NW != GEPNoWrapFlags::none()) {
// We'd like to propagate flags from the IR to the corresponding SCEV nodes,
// but to do that, we have to ensure that said flag is valid in the entire
// defined scope of the SCEV.
// TODO: non-instructions have global scope. We might be able to prove
// some global scope cases
auto *GEPI = dyn_cast<Instruction>(GEP);
if (!GEPI || !isSCEVExprNeverPoison(GEPI))
NW = GEPNoWrapFlags::none();
}
SCEV::NoWrapFlags OffsetWrap = SCEV::FlagAnyWrap;
if (NW.hasNoUnsignedSignedWrap())
OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNSW);
if (NW.hasNoUnsignedWrap())
OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNUW);
Type *CurTy = GEP->getType();
bool FirstIter = true;
SmallVector<const SCEV *, 4> Offsets;
for (const SCEV *IndexExpr : IndexExprs) {
// Compute the (potentially symbolic) offset in bytes for this index.
if (StructType *STy = dyn_cast<StructType>(CurTy)) {
// For a struct, add the member offset.
ConstantInt *Index = cast<SCEVConstant>(IndexExpr)->getValue();
unsigned FieldNo = Index->getZExtValue();
const SCEV *FieldOffset = getOffsetOfExpr(IntIdxTy, STy, FieldNo);
Offsets.push_back(FieldOffset);
// Update CurTy to the type of the field at Index.
CurTy = STy->getTypeAtIndex(Index);
} else {
// Update CurTy to its element type.
if (FirstIter) {
assert(isa<PointerType>(CurTy) &&
"The first index of a GEP indexes a pointer");
CurTy = GEP->getSourceElementType();
FirstIter = false;
} else {
CurTy = GetElementPtrInst::getTypeAtIndex(CurTy, (uint64_t)0);
}
// For an array, add the element offset, explicitly scaled.
const SCEV *ElementSize = getSizeOfExpr(IntIdxTy, CurTy);
// Getelementptr indices are signed.
IndexExpr = getTruncateOrSignExtend(IndexExpr, IntIdxTy);
// Multiply the index by the element size to compute the element offset.
const SCEV *LocalOffset = getMulExpr(IndexExpr, ElementSize, OffsetWrap);
Offsets.push_back(LocalOffset);
}
}
// Handle degenerate case of GEP without offsets.
if (Offsets.empty())
return BaseExpr;
// Add the offsets together, assuming nsw if inbounds.
const SCEV *Offset = getAddExpr(Offsets, OffsetWrap);
// Add the base address and the offset. We cannot use the nsw flag, as the
// base address is unsigned. However, if we know that the offset is
// non-negative, we can use nuw.
bool NUW = NW.hasNoUnsignedWrap() ||
(NW.hasNoUnsignedSignedWrap() && isKnownNonNegative(Offset));
SCEV::NoWrapFlags BaseWrap = NUW ? SCEV::FlagNUW : SCEV::FlagAnyWrap;
auto *GEPExpr = getAddExpr(BaseExpr, Offset, BaseWrap);
assert(BaseExpr->getType() == GEPExpr->getType() &&
"GEP should not change type mid-flight.");
return GEPExpr;
}
SCEV *ScalarEvolution::findExistingSCEVInCache(SCEVTypes SCEVType,
ArrayRef<const SCEV *> Ops) {
FoldingSetNodeID ID;
ID.AddInteger(SCEVType);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
void *IP = nullptr;
return UniqueSCEVs.FindNodeOrInsertPos(ID, IP);
}
const SCEV *ScalarEvolution::getAbsExpr(const SCEV *Op, bool IsNSW) {
SCEV::NoWrapFlags Flags = IsNSW ? SCEV::FlagNSW : SCEV::FlagAnyWrap;
return getSMaxExpr(Op, getNegativeSCEV(Op, Flags));
}
const SCEV *ScalarEvolution::getMinMaxExpr(SCEVTypes Kind,
SmallVectorImpl<const SCEV *> &Ops) {
assert(SCEVMinMaxExpr::isMinMaxType(Kind) && "Not a SCEVMinMaxExpr!");
assert(!Ops.empty() && "Cannot get empty (u|s)(min|max)!");
if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
"Operand types don't match!");
assert(Ops[0]->getType()->isPointerTy() ==
Ops[i]->getType()->isPointerTy() &&
"min/max should be consistently pointerish");
}
#endif
bool IsSigned = Kind == scSMaxExpr || Kind == scSMinExpr;
bool IsMax = Kind == scSMaxExpr || Kind == scUMaxExpr;
const SCEV *Folded = constantFoldAndGroupOps(
*this, LI, DT, Ops,
[&](const APInt &C1, const APInt &C2) {
switch (Kind) {
case scSMaxExpr:
return APIntOps::smax(C1, C2);
case scSMinExpr:
return APIntOps::smin(C1, C2);
case scUMaxExpr:
return APIntOps::umax(C1, C2);
case scUMinExpr:
return APIntOps::umin(C1, C2);
default:
llvm_unreachable("Unknown SCEV min/max opcode");
}
},
[&](const APInt &C) {
// identity
if (IsMax)
return IsSigned ? C.isMinSignedValue() : C.isMinValue();
else
return IsSigned ? C.isMaxSignedValue() : C.isMaxValue();
},
[&](const APInt &C) {
// absorber
if (IsMax)
return IsSigned ? C.isMaxSignedValue() : C.isMaxValue();
else
return IsSigned ? C.isMinSignedValue() : C.isMinValue();
});
if (Folded)
return Folded;
// Check if we have created the same expression before.
if (const SCEV *S = findExistingSCEVInCache(Kind, Ops)) {
return S;
}
// Find the first operation of the same kind
unsigned Idx = 0;
while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < Kind)
++Idx;
// Check to see if one of the operands is of the same kind. If so, expand its
// operands onto our operand list, and recurse to simplify.
if (Idx < Ops.size()) {
bool DeletedAny = false;
while (Ops[Idx]->getSCEVType() == Kind) {
const SCEVMinMaxExpr *SMME = cast<SCEVMinMaxExpr>(Ops[Idx]);
Ops.erase(Ops.begin()+Idx);
append_range(Ops, SMME->operands());
DeletedAny = true;
}
if (DeletedAny)
return getMinMaxExpr(Kind, Ops);
}
// Okay, check to see if the same value occurs in the operand list twice. If
// so, delete one. Since we sorted the list, these values are required to
// be adjacent.
llvm::CmpInst::Predicate GEPred =
IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
llvm::CmpInst::Predicate LEPred =
IsSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
llvm::CmpInst::Predicate FirstPred = IsMax ? GEPred : LEPred;
llvm::CmpInst::Predicate SecondPred = IsMax ? LEPred : GEPred;
for (unsigned i = 0, e = Ops.size() - 1; i != e; ++i) {
if (Ops[i] == Ops[i + 1] ||
isKnownViaNonRecursiveReasoning(FirstPred, Ops[i], Ops[i + 1])) {
// X op Y op Y --> X op Y
// X op Y --> X, if we know X, Y are ordered appropriately
Ops.erase(Ops.begin() + i + 1, Ops.begin() + i + 2);
--i;
--e;
} else if (isKnownViaNonRecursiveReasoning(SecondPred, Ops[i],
Ops[i + 1])) {
// X op Y --> Y, if we know X, Y are ordered appropriately
Ops.erase(Ops.begin() + i, Ops.begin() + i + 1);
--i;
--e;
}
}
if (Ops.size() == 1) return Ops[0];
assert(!Ops.empty() && "Reduced smax down to nothing!");
// Okay, it looks like we really DO need an expr. Check to see if we
// already have one, otherwise create a new one.
FoldingSetNodeID ID;
ID.AddInteger(Kind);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
void *IP = nullptr;
const SCEV *ExistingSCEV = UniqueSCEVs.FindNodeOrInsertPos(ID, IP);
if (ExistingSCEV)
return ExistingSCEV;
const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size());
std::uninitialized_copy(Ops.begin(), Ops.end(), O);
SCEV *S = new (SCEVAllocator)
SCEVMinMaxExpr(ID.Intern(SCEVAllocator), Kind, O, Ops.size());
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Ops);
return S;
}
namespace {
class SCEVSequentialMinMaxDeduplicatingVisitor final
: public SCEVVisitor<SCEVSequentialMinMaxDeduplicatingVisitor,
std::optional<const SCEV *>> {
using RetVal = std::optional<const SCEV *>;
using Base = SCEVVisitor<SCEVSequentialMinMaxDeduplicatingVisitor, RetVal>;
ScalarEvolution &SE;
const SCEVTypes RootKind; // Must be a sequential min/max expression.
const SCEVTypes NonSequentialRootKind; // Non-sequential variant of RootKind.
SmallPtrSet<const SCEV *, 16> SeenOps;
bool canRecurseInto(SCEVTypes Kind) const {
// We can only recurse into the SCEV expression of the same effective type
// as the type of our root SCEV expression.
return RootKind == Kind || NonSequentialRootKind == Kind;
};
RetVal visitAnyMinMaxExpr(const SCEV *S) {
assert((isa<SCEVMinMaxExpr>(S) || isa<SCEVSequentialMinMaxExpr>(S)) &&
"Only for min/max expressions.");
SCEVTypes Kind = S->getSCEVType();
if (!canRecurseInto(Kind))
return S;
auto *NAry = cast<SCEVNAryExpr>(S);
SmallVector<const SCEV *> NewOps;
bool Changed = visit(Kind, NAry->operands(), NewOps);
if (!Changed)
return S;
if (NewOps.empty())
return std::nullopt;
return isa<SCEVSequentialMinMaxExpr>(S)
? SE.getSequentialMinMaxExpr(Kind, NewOps)
: SE.getMinMaxExpr(Kind, NewOps);
}
RetVal visit(const SCEV *S) {
// Has the whole operand been seen already?
if (!SeenOps.insert(S).second)
return std::nullopt;
return Base::visit(S);
}
public:
SCEVSequentialMinMaxDeduplicatingVisitor(ScalarEvolution &SE,
SCEVTypes RootKind)
: SE(SE), RootKind(RootKind),
NonSequentialRootKind(
SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(
RootKind)) {}
bool /*Changed*/ visit(SCEVTypes Kind, ArrayRef<const SCEV *> OrigOps,
SmallVectorImpl<const SCEV *> &NewOps) {
bool Changed = false;
SmallVector<const SCEV *> Ops;
Ops.reserve(OrigOps.size());
for (const SCEV *Op : OrigOps) {
RetVal NewOp = visit(Op);
if (NewOp != Op)
Changed = true;
if (NewOp)
Ops.emplace_back(*NewOp);
}
if (Changed)
NewOps = std::move(Ops);
return Changed;
}
RetVal visitConstant(const SCEVConstant *Constant) { return Constant; }
RetVal visitVScale(const SCEVVScale *VScale) { return VScale; }
RetVal visitPtrToIntExpr(const SCEVPtrToIntExpr *Expr) { return Expr; }
RetVal visitTruncateExpr(const SCEVTruncateExpr *Expr) { return Expr; }
RetVal visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) { return Expr; }
RetVal visitSignExtendExpr(const SCEVSignExtendExpr *Expr) { return Expr; }
RetVal visitAddExpr(const SCEVAddExpr *Expr) { return Expr; }
RetVal visitMulExpr(const SCEVMulExpr *Expr) { return Expr; }
RetVal visitUDivExpr(const SCEVUDivExpr *Expr) { return Expr; }
RetVal visitAddRecExpr(const SCEVAddRecExpr *Expr) { return Expr; }
RetVal visitSMaxExpr(const SCEVSMaxExpr *Expr) {
return visitAnyMinMaxExpr(Expr);
}
RetVal visitUMaxExpr(const SCEVUMaxExpr *Expr) {
return visitAnyMinMaxExpr(Expr);
}
RetVal visitSMinExpr(const SCEVSMinExpr *Expr) {
return visitAnyMinMaxExpr(Expr);
}
RetVal visitUMinExpr(const SCEVUMinExpr *Expr) {
return visitAnyMinMaxExpr(Expr);
}
RetVal visitSequentialUMinExpr(const SCEVSequentialUMinExpr *Expr) {
return visitAnyMinMaxExpr(Expr);
}
RetVal visitUnknown(const SCEVUnknown *Expr) { return Expr; }
RetVal visitCouldNotCompute(const SCEVCouldNotCompute *Expr) { return Expr; }
};
} // namespace
static bool scevUnconditionallyPropagatesPoisonFromOperands(SCEVTypes Kind) {
switch (Kind) {
case scConstant:
case scVScale:
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scAddRecExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scUnknown:
// If any operand is poison, the whole expression is poison.
return true;
case scSequentialUMinExpr:
// FIXME: if the *first* operand is poison, the whole expression is poison.
return false; // Pessimistically, say that it does not propagate poison.
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
namespace {
// The only way poison may be introduced in a SCEV expression is from a
// poison SCEVUnknown (ConstantExprs are also represented as SCEVUnknown,
// not SCEVConstant). Notably, nowrap flags in SCEV nodes can *not*
// introduce poison -- they encode guaranteed, non-speculated knowledge.
//
// Additionally, all SCEV nodes propagate poison from inputs to outputs,
// with the notable exception of umin_seq, where only poison from the first
// operand is (unconditionally) propagated.
struct SCEVPoisonCollector {
bool LookThroughMaybePoisonBlocking;
SmallPtrSet<const SCEVUnknown *, 4> MaybePoison;
SCEVPoisonCollector(bool LookThroughMaybePoisonBlocking)
: LookThroughMaybePoisonBlocking(LookThroughMaybePoisonBlocking) {}
bool follow(const SCEV *S) {
if (!LookThroughMaybePoisonBlocking &&
!scevUnconditionallyPropagatesPoisonFromOperands(S->getSCEVType()))
return false;
if (auto *SU = dyn_cast<SCEVUnknown>(S)) {
if (!isGuaranteedNotToBePoison(SU->getValue()))
MaybePoison.insert(SU);
}
return true;
}
bool isDone() const { return false; }
};
} // namespace
/// Return true if V is poison given that AssumedPoison is already poison.
static bool impliesPoison(const SCEV *AssumedPoison, const SCEV *S) {
// First collect all SCEVs that might result in AssumedPoison to be poison.
// We need to look through potentially poison-blocking operations here,
// because we want to find all SCEVs that *might* result in poison, not only
// those that are *required* to.
SCEVPoisonCollector PC1(/* LookThroughMaybePoisonBlocking */ true);
visitAll(AssumedPoison, PC1);
// AssumedPoison is never poison. As the assumption is false, the implication
// is true. Don't bother walking the other SCEV in this case.
if (PC1.MaybePoison.empty())
return true;
// Collect all SCEVs in S that, if poison, *will* result in S being poison
// as well. We cannot look through potentially poison-blocking operations
// here, as their arguments only *may* make the result poison.
SCEVPoisonCollector PC2(/* LookThroughMaybePoisonBlocking */ false);
visitAll(S, PC2);
// Make sure that no matter which SCEV in PC1.MaybePoison is actually poison,
// it will also make S poison by being part of PC2.MaybePoison.
return llvm::set_is_subset(PC1.MaybePoison, PC2.MaybePoison);
}
void ScalarEvolution::getPoisonGeneratingValues(
SmallPtrSetImpl<const Value *> &Result, const SCEV *S) {
SCEVPoisonCollector PC(/* LookThroughMaybePoisonBlocking */ false);
visitAll(S, PC);
for (const SCEVUnknown *SU : PC.MaybePoison)
Result.insert(SU->getValue());
}
bool ScalarEvolution::canReuseInstruction(
const SCEV *S, Instruction *I,
SmallVectorImpl<Instruction *> &DropPoisonGeneratingInsts) {
// If the instruction cannot be poison, it's always safe to reuse.
if (programUndefinedIfPoison(I))
return true;
// Otherwise, it is possible that I is more poisonous that S. Collect the
// poison-contributors of S, and then check whether I has any additional
// poison-contributors. Poison that is contributed through poison-generating
// flags is handled by dropping those flags instead.
SmallPtrSet<const Value *, 8> PoisonVals;
getPoisonGeneratingValues(PoisonVals, S);
SmallVector<Value *> Worklist;
SmallPtrSet<Value *, 8> Visited;
Worklist.push_back(I);
while (!Worklist.empty()) {
Value *V = Worklist.pop_back_val();
if (!Visited.insert(V).second)
continue;
// Avoid walking large instruction graphs.
if (Visited.size() > 16)
return false;
// Either the value can't be poison, or the S would also be poison if it
// is.
if (PoisonVals.contains(V) || ::isGuaranteedNotToBePoison(V))
continue;
auto *I = dyn_cast<Instruction>(V);
if (!I)
return false;
// Disjoint or instructions are interpreted as adds by SCEV. However, we
// can't replace an arbitrary add with disjoint or, even if we drop the
// flag. We would need to convert the or into an add.
if (auto *PDI = dyn_cast<PossiblyDisjointInst>(I))
if (PDI->isDisjoint())
return false;
// FIXME: Ignore vscale, even though it technically could be poison. Do this
// because SCEV currently assumes it can't be poison. Remove this special
// case once we proper model when vscale can be poison.
if (auto *II = dyn_cast<IntrinsicInst>(I);
II && II->getIntrinsicID() == Intrinsic::vscale)
continue;
if (canCreatePoison(cast<Operator>(I), /*ConsiderFlagsAndMetadata*/ false))
return false;
// If the instruction can't create poison, we can recurse to its operands.
if (I->hasPoisonGeneratingAnnotations())
DropPoisonGeneratingInsts.push_back(I);
llvm::append_range(Worklist, I->operands());
}
return true;
}
const SCEV *
ScalarEvolution::getSequentialMinMaxExpr(SCEVTypes Kind,
SmallVectorImpl<const SCEV *> &Ops) {
assert(SCEVSequentialMinMaxExpr::isSequentialMinMaxType(Kind) &&
"Not a SCEVSequentialMinMaxExpr!");
assert(!Ops.empty() && "Cannot get empty (u|s)(min|max)!");
if (Ops.size() == 1)
return Ops[0];
#ifndef NDEBUG
Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
"Operand types don't match!");
assert(Ops[0]->getType()->isPointerTy() ==
Ops[i]->getType()->isPointerTy() &&
"min/max should be consistently pointerish");
}
#endif
// Note that SCEVSequentialMinMaxExpr is *NOT* commutative,
// so we can *NOT* do any kind of sorting of the expressions!
// Check if we have created the same expression before.
if (const SCEV *S = findExistingSCEVInCache(Kind, Ops))
return S;
// FIXME: there are *some* simplifications that we can do here.
// Keep only the first instance of an operand.
{
SCEVSequentialMinMaxDeduplicatingVisitor Deduplicator(*this, Kind);
bool Changed = Deduplicator.visit(Kind, Ops, Ops);
if (Changed)
return getSequentialMinMaxExpr(Kind, Ops);
}
// Check to see if one of the operands is of the same kind. If so, expand its
// operands onto our operand list, and recurse to simplify.
{
unsigned Idx = 0;
bool DeletedAny = false;
while (Idx < Ops.size()) {
if (Ops[Idx]->getSCEVType() != Kind) {
++Idx;
continue;
}
const auto *SMME = cast<SCEVSequentialMinMaxExpr>(Ops[Idx]);
Ops.erase(Ops.begin() + Idx);
Ops.insert(Ops.begin() + Idx, SMME->operands().begin(),
SMME->operands().end());
DeletedAny = true;
}
if (DeletedAny)
return getSequentialMinMaxExpr(Kind, Ops);
}
const SCEV *SaturationPoint;
ICmpInst::Predicate Pred;
switch (Kind) {
case scSequentialUMinExpr:
SaturationPoint = getZero(Ops[0]->getType());
Pred = ICmpInst::ICMP_ULE;
break;
default:
llvm_unreachable("Not a sequential min/max type.");
}
for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
if (!isGuaranteedNotToCauseUB(Ops[i]))
continue;
// We can replace %x umin_seq %y with %x umin %y if either:
// * %y being poison implies %x is also poison.
// * %x cannot be the saturating value (e.g. zero for umin).
if (::impliesPoison(Ops[i], Ops[i - 1]) ||
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_NE, Ops[i - 1],
SaturationPoint)) {
SmallVector<const SCEV *> SeqOps = {Ops[i - 1], Ops[i]};
Ops[i - 1] = getMinMaxExpr(
SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(Kind),
SeqOps);
Ops.erase(Ops.begin() + i);
return getSequentialMinMaxExpr(Kind, Ops);
}
// Fold %x umin_seq %y to %x if %x ule %y.
// TODO: We might be able to prove the predicate for a later operand.
if (isKnownViaNonRecursiveReasoning(Pred, Ops[i - 1], Ops[i])) {
Ops.erase(Ops.begin() + i);
return getSequentialMinMaxExpr(Kind, Ops);
}
}
// Okay, it looks like we really DO need an expr. Check to see if we
// already have one, otherwise create a new one.
FoldingSetNodeID ID;
ID.AddInteger(Kind);
for (const SCEV *Op : Ops)
ID.AddPointer(Op);
void *IP = nullptr;
const SCEV *ExistingSCEV = UniqueSCEVs.FindNodeOrInsertPos(ID, IP);
if (ExistingSCEV)
return ExistingSCEV;
const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size());
std::uninitialized_copy(Ops.begin(), Ops.end(), O);
SCEV *S = new (SCEVAllocator)
SCEVSequentialMinMaxExpr(ID.Intern(SCEVAllocator), Kind, O, Ops.size());
UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Ops);
return S;
}
const SCEV *ScalarEvolution::getSMaxExpr(const SCEV *LHS, const SCEV *RHS) {
SmallVector<const SCEV *, 2> Ops = {LHS, RHS};
return getSMaxExpr(Ops);
}
const SCEV *ScalarEvolution::getSMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
return getMinMaxExpr(scSMaxExpr, Ops);
}
const SCEV *ScalarEvolution::getUMaxExpr(const SCEV *LHS, const SCEV *RHS) {
SmallVector<const SCEV *, 2> Ops = {LHS, RHS};
return getUMaxExpr(Ops);
}
const SCEV *ScalarEvolution::getUMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
return getMinMaxExpr(scUMaxExpr, Ops);
}
const SCEV *ScalarEvolution::getSMinExpr(const SCEV *LHS,
const SCEV *RHS) {
SmallVector<const SCEV *, 2> Ops = { LHS, RHS };
return getSMinExpr(Ops);
}
const SCEV *ScalarEvolution::getSMinExpr(SmallVectorImpl<const SCEV *> &Ops) {
return getMinMaxExpr(scSMinExpr, Ops);
}
const SCEV *ScalarEvolution::getUMinExpr(const SCEV *LHS, const SCEV *RHS,
bool Sequential) {
SmallVector<const SCEV *, 2> Ops = { LHS, RHS };
return getUMinExpr(Ops, Sequential);
}
const SCEV *ScalarEvolution::getUMinExpr(SmallVectorImpl<const SCEV *> &Ops,
bool Sequential) {
return Sequential ? getSequentialMinMaxExpr(scSequentialUMinExpr, Ops)
: getMinMaxExpr(scUMinExpr, Ops);
}
const SCEV *
ScalarEvolution::getSizeOfExpr(Type *IntTy, TypeSize Size) {
const SCEV *Res = getConstant(IntTy, Size.getKnownMinValue());
if (Size.isScalable())
Res = getMulExpr(Res, getVScale(IntTy));
return Res;
}
const SCEV *ScalarEvolution::getSizeOfExpr(Type *IntTy, Type *AllocTy) {
return getSizeOfExpr(IntTy, getDataLayout().getTypeAllocSize(AllocTy));
}
const SCEV *ScalarEvolution::getStoreSizeOfExpr(Type *IntTy, Type *StoreTy) {
return getSizeOfExpr(IntTy, getDataLayout().getTypeStoreSize(StoreTy));
}
const SCEV *ScalarEvolution::getOffsetOfExpr(Type *IntTy,
StructType *STy,
unsigned FieldNo) {
// We can bypass creating a target-independent constant expression and then
// folding it back into a ConstantInt. This is just a compile-time
// optimization.
const StructLayout *SL = getDataLayout().getStructLayout(STy);
assert(!SL->getSizeInBits().isScalable() &&
"Cannot get offset for structure containing scalable vector types");
return getConstant(IntTy, SL->getElementOffset(FieldNo));
}
const SCEV *ScalarEvolution::getUnknown(Value *V) {
// Don't attempt to do anything other than create a SCEVUnknown object
// here. createSCEV only calls getUnknown after checking for all other
// interesting possibilities, and any other code that calls getUnknown
// is doing so in order to hide a value from SCEV canonicalization.
FoldingSetNodeID ID;
ID.AddInteger(scUnknown);
ID.AddPointer(V);
void *IP = nullptr;
if (SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) {
assert(cast<SCEVUnknown>(S)->getValue() == V &&
"Stale SCEVUnknown in uniquing map!");
return S;
}
SCEV *S = new (SCEVAllocator) SCEVUnknown(ID.Intern(SCEVAllocator), V, this,
FirstUnknown);
FirstUnknown = cast<SCEVUnknown>(S);
UniqueSCEVs.InsertNode(S, IP);
return S;
}
//===----------------------------------------------------------------------===//
// Basic SCEV Analysis and PHI Idiom Recognition Code
//
/// Test if values of the given type are analyzable within the SCEV
/// framework. This primarily includes integer types, and it can optionally
/// include pointer types if the ScalarEvolution class has access to
/// target-specific information.
bool ScalarEvolution::isSCEVable(Type *Ty) const {
// Integers and pointers are always SCEVable.
return Ty->isIntOrPtrTy();
}
/// Return the size in bits of the specified type, for which isSCEVable must
/// return true.
uint64_t ScalarEvolution::getTypeSizeInBits(Type *Ty) const {
assert(isSCEVable(Ty) && "Type is not SCEVable!");
if (Ty->isPointerTy())
return getDataLayout().getIndexTypeSizeInBits(Ty);
return getDataLayout().getTypeSizeInBits(Ty);
}
/// Return a type with the same bitwidth as the given type and which represents
/// how SCEV will treat the given type, for which isSCEVable must return
/// true. For pointer types, this is the pointer index sized integer type.
Type *ScalarEvolution::getEffectiveSCEVType(Type *Ty) const {
assert(isSCEVable(Ty) && "Type is not SCEVable!");
if (Ty->isIntegerTy())
return Ty;
// The only other support type is pointer.
assert(Ty->isPointerTy() && "Unexpected non-pointer non-integer type!");
return getDataLayout().getIndexType(Ty);
}
Type *ScalarEvolution::getWiderType(Type *T1, Type *T2) const {
return getTypeSizeInBits(T1) >= getTypeSizeInBits(T2) ? T1 : T2;
}
bool ScalarEvolution::instructionCouldExistWithOperands(const SCEV *A,
const SCEV *B) {
/// For a valid use point to exist, the defining scope of one operand
/// must dominate the other.
bool PreciseA, PreciseB;
auto *ScopeA = getDefiningScopeBound({A}, PreciseA);
auto *ScopeB = getDefiningScopeBound({B}, PreciseB);
if (!PreciseA || !PreciseB)
// Can't tell.
return false;
return (ScopeA == ScopeB) || DT.dominates(ScopeA, ScopeB) ||
DT.dominates(ScopeB, ScopeA);
}
const SCEV *ScalarEvolution::getCouldNotCompute() {
return CouldNotCompute.get();
}
bool ScalarEvolution::checkValidity(const SCEV *S) const {
bool ContainsNulls = SCEVExprContains(S, [](const SCEV *S) {
auto *SU = dyn_cast<SCEVUnknown>(S);
return SU && SU->getValue() == nullptr;
});
return !ContainsNulls;
}
bool ScalarEvolution::containsAddRecurrence(const SCEV *S) {
HasRecMapType::iterator I = HasRecMap.find(S);
if (I != HasRecMap.end())
return I->second;
bool FoundAddRec =
SCEVExprContains(S, [](const SCEV *S) { return isa<SCEVAddRecExpr>(S); });
HasRecMap.insert({S, FoundAddRec});
return FoundAddRec;
}
/// Return the ValueOffsetPair set for \p S. \p S can be represented
/// by the value and offset from any ValueOffsetPair in the set.
ArrayRef<Value *> ScalarEvolution::getSCEVValues(const SCEV *S) {
ExprValueMapType::iterator SI = ExprValueMap.find_as(S);
if (SI == ExprValueMap.end())
return {};
return SI->second.getArrayRef();
}
/// Erase Value from ValueExprMap and ExprValueMap. ValueExprMap.erase(V)
/// cannot be used separately. eraseValueFromMap should be used to remove
/// V from ValueExprMap and ExprValueMap at the same time.
void ScalarEvolution::eraseValueFromMap(Value *V) {
ValueExprMapType::iterator I = ValueExprMap.find_as(V);
if (I != ValueExprMap.end()) {
auto EVIt = ExprValueMap.find(I->second);
bool Removed = EVIt->second.remove(V);
(void) Removed;
assert(Removed && "Value not in ExprValueMap?");
ValueExprMap.erase(I);
}
}
void ScalarEvolution::insertValueToMap(Value *V, const SCEV *S) {
// A recursive query may have already computed the SCEV. It should be
// equivalent, but may not necessarily be exactly the same, e.g. due to lazily
// inferred nowrap flags.
auto It = ValueExprMap.find_as(V);
if (It == ValueExprMap.end()) {
ValueExprMap.insert({SCEVCallbackVH(V, this), S});
ExprValueMap[S].insert(V);
}
}
/// Return an existing SCEV if it exists, otherwise analyze the expression and
/// create a new one.
const SCEV *ScalarEvolution::getSCEV(Value *V) {
assert(isSCEVable(V->getType()) && "Value is not SCEVable!");
if (const SCEV *S = getExistingSCEV(V))
return S;
return createSCEVIter(V);
}
const SCEV *ScalarEvolution::getExistingSCEV(Value *V) {
assert(isSCEVable(V->getType()) && "Value is not SCEVable!");
ValueExprMapType::iterator I = ValueExprMap.find_as(V);
if (I != ValueExprMap.end()) {
const SCEV *S = I->second;
assert(checkValidity(S) &&
"existing SCEV has not been properly invalidated");
return S;
}
return nullptr;
}
/// Return a SCEV corresponding to -V = -1*V
const SCEV *ScalarEvolution::getNegativeSCEV(const SCEV *V,
SCEV::NoWrapFlags Flags) {
if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
return getConstant(
cast<ConstantInt>(ConstantExpr::getNeg(VC->getValue())));
Type *Ty = V->getType();
Ty = getEffectiveSCEVType(Ty);
return getMulExpr(V, getMinusOne(Ty), Flags);
}
/// If Expr computes ~A, return A else return nullptr
static const SCEV *MatchNotExpr(const SCEV *Expr) {
const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Expr);
if (!Add || Add->getNumOperands() != 2 ||
!Add->getOperand(0)->isAllOnesValue())
return nullptr;
const SCEVMulExpr *AddRHS = dyn_cast<SCEVMulExpr>(Add->getOperand(1));
if (!AddRHS || AddRHS->getNumOperands() != 2 ||
!AddRHS->getOperand(0)->isAllOnesValue())
return nullptr;
return AddRHS->getOperand(1);
}
/// Return a SCEV corresponding to ~V = -1-V
const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) {
assert(!V->getType()->isPointerTy() && "Can't negate pointer");
if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
return getConstant(
cast<ConstantInt>(ConstantExpr::getNot(VC->getValue())));
// Fold ~(u|s)(min|max)(~x, ~y) to (u|s)(max|min)(x, y)
if (const SCEVMinMaxExpr *MME = dyn_cast<SCEVMinMaxExpr>(V)) {
auto MatchMinMaxNegation = [&](const SCEVMinMaxExpr *MME) {
SmallVector<const SCEV *, 2> MatchedOperands;
for (const SCEV *Operand : MME->operands()) {
const SCEV *Matched = MatchNotExpr(Operand);
if (!Matched)
return (const SCEV *)nullptr;
MatchedOperands.push_back(Matched);
}
return getMinMaxExpr(SCEVMinMaxExpr::negate(MME->getSCEVType()),
MatchedOperands);
};
if (const SCEV *Replaced = MatchMinMaxNegation(MME))
return Replaced;
}
Type *Ty = V->getType();
Ty = getEffectiveSCEVType(Ty);
return getMinusSCEV(getMinusOne(Ty), V);
}
const SCEV *ScalarEvolution::removePointerBase(const SCEV *P) {
assert(P->getType()->isPointerTy());
if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(P)) {
// The base of an AddRec is the first operand.
SmallVector<const SCEV *> Ops{AddRec->operands()};
Ops[0] = removePointerBase(Ops[0]);
// Don't try to transfer nowrap flags for now. We could in some cases
// (for example, if pointer operand of the AddRec is a SCEVUnknown).
return getAddRecExpr(Ops, AddRec->getLoop(), SCEV::FlagAnyWrap);
}
if (auto *Add = dyn_cast<SCEVAddExpr>(P)) {
// The base of an Add is the pointer operand.
SmallVector<const SCEV *> Ops{Add->operands()};
const SCEV **PtrOp = nullptr;
for (const SCEV *&AddOp : Ops) {
if (AddOp->getType()->isPointerTy()) {
assert(!PtrOp && "Cannot have multiple pointer ops");
PtrOp = &AddOp;
}
}
*PtrOp = removePointerBase(*PtrOp);
// Don't try to transfer nowrap flags for now. We could in some cases
// (for example, if the pointer operand of the Add is a SCEVUnknown).
return getAddExpr(Ops);
}
// Any other expression must be a pointer base.
return getZero(P->getType());
}
const SCEV *ScalarEvolution::getMinusSCEV(const SCEV *LHS, const SCEV *RHS,
SCEV::NoWrapFlags Flags,
unsigned Depth) {
// Fast path: X - X --> 0.
if (LHS == RHS)
return getZero(LHS->getType());
// If we subtract two pointers with different pointer bases, bail.
// Eventually, we're going to add an assertion to getMulExpr that we
// can't multiply by a pointer.
if (RHS->getType()->isPointerTy()) {
if (!LHS->getType()->isPointerTy() ||
getPointerBase(LHS) != getPointerBase(RHS))
return getCouldNotCompute();
LHS = removePointerBase(LHS);
RHS = removePointerBase(RHS);
}
// We represent LHS - RHS as LHS + (-1)*RHS. This transformation
// makes it so that we cannot make much use of NUW.
auto AddFlags = SCEV::FlagAnyWrap;
const bool RHSIsNotMinSigned =
!getSignedRangeMin(RHS).isMinSignedValue();
if (hasFlags(Flags, SCEV::FlagNSW)) {
// Let M be the minimum representable signed value. Then (-1)*RHS
// signed-wraps if and only if RHS is M. That can happen even for
// a NSW subtraction because e.g. (-1)*M signed-wraps even though
// -1 - M does not. So to transfer NSW from LHS - RHS to LHS +
// (-1)*RHS, we need to prove that RHS != M.
//
// If LHS is non-negative and we know that LHS - RHS does not
// signed-wrap, then RHS cannot be M. So we can rule out signed-wrap
// either by proving that RHS > M or that LHS >= 0.
if (RHSIsNotMinSigned || isKnownNonNegative(LHS)) {
AddFlags = SCEV::FlagNSW;
}
}
// FIXME: Find a correct way to transfer NSW to (-1)*M when LHS -
// RHS is NSW and LHS >= 0.
//
// The difficulty here is that the NSW flag may have been proven
// relative to a loop that is to be found in a recurrence in LHS and
// not in RHS. Applying NSW to (-1)*M may then let the NSW have a
// larger scope than intended.
auto NegFlags = RHSIsNotMinSigned ? SCEV::FlagNSW : SCEV::FlagAnyWrap;
return getAddExpr(LHS, getNegativeSCEV(RHS, NegFlags), AddFlags, Depth);
}
const SCEV *ScalarEvolution::getTruncateOrZeroExtend(const SCEV *V, Type *Ty,
unsigned Depth) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot truncate or zero extend with non-integer arguments!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty))
return getTruncateExpr(V, Ty, Depth);
return getZeroExtendExpr(V, Ty, Depth);
}
const SCEV *ScalarEvolution::getTruncateOrSignExtend(const SCEV *V, Type *Ty,
unsigned Depth) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot truncate or zero extend with non-integer arguments!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty))
return getTruncateExpr(V, Ty, Depth);
return getSignExtendExpr(V, Ty, Depth);
}
const SCEV *
ScalarEvolution::getNoopOrZeroExtend(const SCEV *V, Type *Ty) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot noop or zero extend with non-integer arguments!");
assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
"getNoopOrZeroExtend cannot truncate!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
return getZeroExtendExpr(V, Ty);
}
const SCEV *
ScalarEvolution::getNoopOrSignExtend(const SCEV *V, Type *Ty) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot noop or sign extend with non-integer arguments!");
assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
"getNoopOrSignExtend cannot truncate!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
return getSignExtendExpr(V, Ty);
}
const SCEV *
ScalarEvolution::getNoopOrAnyExtend(const SCEV *V, Type *Ty) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot noop or any extend with non-integer arguments!");
assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
"getNoopOrAnyExtend cannot truncate!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
return getAnyExtendExpr(V, Ty);
}
const SCEV *
ScalarEvolution::getTruncateOrNoop(const SCEV *V, Type *Ty) {
Type *SrcTy = V->getType();
assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
"Cannot truncate or noop with non-integer arguments!");
assert(getTypeSizeInBits(SrcTy) >= getTypeSizeInBits(Ty) &&
"getTruncateOrNoop cannot extend!");
if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
return V; // No conversion
return getTruncateExpr(V, Ty);
}
const SCEV *ScalarEvolution::getUMaxFromMismatchedTypes(const SCEV *LHS,
const SCEV *RHS) {
const SCEV *PromotedLHS = LHS;
const SCEV *PromotedRHS = RHS;
if (getTypeSizeInBits(LHS->getType()) > getTypeSizeInBits(RHS->getType()))
PromotedRHS = getZeroExtendExpr(RHS, LHS->getType());
else
PromotedLHS = getNoopOrZeroExtend(LHS, RHS->getType());
return getUMaxExpr(PromotedLHS, PromotedRHS);
}
const SCEV *ScalarEvolution::getUMinFromMismatchedTypes(const SCEV *LHS,
const SCEV *RHS,
bool Sequential) {
SmallVector<const SCEV *, 2> Ops = { LHS, RHS };
return getUMinFromMismatchedTypes(Ops, Sequential);
}
const SCEV *
ScalarEvolution::getUMinFromMismatchedTypes(SmallVectorImpl<const SCEV *> &Ops,
bool Sequential) {
assert(!Ops.empty() && "At least one operand must be!");
// Trivial case.
if (Ops.size() == 1)
return Ops[0];
// Find the max type first.
Type *MaxType = nullptr;
for (const auto *S : Ops)
if (MaxType)
MaxType = getWiderType(MaxType, S->getType());
else
MaxType = S->getType();
assert(MaxType && "Failed to find maximum type!");
// Extend all ops to max type.
SmallVector<const SCEV *, 2> PromotedOps;
for (const auto *S : Ops)
PromotedOps.push_back(getNoopOrZeroExtend(S, MaxType));
// Generate umin.
return getUMinExpr(PromotedOps, Sequential);
}
const SCEV *ScalarEvolution::getPointerBase(const SCEV *V) {
// A pointer operand may evaluate to a nonpointer expression, such as null.
if (!V->getType()->isPointerTy())
return V;
while (true) {
if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(V)) {
V = AddRec->getStart();
} else if (auto *Add = dyn_cast<SCEVAddExpr>(V)) {
const SCEV *PtrOp = nullptr;
for (const SCEV *AddOp : Add->operands()) {
if (AddOp->getType()->isPointerTy()) {
assert(!PtrOp && "Cannot have multiple pointer ops");
PtrOp = AddOp;
}
}
assert(PtrOp && "Must have pointer op");
V = PtrOp;
} else // Not something we can look further into.
return V;
}
}
/// Push users of the given Instruction onto the given Worklist.
static void PushDefUseChildren(Instruction *I,
SmallVectorImpl<Instruction *> &Worklist,
SmallPtrSetImpl<Instruction *> &Visited) {
// Push the def-use children onto the Worklist stack.
for (User *U : I->users()) {
auto *UserInsn = cast<Instruction>(U);
if (Visited.insert(UserInsn).second)
Worklist.push_back(UserInsn);
}
}
namespace {
/// Takes SCEV S and Loop L. For each AddRec sub-expression, use its start
/// expression in case its Loop is L. If it is not L then
/// if IgnoreOtherLoops is true then use AddRec itself
/// otherwise rewrite cannot be done.
/// If SCEV contains non-invariant unknown SCEV rewrite cannot be done.
class SCEVInitRewriter : public SCEVRewriteVisitor<SCEVInitRewriter> {
public:
static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE,
bool IgnoreOtherLoops = true) {
SCEVInitRewriter Rewriter(L, SE);
const SCEV *Result = Rewriter.visit(S);
if (Rewriter.hasSeenLoopVariantSCEVUnknown())
return SE.getCouldNotCompute();
return Rewriter.hasSeenOtherLoops() && !IgnoreOtherLoops
? SE.getCouldNotCompute()
: Result;
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
if (!SE.isLoopInvariant(Expr, L))
SeenLoopVariantSCEVUnknown = true;
return Expr;
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
// Only re-write AddRecExprs for this loop.
if (Expr->getLoop() == L)
return Expr->getStart();
SeenOtherLoops = true;
return Expr;
}
bool hasSeenLoopVariantSCEVUnknown() { return SeenLoopVariantSCEVUnknown; }
bool hasSeenOtherLoops() { return SeenOtherLoops; }
private:
explicit SCEVInitRewriter(const Loop *L, ScalarEvolution &SE)
: SCEVRewriteVisitor(SE), L(L) {}
const Loop *L;
bool SeenLoopVariantSCEVUnknown = false;
bool SeenOtherLoops = false;
};
/// Takes SCEV S and Loop L. For each AddRec sub-expression, use its post
/// increment expression in case its Loop is L. If it is not L then
/// use AddRec itself.
/// If SCEV contains non-invariant unknown SCEV rewrite cannot be done.
class SCEVPostIncRewriter : public SCEVRewriteVisitor<SCEVPostIncRewriter> {
public:
static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE) {
SCEVPostIncRewriter Rewriter(L, SE);
const SCEV *Result = Rewriter.visit(S);
return Rewriter.hasSeenLoopVariantSCEVUnknown()
? SE.getCouldNotCompute()
: Result;
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
if (!SE.isLoopInvariant(Expr, L))
SeenLoopVariantSCEVUnknown = true;
return Expr;
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
// Only re-write AddRecExprs for this loop.
if (Expr->getLoop() == L)
return Expr->getPostIncExpr(SE);
SeenOtherLoops = true;
return Expr;
}
bool hasSeenLoopVariantSCEVUnknown() { return SeenLoopVariantSCEVUnknown; }
bool hasSeenOtherLoops() { return SeenOtherLoops; }
private:
explicit SCEVPostIncRewriter(const Loop *L, ScalarEvolution &SE)
: SCEVRewriteVisitor(SE), L(L) {}
const Loop *L;
bool SeenLoopVariantSCEVUnknown = false;
bool SeenOtherLoops = false;
};
/// This class evaluates the compare condition by matching it against the
/// condition of loop latch. If there is a match we assume a true value
/// for the condition while building SCEV nodes.
class SCEVBackedgeConditionFolder
: public SCEVRewriteVisitor<SCEVBackedgeConditionFolder> {
public:
static const SCEV *rewrite(const SCEV *S, const Loop *L,
ScalarEvolution &SE) {
bool IsPosBECond = false;
Value *BECond = nullptr;
if (BasicBlock *Latch = L->getLoopLatch()) {
BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
if (BI && BI->isConditional()) {
assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&
"Both outgoing branches should not target same header!");
BECond = BI->getCondition();
IsPosBECond = BI->getSuccessor(0) == L->getHeader();
} else {
return S;
}
}
SCEVBackedgeConditionFolder Rewriter(L, BECond, IsPosBECond, SE);
return Rewriter.visit(S);
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
const SCEV *Result = Expr;
bool InvariantF = SE.isLoopInvariant(Expr, L);
if (!InvariantF) {
Instruction *I = cast<Instruction>(Expr->getValue());
switch (I->getOpcode()) {
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
std::optional<const SCEV *> Res =
compareWithBackedgeCondition(SI->getCondition());
if (Res) {
bool IsOne = cast<SCEVConstant>(*Res)->getValue()->isOne();
Result = SE.getSCEV(IsOne ? SI->getTrueValue() : SI->getFalseValue());
}
break;
}
default: {
std::optional<const SCEV *> Res = compareWithBackedgeCondition(I);
if (Res)
Result = *Res;
break;
}
}
}
return Result;
}
private:
explicit SCEVBackedgeConditionFolder(const Loop *L, Value *BECond,
bool IsPosBECond, ScalarEvolution &SE)
: SCEVRewriteVisitor(SE), L(L), BackedgeCond(BECond),
IsPositiveBECond(IsPosBECond) {}
std::optional<const SCEV *> compareWithBackedgeCondition(Value *IC);
const Loop *L;
/// Loop back condition.
Value *BackedgeCond = nullptr;
/// Set to true if loop back is on positive branch condition.
bool IsPositiveBECond;
};
std::optional<const SCEV *>
SCEVBackedgeConditionFolder::compareWithBackedgeCondition(Value *IC) {
// If value matches the backedge condition for loop latch,
// then return a constant evolution node based on loopback
// branch taken.
if (BackedgeCond == IC)
return IsPositiveBECond ? SE.getOne(Type::getInt1Ty(SE.getContext()))
: SE.getZero(Type::getInt1Ty(SE.getContext()));
return std::nullopt;
}
class SCEVShiftRewriter : public SCEVRewriteVisitor<SCEVShiftRewriter> {
public:
static const SCEV *rewrite(const SCEV *S, const Loop *L,
ScalarEvolution &SE) {
SCEVShiftRewriter Rewriter(L, SE);
const SCEV *Result = Rewriter.visit(S);
return Rewriter.isValid() ? Result : SE.getCouldNotCompute();
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
// Only allow AddRecExprs for this loop.
if (!SE.isLoopInvariant(Expr, L))
Valid = false;
return Expr;
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
if (Expr->getLoop() == L && Expr->isAffine())
return SE.getMinusSCEV(Expr, Expr->getStepRecurrence(SE));
Valid = false;
return Expr;
}
bool isValid() { return Valid; }
private:
explicit SCEVShiftRewriter(const Loop *L, ScalarEvolution &SE)
: SCEVRewriteVisitor(SE), L(L) {}
const Loop *L;
bool Valid = true;
};
} // end anonymous namespace
SCEV::NoWrapFlags
ScalarEvolution::proveNoWrapViaConstantRanges(const SCEVAddRecExpr *AR) {
if (!AR->isAffine())
return SCEV::FlagAnyWrap;
using OBO = OverflowingBinaryOperator;
SCEV::NoWrapFlags Result = SCEV::FlagAnyWrap;
if (!AR->hasNoSelfWrap()) {
const SCEV *BECount = getConstantMaxBackedgeTakenCount(AR->getLoop());
if (const SCEVConstant *BECountMax = dyn_cast<SCEVConstant>(BECount)) {
ConstantRange StepCR = getSignedRange(AR->getStepRecurrence(*this));
const APInt &BECountAP = BECountMax->getAPInt();
unsigned NoOverflowBitWidth =
BECountAP.getActiveBits() + StepCR.getMinSignedBits();
if (NoOverflowBitWidth <= getTypeSizeInBits(AR->getType()))
Result = ScalarEvolution::setFlags(Result, SCEV::FlagNW);
}
}
if (!AR->hasNoSignedWrap()) {
ConstantRange AddRecRange = getSignedRange(AR);
ConstantRange IncRange = getSignedRange(AR->getStepRecurrence(*this));
auto NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
Instruction::Add, IncRange, OBO::NoSignedWrap);
if (NSWRegion.contains(AddRecRange))
Result = ScalarEvolution::setFlags(Result, SCEV::FlagNSW);
}
if (!AR->hasNoUnsignedWrap()) {
ConstantRange AddRecRange = getUnsignedRange(AR);
ConstantRange IncRange = getUnsignedRange(AR->getStepRecurrence(*this));
auto NUWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
Instruction::Add, IncRange, OBO::NoUnsignedWrap);
if (NUWRegion.contains(AddRecRange))
Result = ScalarEvolution::setFlags(Result, SCEV::FlagNUW);
}
return Result;
}
SCEV::NoWrapFlags
ScalarEvolution::proveNoSignedWrapViaInduction(const SCEVAddRecExpr *AR) {
SCEV::NoWrapFlags Result = AR->getNoWrapFlags();
if (AR->hasNoSignedWrap())
return Result;
if (!AR->isAffine())
return Result;
// This function can be expensive, only try to prove NSW once per AddRec.
if (!SignedWrapViaInductionTried.insert(AR).second)
return Result;
const SCEV *Step = AR->getStepRecurrence(*this);
const Loop *L = AR->getLoop();
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
// being called from within backedge-taken count analysis, such that
// attempting to ask for the backedge-taken count would likely result
// in infinite recursion. In the later case, the analysis code will
// cope with a conservative value, and it will take care to purge
// that value once it has finished.
const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
// Normally, in the cases we can prove no-overflow via a
// backedge guarding condition, we can also compute a backedge
// taken count for the loop. The exceptions are assumptions and
// guards present in the loop -- SCEV is not great at exploiting
// these to compute max backedge taken counts, but can still use
// these to prove lack of overflow. Use this fact to avoid
// doing extra work that may not pay off.
if (isa<SCEVCouldNotCompute>(MaxBECount) && !HasGuards &&
AC.assumptions().empty())
return Result;
// If the backedge is guarded by a comparison with the pre-inc value the
// addrec is safe. Also, if the entry is guarded by a comparison with the
// start value and the backedge is guarded by a comparison with the post-inc
// value, the addrec is safe.
ICmpInst::Predicate Pred;
const SCEV *OverflowLimit =
getSignedOverflowLimitForStep(Step, &Pred, this);
if (OverflowLimit &&
(isLoopBackedgeGuardedByCond(L, Pred, AR, OverflowLimit) ||
isKnownOnEveryIteration(Pred, AR, OverflowLimit))) {
Result = setFlags(Result, SCEV::FlagNSW);
}
return Result;
}
SCEV::NoWrapFlags
ScalarEvolution::proveNoUnsignedWrapViaInduction(const SCEVAddRecExpr *AR) {
SCEV::NoWrapFlags Result = AR->getNoWrapFlags();
if (AR->hasNoUnsignedWrap())
return Result;
if (!AR->isAffine())
return Result;
// This function can be expensive, only try to prove NUW once per AddRec.
if (!UnsignedWrapViaInductionTried.insert(AR).second)
return Result;
const SCEV *Step = AR->getStepRecurrence(*this);
unsigned BitWidth = getTypeSizeInBits(AR->getType());
const Loop *L = AR->getLoop();
// Check whether the backedge-taken count is SCEVCouldNotCompute.
// Note that this serves two purposes: It filters out loops that are
// simply not analyzable, and it covers the case where this code is
// being called from within backedge-taken count analysis, such that
// attempting to ask for the backedge-taken count would likely result
// in infinite recursion. In the later case, the analysis code will
// cope with a conservative value, and it will take care to purge
// that value once it has finished.
const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
// Normally, in the cases we can prove no-overflow via a
// backedge guarding condition, we can also compute a backedge
// taken count for the loop. The exceptions are assumptions and
// guards present in the loop -- SCEV is not great at exploiting
// these to compute max backedge taken counts, but can still use
// these to prove lack of overflow. Use this fact to avoid
// doing extra work that may not pay off.
if (isa<SCEVCouldNotCompute>(MaxBECount) && !HasGuards &&
AC.assumptions().empty())
return Result;
// If the backedge is guarded by a comparison with the pre-inc value the
// addrec is safe. Also, if the entry is guarded by a comparison with the
// start value and the backedge is guarded by a comparison with the post-inc
// value, the addrec is safe.
if (isKnownPositive(Step)) {
const SCEV *N = getConstant(APInt::getMinValue(BitWidth) -
getUnsignedRangeMax(Step));
if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_ULT, AR, N) ||
isKnownOnEveryIteration(ICmpInst::ICMP_ULT, AR, N)) {
Result = setFlags(Result, SCEV::FlagNUW);
}
}
return Result;
}
namespace {
/// Represents an abstract binary operation. This may exist as a
/// normal instruction or constant expression, or may have been
/// derived from an expression tree.
struct BinaryOp {
unsigned Opcode;
Value *LHS;
Value *RHS;
bool IsNSW = false;
bool IsNUW = false;
/// Op is set if this BinaryOp corresponds to a concrete LLVM instruction or
/// constant expression.
Operator *Op = nullptr;
explicit BinaryOp(Operator *Op)
: Opcode(Op->getOpcode()), LHS(Op->getOperand(0)), RHS(Op->getOperand(1)),
Op(Op) {
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(Op)) {
IsNSW = OBO->hasNoSignedWrap();
IsNUW = OBO->hasNoUnsignedWrap();
}
}
explicit BinaryOp(unsigned Opcode, Value *LHS, Value *RHS, bool IsNSW = false,
bool IsNUW = false)
: Opcode(Opcode), LHS(LHS), RHS(RHS), IsNSW(IsNSW), IsNUW(IsNUW) {}
};
} // end anonymous namespace
/// Try to map \p V into a BinaryOp, and return \c std::nullopt on failure.
static std::optional<BinaryOp> MatchBinaryOp(Value *V, const DataLayout &DL,
AssumptionCache &AC,
const DominatorTree &DT,
const Instruction *CxtI) {
auto *Op = dyn_cast<Operator>(V);
if (!Op)
return std::nullopt;
// Implementation detail: all the cleverness here should happen without
// creating new SCEV expressions -- our caller knowns tricks to avoid creating
// SCEV expressions when possible, and we should not break that.
switch (Op->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::UDiv:
case Instruction::URem:
case Instruction::And:
case Instruction::AShr:
case Instruction::Shl:
return BinaryOp(Op);
case Instruction::Or: {
// Convert or disjoint into add nuw nsw.
if (cast<PossiblyDisjointInst>(Op)->isDisjoint())
return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1),
/*IsNSW=*/true, /*IsNUW=*/true);
return BinaryOp(Op);
}
case Instruction::Xor:
if (auto *RHSC = dyn_cast<ConstantInt>(Op->getOperand(1)))
// If the RHS of the xor is a signmask, then this is just an add.
// Instcombine turns add of signmask into xor as a strength reduction step.
if (RHSC->getValue().isSignMask())
return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
// Binary `xor` is a bit-wise `add`.
if (V->getType()->isIntegerTy(1))
return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
return BinaryOp(Op);
case Instruction::LShr:
// Turn logical shift right of a constant into a unsigned divide.
if (ConstantInt *SA = dyn_cast<ConstantInt>(Op->getOperand(1))) {
uint32_t BitWidth = cast<IntegerType>(Op->getType())->getBitWidth();
// If the shift count is not less than the bitwidth, the result of
// the shift is undefined. Don't try to analyze it, because the
// resolution chosen here may differ from the resolution chosen in
// other parts of the compiler.
if (SA->getValue().ult(BitWidth)) {
Constant *X =
ConstantInt::get(SA->getContext(),
APInt::getOneBitSet(BitWidth, SA->getZExtValue()));
return BinaryOp(Instruction::UDiv, Op->getOperand(0), X);
}
}
return BinaryOp(Op);
case Instruction::ExtractValue: {
auto *EVI = cast<ExtractValueInst>(Op);
if (EVI->getNumIndices() != 1 || EVI->getIndices()[0] != 0)
break;
auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand());
if (!WO)
break;
Instruction::BinaryOps BinOp = WO->getBinaryOp();
bool Signed = WO->isSigned();
// TODO: Should add nuw/nsw flags for mul as well.
if (BinOp == Instruction::Mul || !isOverflowIntrinsicNoWrap(WO, DT))
return BinaryOp(BinOp, WO->getLHS(), WO->getRHS());
// Now that we know that all uses of the arithmetic-result component of
// CI are guarded by the overflow check, we can go ahead and pretend
// that the arithmetic is non-overflowing.
return BinaryOp(BinOp, WO->getLHS(), WO->getRHS(),
/* IsNSW = */ Signed, /* IsNUW = */ !Signed);
}
default:
break;
}
// Recognise intrinsic loop.decrement.reg, and as this has exactly the same
// semantics as a Sub, return a binary sub expression.
if (auto *II = dyn_cast<IntrinsicInst>(V))
if (II->getIntrinsicID() == Intrinsic::loop_decrement_reg)
return BinaryOp(Instruction::Sub, II->getOperand(0), II->getOperand(1));
return std::nullopt;
}
/// Helper function to createAddRecFromPHIWithCasts. We have a phi
/// node whose symbolic (unknown) SCEV is \p SymbolicPHI, which is updated via
/// the loop backedge by a SCEVAddExpr, possibly also with a few casts on the
/// way. This function checks if \p Op, an operand of this SCEVAddExpr,
/// follows one of the following patterns:
/// Op == (SExt ix (Trunc iy (%SymbolicPHI) to ix) to iy)
/// Op == (ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy)
/// If the SCEV expression of \p Op conforms with one of the expected patterns
/// we return the type of the truncation operation, and indicate whether the
/// truncated type should be treated as signed/unsigned by setting
/// \p Signed to true/false, respectively.
static Type *isSimpleCastedPHI(const SCEV *Op, const SCEVUnknown *SymbolicPHI,
bool &Signed, ScalarEvolution &SE) {
// The case where Op == SymbolicPHI (that is, with no type conversions on
// the way) is handled by the regular add recurrence creating logic and
// would have already been triggered in createAddRecForPHI. Reaching it here
// means that createAddRecFromPHI had failed for this PHI before (e.g.,
// because one of the other operands of the SCEVAddExpr updating this PHI is
// not invariant).
//
// Here we look for the case where Op = (ext(trunc(SymbolicPHI))), and in
// this case predicates that allow us to prove that Op == SymbolicPHI will
// be added.
if (Op == SymbolicPHI)
return nullptr;
unsigned SourceBits = SE.getTypeSizeInBits(SymbolicPHI->getType());
unsigned NewBits = SE.getTypeSizeInBits(Op->getType());
if (SourceBits != NewBits)
return nullptr;
const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(Op);
const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(Op);
if (!SExt && !ZExt)
return nullptr;
const SCEVTruncateExpr *Trunc =
SExt ? dyn_cast<SCEVTruncateExpr>(SExt->getOperand())
: dyn_cast<SCEVTruncateExpr>(ZExt->getOperand());
if (!Trunc)
return nullptr;
const SCEV *X = Trunc->getOperand();
if (X != SymbolicPHI)
return nullptr;
Signed = SExt != nullptr;
return Trunc->getType();
}
static const Loop *isIntegerLoopHeaderPHI(const PHINode *PN, LoopInfo &LI) {
if (!PN->getType()->isIntegerTy())
return nullptr;
const Loop *L = LI.getLoopFor(PN->getParent());
if (!L || L->getHeader() != PN->getParent())
return nullptr;
return L;
}
// Analyze \p SymbolicPHI, a SCEV expression of a phi node, and check if the
// computation that updates the phi follows the following pattern:
// (SExt/ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy) + InvariantAccum
// which correspond to a phi->trunc->sext/zext->add->phi update chain.
// If so, try to see if it can be rewritten as an AddRecExpr under some
// Predicates. If successful, return them as a pair. Also cache the results
// of the analysis.
//
// Example usage scenario:
// Say the Rewriter is called for the following SCEV:
// 8 * ((sext i32 (trunc i64 %X to i32) to i64) + %Step)
// where:
// %X = phi i64 (%Start, %BEValue)
// It will visitMul->visitAdd->visitSExt->visitTrunc->visitUnknown(%X),
// and call this function with %SymbolicPHI = %X.
//
// The analysis will find that the value coming around the backedge has
// the following SCEV:
// BEValue = ((sext i32 (trunc i64 %X to i32) to i64) + %Step)
// Upon concluding that this matches the desired pattern, the function
// will return the pair {NewAddRec, SmallPredsVec} where:
// NewAddRec = {%Start,+,%Step}
// SmallPredsVec = {P1, P2, P3} as follows:
// P1(WrapPred): AR: {trunc(%Start),+,(trunc %Step)}<nsw> Flags: <nssw>
// P2(EqualPred): %Start == (sext i32 (trunc i64 %Start to i32) to i64)
// P3(EqualPred): %Step == (sext i32 (trunc i64 %Step to i32) to i64)
// The returned pair means that SymbolicPHI can be rewritten into NewAddRec
// under the predicates {P1,P2,P3}.
// This predicated rewrite will be cached in PredicatedSCEVRewrites:
// PredicatedSCEVRewrites[{%X,L}] = {NewAddRec, {P1,P2,P3)}
//
// TODO's:
//
// 1) Extend the Induction descriptor to also support inductions that involve
// casts: When needed (namely, when we are called in the context of the
// vectorizer induction analysis), a Set of cast instructions will be
// populated by this method, and provided back to isInductionPHI. This is
// needed to allow the vectorizer to properly record them to be ignored by
// the cost model and to avoid vectorizing them (otherwise these casts,
// which are redundant under the runtime overflow checks, will be
// vectorized, which can be costly).
//
// 2) Support additional induction/PHISCEV patterns: We also want to support
// inductions where the sext-trunc / zext-trunc operations (partly) occur
// after the induction update operation (the induction increment):
//
// (Trunc iy (SExt/ZExt ix (%SymbolicPHI + InvariantAccum) to iy) to ix)
// which correspond to a phi->add->trunc->sext/zext->phi update chain.
//
// (Trunc iy ((SExt/ZExt ix (%SymbolicPhi) to iy) + InvariantAccum) to ix)
// which correspond to a phi->trunc->add->sext/zext->phi update chain.
//
// 3) Outline common code with createAddRecFromPHI to avoid duplication.
std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
ScalarEvolution::createAddRecFromPHIWithCastsImpl(const SCEVUnknown *SymbolicPHI) {
SmallVector<const SCEVPredicate *, 3> Predicates;
// *** Part1: Analyze if we have a phi-with-cast pattern for which we can
// return an AddRec expression under some predicate.
auto *PN = cast<PHINode>(SymbolicPHI->getValue());
const Loop *L = isIntegerLoopHeaderPHI(PN, LI);
assert(L && "Expecting an integer loop header phi");
// The loop may have multiple entrances or multiple exits; we can analyze
// this phi as an addrec if it has a unique entry value and a unique
// backedge value.
Value *BEValueV = nullptr, *StartValueV = nullptr;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *V = PN->getIncomingValue(i);
if (L->contains(PN->getIncomingBlock(i))) {
if (!BEValueV) {
BEValueV = V;
} else if (BEValueV != V) {
BEValueV = nullptr;
break;
}
} else if (!StartValueV) {
StartValueV = V;
} else if (StartValueV != V) {
StartValueV = nullptr;
break;
}
}
if (!BEValueV || !StartValueV)
return std::nullopt;
const SCEV *BEValue = getSCEV(BEValueV);
// If the value coming around the backedge is an add with the symbolic
// value we just inserted, possibly with casts that we can ignore under
// an appropriate runtime guard, then we found a simple induction variable!
const auto *Add = dyn_cast<SCEVAddExpr>(BEValue);
if (!Add)
return std::nullopt;
// If there is a single occurrence of the symbolic value, possibly
// casted, replace it with a recurrence.
unsigned FoundIndex = Add->getNumOperands();
Type *TruncTy = nullptr;
bool Signed;
for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
if ((TruncTy =
isSimpleCastedPHI(Add->getOperand(i), SymbolicPHI, Signed, *this)))
if (FoundIndex == e) {
FoundIndex = i;
break;
}
if (FoundIndex == Add->getNumOperands())
return std::nullopt;
// Create an add with everything but the specified operand.
SmallVector<const SCEV *, 8> Ops;
for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
if (i != FoundIndex)
Ops.push_back(Add->getOperand(i));
const SCEV *Accum = getAddExpr(Ops);
// The runtime checks will not be valid if the step amount is
// varying inside the loop.
if (!isLoopInvariant(Accum, L))
return std::nullopt;
// *** Part2: Create the predicates
// Analysis was successful: we have a phi-with-cast pattern for which we
// can return an AddRec expression under the following predicates:
//
// P1: A Wrap predicate that guarantees that Trunc(Start) + i*Trunc(Accum)
// fits within the truncated type (does not overflow) for i = 0 to n-1.
// P2: An Equal predicate that guarantees that
// Start = (Ext ix (Trunc iy (Start) to ix) to iy)
// P3: An Equal predicate that guarantees that
// Accum = (Ext ix (Trunc iy (Accum) to ix) to iy)
//
// As we next prove, the above predicates guarantee that:
// Start + i*Accum = (Ext ix (Trunc iy ( Start + i*Accum ) to ix) to iy)
//
//
// More formally, we want to prove that:
// Expr(i+1) = Start + (i+1) * Accum
// = (Ext ix (Trunc iy (Expr(i)) to ix) to iy) + Accum
//
// Given that:
// 1) Expr(0) = Start
// 2) Expr(1) = Start + Accum
// = (Ext ix (Trunc iy (Start) to ix) to iy) + Accum :: from P2
// 3) Induction hypothesis (step i):
// Expr(i) = (Ext ix (Trunc iy (Expr(i-1)) to ix) to iy) + Accum
//
// Proof:
// Expr(i+1) =
// = Start + (i+1)*Accum
// = (Start + i*Accum) + Accum
// = Expr(i) + Accum
// = (Ext ix (Trunc iy (Expr(i-1)) to ix) to iy) + Accum + Accum
// :: from step i
//
// = (Ext ix (Trunc iy (Start + (i-1)*Accum) to ix) to iy) + Accum + Accum
//
// = (Ext ix (Trunc iy (Start + (i-1)*Accum) to ix) to iy)
// + (Ext ix (Trunc iy (Accum) to ix) to iy)
// + Accum :: from P3
//
// = (Ext ix (Trunc iy ((Start + (i-1)*Accum) + Accum) to ix) to iy)
// + Accum :: from P1: Ext(x)+Ext(y)=>Ext(x+y)
//
// = (Ext ix (Trunc iy (Start + i*Accum) to ix) to iy) + Accum
// = (Ext ix (Trunc iy (Expr(i)) to ix) to iy) + Accum
//
// By induction, the same applies to all iterations 1<=i<n:
//
// Create a truncated addrec for which we will add a no overflow check (P1).
const SCEV *StartVal = getSCEV(StartValueV);
const SCEV *PHISCEV =
getAddRecExpr(getTruncateExpr(StartVal, TruncTy),
getTruncateExpr(Accum, TruncTy), L, SCEV::FlagAnyWrap);
// PHISCEV can be either a SCEVConstant or a SCEVAddRecExpr.
// ex: If truncated Accum is 0 and StartVal is a constant, then PHISCEV
// will be constant.
//
// If PHISCEV is a constant, then P1 degenerates into P2 or P3, so we don't
// add P1.
if (const auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV)) {
SCEVWrapPredicate::IncrementWrapFlags AddedFlags =
Signed ? SCEVWrapPredicate::IncrementNSSW
: SCEVWrapPredicate::IncrementNUSW;
const SCEVPredicate *AddRecPred = getWrapPredicate(AR, AddedFlags);
Predicates.push_back(AddRecPred);
}
// Create the Equal Predicates P2,P3:
// It is possible that the predicates P2 and/or P3 are computable at
// compile time due to StartVal and/or Accum being constants.
// If either one is, then we can check that now and escape if either P2
// or P3 is false.
// Construct the extended SCEV: (Ext ix (Trunc iy (Expr) to ix) to iy)
// for each of StartVal and Accum
auto getExtendedExpr = [&](const SCEV *Expr,
bool CreateSignExtend) -> const SCEV * {
assert(isLoopInvariant(Expr, L) && "Expr is expected to be invariant");
const SCEV *TruncatedExpr = getTruncateExpr(Expr, TruncTy);
const SCEV *ExtendedExpr =
CreateSignExtend ? getSignExtendExpr(TruncatedExpr, Expr->getType())
: getZeroExtendExpr(TruncatedExpr, Expr->getType());
return ExtendedExpr;
};
// Given:
// ExtendedExpr = (Ext ix (Trunc iy (Expr) to ix) to iy
// = getExtendedExpr(Expr)
// Determine whether the predicate P: Expr == ExtendedExpr
// is known to be false at compile time
auto PredIsKnownFalse = [&](const SCEV *Expr,
const SCEV *ExtendedExpr) -> bool {
return Expr != ExtendedExpr &&
isKnownPredicate(ICmpInst::ICMP_NE, Expr, ExtendedExpr);
};
const SCEV *StartExtended = getExtendedExpr(StartVal, Signed);
if (PredIsKnownFalse(StartVal, StartExtended)) {
LLVM_DEBUG(dbgs() << "P2 is compile-time false\n";);
return std::nullopt;
}
// The Step is always Signed (because the overflow checks are either
// NSSW or NUSW)
const SCEV *AccumExtended = getExtendedExpr(Accum, /*CreateSignExtend=*/true);
if (PredIsKnownFalse(Accum, AccumExtended)) {
LLVM_DEBUG(dbgs() << "P3 is compile-time false\n";);
return std::nullopt;
}
auto AppendPredicate = [&](const SCEV *Expr,
const SCEV *ExtendedExpr) -> void {
if (Expr != ExtendedExpr &&
!isKnownPredicate(ICmpInst::ICMP_EQ, Expr, ExtendedExpr)) {
const SCEVPredicate *Pred = getEqualPredicate(Expr, ExtendedExpr);
LLVM_DEBUG(dbgs() << "Added Predicate: " << *Pred);
Predicates.push_back(Pred);
}
};
AppendPredicate(StartVal, StartExtended);
AppendPredicate(Accum, AccumExtended);
// *** Part3: Predicates are ready. Now go ahead and create the new addrec in
// which the casts had been folded away. The caller can rewrite SymbolicPHI
// into NewAR if it will also add the runtime overflow checks specified in
// Predicates.
auto *NewAR = getAddRecExpr(StartVal, Accum, L, SCEV::FlagAnyWrap);
std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>> PredRewrite =
std::make_pair(NewAR, Predicates);
// Remember the result of the analysis for this SCEV at this locayyytion.
PredicatedSCEVRewrites[{SymbolicPHI, L}] = PredRewrite;
return PredRewrite;
}
std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
ScalarEvolution::createAddRecFromPHIWithCasts(const SCEVUnknown *SymbolicPHI) {
auto *PN = cast<PHINode>(SymbolicPHI->getValue());
const Loop *L = isIntegerLoopHeaderPHI(PN, LI);
if (!L)
return std::nullopt;
// Check to see if we already analyzed this PHI.
auto I = PredicatedSCEVRewrites.find({SymbolicPHI, L});
if (I != PredicatedSCEVRewrites.end()) {
std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>> Rewrite =
I->second;
// Analysis was done before and failed to create an AddRec:
if (Rewrite.first == SymbolicPHI)
return std::nullopt;
// Analysis was done before and succeeded to create an AddRec under
// a predicate:
assert(isa<SCEVAddRecExpr>(Rewrite.first) && "Expected an AddRec");
assert(!(Rewrite.second).empty() && "Expected to find Predicates");
return Rewrite;
}
std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
Rewrite = createAddRecFromPHIWithCastsImpl(SymbolicPHI);
// Record in the cache that the analysis failed
if (!Rewrite) {
SmallVector<const SCEVPredicate *, 3> Predicates;
PredicatedSCEVRewrites[{SymbolicPHI, L}] = {SymbolicPHI, Predicates};
return std::nullopt;
}
return Rewrite;
}
// FIXME: This utility is currently required because the Rewriter currently
// does not rewrite this expression:
// {0, +, (sext ix (trunc iy to ix) to iy)}
// into {0, +, %step},
// even when the following Equal predicate exists:
// "%step == (sext ix (trunc iy to ix) to iy)".
bool PredicatedScalarEvolution::areAddRecsEqualWithPreds(
const SCEVAddRecExpr *AR1, const SCEVAddRecExpr *AR2) const {
if (AR1 == AR2)
return true;
auto areExprsEqual = [&](const SCEV *Expr1, const SCEV *Expr2) -> bool {
if (Expr1 != Expr2 &&
!Preds->implies(SE.getEqualPredicate(Expr1, Expr2), SE) &&
!Preds->implies(SE.getEqualPredicate(Expr2, Expr1), SE))
return false;
return true;
};
if (!areExprsEqual(AR1->getStart(), AR2->getStart()) ||
!areExprsEqual(AR1->getStepRecurrence(SE), AR2->getStepRecurrence(SE)))
return false;
return true;
}
/// A helper function for createAddRecFromPHI to handle simple cases.
///
/// This function tries to find an AddRec expression for the simplest (yet most
/// common) cases: PN = PHI(Start, OP(Self, LoopInvariant)).
/// If it fails, createAddRecFromPHI will use a more general, but slow,
/// technique for finding the AddRec expression.
const SCEV *ScalarEvolution::createSimpleAffineAddRec(PHINode *PN,
Value *BEValueV,
Value *StartValueV) {
const Loop *L = LI.getLoopFor(PN->getParent());
assert(L && L->getHeader() == PN->getParent());
assert(BEValueV && StartValueV);
auto BO = MatchBinaryOp(BEValueV, getDataLayout(), AC, DT, PN);
if (!BO)
return nullptr;
if (BO->Opcode != Instruction::Add)
return nullptr;
const SCEV *Accum = nullptr;
if (BO->LHS == PN && L->isLoopInvariant(BO->RHS))
Accum = getSCEV(BO->RHS);
else if (BO->RHS == PN && L->isLoopInvariant(BO->LHS))
Accum = getSCEV(BO->LHS);
if (!Accum)
return nullptr;
SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
if (BO->IsNUW)
Flags = setFlags(Flags, SCEV::FlagNUW);
if (BO->IsNSW)
Flags = setFlags(Flags, SCEV::FlagNSW);
const SCEV *StartVal = getSCEV(StartValueV);
const SCEV *PHISCEV = getAddRecExpr(StartVal, Accum, L, Flags);
insertValueToMap(PN, PHISCEV);
if (auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV)) {
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR),
(SCEV::NoWrapFlags)(AR->getNoWrapFlags() |
proveNoWrapViaConstantRanges(AR)));
}
// We can add Flags to the post-inc expression only if we
// know that it is *undefined behavior* for BEValueV to
// overflow.
if (auto *BEInst = dyn_cast<Instruction>(BEValueV)) {
assert(isLoopInvariant(Accum, L) &&
"Accum is defined outside L, but is not invariant?");
if (isAddRecNeverPoison(BEInst, L))
(void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
}
return PHISCEV;
}
const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
const Loop *L = LI.getLoopFor(PN->getParent());
if (!L || L->getHeader() != PN->getParent())
return nullptr;
// The loop may have multiple entrances or multiple exits; we can analyze
// this phi as an addrec if it has a unique entry value and a unique
// backedge value.
Value *BEValueV = nullptr, *StartValueV = nullptr;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *V = PN->getIncomingValue(i);
if (L->contains(PN->getIncomingBlock(i))) {
if (!BEValueV) {
BEValueV = V;
} else if (BEValueV != V) {
BEValueV = nullptr;
break;
}
} else if (!StartValueV) {
StartValueV = V;
} else if (StartValueV != V) {
StartValueV = nullptr;
break;
}
}
if (!BEValueV || !StartValueV)
return nullptr;
assert(ValueExprMap.find_as(PN) == ValueExprMap.end() &&
"PHI node already processed?");
// First, try to find AddRec expression without creating a fictituos symbolic
// value for PN.
if (auto *S = createSimpleAffineAddRec(PN, BEValueV, StartValueV))
return S;
// Handle PHI node value symbolically.
const SCEV *SymbolicName = getUnknown(PN);
insertValueToMap(PN, SymbolicName);
// Using this symbolic name for the PHI, analyze the value coming around
// the back-edge.
const SCEV *BEValue = getSCEV(BEValueV);
// NOTE: If BEValue is loop invariant, we know that the PHI node just
// has a special value for the first iteration of the loop.
// If the value coming around the backedge is an add with the symbolic
// value we just inserted, then we found a simple induction variable!
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(BEValue)) {
// If there is a single occurrence of the symbolic value, replace it
// with a recurrence.
unsigned FoundIndex = Add->getNumOperands();
for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
if (Add->getOperand(i) == SymbolicName)
if (FoundIndex == e) {
FoundIndex = i;
break;
}
if (FoundIndex != Add->getNumOperands()) {
// Create an add with everything but the specified operand.
SmallVector<const SCEV *, 8> Ops;
for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
if (i != FoundIndex)
Ops.push_back(SCEVBackedgeConditionFolder::rewrite(Add->getOperand(i),
L, *this));
const SCEV *Accum = getAddExpr(Ops);
// This is not a valid addrec if the step amount is varying each
// loop iteration, but is not itself an addrec in this loop.
if (isLoopInvariant(Accum, L) ||
(isa<SCEVAddRecExpr>(Accum) &&
cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
if (auto BO = MatchBinaryOp(BEValueV, getDataLayout(), AC, DT, PN)) {
if (BO->Opcode == Instruction::Add && BO->LHS == PN) {
if (BO->IsNUW)
Flags = setFlags(Flags, SCEV::FlagNUW);
if (BO->IsNSW)
Flags = setFlags(Flags, SCEV::FlagNSW);
}
} else if (GEPOperator *GEP = dyn_cast<GEPOperator>(BEValueV)) {
if (GEP->getOperand(0) == PN) {
GEPNoWrapFlags NW = GEP->getNoWrapFlags();
// If the increment has any nowrap flags, then we know the address
// space cannot be wrapped around.
if (NW != GEPNoWrapFlags::none())
Flags = setFlags(Flags, SCEV::FlagNW);
// If the GEP is nuw or nusw with non-negative offset, we know that
// no unsigned wrap occurs. We cannot set the nsw flag as only the
// offset is treated as signed, while the base is unsigned.
if (NW.hasNoUnsignedWrap() ||
(NW.hasNoUnsignedSignedWrap() && isKnownNonNegative(Accum)))
Flags = setFlags(Flags, SCEV::FlagNUW);
}
// We cannot transfer nuw and nsw flags from subtraction
// operations -- sub nuw X, Y is not the same as add nuw X, -Y
// for instance.
}
const SCEV *StartVal = getSCEV(StartValueV);
const SCEV *PHISCEV = getAddRecExpr(StartVal, Accum, L, Flags);
// Okay, for the entire analysis of this edge we assumed the PHI
// to be symbolic. We now need to go back and purge all of the
// entries for the scalars that use the symbolic expression.
forgetMemoizedResults(SymbolicName);
insertValueToMap(PN, PHISCEV);
if (auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV)) {
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR),
(SCEV::NoWrapFlags)(AR->getNoWrapFlags() |
proveNoWrapViaConstantRanges(AR)));
}
// We can add Flags to the post-inc expression only if we
// know that it is *undefined behavior* for BEValueV to
// overflow.
if (auto *BEInst = dyn_cast<Instruction>(BEValueV))
if (isLoopInvariant(Accum, L) && isAddRecNeverPoison(BEInst, L))
(void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
return PHISCEV;
}
}
} else {
// Otherwise, this could be a loop like this:
// i = 0; for (j = 1; ..; ++j) { .... i = j; }
// In this case, j = {1,+,1} and BEValue is j.
// Because the other in-value of i (0) fits the evolution of BEValue
// i really is an addrec evolution.
//
// We can generalize this saying that i is the shifted value of BEValue
// by one iteration:
// PHI(f(0), f({1,+,1})) --> f({0,+,1})
// Do not allow refinement in rewriting of BEValue.
const SCEV *Shifted = SCEVShiftRewriter::rewrite(BEValue, L, *this);
const SCEV *Start = SCEVInitRewriter::rewrite(Shifted, L, *this, false);
if (Shifted != getCouldNotCompute() && Start != getCouldNotCompute() &&
isGuaranteedNotToCauseUB(Shifted) && ::impliesPoison(Shifted, Start)) {
const SCEV *StartVal = getSCEV(StartValueV);
if (Start == StartVal) {
// Okay, for the entire analysis of this edge we assumed the PHI
// to be symbolic. We now need to go back and purge all of the
// entries for the scalars that use the symbolic expression.
forgetMemoizedResults(SymbolicName);
insertValueToMap(PN, Shifted);
return Shifted;
}
}
}
// Remove the temporary PHI node SCEV that has been inserted while intending
// to create an AddRecExpr for this PHI node. We can not keep this temporary
// as it will prevent later (possibly simpler) SCEV expressions to be added
// to the ValueExprMap.
eraseValueFromMap(PN);
return nullptr;
}
// Try to match a control flow sequence that branches out at BI and merges back
// at Merge into a "C ? LHS : RHS" select pattern. Return true on a successful
// match.
static bool BrPHIToSelect(DominatorTree &DT, BranchInst *BI, PHINode *Merge,
Value *&C, Value *&LHS, Value *&RHS) {
C = BI->getCondition();
BasicBlockEdge LeftEdge(BI->getParent(), BI->getSuccessor(0));
BasicBlockEdge RightEdge(BI->getParent(), BI->getSuccessor(1));
if (!LeftEdge.isSingleEdge())
return false;
assert(RightEdge.isSingleEdge() && "Follows from LeftEdge.isSingleEdge()");
Use &LeftUse = Merge->getOperandUse(0);
Use &RightUse = Merge->getOperandUse(1);
if (DT.dominates(LeftEdge, LeftUse) && DT.dominates(RightEdge, RightUse)) {
LHS = LeftUse;
RHS = RightUse;
return true;
}
if (DT.dominates(LeftEdge, RightUse) && DT.dominates(RightEdge, LeftUse)) {
LHS = RightUse;
RHS = LeftUse;
return true;
}
return false;
}
const SCEV *ScalarEvolution::createNodeFromSelectLikePHI(PHINode *PN) {
auto IsReachable =
[&](BasicBlock *BB) { return DT.isReachableFromEntry(BB); };
if (PN->getNumIncomingValues() == 2 && all_of(PN->blocks(), IsReachable)) {
// Try to match
//
// br %cond, label %left, label %right
// left:
// br label %merge
// right:
// br label %merge
// merge:
// V = phi [ %x, %left ], [ %y, %right ]
//
// as "select %cond, %x, %y"
BasicBlock *IDom = DT[PN->getParent()]->getIDom()->getBlock();
assert(IDom && "At least the entry block should dominate PN");
auto *BI = dyn_cast<BranchInst>(IDom->getTerminator());
Value *Cond = nullptr, *LHS = nullptr, *RHS = nullptr;
if (BI && BI->isConditional() &&
BrPHIToSelect(DT, BI, PN, Cond, LHS, RHS) &&
properlyDominates(getSCEV(LHS), PN->getParent()) &&
properlyDominates(getSCEV(RHS), PN->getParent()))
return createNodeForSelectOrPHI(PN, Cond, LHS, RHS);
}
return nullptr;
}
/// Returns SCEV for the first operand of a phi if all phi operands have
/// identical opcodes and operands
/// eg.
/// a: %add = %a + %b
/// br %c
/// b: %add1 = %a + %b
/// br %c
/// c: %phi = phi [%add, a], [%add1, b]
/// scev(%phi) => scev(%add)
const SCEV *
ScalarEvolution::createNodeForPHIWithIdenticalOperands(PHINode *PN) {
BinaryOperator *CommonInst = nullptr;
// Check if instructions are identical.
for (Value *Incoming : PN->incoming_values()) {
auto *IncomingInst = dyn_cast<BinaryOperator>(Incoming);
if (!IncomingInst)
return nullptr;
if (CommonInst) {
if (!CommonInst->isIdenticalToWhenDefined(IncomingInst))
return nullptr; // Not identical, give up
} else {
// Remember binary operator
CommonInst = IncomingInst;
}
}
if (!CommonInst)
return nullptr;
// Check if SCEV exprs for instructions are identical.
const SCEV *CommonSCEV = getSCEV(CommonInst);
bool SCEVExprsIdentical =
all_of(drop_begin(PN->incoming_values()),
[this, CommonSCEV](Value *V) { return CommonSCEV == getSCEV(V); });
return SCEVExprsIdentical ? CommonSCEV : nullptr;
}
const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
if (const SCEV *S = createAddRecFromPHI(PN))
return S;
// We do not allow simplifying phi (undef, X) to X here, to avoid reusing the
// phi node for X.
if (Value *V = simplifyInstruction(
PN, {getDataLayout(), &TLI, &DT, &AC, /*CtxI=*/nullptr,
/*UseInstrInfo=*/true, /*CanUseUndef=*/false}))
return getSCEV(V);
if (const SCEV *S = createNodeForPHIWithIdenticalOperands(PN))
return S;
if (const SCEV *S = createNodeFromSelectLikePHI(PN))
return S;
// If it's not a loop phi, we can't handle it yet.
return getUnknown(PN);
}
bool SCEVMinMaxExprContains(const SCEV *Root, const SCEV *OperandToFind,
SCEVTypes RootKind) {
struct FindClosure {
const SCEV *OperandToFind;
const SCEVTypes RootKind; // Must be a sequential min/max expression.
const SCEVTypes NonSequentialRootKind; // Non-seq variant of RootKind.
bool Found = false;
bool canRecurseInto(SCEVTypes Kind) const {
// We can only recurse into the SCEV expression of the same effective type
// as the type of our root SCEV expression, and into zero-extensions.
return RootKind == Kind || NonSequentialRootKind == Kind ||
scZeroExtend == Kind;
};
FindClosure(const SCEV *OperandToFind, SCEVTypes RootKind)
: OperandToFind(OperandToFind), RootKind(RootKind),
NonSequentialRootKind(
SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(
RootKind)) {}
bool follow(const SCEV *S) {
Found = S == OperandToFind;
return !isDone() && canRecurseInto(S->getSCEVType());
}
bool isDone() const { return Found; }
};
FindClosure FC(OperandToFind, RootKind);
visitAll(Root, FC);
return FC.Found;
}
std::optional<const SCEV *>
ScalarEvolution::createNodeForSelectOrPHIInstWithICmpInstCond(Type *Ty,
ICmpInst *Cond,
Value *TrueVal,
Value *FalseVal) {
// Try to match some simple smax or umax patterns.
auto *ICI = Cond;
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
switch (ICI->getPredicate()) {
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE:
// a > b ? a+x : b+x -> max(a, b)+x
// a > b ? b+x : a+x -> min(a, b)+x
if (getTypeSizeInBits(LHS->getType()) <= getTypeSizeInBits(Ty)) {
bool Signed = ICI->isSigned();
const SCEV *LA = getSCEV(TrueVal);
const SCEV *RA = getSCEV(FalseVal);
const SCEV *LS = getSCEV(LHS);
const SCEV *RS = getSCEV(RHS);
if (LA->getType()->isPointerTy()) {
// FIXME: Handle cases where LS/RS are pointers not equal to LA/RA.
// Need to make sure we can't produce weird expressions involving
// negated pointers.
if (LA == LS && RA == RS)
return Signed ? getSMaxExpr(LS, RS) : getUMaxExpr(LS, RS);
if (LA == RS && RA == LS)
return Signed ? getSMinExpr(LS, RS) : getUMinExpr(LS, RS);
}
auto CoerceOperand = [&](const SCEV *Op) -> const SCEV * {
if (Op->getType()->isPointerTy()) {
Op = getLosslessPtrToIntExpr(Op);
if (isa<SCEVCouldNotCompute>(Op))
return Op;
}
if (Signed)
Op = getNoopOrSignExtend(Op, Ty);
else
Op = getNoopOrZeroExtend(Op, Ty);
return Op;
};
LS = CoerceOperand(LS);
RS = CoerceOperand(RS);
if (isa<SCEVCouldNotCompute>(LS) || isa<SCEVCouldNotCompute>(RS))
break;
const SCEV *LDiff = getMinusSCEV(LA, LS);
const SCEV *RDiff = getMinusSCEV(RA, RS);
if (LDiff == RDiff)
return getAddExpr(Signed ? getSMaxExpr(LS, RS) : getUMaxExpr(LS, RS),
LDiff);
LDiff = getMinusSCEV(LA, RS);
RDiff = getMinusSCEV(RA, LS);
if (LDiff == RDiff)
return getAddExpr(Signed ? getSMinExpr(LS, RS) : getUMinExpr(LS, RS),
LDiff);
}
break;
case ICmpInst::ICMP_NE:
// x != 0 ? x+y : C+y -> x == 0 ? C+y : x+y
std::swap(TrueVal, FalseVal);
[[fallthrough]];
case ICmpInst::ICMP_EQ:
// x == 0 ? C+y : x+y -> umax(x, C)+y iff C u<= 1
if (getTypeSizeInBits(LHS->getType()) <= getTypeSizeInBits(Ty) &&
isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()) {
const SCEV *X = getNoopOrZeroExtend(getSCEV(LHS), Ty);
const SCEV *TrueValExpr = getSCEV(TrueVal); // C+y
const SCEV *FalseValExpr = getSCEV(FalseVal); // x+y
const SCEV *Y = getMinusSCEV(FalseValExpr, X); // y = (x+y)-x
const SCEV *C = getMinusSCEV(TrueValExpr, Y); // C = (C+y)-y
if (isa<SCEVConstant>(C) && cast<SCEVConstant>(C)->getAPInt().ule(1))
return getAddExpr(getUMaxExpr(X, C), Y);
}
// x == 0 ? 0 : umin (..., x, ...) -> umin_seq(x, umin (...))
// x == 0 ? 0 : umin_seq(..., x, ...) -> umin_seq(x, umin_seq(...))
// x == 0 ? 0 : umin (..., umin_seq(..., x, ...), ...)
// -> umin_seq(x, umin (..., umin_seq(...), ...))
if (isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero() &&
isa<ConstantInt>(TrueVal) && cast<ConstantInt>(TrueVal)->isZero()) {
const SCEV *X = getSCEV(LHS);
while (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(X))
X = ZExt->getOperand();
if (getTypeSizeInBits(X->getType()) <= getTypeSizeInBits(Ty)) {
const SCEV *FalseValExpr = getSCEV(FalseVal);
if (SCEVMinMaxExprContains(FalseValExpr, X, scSequentialUMinExpr))
return getUMinExpr(getNoopOrZeroExtend(X, Ty), FalseValExpr,
/*Sequential=*/true);
}
}
break;
default:
break;
}
return std::nullopt;
}
static std::optional<const SCEV *>
createNodeForSelectViaUMinSeq(ScalarEvolution *SE, const SCEV *CondExpr,
const SCEV *TrueExpr, const SCEV *FalseExpr) {
assert(CondExpr->getType()->isIntegerTy(1) &&
TrueExpr->getType() == FalseExpr->getType() &&
TrueExpr->getType()->isIntegerTy(1) &&
"Unexpected operands of a select.");
// i1 cond ? i1 x : i1 C --> C + (i1 cond ? (i1 x - i1 C) : i1 0)
// --> C + (umin_seq cond, x - C)
//
// i1 cond ? i1 C : i1 x --> C + (i1 cond ? i1 0 : (i1 x - i1 C))
// --> C + (i1 ~cond ? (i1 x - i1 C) : i1 0)
// --> C + (umin_seq ~cond, x - C)
// FIXME: while we can't legally model the case where both of the hands
// are fully variable, we only require that the *difference* is constant.
if (!isa<SCEVConstant>(TrueExpr) && !isa<SCEVConstant>(FalseExpr))
return std::nullopt;
const SCEV *X, *C;
if (isa<SCEVConstant>(TrueExpr)) {
CondExpr = SE->getNotSCEV(CondExpr);
X = FalseExpr;
C = TrueExpr;
} else {
X = TrueExpr;
C = FalseExpr;
}
return SE->getAddExpr(C, SE->getUMinExpr(CondExpr, SE->getMinusSCEV(X, C),
/*Sequential=*/true));
}
static std::optional<const SCEV *>
createNodeForSelectViaUMinSeq(ScalarEvolution *SE, Value *Cond, Value *TrueVal,
Value *FalseVal) {
if (!isa<ConstantInt>(TrueVal) && !isa<ConstantInt>(FalseVal))
return std::nullopt;
const auto *SECond = SE->getSCEV(Cond);
const auto *SETrue = SE->getSCEV(TrueVal);
const auto *SEFalse = SE->getSCEV(FalseVal);
return createNodeForSelectViaUMinSeq(SE, SECond, SETrue, SEFalse);
}
const SCEV *ScalarEvolution::createNodeForSelectOrPHIViaUMinSeq(
Value *V, Value *Cond, Value *TrueVal, Value *FalseVal) {
assert(Cond->getType()->isIntegerTy(1) && "Select condition is not an i1?");
assert(TrueVal->getType() == FalseVal->getType() &&
V->getType() == TrueVal->getType() &&
"Types of select hands and of the result must match.");
// For now, only deal with i1-typed `select`s.
if (!V->getType()->isIntegerTy(1))
return getUnknown(V);
if (std::optional<const SCEV *> S =
createNodeForSelectViaUMinSeq(this, Cond, TrueVal, FalseVal))
return *S;
return getUnknown(V);
}
const SCEV *ScalarEvolution::createNodeForSelectOrPHI(Value *V, Value *Cond,
Value *TrueVal,
Value *FalseVal) {
// Handle "constant" branch or select. This can occur for instance when a
// loop pass transforms an inner loop and moves on to process the outer loop.
if (auto *CI = dyn_cast<ConstantInt>(Cond))
return getSCEV(CI->isOne() ? TrueVal : FalseVal);
if (auto *I = dyn_cast<Instruction>(V)) {
if (auto *ICI = dyn_cast<ICmpInst>(Cond)) {
if (std::optional<const SCEV *> S =
createNodeForSelectOrPHIInstWithICmpInstCond(I->getType(), ICI,
TrueVal, FalseVal))
return *S;
}
}
return createNodeForSelectOrPHIViaUMinSeq(V, Cond, TrueVal, FalseVal);
}
/// Expand GEP instructions into add and multiply operations. This allows them
/// to be analyzed by regular SCEV code.
const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
assert(GEP->getSourceElementType()->isSized() &&
"GEP source element type must be sized");
SmallVector<const SCEV *, 4> IndexExprs;
for (Value *Index : GEP->indices())
IndexExprs.push_back(getSCEV(Index));
return getGEPExpr(GEP, IndexExprs);
}
APInt ScalarEvolution::getConstantMultipleImpl(const SCEV *S) {
uint64_t BitWidth = getTypeSizeInBits(S->getType());
auto GetShiftedByZeros = [BitWidth](uint32_t TrailingZeros) {
return TrailingZeros >= BitWidth
? APInt::getZero(BitWidth)
: APInt::getOneBitSet(BitWidth, TrailingZeros);
};
auto GetGCDMultiple = [this](const SCEVNAryExpr *N) {
// The result is GCD of all operands results.
APInt Res = getConstantMultiple(N->getOperand(0));
for (unsigned I = 1, E = N->getNumOperands(); I < E && Res != 1; ++I)
Res = APIntOps::GreatestCommonDivisor(
Res, getConstantMultiple(N->getOperand(I)));
return Res;
};
switch (S->getSCEVType()) {
case scConstant:
return cast<SCEVConstant>(S)->getAPInt();
case scPtrToInt:
return getConstantMultiple(cast<SCEVPtrToIntExpr>(S)->getOperand());
case scUDivExpr:
case scVScale:
return APInt(BitWidth, 1);
case scTruncate: {
// Only multiples that are a power of 2 will hold after truncation.
const SCEVTruncateExpr *T = cast<SCEVTruncateExpr>(S);
uint32_t TZ = getMinTrailingZeros(T->getOperand());
return GetShiftedByZeros(TZ);
}
case scZeroExtend: {
const SCEVZeroExtendExpr *Z = cast<SCEVZeroExtendExpr>(S);
return getConstantMultiple(Z->getOperand()).zext(BitWidth);
}
case scSignExtend: {
// Only multiples that are a power of 2 will hold after sext.
const SCEVSignExtendExpr *E = cast<SCEVSignExtendExpr>(S);
uint32_t TZ = getMinTrailingZeros(E->getOperand());
return GetShiftedByZeros(TZ);
}
case scMulExpr: {
const SCEVMulExpr *M = cast<SCEVMulExpr>(S);
if (M->hasNoUnsignedWrap()) {
// The result is the product of all operand results.
APInt Res = getConstantMultiple(M->getOperand(0));
for (const SCEV *Operand : M->operands().drop_front())
Res = Res * getConstantMultiple(Operand);
return Res;
}
// If there are no wrap guarentees, find the trailing zeros, which is the
// sum of trailing zeros for all its operands.
uint32_t TZ = 0;
for (const SCEV *Operand : M->operands())
TZ += getMinTrailingZeros(Operand);
return GetShiftedByZeros(TZ);
}
case scAddExpr:
case scAddRecExpr: {
const SCEVNAryExpr *N = cast<SCEVNAryExpr>(S);
if (N->hasNoUnsignedWrap())
return GetGCDMultiple(N);
// Find the trailing bits, which is the minimum of its operands.
uint32_t TZ = getMinTrailingZeros(N->getOperand(0));
for (const SCEV *Operand : N->operands().drop_front())
TZ = std::min(TZ, getMinTrailingZeros(Operand));
return GetShiftedByZeros(TZ);
}
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr:
return GetGCDMultiple(cast<SCEVNAryExpr>(S));
case scUnknown: {
// ask ValueTracking for known bits
const SCEVUnknown *U = cast<SCEVUnknown>(S);
unsigned Known =
computeKnownBits(U->getValue(), getDataLayout(), 0, &AC, nullptr, &DT)
.countMinTrailingZeros();
return GetShiftedByZeros(Known);
}
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
APInt ScalarEvolution::getConstantMultiple(const SCEV *S) {
auto I = ConstantMultipleCache.find(S);
if (I != ConstantMultipleCache.end())
return I->second;
APInt Result = getConstantMultipleImpl(S);
auto InsertPair = ConstantMultipleCache.insert({S, Result});
assert(InsertPair.second && "Should insert a new key");
return InsertPair.first->second;
}
APInt ScalarEvolution::getNonZeroConstantMultiple(const SCEV *S) {
APInt Multiple = getConstantMultiple(S);
return Multiple == 0 ? APInt(Multiple.getBitWidth(), 1) : Multiple;
}
uint32_t ScalarEvolution::getMinTrailingZeros(const SCEV *S) {
return std::min(getConstantMultiple(S).countTrailingZeros(),
(unsigned)getTypeSizeInBits(S->getType()));
}
/// Helper method to assign a range to V from metadata present in the IR.
static std::optional<ConstantRange> GetRangeFromMetadata(Value *V) {
if (Instruction *I = dyn_cast<Instruction>(V)) {
if (MDNode *MD = I->getMetadata(LLVMContext::MD_range))
return getConstantRangeFromMetadata(*MD);
if (const auto *CB = dyn_cast<CallBase>(V))
if (std::optional<ConstantRange> Range = CB->getRange())
return Range;
}
if (auto *A = dyn_cast<Argument>(V))
if (std::optional<ConstantRange> Range = A->getRange())
return Range;
return std::nullopt;
}
void ScalarEvolution::setNoWrapFlags(SCEVAddRecExpr *AddRec,
SCEV::NoWrapFlags Flags) {
if (AddRec->getNoWrapFlags(Flags) != Flags) {
AddRec->setNoWrapFlags(Flags);
UnsignedRanges.erase(AddRec);
SignedRanges.erase(AddRec);
ConstantMultipleCache.erase(AddRec);
}
}
ConstantRange ScalarEvolution::
getRangeForUnknownRecurrence(const SCEVUnknown *U) {
const DataLayout &DL = getDataLayout();
unsigned BitWidth = getTypeSizeInBits(U->getType());
const ConstantRange FullSet(BitWidth, /*isFullSet=*/true);
// Match a simple recurrence of the form: <start, ShiftOp, Step>, and then
// use information about the trip count to improve our available range. Note
// that the trip count independent cases are already handled by known bits.
// WARNING: The definition of recurrence used here is subtly different than
// the one used by AddRec (and thus most of this file). Step is allowed to
// be arbitrarily loop varying here, where AddRec allows only loop invariant
// and other addrecs in the same loop (for non-affine addrecs). The code
// below intentionally handles the case where step is not loop invariant.
auto *P = dyn_cast<PHINode>(U->getValue());
if (!P)
return FullSet;
// Make sure that no Phi input comes from an unreachable block. Otherwise,
// even the values that are not available in these blocks may come from them,
// and this leads to false-positive recurrence test.
for (auto *Pred : predecessors(P->getParent()))
if (!DT.isReachableFromEntry(Pred))
return FullSet;
BinaryOperator *BO;
Value *Start, *Step;
if (!matchSimpleRecurrence(P, BO, Start, Step))
return FullSet;
// If we found a recurrence in reachable code, we must be in a loop. Note
// that BO might be in some subloop of L, and that's completely okay.
auto *L = LI.getLoopFor(P->getParent());
assert(L && L->getHeader() == P->getParent());
if (!L->contains(BO->getParent()))
// NOTE: This bailout should be an assert instead. However, asserting
// the condition here exposes a case where LoopFusion is querying SCEV
// with malformed loop information during the midst of the transform.
// There doesn't appear to be an obvious fix, so for the moment bailout
// until the caller issue can be fixed. PR49566 tracks the bug.
return FullSet;
// TODO: Extend to other opcodes such as mul, and div
switch (BO->getOpcode()) {
default:
return FullSet;
case Instruction::AShr:
case Instruction::LShr:
case Instruction::Shl:
break;
};
if (BO->getOperand(0) != P)
// TODO: Handle the power function forms some day.
return FullSet;
unsigned TC = getSmallConstantMaxTripCount(L);
if (!TC || TC >= BitWidth)
return FullSet;
auto KnownStart = computeKnownBits(Start, DL, 0, &AC, nullptr, &DT);
auto KnownStep = computeKnownBits(Step, DL, 0, &AC, nullptr, &DT);
assert(KnownStart.getBitWidth() == BitWidth &&
KnownStep.getBitWidth() == BitWidth);
// Compute total shift amount, being careful of overflow and bitwidths.
auto MaxShiftAmt = KnownStep.getMaxValue();
APInt TCAP(BitWidth, TC-1);
bool Overflow = false;
auto TotalShift = MaxShiftAmt.umul_ov(TCAP, Overflow);
if (Overflow)
return FullSet;
switch (BO->getOpcode()) {
default:
llvm_unreachable("filtered out above");
case Instruction::AShr: {
// For each ashr, three cases:
// shift = 0 => unchanged value
// saturation => 0 or -1
// other => a value closer to zero (of the same sign)
// Thus, the end value is closer to zero than the start.
auto KnownEnd = KnownBits::ashr(KnownStart,
KnownBits::makeConstant(TotalShift));
if (KnownStart.isNonNegative())
// Analogous to lshr (simply not yet canonicalized)
return ConstantRange::getNonEmpty(KnownEnd.getMinValue(),
KnownStart.getMaxValue() + 1);
if (KnownStart.isNegative())
// End >=u Start && End <=s Start
return ConstantRange::getNonEmpty(KnownStart.getMinValue(),
KnownEnd.getMaxValue() + 1);
break;
}
case Instruction::LShr: {
// For each lshr, three cases:
// shift = 0 => unchanged value
// saturation => 0
// other => a smaller positive number
// Thus, the low end of the unsigned range is the last value produced.
auto KnownEnd = KnownBits::lshr(KnownStart,
KnownBits::makeConstant(TotalShift));
return ConstantRange::getNonEmpty(KnownEnd.getMinValue(),
KnownStart.getMaxValue() + 1);
}
case Instruction::Shl: {
// Iff no bits are shifted out, value increases on every shift.
auto KnownEnd = KnownBits::shl(KnownStart,
KnownBits::makeConstant(TotalShift));
if (TotalShift.ult(KnownStart.countMinLeadingZeros()))
return ConstantRange(KnownStart.getMinValue(),
KnownEnd.getMaxValue() + 1);
break;
}
};
return FullSet;
}
const ConstantRange &
ScalarEvolution::getRangeRefIter(const SCEV *S,
ScalarEvolution::RangeSignHint SignHint) {
DenseMap<const SCEV *, ConstantRange> &Cache =
SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? UnsignedRanges
: SignedRanges;
SmallVector<const SCEV *> WorkList;
SmallPtrSet<const SCEV *, 8> Seen;
// Add Expr to the worklist, if Expr is either an N-ary expression or a
// SCEVUnknown PHI node.
auto AddToWorklist = [&WorkList, &Seen, &Cache](const SCEV *Expr) {
if (!Seen.insert(Expr).second)
return;
if (Cache.contains(Expr))
return;
switch (Expr->getSCEVType()) {
case scUnknown:
if (!isa<PHINode>(cast<SCEVUnknown>(Expr)->getValue()))
break;
[[fallthrough]];
case scConstant:
case scVScale:
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scAddRecExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr:
WorkList.push_back(Expr);
break;
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
};
AddToWorklist(S);
// Build worklist by queuing operands of N-ary expressions and phi nodes.
for (unsigned I = 0; I != WorkList.size(); ++I) {
const SCEV *P = WorkList[I];
auto *UnknownS = dyn_cast<SCEVUnknown>(P);
// If it is not a `SCEVUnknown`, just recurse into operands.
if (!UnknownS) {
for (const SCEV *Op : P->operands())
AddToWorklist(Op);
continue;
}
// `SCEVUnknown`'s require special treatment.
if (const PHINode *P = dyn_cast<PHINode>(UnknownS->getValue())) {
if (!PendingPhiRangesIter.insert(P).second)
continue;
for (auto &Op : reverse(P->operands()))
AddToWorklist(getSCEV(Op));
}
}
if (!WorkList.empty()) {
// Use getRangeRef to compute ranges for items in the worklist in reverse
// order. This will force ranges for earlier operands to be computed before
// their users in most cases.
for (const SCEV *P : reverse(drop_begin(WorkList))) {
getRangeRef(P, SignHint);
if (auto *UnknownS = dyn_cast<SCEVUnknown>(P))
if (const PHINode *P = dyn_cast<PHINode>(UnknownS->getValue()))
PendingPhiRangesIter.erase(P);
}
}
return getRangeRef(S, SignHint, 0);
}
/// Determine the range for a particular SCEV. If SignHint is
/// HINT_RANGE_UNSIGNED (resp. HINT_RANGE_SIGNED) then getRange prefers ranges
/// with a "cleaner" unsigned (resp. signed) representation.
const ConstantRange &ScalarEvolution::getRangeRef(
const SCEV *S, ScalarEvolution::RangeSignHint SignHint, unsigned Depth) {
DenseMap<const SCEV *, ConstantRange> &Cache =
SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? UnsignedRanges
: SignedRanges;
ConstantRange::PreferredRangeType RangeType =
SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? ConstantRange::Unsigned
: ConstantRange::Signed;
// See if we've computed this range already.
DenseMap<const SCEV *, ConstantRange>::iterator I = Cache.find(S);
if (I != Cache.end())
return I->second;
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
return setRange(C, SignHint, ConstantRange(C->getAPInt()));
// Switch to iteratively computing the range for S, if it is part of a deeply
// nested expression.
if (Depth > RangeIterThreshold)
return getRangeRefIter(S, SignHint);
unsigned BitWidth = getTypeSizeInBits(S->getType());
ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true);
using OBO = OverflowingBinaryOperator;
// If the value has known zeros, the maximum value will have those known zeros
// as well.
if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED) {
APInt Multiple = getNonZeroConstantMultiple(S);
APInt Remainder = APInt::getMaxValue(BitWidth).urem(Multiple);
if (!Remainder.isZero())
ConservativeResult =
ConstantRange(APInt::getMinValue(BitWidth),
APInt::getMaxValue(BitWidth) - Remainder + 1);
}
else {
uint32_t TZ = getMinTrailingZeros(S);
if (TZ != 0) {
ConservativeResult = ConstantRange(
APInt::getSignedMinValue(BitWidth),
APInt::getSignedMaxValue(BitWidth).ashr(TZ).shl(TZ) + 1);
}
}
switch (S->getSCEVType()) {
case scConstant:
llvm_unreachable("Already handled above.");
case scVScale:
return setRange(S, SignHint, getVScaleRange(&F, BitWidth));
case scTruncate: {
const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(S);
ConstantRange X = getRangeRef(Trunc->getOperand(), SignHint, Depth + 1);
return setRange(
Trunc, SignHint,
ConservativeResult.intersectWith(X.truncate(BitWidth), RangeType));
}
case scZeroExtend: {
const SCEVZeroExtendExpr *ZExt = cast<SCEVZeroExtendExpr>(S);
ConstantRange X = getRangeRef(ZExt->getOperand(), SignHint, Depth + 1);
return setRange(
ZExt, SignHint,
ConservativeResult.intersectWith(X.zeroExtend(BitWidth), RangeType));
}
case scSignExtend: {
const SCEVSignExtendExpr *SExt = cast<SCEVSignExtendExpr>(S);
ConstantRange X = getRangeRef(SExt->getOperand(), SignHint, Depth + 1);
return setRange(
SExt, SignHint,
ConservativeResult.intersectWith(X.signExtend(BitWidth), RangeType));
}
case scPtrToInt: {
const SCEVPtrToIntExpr *PtrToInt = cast<SCEVPtrToIntExpr>(S);
ConstantRange X = getRangeRef(PtrToInt->getOperand(), SignHint, Depth + 1);
return setRange(PtrToInt, SignHint, X);
}
case scAddExpr: {
const SCEVAddExpr *Add = cast<SCEVAddExpr>(S);
ConstantRange X = getRangeRef(Add->getOperand(0), SignHint, Depth + 1);
unsigned WrapType = OBO::AnyWrap;
if (Add->hasNoSignedWrap())
WrapType |= OBO::NoSignedWrap;
if (Add->hasNoUnsignedWrap())
WrapType |= OBO::NoUnsignedWrap;
for (const SCEV *Op : drop_begin(Add->operands()))
X = X.addWithNoWrap(getRangeRef(Op, SignHint, Depth + 1), WrapType,
RangeType);
return setRange(Add, SignHint,
ConservativeResult.intersectWith(X, RangeType));
}
case scMulExpr: {
const SCEVMulExpr *Mul = cast<SCEVMulExpr>(S);
ConstantRange X = getRangeRef(Mul->getOperand(0), SignHint, Depth + 1);
for (const SCEV *Op : drop_begin(Mul->operands()))
X = X.multiply(getRangeRef(Op, SignHint, Depth + 1));
return setRange(Mul, SignHint,
ConservativeResult.intersectWith(X, RangeType));
}
case scUDivExpr: {
const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(S);
ConstantRange X = getRangeRef(UDiv->getLHS(), SignHint, Depth + 1);
ConstantRange Y = getRangeRef(UDiv->getRHS(), SignHint, Depth + 1);
return setRange(UDiv, SignHint,
ConservativeResult.intersectWith(X.udiv(Y), RangeType));
}
case scAddRecExpr: {
const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(S);
// If there's no unsigned wrap, the value will never be less than its
// initial value.
if (AddRec->hasNoUnsignedWrap()) {
APInt UnsignedMinValue = getUnsignedRangeMin(AddRec->getStart());
if (!UnsignedMinValue.isZero())
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange(UnsignedMinValue, APInt(BitWidth, 0)), RangeType);
}
// If there's no signed wrap, and all the operands except initial value have
// the same sign or zero, the value won't ever be:
// 1: smaller than initial value if operands are non negative,
// 2: bigger than initial value if operands are non positive.
// For both cases, value can not cross signed min/max boundary.
if (AddRec->hasNoSignedWrap()) {
bool AllNonNeg = true;
bool AllNonPos = true;
for (unsigned i = 1, e = AddRec->getNumOperands(); i != e; ++i) {
if (!isKnownNonNegative(AddRec->getOperand(i)))
AllNonNeg = false;
if (!isKnownNonPositive(AddRec->getOperand(i)))
AllNonPos = false;
}
if (AllNonNeg)
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange::getNonEmpty(getSignedRangeMin(AddRec->getStart()),
APInt::getSignedMinValue(BitWidth)),
RangeType);
else if (AllNonPos)
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange::getNonEmpty(APInt::getSignedMinValue(BitWidth),
getSignedRangeMax(AddRec->getStart()) +
1),
RangeType);
}
// TODO: non-affine addrec
if (AddRec->isAffine()) {
const SCEV *MaxBEScev =
getConstantMaxBackedgeTakenCount(AddRec->getLoop());
if (!isa<SCEVCouldNotCompute>(MaxBEScev)) {
APInt MaxBECount = cast<SCEVConstant>(MaxBEScev)->getAPInt();
// Adjust MaxBECount to the same bitwidth as AddRec. We can truncate if
// MaxBECount's active bits are all <= AddRec's bit width.
if (MaxBECount.getBitWidth() > BitWidth &&
MaxBECount.getActiveBits() <= BitWidth)
MaxBECount = MaxBECount.trunc(BitWidth);
else if (MaxBECount.getBitWidth() < BitWidth)
MaxBECount = MaxBECount.zext(BitWidth);
if (MaxBECount.getBitWidth() == BitWidth) {
auto RangeFromAffine = getRangeForAffineAR(
AddRec->getStart(), AddRec->getStepRecurrence(*this), MaxBECount);
ConservativeResult =
ConservativeResult.intersectWith(RangeFromAffine, RangeType);
auto RangeFromFactoring = getRangeViaFactoring(
AddRec->getStart(), AddRec->getStepRecurrence(*this), MaxBECount);
ConservativeResult =
ConservativeResult.intersectWith(RangeFromFactoring, RangeType);
}
}
// Now try symbolic BE count and more powerful methods.
if (UseExpensiveRangeSharpening) {
const SCEV *SymbolicMaxBECount =
getSymbolicMaxBackedgeTakenCount(AddRec->getLoop());
if (!isa<SCEVCouldNotCompute>(SymbolicMaxBECount) &&
getTypeSizeInBits(MaxBEScev->getType()) <= BitWidth &&
AddRec->hasNoSelfWrap()) {
auto RangeFromAffineNew = getRangeForAffineNoSelfWrappingAR(
AddRec, SymbolicMaxBECount, BitWidth, SignHint);
ConservativeResult =
ConservativeResult.intersectWith(RangeFromAffineNew, RangeType);
}
}
}
return setRange(AddRec, SignHint, std::move(ConservativeResult));
}
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr: {
Intrinsic::ID ID;
switch (S->getSCEVType()) {
case scUMaxExpr:
ID = Intrinsic::umax;
break;
case scSMaxExpr:
ID = Intrinsic::smax;
break;
case scUMinExpr:
case scSequentialUMinExpr:
ID = Intrinsic::umin;
break;
case scSMinExpr:
ID = Intrinsic::smin;
break;
default:
llvm_unreachable("Unknown SCEVMinMaxExpr/SCEVSequentialMinMaxExpr.");
}
const auto *NAry = cast<SCEVNAryExpr>(S);
ConstantRange X = getRangeRef(NAry->getOperand(0), SignHint, Depth + 1);
for (unsigned i = 1, e = NAry->getNumOperands(); i != e; ++i)
X = X.intrinsic(
ID, {X, getRangeRef(NAry->getOperand(i), SignHint, Depth + 1)});
return setRange(S, SignHint,
ConservativeResult.intersectWith(X, RangeType));
}
case scUnknown: {
const SCEVUnknown *U = cast<SCEVUnknown>(S);
Value *V = U->getValue();
// Check if the IR explicitly contains !range metadata.
std::optional<ConstantRange> MDRange = GetRangeFromMetadata(V);
if (MDRange)
ConservativeResult =
ConservativeResult.intersectWith(*MDRange, RangeType);
// Use facts about recurrences in the underlying IR. Note that add
// recurrences are AddRecExprs and thus don't hit this path. This
// primarily handles shift recurrences.
auto CR = getRangeForUnknownRecurrence(U);
ConservativeResult = ConservativeResult.intersectWith(CR);
// See if ValueTracking can give us a useful range.
const DataLayout &DL = getDataLayout();
KnownBits Known = computeKnownBits(V, DL, 0, &AC, nullptr, &DT);
if (Known.getBitWidth() != BitWidth)
Known = Known.zextOrTrunc(BitWidth);
// ValueTracking may be able to compute a tighter result for the number of
// sign bits than for the value of those sign bits.
unsigned NS = ComputeNumSignBits(V, DL, 0, &AC, nullptr, &DT);
if (U->getType()->isPointerTy()) {
// If the pointer size is larger than the index size type, this can cause
// NS to be larger than BitWidth. So compensate for this.
unsigned ptrSize = DL.getPointerTypeSizeInBits(U->getType());
int ptrIdxDiff = ptrSize - BitWidth;
if (ptrIdxDiff > 0 && ptrSize > BitWidth && NS > (unsigned)ptrIdxDiff)
NS -= ptrIdxDiff;
}
if (NS > 1) {
// If we know any of the sign bits, we know all of the sign bits.
if (!Known.Zero.getHiBits(NS).isZero())
Known.Zero.setHighBits(NS);
if (!Known.One.getHiBits(NS).isZero())
Known.One.setHighBits(NS);
}
if (Known.getMinValue() != Known.getMaxValue() + 1)
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange(Known.getMinValue(), Known.getMaxValue() + 1),
RangeType);
if (NS > 1)
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),
APInt::getSignedMaxValue(BitWidth).ashr(NS - 1) + 1),
RangeType);
if (U->getType()->isPointerTy() && SignHint == HINT_RANGE_UNSIGNED) {
// Strengthen the range if the underlying IR value is a
// global/alloca/heap allocation using the size of the object.
bool CanBeNull, CanBeFreed;
uint64_t DerefBytes =
V->getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed);
if (DerefBytes > 1 && isUIntN(BitWidth, DerefBytes)) {
// The highest address the object can start is DerefBytes bytes before
// the end (unsigned max value). If this value is not a multiple of the
// alignment, the last possible start value is the next lowest multiple
// of the alignment. Note: The computations below cannot overflow,
// because if they would there's no possible start address for the
// object.
APInt MaxVal =
APInt::getMaxValue(BitWidth) - APInt(BitWidth, DerefBytes);
uint64_t Align = U->getValue()->getPointerAlignment(DL).value();
uint64_t Rem = MaxVal.urem(Align);
MaxVal -= APInt(BitWidth, Rem);
APInt MinVal = APInt::getZero(BitWidth);
if (llvm::isKnownNonZero(V, DL))
MinVal = Align;
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange::getNonEmpty(MinVal, MaxVal + 1), RangeType);
}
}
// A range of Phi is a subset of union of all ranges of its input.
if (PHINode *Phi = dyn_cast<PHINode>(V)) {
// Make sure that we do not run over cycled Phis.
if (PendingPhiRanges.insert(Phi).second) {
ConstantRange RangeFromOps(BitWidth, /*isFullSet=*/false);
for (const auto &Op : Phi->operands()) {
auto OpRange = getRangeRef(getSCEV(Op), SignHint, Depth + 1);
RangeFromOps = RangeFromOps.unionWith(OpRange);
// No point to continue if we already have a full set.
if (RangeFromOps.isFullSet())
break;
}
ConservativeResult =
ConservativeResult.intersectWith(RangeFromOps, RangeType);
bool Erased = PendingPhiRanges.erase(Phi);
assert(Erased && "Failed to erase Phi properly?");
(void)Erased;
}
}
// vscale can't be equal to zero
if (const auto *II = dyn_cast<IntrinsicInst>(V))
if (II->getIntrinsicID() == Intrinsic::vscale) {
ConstantRange Disallowed = APInt::getZero(BitWidth);
ConservativeResult = ConservativeResult.difference(Disallowed);
}
return setRange(U, SignHint, std::move(ConservativeResult));
}
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
return setRange(S, SignHint, std::move(ConservativeResult));
}
// Given a StartRange, Step and MaxBECount for an expression compute a range of
// values that the expression can take. Initially, the expression has a value
// from StartRange and then is changed by Step up to MaxBECount times. Signed
// argument defines if we treat Step as signed or unsigned.
static ConstantRange getRangeForAffineARHelper(APInt Step,
const ConstantRange &StartRange,
const APInt &MaxBECount,
bool Signed) {
unsigned BitWidth = Step.getBitWidth();
assert(BitWidth == StartRange.getBitWidth() &&
BitWidth == MaxBECount.getBitWidth() && "mismatched bit widths");
// If either Step or MaxBECount is 0, then the expression won't change, and we
// just need to return the initial range.
if (Step == 0 || MaxBECount == 0)
return StartRange;
// If we don't know anything about the initial value (i.e. StartRange is
// FullRange), then we don't know anything about the final range either.
// Return FullRange.
if (StartRange.isFullSet())
return ConstantRange::getFull(BitWidth);
// If Step is signed and negative, then we use its absolute value, but we also
// note that we're moving in the opposite direction.
bool Descending = Signed && Step.isNegative();
if (Signed)
// This is correct even for INT_SMIN. Let's look at i8 to illustrate this:
// abs(INT_SMIN) = abs(-128) = abs(0x80) = -0x80 = 0x80 = 128.
// This equations hold true due to the well-defined wrap-around behavior of
// APInt.
Step = Step.abs();
// Check if Offset is more than full span of BitWidth. If it is, the
// expression is guaranteed to overflow.
if (APInt::getMaxValue(StartRange.getBitWidth()).udiv(Step).ult(MaxBECount))
return ConstantRange::getFull(BitWidth);
// Offset is by how much the expression can change. Checks above guarantee no
// overflow here.
APInt Offset = Step * MaxBECount;
// Minimum value of the final range will match the minimal value of StartRange
// if the expression is increasing and will be decreased by Offset otherwise.
// Maximum value of the final range will match the maximal value of StartRange
// if the expression is decreasing and will be increased by Offset otherwise.
APInt StartLower = StartRange.getLower();
APInt StartUpper = StartRange.getUpper() - 1;
APInt MovedBoundary = Descending ? (StartLower - std::move(Offset))
: (StartUpper + std::move(Offset));
// It's possible that the new minimum/maximum value will fall into the initial
// range (due to wrap around). This means that the expression can take any
// value in this bitwidth, and we have to return full range.
if (StartRange.contains(MovedBoundary))
return ConstantRange::getFull(BitWidth);
APInt NewLower =
Descending ? std::move(MovedBoundary) : std::move(StartLower);
APInt NewUpper =
Descending ? std::move(StartUpper) : std::move(MovedBoundary);
NewUpper += 1;
// No overflow detected, return [StartLower, StartUpper + Offset + 1) range.
return ConstantRange::getNonEmpty(std::move(NewLower), std::move(NewUpper));
}
ConstantRange ScalarEvolution::getRangeForAffineAR(const SCEV *Start,
const SCEV *Step,
const APInt &MaxBECount) {
assert(getTypeSizeInBits(Start->getType()) ==
getTypeSizeInBits(Step->getType()) &&
getTypeSizeInBits(Start->getType()) == MaxBECount.getBitWidth() &&
"mismatched bit widths");
// First, consider step signed.
ConstantRange StartSRange = getSignedRange(Start);
ConstantRange StepSRange = getSignedRange(Step);
// If Step can be both positive and negative, we need to find ranges for the
// maximum absolute step values in both directions and union them.
ConstantRange SR = getRangeForAffineARHelper(
StepSRange.getSignedMin(), StartSRange, MaxBECount, /* Signed = */ true);
SR = SR.unionWith(getRangeForAffineARHelper(StepSRange.getSignedMax(),
StartSRange, MaxBECount,
/* Signed = */ true));
// Next, consider step unsigned.
ConstantRange UR = getRangeForAffineARHelper(
getUnsignedRangeMax(Step), getUnsignedRange(Start), MaxBECount,
/* Signed = */ false);
// Finally, intersect signed and unsigned ranges.
return SR.intersectWith(UR, ConstantRange::Smallest);
}
ConstantRange ScalarEvolution::getRangeForAffineNoSelfWrappingAR(
const SCEVAddRecExpr *AddRec, const SCEV *MaxBECount, unsigned BitWidth,
ScalarEvolution::RangeSignHint SignHint) {
assert(AddRec->isAffine() && "Non-affine AddRecs are not suppored!\n");
assert(AddRec->hasNoSelfWrap() &&
"This only works for non-self-wrapping AddRecs!");
const bool IsSigned = SignHint == HINT_RANGE_SIGNED;
const SCEV *Step = AddRec->getStepRecurrence(*this);
// Only deal with constant step to save compile time.
if (!isa<SCEVConstant>(Step))
return ConstantRange::getFull(BitWidth);
// Let's make sure that we can prove that we do not self-wrap during
// MaxBECount iterations. We need this because MaxBECount is a maximum
// iteration count estimate, and we might infer nw from some exit for which we
// do not know max exit count (or any other side reasoning).
// TODO: Turn into assert at some point.
if (getTypeSizeInBits(MaxBECount->getType()) >
getTypeSizeInBits(AddRec->getType()))
return ConstantRange::getFull(BitWidth);
MaxBECount = getNoopOrZeroExtend(MaxBECount, AddRec->getType());
const SCEV *RangeWidth = getMinusOne(AddRec->getType());
const SCEV *StepAbs = getUMinExpr(Step, getNegativeSCEV(Step));
const SCEV *MaxItersWithoutWrap = getUDivExpr(RangeWidth, StepAbs);
if (!isKnownPredicateViaConstantRanges(ICmpInst::ICMP_ULE, MaxBECount,
MaxItersWithoutWrap))
return ConstantRange::getFull(BitWidth);
ICmpInst::Predicate LEPred =
IsSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
ICmpInst::Predicate GEPred =
IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
// We know that there is no self-wrap. Let's take Start and End values and
// look at all intermediate values V1, V2, ..., Vn that IndVar takes during
// the iteration. They either lie inside the range [Min(Start, End),
// Max(Start, End)] or outside it:
//
// Case 1: RangeMin ... Start V1 ... VN End ... RangeMax;
// Case 2: RangeMin Vk ... V1 Start ... End Vn ... Vk + 1 RangeMax;
//
// No self wrap flag guarantees that the intermediate values cannot be BOTH
// outside and inside the range [Min(Start, End), Max(Start, End)]. Using that
// knowledge, let's try to prove that we are dealing with Case 1. It is so if
// Start <= End and step is positive, or Start >= End and step is negative.
const SCEV *Start = applyLoopGuards(AddRec->getStart(), AddRec->getLoop());
ConstantRange StartRange = getRangeRef(Start, SignHint);
ConstantRange EndRange = getRangeRef(End, SignHint);
ConstantRange RangeBetween = StartRange.unionWith(EndRange);
// If they already cover full iteration space, we will know nothing useful
// even if we prove what we want to prove.
if (RangeBetween.isFullSet())
return RangeBetween;
// Only deal with ranges that do not wrap (i.e. RangeMin < RangeMax).
bool IsWrappedSet = IsSigned ? RangeBetween.isSignWrappedSet()
: RangeBetween.isWrappedSet();
if (IsWrappedSet)
return ConstantRange::getFull(BitWidth);
if (isKnownPositive(Step) &&
isKnownPredicateViaConstantRanges(LEPred, Start, End))
return RangeBetween;
if (isKnownNegative(Step) &&
isKnownPredicateViaConstantRanges(GEPred, Start, End))
return RangeBetween;
return ConstantRange::getFull(BitWidth);
}
ConstantRange ScalarEvolution::getRangeViaFactoring(const SCEV *Start,
const SCEV *Step,
const APInt &MaxBECount) {
// RangeOf({C?A:B,+,C?P:Q}) == RangeOf(C?{A,+,P}:{B,+,Q})
// == RangeOf({A,+,P}) union RangeOf({B,+,Q})
unsigned BitWidth = MaxBECount.getBitWidth();
assert(getTypeSizeInBits(Start->getType()) == BitWidth &&
getTypeSizeInBits(Step->getType()) == BitWidth &&
"mismatched bit widths");
struct SelectPattern {
Value *Condition = nullptr;
APInt TrueValue;
APInt FalseValue;
explicit SelectPattern(ScalarEvolution &SE, unsigned BitWidth,
const SCEV *S) {
std::optional<unsigned> CastOp;
APInt Offset(BitWidth, 0);
assert(SE.getTypeSizeInBits(S->getType()) == BitWidth &&
"Should be!");
// Peel off a constant offset:
if (auto *SA = dyn_cast<SCEVAddExpr>(S)) {
// In the future we could consider being smarter here and handle
// {Start+Step,+,Step} too.
if (SA->getNumOperands() != 2 || !isa<SCEVConstant>(SA->getOperand(0)))
return;
Offset = cast<SCEVConstant>(SA->getOperand(0))->getAPInt();
S = SA->getOperand(1);
}
// Peel off a cast operation
if (auto *SCast = dyn_cast<SCEVIntegralCastExpr>(S)) {
CastOp = SCast->getSCEVType();
S = SCast->getOperand();
}
using namespace llvm::PatternMatch;
auto *SU = dyn_cast<SCEVUnknown>(S);
const APInt *TrueVal, *FalseVal;
if (!SU ||
!match(SU->getValue(), m_Select(m_Value(Condition), m_APInt(TrueVal),
m_APInt(FalseVal)))) {
Condition = nullptr;
return;
}
TrueValue = *TrueVal;
FalseValue = *FalseVal;
// Re-apply the cast we peeled off earlier
if (CastOp)
switch (*CastOp) {
default:
llvm_unreachable("Unknown SCEV cast type!");
case scTruncate:
TrueValue = TrueValue.trunc(BitWidth);
FalseValue = FalseValue.trunc(BitWidth);
break;
case scZeroExtend:
TrueValue = TrueValue.zext(BitWidth);
FalseValue = FalseValue.zext(BitWidth);
break;
case scSignExtend:
TrueValue = TrueValue.sext(BitWidth);
FalseValue = FalseValue.sext(BitWidth);
break;
}
// Re-apply the constant offset we peeled off earlier
TrueValue += Offset;
FalseValue += Offset;
}
bool isRecognized() { return Condition != nullptr; }
};
SelectPattern StartPattern(*this, BitWidth, Start);
if (!StartPattern.isRecognized())
return ConstantRange::getFull(BitWidth);
SelectPattern StepPattern(*this, BitWidth, Step);
if (!StepPattern.isRecognized())
return ConstantRange::getFull(BitWidth);
if (StartPattern.Condition != StepPattern.Condition) {
// We don't handle this case today; but we could, by considering four
// possibilities below instead of two. I'm not sure if there are cases where
// that will help over what getRange already does, though.
return ConstantRange::getFull(BitWidth);
}
// NB! Calling ScalarEvolution::getConstant is fine, but we should not try to
// construct arbitrary general SCEV expressions here. This function is called
// from deep in the call stack, and calling getSCEV (on a sext instruction,
// say) can end up caching a suboptimal value.
// FIXME: without the explicit `this` receiver below, MSVC errors out with
// C2352 and C2512 (otherwise it isn't needed).
const SCEV *TrueStart = this->getConstant(StartPattern.TrueValue);
const SCEV *TrueStep = this->getConstant(StepPattern.TrueValue);
const SCEV *FalseStart = this->getConstant(StartPattern.FalseValue);
const SCEV *FalseStep = this->getConstant(StepPattern.FalseValue);
ConstantRange TrueRange =
this->getRangeForAffineAR(TrueStart, TrueStep, MaxBECount);
ConstantRange FalseRange =
this->getRangeForAffineAR(FalseStart, FalseStep, MaxBECount);
return TrueRange.unionWith(FalseRange);
}
SCEV::NoWrapFlags ScalarEvolution::getNoWrapFlagsFromUB(const Value *V) {
if (isa<ConstantExpr>(V)) return SCEV::FlagAnyWrap;
const BinaryOperator *BinOp = cast<BinaryOperator>(V);
// Return early if there are no flags to propagate to the SCEV.
SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
if (BinOp->hasNoUnsignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
if (BinOp->hasNoSignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
if (Flags == SCEV::FlagAnyWrap)
return SCEV::FlagAnyWrap;
return isSCEVExprNeverPoison(BinOp) ? Flags : SCEV::FlagAnyWrap;
}
const Instruction *
ScalarEvolution::getNonTrivialDefiningScopeBound(const SCEV *S) {
if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S))
return &*AddRec->getLoop()->getHeader()->begin();
if (auto *U = dyn_cast<SCEVUnknown>(S))
if (auto *I = dyn_cast<Instruction>(U->getValue()))
return I;
return nullptr;
}
const Instruction *
ScalarEvolution::getDefiningScopeBound(ArrayRef<const SCEV *> Ops,
bool &Precise) {
Precise = true;
// Do a bounded search of the def relation of the requested SCEVs.
SmallSet<const SCEV *, 16> Visited;
SmallVector<const SCEV *> Worklist;
auto pushOp = [&](const SCEV *S) {
if (!Visited.insert(S).second)
return;
// Threshold of 30 here is arbitrary.
if (Visited.size() > 30) {
Precise = false;
return;
}
Worklist.push_back(S);
};
for (const auto *S : Ops)
pushOp(S);
const Instruction *Bound = nullptr;
while (!Worklist.empty()) {
auto *S = Worklist.pop_back_val();
if (auto *DefI = getNonTrivialDefiningScopeBound(S)) {
if (!Bound || DT.dominates(Bound, DefI))
Bound = DefI;
} else {
for (const auto *Op : S->operands())
pushOp(Op);
}
}
return Bound ? Bound : &*F.getEntryBlock().begin();
}
const Instruction *
ScalarEvolution::getDefiningScopeBound(ArrayRef<const SCEV *> Ops) {
bool Discard;
return getDefiningScopeBound(Ops, Discard);
}
bool ScalarEvolution::isGuaranteedToTransferExecutionTo(const Instruction *A,
const Instruction *B) {
if (A->getParent() == B->getParent() &&
isGuaranteedToTransferExecutionToSuccessor(A->getIterator(),
B->getIterator()))
return true;
auto *BLoop = LI.getLoopFor(B->getParent());
if (BLoop && BLoop->getHeader() == B->getParent() &&
BLoop->getLoopPreheader() == A->getParent() &&
isGuaranteedToTransferExecutionToSuccessor(A->getIterator(),
A->getParent()->end()) &&
isGuaranteedToTransferExecutionToSuccessor(B->getParent()->begin(),
B->getIterator()))
return true;
return false;
}
bool ScalarEvolution::isGuaranteedNotToBePoison(const SCEV *Op) {
SCEVPoisonCollector PC(/* LookThroughMaybePoisonBlocking */ true);
visitAll(Op, PC);
return PC.MaybePoison.empty();
}
bool ScalarEvolution::isGuaranteedNotToCauseUB(const SCEV *Op) {
return !SCEVExprContains(Op, [this](const SCEV *S) {
auto *UDiv = dyn_cast<SCEVUDivExpr>(S);
// The UDiv may be UB if the divisor is poison or zero. Unless the divisor
// is a non-zero constant, we have to assume the UDiv may be UB.
return UDiv && (!isKnownNonZero(UDiv->getOperand(1)) ||
!isGuaranteedNotToBePoison(UDiv->getOperand(1)));
});
}
bool ScalarEvolution::isSCEVExprNeverPoison(const Instruction *I) {
// Only proceed if we can prove that I does not yield poison.
if (!programUndefinedIfPoison(I))
return false;
// At this point we know that if I is executed, then it does not wrap
// according to at least one of NSW or NUW. If I is not executed, then we do
// not know if the calculation that I represents would wrap. Multiple
// instructions can map to the same SCEV. If we apply NSW or NUW from I to
// the SCEV, we must guarantee no wrapping for that SCEV also when it is
// derived from other instructions that map to the same SCEV. We cannot make
// that guarantee for cases where I is not executed. So we need to find a
// upper bound on the defining scope for the SCEV, and prove that I is
// executed every time we enter that scope. When the bounding scope is a
// loop (the common case), this is equivalent to proving I executes on every
// iteration of that loop.
SmallVector<const SCEV *> SCEVOps;
for (const Use &Op : I->operands()) {
// I could be an extractvalue from a call to an overflow intrinsic.
// TODO: We can do better here in some cases.
if (isSCEVable(Op->getType()))
SCEVOps.push_back(getSCEV(Op));
}
auto *DefI = getDefiningScopeBound(SCEVOps);
return isGuaranteedToTransferExecutionTo(DefI, I);
}
bool ScalarEvolution::isAddRecNeverPoison(const Instruction *I, const Loop *L) {
// If we know that \c I can never be poison period, then that's enough.
if (isSCEVExprNeverPoison(I))
return true;
// If the loop only has one exit, then we know that, if the loop is entered,
// any instruction dominating that exit will be executed. If any such
// instruction would result in UB, the addrec cannot be poison.
//
// This is basically the same reasoning as in isSCEVExprNeverPoison(), but
// also handles uses outside the loop header (they just need to dominate the
// single exit).
auto *ExitingBB = L->getExitingBlock();
if (!ExitingBB || !loopHasNoAbnormalExits(L))
return false;
SmallPtrSet<const Value *, 16> KnownPoison;
SmallVector<const Instruction *, 8> Worklist;
// We start by assuming \c I, the post-inc add recurrence, is poison. Only
// things that are known to be poison under that assumption go on the
// Worklist.
KnownPoison.insert(I);
Worklist.push_back(I);
while (!Worklist.empty()) {
const Instruction *Poison = Worklist.pop_back_val();
for (const Use &U : Poison->uses()) {
const Instruction *PoisonUser = cast<Instruction>(U.getUser());
if (mustTriggerUB(PoisonUser, KnownPoison) &&
DT.dominates(PoisonUser->getParent(), ExitingBB))
return true;
if (propagatesPoison(U) && L->contains(PoisonUser))
if (KnownPoison.insert(PoisonUser).second)
Worklist.push_back(PoisonUser);
}
}
return false;
}
ScalarEvolution::LoopProperties
ScalarEvolution::getLoopProperties(const Loop *L) {
using LoopProperties = ScalarEvolution::LoopProperties;
auto Itr = LoopPropertiesCache.find(L);
if (Itr == LoopPropertiesCache.end()) {
auto HasSideEffects = [](Instruction *I) {
if (auto *SI = dyn_cast<StoreInst>(I))
return !SI->isSimple();
return I->mayThrow() || I->mayWriteToMemory();
};
LoopProperties LP = {/* HasNoAbnormalExits */ true,
/*HasNoSideEffects*/ true};
for (auto *BB : L->getBlocks())
for (auto &I : *BB) {
if (!isGuaranteedToTransferExecutionToSuccessor(&I))
LP.HasNoAbnormalExits = false;
if (HasSideEffects(&I))
LP.HasNoSideEffects = false;
if (!LP.HasNoAbnormalExits && !LP.HasNoSideEffects)
break; // We're already as pessimistic as we can get.
}
auto InsertPair = LoopPropertiesCache.insert({L, LP});
assert(InsertPair.second && "We just checked!");
Itr = InsertPair.first;
}
return Itr->second;
}
bool ScalarEvolution::loopIsFiniteByAssumption(const Loop *L) {
// A mustprogress loop without side effects must be finite.
// TODO: The check used here is very conservative. It's only *specific*
// side effects which are well defined in infinite loops.
return isFinite(L) || (isMustProgress(L) && loopHasNoSideEffects(L));
}
const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
// Worklist item with a Value and a bool indicating whether all operands have
// been visited already.
using PointerTy = PointerIntPair<Value *, 1, bool>;
SmallVector<PointerTy> Stack;
Stack.emplace_back(V, true);
Stack.emplace_back(V, false);
while (!Stack.empty()) {
auto E = Stack.pop_back_val();
Value *CurV = E.getPointer();
if (getExistingSCEV(CurV))
continue;
SmallVector<Value *> Ops;
const SCEV *CreatedSCEV = nullptr;
// If all operands have been visited already, create the SCEV.
if (E.getInt()) {
CreatedSCEV = createSCEV(CurV);
} else {
// Otherwise get the operands we need to create SCEV's for before creating
// the SCEV for CurV. If the SCEV for CurV can be constructed trivially,
// just use it.
CreatedSCEV = getOperandsToCreate(CurV, Ops);
}
if (CreatedSCEV) {
insertValueToMap(CurV, CreatedSCEV);
} else {
// Queue CurV for SCEV creation, followed by its's operands which need to
// be constructed first.
Stack.emplace_back(CurV, true);
for (Value *Op : Ops)
Stack.emplace_back(Op, false);
}
}
return getExistingSCEV(V);
}
const SCEV *
ScalarEvolution::getOperandsToCreate(Value *V, SmallVectorImpl<Value *> &Ops) {
if (!isSCEVable(V->getType()))
return getUnknown(V);
if (Instruction *I = dyn_cast<Instruction>(V)) {
// Don't attempt to analyze instructions in blocks that aren't
// reachable. Such instructions don't matter, and they aren't required
// to obey basic rules for definitions dominating uses which this
// analysis depends on.
if (!DT.isReachableFromEntry(I->getParent()))
return getUnknown(PoisonValue::get(V->getType()));
} else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return getConstant(CI);
else if (isa<GlobalAlias>(V))
return getUnknown(V);
else if (!isa<ConstantExpr>(V))
return getUnknown(V);
Operator *U = cast<Operator>(V);
if (auto BO =
MatchBinaryOp(U, getDataLayout(), AC, DT, dyn_cast<Instruction>(V))) {
bool IsConstArg = isa<ConstantInt>(BO->RHS);
switch (BO->Opcode) {
case Instruction::Add:
case Instruction::Mul: {
// For additions and multiplications, traverse add/mul chains for which we
// can potentially create a single SCEV, to reduce the number of
// get{Add,Mul}Expr calls.
do {
if (BO->Op) {
if (BO->Op != V && getExistingSCEV(BO->Op)) {
Ops.push_back(BO->Op);
break;
}
}
Ops.push_back(BO->RHS);
auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
dyn_cast<Instruction>(V));
if (!NewBO ||
(BO->Opcode == Instruction::Add &&
(NewBO->Opcode != Instruction::Add &&
NewBO->Opcode != Instruction::Sub)) ||
(BO->Opcode == Instruction::Mul &&
NewBO->Opcode != Instruction::Mul)) {
Ops.push_back(BO->LHS);
break;
}
// CreateSCEV calls getNoWrapFlagsFromUB, which under certain conditions
// requires a SCEV for the LHS.
if (BO->Op && (BO->IsNSW || BO->IsNUW)) {
auto *I = dyn_cast<Instruction>(BO->Op);
if (I && programUndefinedIfPoison(I)) {
Ops.push_back(BO->LHS);
break;
}
}
BO = NewBO;
} while (true);
return nullptr;
}
case Instruction::Sub:
case Instruction::UDiv:
case Instruction::URem:
break;
case Instruction::AShr:
case Instruction::Shl:
case Instruction::Xor:
if (!IsConstArg)
return nullptr;
break;
case Instruction::And:
case Instruction::Or:
if (!IsConstArg && !BO->LHS->getType()->isIntegerTy(1))
return nullptr;
break;
case Instruction::LShr:
return getUnknown(V);
default:
llvm_unreachable("Unhandled binop");
break;
}
Ops.push_back(BO->LHS);
Ops.push_back(BO->RHS);
return nullptr;
}
switch (U->getOpcode()) {
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::PtrToInt:
Ops.push_back(U->getOperand(0));
return nullptr;
case Instruction::BitCast:
if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType())) {
Ops.push_back(U->getOperand(0));
return nullptr;
}
return getUnknown(V);
case Instruction::SDiv:
case Instruction::SRem:
Ops.push_back(U->getOperand(0));
Ops.push_back(U->getOperand(1));
return nullptr;
case Instruction::GetElementPtr:
assert(cast<GEPOperator>(U)->getSourceElementType()->isSized() &&
"GEP source element type must be sized");
llvm::append_range(Ops, U->operands());
return nullptr;
case Instruction::IntToPtr:
return getUnknown(V);
case Instruction::PHI:
// Keep constructing SCEVs' for phis recursively for now.
return nullptr;
case Instruction::Select: {
// Check if U is a select that can be simplified to a SCEVUnknown.
auto CanSimplifyToUnknown = [this, U]() {
if (U->getType()->isIntegerTy(1) || isa<ConstantInt>(U->getOperand(0)))
return false;
auto *ICI = dyn_cast<ICmpInst>(U->getOperand(0));
if (!ICI)
return false;
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
if (ICI->getPredicate() == CmpInst::ICMP_EQ ||
ICI->getPredicate() == CmpInst::ICMP_NE) {
if (!(isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()))
return true;
} else if (getTypeSizeInBits(LHS->getType()) >
getTypeSizeInBits(U->getType()))
return true;
return false;
};
if (CanSimplifyToUnknown())
return getUnknown(U);
llvm::append_range(Ops, U->operands());
return nullptr;
break;
}
case Instruction::Call:
case Instruction::Invoke:
if (Value *RV = cast<CallBase>(U)->getReturnedArgOperand()) {
Ops.push_back(RV);
return nullptr;
}
if (auto *II = dyn_cast<IntrinsicInst>(U)) {
switch (II->getIntrinsicID()) {
case Intrinsic::abs:
Ops.push_back(II->getArgOperand(0));
return nullptr;
case Intrinsic::umax:
case Intrinsic::umin:
case Intrinsic::smax:
case Intrinsic::smin:
case Intrinsic::usub_sat:
case Intrinsic::uadd_sat:
Ops.push_back(II->getArgOperand(0));
Ops.push_back(II->getArgOperand(1));
return nullptr;
case Intrinsic::start_loop_iterations:
case Intrinsic::annotation:
case Intrinsic::ptr_annotation:
Ops.push_back(II->getArgOperand(0));
return nullptr;
default:
break;
}
}
break;
}
return nullptr;
}
const SCEV *ScalarEvolution::createSCEV(Value *V) {
if (!isSCEVable(V->getType()))
return getUnknown(V);
if (Instruction *I = dyn_cast<Instruction>(V)) {
// Don't attempt to analyze instructions in blocks that aren't
// reachable. Such instructions don't matter, and they aren't required
// to obey basic rules for definitions dominating uses which this
// analysis depends on.
if (!DT.isReachableFromEntry(I->getParent()))
return getUnknown(PoisonValue::get(V->getType()));
} else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return getConstant(CI);
else if (isa<GlobalAlias>(V))
return getUnknown(V);
else if (!isa<ConstantExpr>(V))
return getUnknown(V);
const SCEV *LHS;
const SCEV *RHS;
Operator *U = cast<Operator>(V);
if (auto BO =
MatchBinaryOp(U, getDataLayout(), AC, DT, dyn_cast<Instruction>(V))) {
switch (BO->Opcode) {
case Instruction::Add: {
// The simple thing to do would be to just call getSCEV on both operands
// and call getAddExpr with the result. However if we're looking at a
// bunch of things all added together, this can be quite inefficient,
// because it leads to N-1 getAddExpr calls for N ultimate operands.
// Instead, gather up all the operands and make a single getAddExpr call.
// LLVM IR canonical form means we need only traverse the left operands.
SmallVector<const SCEV *, 4> AddOps;
do {
if (BO->Op) {
if (auto *OpSCEV = getExistingSCEV(BO->Op)) {
AddOps.push_back(OpSCEV);
break;
}
// If a NUW or NSW flag can be applied to the SCEV for this
// addition, then compute the SCEV for this addition by itself
// with a separate call to getAddExpr. We need to do that
// instead of pushing the operands of the addition onto AddOps,
// since the flags are only known to apply to this particular
// addition - they may not apply to other additions that can be
// formed with operands from AddOps.
const SCEV *RHS = getSCEV(BO->RHS);
SCEV::NoWrapFlags Flags = getNoWrapFlagsFromUB(BO->Op);
if (Flags != SCEV::FlagAnyWrap) {
const SCEV *LHS = getSCEV(BO->LHS);
if (BO->Opcode == Instruction::Sub)
AddOps.push_back(getMinusSCEV(LHS, RHS, Flags));
else
AddOps.push_back(getAddExpr(LHS, RHS, Flags));
break;
}
}
if (BO->Opcode == Instruction::Sub)
AddOps.push_back(getNegativeSCEV(getSCEV(BO->RHS)));
else
AddOps.push_back(getSCEV(BO->RHS));
auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
dyn_cast<Instruction>(V));
if (!NewBO || (NewBO->Opcode != Instruction::Add &&
NewBO->Opcode != Instruction::Sub)) {
AddOps.push_back(getSCEV(BO->LHS));
break;
}
BO = NewBO;
} while (true);
return getAddExpr(AddOps);
}
case Instruction::Mul: {
SmallVector<const SCEV *, 4> MulOps;
do {
if (BO->Op) {
if (auto *OpSCEV = getExistingSCEV(BO->Op)) {
MulOps.push_back(OpSCEV);
break;
}
SCEV::NoWrapFlags Flags = getNoWrapFlagsFromUB(BO->Op);
if (Flags != SCEV::FlagAnyWrap) {
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
MulOps.push_back(getMulExpr(LHS, RHS, Flags));
break;
}
}
MulOps.push_back(getSCEV(BO->RHS));
auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
dyn_cast<Instruction>(V));
if (!NewBO || NewBO->Opcode != Instruction::Mul) {
MulOps.push_back(getSCEV(BO->LHS));
break;
}
BO = NewBO;
} while (true);
return getMulExpr(MulOps);
}
case Instruction::UDiv:
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
return getUDivExpr(LHS, RHS);
case Instruction::URem:
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
return getURemExpr(LHS, RHS);
case Instruction::Sub: {
SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
if (BO->Op)
Flags = getNoWrapFlagsFromUB(BO->Op);
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
return getMinusSCEV(LHS, RHS, Flags);
}
case Instruction::And:
// For an expression like x&255 that merely masks off the high bits,
// use zext(trunc(x)) as the SCEV expression.
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
if (CI->isZero())
return getSCEV(BO->RHS);
if (CI->isMinusOne())
return getSCEV(BO->LHS);
const APInt &A = CI->getValue();
// Instcombine's ShrinkDemandedConstant may strip bits out of
// constants, obscuring what would otherwise be a low-bits mask.
// Use computeKnownBits to compute what ShrinkDemandedConstant
// knew about to reconstruct a low-bits mask value.
unsigned LZ = A.countl_zero();
unsigned TZ = A.countr_zero();
unsigned BitWidth = A.getBitWidth();
KnownBits Known(BitWidth);
computeKnownBits(BO->LHS, Known, getDataLayout(),
0, &AC, nullptr, &DT);
APInt EffectiveMask =
APInt::getLowBitsSet(BitWidth, BitWidth - LZ - TZ).shl(TZ);
if ((LZ != 0 || TZ != 0) && !((~A & ~Known.Zero) & EffectiveMask)) {
const SCEV *MulCount = getConstant(APInt::getOneBitSet(BitWidth, TZ));
const SCEV *LHS = getSCEV(BO->LHS);
const SCEV *ShiftedLHS = nullptr;
if (auto *LHSMul = dyn_cast<SCEVMulExpr>(LHS)) {
if (auto *OpC = dyn_cast<SCEVConstant>(LHSMul->getOperand(0))) {
// For an expression like (x * 8) & 8, simplify the multiply.
unsigned MulZeros = OpC->getAPInt().countr_zero();
unsigned GCD = std::min(MulZeros, TZ);
APInt DivAmt = APInt::getOneBitSet(BitWidth, TZ - GCD);
SmallVector<const SCEV*, 4> MulOps;
MulOps.push_back(getConstant(OpC->getAPInt().ashr(GCD)));
append_range(MulOps, LHSMul->operands().drop_front());
auto *NewMul = getMulExpr(MulOps, LHSMul->getNoWrapFlags());
ShiftedLHS = getUDivExpr(NewMul, getConstant(DivAmt));
}
}
if (!ShiftedLHS)
ShiftedLHS = getUDivExpr(LHS, MulCount);
return getMulExpr(
getZeroExtendExpr(
getTruncateExpr(ShiftedLHS,
IntegerType::get(getContext(), BitWidth - LZ - TZ)),
BO->LHS->getType()),
MulCount);
}
}
// Binary `and` is a bit-wise `umin`.
if (BO->LHS->getType()->isIntegerTy(1)) {
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
return getUMinExpr(LHS, RHS);
}
break;
case Instruction::Or:
// Binary `or` is a bit-wise `umax`.
if (BO->LHS->getType()->isIntegerTy(1)) {
LHS = getSCEV(BO->LHS);
RHS = getSCEV(BO->RHS);
return getUMaxExpr(LHS, RHS);
}
break;
case Instruction::Xor:
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
// If the RHS of xor is -1, then this is a not operation.
if (CI->isMinusOne())
return getNotSCEV(getSCEV(BO->LHS));
// Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask.
// This is a variant of the check for xor with -1, and it handles
// the case where instcombine has trimmed non-demanded bits out
// of an xor with -1.
if (auto *LBO = dyn_cast<BinaryOperator>(BO->LHS))
if (ConstantInt *LCI = dyn_cast<ConstantInt>(LBO->getOperand(1)))
if (LBO->getOpcode() == Instruction::And &&
LCI->getValue() == CI->getValue())
if (const SCEVZeroExtendExpr *Z =
dyn_cast<SCEVZeroExtendExpr>(getSCEV(BO->LHS))) {
Type *UTy = BO->LHS->getType();
const SCEV *Z0 = Z->getOperand();
Type *Z0Ty = Z0->getType();
unsigned Z0TySize = getTypeSizeInBits(Z0Ty);
// If C is a low-bits mask, the zero extend is serving to
// mask off the high bits. Complement the operand and
// re-apply the zext.
if (CI->getValue().isMask(Z0TySize))
return getZeroExtendExpr(getNotSCEV(Z0), UTy);
// If C is a single bit, it may be in the sign-bit position
// before the zero-extend. In this case, represent the xor
// using an add, which is equivalent, and re-apply the zext.
APInt Trunc = CI->getValue().trunc(Z0TySize);
if (Trunc.zext(getTypeSizeInBits(UTy)) == CI->getValue() &&
Trunc.isSignMask())
return getZeroExtendExpr(getAddExpr(Z0, getConstant(Trunc)),
UTy);
}
}
break;
case Instruction::Shl:
// Turn shift left of a constant amount into a multiply.
if (ConstantInt *SA = dyn_cast<ConstantInt>(BO->RHS)) {
uint32_t BitWidth = cast<IntegerType>(SA->getType())->getBitWidth();
// If the shift count is not less than the bitwidth, the result of
// the shift is undefined. Don't try to analyze it, because the
// resolution chosen here may differ from the resolution chosen in
// other parts of the compiler.
if (SA->getValue().uge(BitWidth))
break;
// We can safely preserve the nuw flag in all cases. It's also safe to
// turn a nuw nsw shl into a nuw nsw mul. However, nsw in isolation
// requires special handling. It can be preserved as long as we're not
// left shifting by bitwidth - 1.
auto Flags = SCEV::FlagAnyWrap;
if (BO->Op) {
auto MulFlags = getNoWrapFlagsFromUB(BO->Op);
if ((MulFlags & SCEV::FlagNSW) &&
((MulFlags & SCEV::FlagNUW) || SA->getValue().ult(BitWidth - 1)))
Flags = (SCEV::NoWrapFlags)(Flags | SCEV::FlagNSW);
if (MulFlags & SCEV::FlagNUW)
Flags = (SCEV::NoWrapFlags)(Flags | SCEV::FlagNUW);
}
ConstantInt *X = ConstantInt::get(
getContext(), APInt::getOneBitSet(BitWidth, SA->getZExtValue()));
return getMulExpr(getSCEV(BO->LHS), getConstant(X), Flags);
}
break;
case Instruction::AShr:
// AShr X, C, where C is a constant.
ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS);
if (!CI)
break;
Type *OuterTy = BO->LHS->getType();
uint64_t BitWidth = getTypeSizeInBits(OuterTy);
// If the shift count is not less than the bitwidth, the result of
// the shift is undefined. Don't try to analyze it, because the
// resolution chosen here may differ from the resolution chosen in
// other parts of the compiler.
if (CI->getValue().uge(BitWidth))
break;
if (CI->isZero())
return getSCEV(BO->LHS); // shift by zero --> noop
uint64_t AShrAmt = CI->getZExtValue();
Type *TruncTy = IntegerType::get(getContext(), BitWidth - AShrAmt);
Operator *L = dyn_cast<Operator>(BO->LHS);
const SCEV *AddTruncateExpr = nullptr;
ConstantInt *ShlAmtCI = nullptr;
const SCEV *AddConstant = nullptr;
if (L && L->getOpcode() == Instruction::Add) {
// X = Shl A, n
// Y = Add X, c
// Z = AShr Y, m
// n, c and m are constants.
Operator *LShift = dyn_cast<Operator>(L->getOperand(0));
ConstantInt *AddOperandCI = dyn_cast<ConstantInt>(L->getOperand(1));
if (LShift && LShift->getOpcode() == Instruction::Shl) {
if (AddOperandCI) {
const SCEV *ShlOp0SCEV = getSCEV(LShift->getOperand(0));
ShlAmtCI = dyn_cast<ConstantInt>(LShift->getOperand(1));
// since we truncate to TruncTy, the AddConstant should be of the
// same type, so create a new Constant with type same as TruncTy.
// Also, the Add constant should be shifted right by AShr amount.
APInt AddOperand = AddOperandCI->getValue().ashr(AShrAmt);
AddConstant = getConstant(AddOperand.trunc(BitWidth - AShrAmt));
// we model the expression as sext(add(trunc(A), c << n)), since the
// sext(trunc) part is already handled below, we create a
// AddExpr(TruncExp) which will be used later.
AddTruncateExpr = getTruncateExpr(ShlOp0SCEV, TruncTy);
}
}
} else if (L && L->getOpcode() == Instruction::Shl) {
// X = Shl A, n
// Y = AShr X, m
// Both n and m are constant.
const SCEV *ShlOp0SCEV = getSCEV(L->getOperand(0));
ShlAmtCI = dyn_cast<ConstantInt>(L->getOperand(1));
AddTruncateExpr = getTruncateExpr(ShlOp0SCEV, TruncTy);
}
if (AddTruncateExpr && ShlAmtCI) {
// We can merge the two given cases into a single SCEV statement,
// incase n = m, the mul expression will be 2^0, so it gets resolved to
// a simpler case. The following code handles the two cases:
//
// 1) For a two-shift sext-inreg, i.e. n = m,
// use sext(trunc(x)) as the SCEV expression.
//
// 2) When n > m, use sext(mul(trunc(x), 2^(n-m)))) as the SCEV
// expression. We already checked that ShlAmt < BitWidth, so
// the multiplier, 1 << (ShlAmt - AShrAmt), fits into TruncTy as
// ShlAmt - AShrAmt < Amt.
const APInt &ShlAmt = ShlAmtCI->getValue();
if (ShlAmt.ult(BitWidth) && ShlAmt.uge(AShrAmt)) {
APInt Mul = APInt::getOneBitSet(BitWidth - AShrAmt,
ShlAmtCI->getZExtValue() - AShrAmt);
const SCEV *CompositeExpr =
getMulExpr(AddTruncateExpr, getConstant(Mul));
if (L->getOpcode() != Instruction::Shl)
CompositeExpr = getAddExpr(CompositeExpr, AddConstant);
return getSignExtendExpr(CompositeExpr, OuterTy);
}
}
break;
}
}
switch (U->getOpcode()) {
case Instruction::Trunc:
return getTruncateExpr(getSCEV(U->getOperand(0)), U->getType());
case Instruction::ZExt:
return getZeroExtendExpr(getSCEV(U->getOperand(0)), U->getType());
case Instruction::SExt:
if (auto BO = MatchBinaryOp(U->getOperand(0), getDataLayout(), AC, DT,
dyn_cast<Instruction>(V))) {
// The NSW flag of a subtract does not always survive the conversion to
// A + (-1)*B. By pushing sign extension onto its operands we are much
// more likely to preserve NSW and allow later AddRec optimisations.
//
// NOTE: This is effectively duplicating this logic from getSignExtend:
// sext((A + B + ...)<nsw>) --> (sext(A) + sext(B) + ...)<nsw>
// but by that point the NSW information has potentially been lost.
if (BO->Opcode == Instruction::Sub && BO->IsNSW) {
Type *Ty = U->getType();
auto *V1 = getSignExtendExpr(getSCEV(BO->LHS), Ty);
auto *V2 = getSignExtendExpr(getSCEV(BO->RHS), Ty);
return getMinusSCEV(V1, V2, SCEV::FlagNSW);
}
}
return getSignExtendExpr(getSCEV(U->getOperand(0)), U->getType());
case Instruction::BitCast:
// BitCasts are no-op casts so we just eliminate the cast.
if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType()))
return getSCEV(U->getOperand(0));
break;
case Instruction::PtrToInt: {
// Pointer to integer cast is straight-forward, so do model it.
const SCEV *Op = getSCEV(U->getOperand(0));
Type *DstIntTy = U->getType();
// But only if effective SCEV (integer) type is wide enough to represent
// all possible pointer values.
const SCEV *IntOp = getPtrToIntExpr(Op, DstIntTy);
if (isa<SCEVCouldNotCompute>(IntOp))
return getUnknown(V);
return IntOp;
}
case Instruction::IntToPtr:
// Just don't deal with inttoptr casts.
return getUnknown(V);
case Instruction::SDiv:
// If both operands are non-negative, this is just an udiv.
if (isKnownNonNegative(getSCEV(U->getOperand(0))) &&
isKnownNonNegative(getSCEV(U->getOperand(1))))
return getUDivExpr(getSCEV(U->getOperand(0)), getSCEV(U->getOperand(1)));
break;
case Instruction::SRem:
// If both operands are non-negative, this is just an urem.
if (isKnownNonNegative(getSCEV(U->getOperand(0))) &&
isKnownNonNegative(getSCEV(U->getOperand(1))))
return getURemExpr(getSCEV(U->getOperand(0)), getSCEV(U->getOperand(1)));
break;
case Instruction::GetElementPtr:
return createNodeForGEP(cast<GEPOperator>(U));
case Instruction::PHI:
return createNodeForPHI(cast<PHINode>(U));
case Instruction::Select:
return createNodeForSelectOrPHI(U, U->getOperand(0), U->getOperand(1),
U->getOperand(2));
case Instruction::Call:
case Instruction::Invoke:
if (Value *RV = cast<CallBase>(U)->getReturnedArgOperand())
return getSCEV(RV);
if (auto *II = dyn_cast<IntrinsicInst>(U)) {
switch (II->getIntrinsicID()) {
case Intrinsic::abs:
return getAbsExpr(
getSCEV(II->getArgOperand(0)),
/*IsNSW=*/cast<ConstantInt>(II->getArgOperand(1))->isOne());
case Intrinsic::umax:
LHS = getSCEV(II->getArgOperand(0));
RHS = getSCEV(II->getArgOperand(1));
return getUMaxExpr(LHS, RHS);
case Intrinsic::umin:
LHS = getSCEV(II->getArgOperand(0));
RHS = getSCEV(II->getArgOperand(1));
return getUMinExpr(LHS, RHS);
case Intrinsic::smax:
LHS = getSCEV(II->getArgOperand(0));
RHS = getSCEV(II->getArgOperand(1));
return getSMaxExpr(LHS, RHS);
case Intrinsic::smin:
LHS = getSCEV(II->getArgOperand(0));
RHS = getSCEV(II->getArgOperand(1));
return getSMinExpr(LHS, RHS);
case Intrinsic::usub_sat: {
const SCEV *X = getSCEV(II->getArgOperand(0));
const SCEV *Y = getSCEV(II->getArgOperand(1));
const SCEV *ClampedY = getUMinExpr(X, Y);
return getMinusSCEV(X, ClampedY, SCEV::FlagNUW);
}
case Intrinsic::uadd_sat: {
const SCEV *X = getSCEV(II->getArgOperand(0));
const SCEV *Y = getSCEV(II->getArgOperand(1));
const SCEV *ClampedX = getUMinExpr(X, getNotSCEV(Y));
return getAddExpr(ClampedX, Y, SCEV::FlagNUW);
}
case Intrinsic::start_loop_iterations:
case Intrinsic::annotation:
case Intrinsic::ptr_annotation:
// A start_loop_iterations or llvm.annotation or llvm.prt.annotation is
// just eqivalent to the first operand for SCEV purposes.
return getSCEV(II->getArgOperand(0));
case Intrinsic::vscale:
return getVScale(II->getType());
default:
break;
}
}
break;
}
return getUnknown(V);
}
//===----------------------------------------------------------------------===//
// Iteration Count Computation Code
//
const SCEV *ScalarEvolution::getTripCountFromExitCount(const SCEV *ExitCount) {
if (isa<SCEVCouldNotCompute>(ExitCount))
return getCouldNotCompute();
auto *ExitCountType = ExitCount->getType();
assert(ExitCountType->isIntegerTy());
auto *EvalTy = Type::getIntNTy(ExitCountType->getContext(),
1 + ExitCountType->getScalarSizeInBits());
return getTripCountFromExitCount(ExitCount, EvalTy, nullptr);
}
const SCEV *ScalarEvolution::getTripCountFromExitCount(const SCEV *ExitCount,
Type *EvalTy,
const Loop *L) {
if (isa<SCEVCouldNotCompute>(ExitCount))
return getCouldNotCompute();
unsigned ExitCountSize = getTypeSizeInBits(ExitCount->getType());
unsigned EvalSize = EvalTy->getPrimitiveSizeInBits();
auto CanAddOneWithoutOverflow = [&]() {
ConstantRange ExitCountRange =
getRangeRef(ExitCount, RangeSignHint::HINT_RANGE_UNSIGNED);
if (!ExitCountRange.contains(APInt::getMaxValue(ExitCountSize)))
return true;
return L && isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, ExitCount,
getMinusOne(ExitCount->getType()));
};
// If we need to zero extend the backedge count, check if we can add one to
// it prior to zero extending without overflow. Provided this is safe, it
// allows better simplification of the +1.
if (EvalSize > ExitCountSize && CanAddOneWithoutOverflow())
return getZeroExtendExpr(
getAddExpr(ExitCount, getOne(ExitCount->getType())), EvalTy);
// Get the total trip count from the count by adding 1. This may wrap.
return getAddExpr(getTruncateOrZeroExtend(ExitCount, EvalTy), getOne(EvalTy));
}
static unsigned getConstantTripCount(const SCEVConstant *ExitCount) {
if (!ExitCount)
return 0;
ConstantInt *ExitConst = ExitCount->getValue();
// Guard against huge trip counts.
if (ExitConst->getValue().getActiveBits() > 32)
return 0;
// In case of integer overflow, this returns 0, which is correct.
return ((unsigned)ExitConst->getZExtValue()) + 1;
}
unsigned ScalarEvolution::getSmallConstantTripCount(const Loop *L) {
auto *ExitCount = dyn_cast<SCEVConstant>(getBackedgeTakenCount(L, Exact));
return getConstantTripCount(ExitCount);
}
unsigned
ScalarEvolution::getSmallConstantTripCount(const Loop *L,
const BasicBlock *ExitingBlock) {
assert(ExitingBlock && "Must pass a non-null exiting block!");
assert(L->isLoopExiting(ExitingBlock) &&
"Exiting block must actually branch out of the loop!");
const SCEVConstant *ExitCount =
dyn_cast<SCEVConstant>(getExitCount(L, ExitingBlock));
return getConstantTripCount(ExitCount);
}
unsigned ScalarEvolution::getSmallConstantMaxTripCount(
const Loop *L, SmallVectorImpl<const SCEVPredicate *> *Predicates) {
const auto *MaxExitCount =
Predicates ? getPredicatedConstantMaxBackedgeTakenCount(L, *Predicates)
: getConstantMaxBackedgeTakenCount(L);
return getConstantTripCount(dyn_cast<SCEVConstant>(MaxExitCount));
}
unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L) {
SmallVector<BasicBlock *, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
std::optional<unsigned> Res;
for (auto *ExitingBB : ExitingBlocks) {
unsigned Multiple = getSmallConstantTripMultiple(L, ExitingBB);
if (!Res)
Res = Multiple;
Res = std::gcd(*Res, Multiple);
}
return Res.value_or(1);
}
unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L,
const SCEV *ExitCount) {
if (isa<SCEVCouldNotCompute>(ExitCount))
return 1;
// Get the trip count
const SCEV *TCExpr = getTripCountFromExitCount(applyLoopGuards(ExitCount, L));
APInt Multiple = getNonZeroConstantMultiple(TCExpr);
// If a trip multiple is huge (>=2^32), the trip count is still divisible by
// the greatest power of 2 divisor less than 2^32.
return Multiple.getActiveBits() > 32
? 1U << std::min(31U, Multiple.countTrailingZeros())
: (unsigned)Multiple.getZExtValue();
}
/// Returns the largest constant divisor of the trip count of this loop as a
/// normal unsigned value, if possible. This means that the actual trip count is
/// always a multiple of the returned value (don't forget the trip count could
/// very well be zero as well!).
///
/// Returns 1 if the trip count is unknown or not guaranteed to be the
/// multiple of a constant (which is also the case if the trip count is simply
/// constant, use getSmallConstantTripCount for that case), Will also return 1
/// if the trip count is very large (>= 2^32).
///
/// As explained in the comments for getSmallConstantTripCount, this assumes
/// that control exits the loop via ExitingBlock.
unsigned
ScalarEvolution::getSmallConstantTripMultiple(const Loop *L,
const BasicBlock *ExitingBlock) {
assert(ExitingBlock && "Must pass a non-null exiting block!");
assert(L->isLoopExiting(ExitingBlock) &&
"Exiting block must actually branch out of the loop!");
const SCEV *ExitCount = getExitCount(L, ExitingBlock);
return getSmallConstantTripMultiple(L, ExitCount);
}
const SCEV *ScalarEvolution::getExitCount(const Loop *L,
const BasicBlock *ExitingBlock,
ExitCountKind Kind) {
switch (Kind) {
case Exact:
return getBackedgeTakenInfo(L).getExact(ExitingBlock, this);
case SymbolicMaximum:
return getBackedgeTakenInfo(L).getSymbolicMax(ExitingBlock, this);
case ConstantMaximum:
return getBackedgeTakenInfo(L).getConstantMax(ExitingBlock, this);
};
llvm_unreachable("Invalid ExitCountKind!");
}
const SCEV *ScalarEvolution::getPredicatedExitCount(
const Loop *L, const BasicBlock *ExitingBlock,
SmallVectorImpl<const SCEVPredicate *> *Predicates, ExitCountKind Kind) {
switch (Kind) {
case Exact:
return getPredicatedBackedgeTakenInfo(L).getExact(ExitingBlock, this,
Predicates);
case SymbolicMaximum:
return getPredicatedBackedgeTakenInfo(L).getSymbolicMax(ExitingBlock, this,
Predicates);
case ConstantMaximum:
return getPredicatedBackedgeTakenInfo(L).getConstantMax(ExitingBlock, this,
Predicates);
};
llvm_unreachable("Invalid ExitCountKind!");
}
const SCEV *ScalarEvolution::getPredicatedBackedgeTakenCount(
const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
return getPredicatedBackedgeTakenInfo(L).getExact(L, this, &Preds);
}
const SCEV *ScalarEvolution::getBackedgeTakenCount(const Loop *L,
ExitCountKind Kind) {
switch (Kind) {
case Exact:
return getBackedgeTakenInfo(L).getExact(L, this);
case ConstantMaximum:
return getBackedgeTakenInfo(L).getConstantMax(this);
case SymbolicMaximum:
return getBackedgeTakenInfo(L).getSymbolicMax(L, this);
};
llvm_unreachable("Invalid ExitCountKind!");
}
const SCEV *ScalarEvolution::getPredicatedSymbolicMaxBackedgeTakenCount(
const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
return getPredicatedBackedgeTakenInfo(L).getSymbolicMax(L, this, &Preds);
}
const SCEV *ScalarEvolution::getPredicatedConstantMaxBackedgeTakenCount(
const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
return getPredicatedBackedgeTakenInfo(L).getConstantMax(this, &Preds);
}
bool ScalarEvolution::isBackedgeTakenCountMaxOrZero(const Loop *L) {
return getBackedgeTakenInfo(L).isConstantMaxOrZero(this);
}
/// Push PHI nodes in the header of the given loop onto the given Worklist.
static void PushLoopPHIs(const Loop *L,
SmallVectorImpl<Instruction *> &Worklist,
SmallPtrSetImpl<Instruction *> &Visited) {
BasicBlock *Header = L->getHeader();
// Push all Loop-header PHIs onto the Worklist stack.
for (PHINode &PN : Header->phis())
if (Visited.insert(&PN).second)
Worklist.push_back(&PN);
}
ScalarEvolution::BackedgeTakenInfo &
ScalarEvolution::getPredicatedBackedgeTakenInfo(const Loop *L) {
auto &BTI = getBackedgeTakenInfo(L);
if (BTI.hasFullInfo())
return BTI;
auto Pair = PredicatedBackedgeTakenCounts.insert({L, BackedgeTakenInfo()});
if (!Pair.second)
return Pair.first->second;
BackedgeTakenInfo Result =
computeBackedgeTakenCount(L, /*AllowPredicates=*/true);
return PredicatedBackedgeTakenCounts.find(L)->second = std::move(Result);
}
ScalarEvolution::BackedgeTakenInfo &
ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
// Initially insert an invalid entry for this loop. If the insertion
// succeeds, proceed to actually compute a backedge-taken count and
// update the value. The temporary CouldNotCompute value tells SCEV
// code elsewhere that it shouldn't attempt to request a new
// backedge-taken count, which could result in infinite recursion.
std::pair<DenseMap<const Loop *, BackedgeTakenInfo>::iterator, bool> Pair =
BackedgeTakenCounts.insert({L, BackedgeTakenInfo()});
if (!Pair.second)
return Pair.first->second;
// computeBackedgeTakenCount may allocate memory for its result. Inserting it
// into the BackedgeTakenCounts map transfers ownership. Otherwise, the result
// must be cleared in this scope.
BackedgeTakenInfo Result = computeBackedgeTakenCount(L);
// Now that we know more about the trip count for this loop, forget any
// existing SCEV values for PHI nodes in this loop since they are only
// conservative estimates made without the benefit of trip count
// information. This invalidation is not necessary for correctness, and is
// only done to produce more precise results.
if (Result.hasAnyInfo()) {
// Invalidate any expression using an addrec in this loop.
SmallVector<const SCEV *, 8> ToForget;
auto LoopUsersIt = LoopUsers.find(L);
if (LoopUsersIt != LoopUsers.end())
append_range(ToForget, LoopUsersIt->second);
forgetMemoizedResults(ToForget);
// Invalidate constant-evolved loop header phis.
for (PHINode &PN : L->getHeader()->phis())
ConstantEvolutionLoopExitValue.erase(&PN);
}
// Re-lookup the insert position, since the call to
// computeBackedgeTakenCount above could result in a
// recusive call to getBackedgeTakenInfo (on a different
// loop), which would invalidate the iterator computed
// earlier.
return BackedgeTakenCounts.find(L)->second = std::move(Result);
}
void ScalarEvolution::forgetAllLoops() {
// This method is intended to forget all info about loops. It should
// invalidate caches as if the following happened:
// - The trip counts of all loops have changed arbitrarily
// - Every llvm::Value has been updated in place to produce a different
// result.
BackedgeTakenCounts.clear();
PredicatedBackedgeTakenCounts.clear();
BECountUsers.clear();
LoopPropertiesCache.clear();
ConstantEvolutionLoopExitValue.clear();
ValueExprMap.clear();
ValuesAtScopes.clear();
ValuesAtScopesUsers.clear();
LoopDispositions.clear();
BlockDispositions.clear();
UnsignedRanges.clear();
SignedRanges.clear();
ExprValueMap.clear();
HasRecMap.clear();
ConstantMultipleCache.clear();
PredicatedSCEVRewrites.clear();
FoldCache.clear();
FoldCacheUser.clear();
}
void ScalarEvolution::visitAndClearUsers(
SmallVectorImpl<Instruction *> &Worklist,
SmallPtrSetImpl<Instruction *> &Visited,
SmallVectorImpl<const SCEV *> &ToForget) {
while (!Worklist.empty()) {
Instruction *I = Worklist.pop_back_val();
if (!isSCEVable(I->getType()) && !isa<WithOverflowInst>(I))
continue;
ValueExprMapType::iterator It =
ValueExprMap.find_as(static_cast<Value *>(I));
if (It != ValueExprMap.end()) {
eraseValueFromMap(It->first);
ToForget.push_back(It->second);
if (PHINode *PN = dyn_cast<PHINode>(I))
ConstantEvolutionLoopExitValue.erase(PN);
}
PushDefUseChildren(I, Worklist, Visited);
}
}
void ScalarEvolution::forgetLoop(const Loop *L) {
SmallVector<const Loop *, 16> LoopWorklist(1, L);
SmallVector<Instruction *, 32> Worklist;
SmallPtrSet<Instruction *, 16> Visited;
SmallVector<const SCEV *, 16> ToForget;
// Iterate over all the loops and sub-loops to drop SCEV information.
while (!LoopWorklist.empty()) {
auto *CurrL = LoopWorklist.pop_back_val();
// Drop any stored trip count value.
forgetBackedgeTakenCounts(CurrL, /* Predicated */ false);
forgetBackedgeTakenCounts(CurrL, /* Predicated */ true);
// Drop information about predicated SCEV rewrites for this loop.
for (auto I = PredicatedSCEVRewrites.begin();
I != PredicatedSCEVRewrites.end();) {
std::pair<const SCEV *, const Loop *> Entry = I->first;
if (Entry.second == CurrL)
PredicatedSCEVRewrites.erase(I++);
else
++I;
}
auto LoopUsersItr = LoopUsers.find(CurrL);
if (LoopUsersItr != LoopUsers.end())
llvm::append_range(ToForget, LoopUsersItr->second);
// Drop information about expressions based on loop-header PHIs.
PushLoopPHIs(CurrL, Worklist, Visited);
visitAndClearUsers(Worklist, Visited, ToForget);
LoopPropertiesCache.erase(CurrL);
// Forget all contained loops too, to avoid dangling entries in the
// ValuesAtScopes map.
LoopWorklist.append(CurrL->begin(), CurrL->end());
}
forgetMemoizedResults(ToForget);
}
void ScalarEvolution::forgetTopmostLoop(const Loop *L) {
forgetLoop(L->getOutermostLoop());
}
void ScalarEvolution::forgetValue(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return;
// Drop information about expressions based on loop-header PHIs.
SmallVector<Instruction *, 16> Worklist;
SmallPtrSet<Instruction *, 8> Visited;
SmallVector<const SCEV *, 8> ToForget;
Worklist.push_back(I);
Visited.insert(I);
visitAndClearUsers(Worklist, Visited, ToForget);
forgetMemoizedResults(ToForget);
}
void ScalarEvolution::forgetLcssaPhiWithNewPredecessor(Loop *L, PHINode *V) {
if (!isSCEVable(V->getType()))
return;
// If SCEV looked through a trivial LCSSA phi node, we might have SCEV's
// directly using a SCEVUnknown/SCEVAddRec defined in the loop. After an
// extra predecessor is added, this is no longer valid. Find all Unknowns and
// AddRecs defined in the loop and invalidate any SCEV's making use of them.
if (const SCEV *S = getExistingSCEV(V)) {
struct InvalidationRootCollector {
Loop *L;
SmallVector<const SCEV *, 8> Roots;
InvalidationRootCollector(Loop *L) : L(L) {}
bool follow(const SCEV *S) {
if (auto *SU = dyn_cast<SCEVUnknown>(S)) {
if (auto *I = dyn_cast<Instruction>(SU->getValue()))
if (L->contains(I))
Roots.push_back(S);
} else if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
if (L->contains(AddRec->getLoop()))
Roots.push_back(S);
}
return true;
}
bool isDone() const { return false; }
};
InvalidationRootCollector C(L);
visitAll(S, C);
forgetMemoizedResults(C.Roots);
}
// Also perform the normal invalidation.
forgetValue(V);
}
void ScalarEvolution::forgetLoopDispositions() { LoopDispositions.clear(); }
void ScalarEvolution::forgetBlockAndLoopDispositions(Value *V) {
// Unless a specific value is passed to invalidation, completely clear both
// caches.
if (!V) {
BlockDispositions.clear();
LoopDispositions.clear();
return;
}
if (!isSCEVable(V->getType()))
return;
const SCEV *S = getExistingSCEV(V);
if (!S)
return;
// Invalidate the block and loop dispositions cached for S. Dispositions of
// S's users may change if S's disposition changes (i.e. a user may change to
// loop-invariant, if S changes to loop invariant), so also invalidate
// dispositions of S's users recursively.
SmallVector<const SCEV *, 8> Worklist = {S};
SmallPtrSet<const SCEV *, 8> Seen = {S};
while (!Worklist.empty()) {
const SCEV *Curr = Worklist.pop_back_val();
bool LoopDispoRemoved = LoopDispositions.erase(Curr);
bool BlockDispoRemoved = BlockDispositions.erase(Curr);
if (!LoopDispoRemoved && !BlockDispoRemoved)
continue;
auto Users = SCEVUsers.find(Curr);
if (Users != SCEVUsers.end())
for (const auto *User : Users->second)
if (Seen.insert(User).second)
Worklist.push_back(User);
}
}
/// Get the exact loop backedge taken count considering all loop exits. A
/// computable result can only be returned for loops with all exiting blocks
/// dominating the latch. howFarToZero assumes that the limit of each loop test
/// is never skipped. This is a valid assumption as long as the loop exits via
/// that test. For precise results, it is the caller's responsibility to specify
/// the relevant loop exiting block using getExact(ExitingBlock, SE).
const SCEV *ScalarEvolution::BackedgeTakenInfo::getExact(
const Loop *L, ScalarEvolution *SE,
SmallVectorImpl<const SCEVPredicate *> *Preds) const {
// If any exits were not computable, the loop is not computable.
if (!isComplete() || ExitNotTaken.empty())
return SE->getCouldNotCompute();
const BasicBlock *Latch = L->getLoopLatch();
// All exiting blocks we have collected must dominate the only backedge.
if (!Latch)
return SE->getCouldNotCompute();
// All exiting blocks we have gathered dominate loop's latch, so exact trip
// count is simply a minimum out of all these calculated exit counts.
SmallVector<const SCEV *, 2> Ops;
for (const auto &ENT : ExitNotTaken) {
const SCEV *BECount = ENT.ExactNotTaken;
assert(BECount != SE->getCouldNotCompute() && "Bad exit SCEV!");
assert(SE->DT.dominates(ENT.ExitingBlock, Latch) &&
"We should only have known counts for exiting blocks that dominate "
"latch!");
Ops.push_back(BECount);
if (Preds)
append_range(*Preds, ENT.Predicates);
assert((Preds || ENT.hasAlwaysTruePredicate()) &&
"Predicate should be always true!");
}
// If an earlier exit exits on the first iteration (exit count zero), then
// a later poison exit count should not propagate into the result. This are
// exactly the semantics provided by umin_seq.
return SE->getUMinFromMismatchedTypes(Ops, /* Sequential */ true);
}
const ScalarEvolution::ExitNotTakenInfo *
ScalarEvolution::BackedgeTakenInfo::getExitNotTaken(
const BasicBlock *ExitingBlock,
SmallVectorImpl<const SCEVPredicate *> *Predicates) const {
for (const auto &ENT : ExitNotTaken)
if (ENT.ExitingBlock == ExitingBlock) {
if (ENT.hasAlwaysTruePredicate())
return &ENT;
else if (Predicates) {
append_range(*Predicates, ENT.Predicates);
return &ENT;
}
}
return nullptr;
}
/// getConstantMax - Get the constant max backedge taken count for the loop.
const SCEV *ScalarEvolution::BackedgeTakenInfo::getConstantMax(
ScalarEvolution *SE,
SmallVectorImpl<const SCEVPredicate *> *Predicates) const {
if (!getConstantMax())
return SE->getCouldNotCompute();
for (const auto &ENT : ExitNotTaken)
if (!ENT.hasAlwaysTruePredicate()) {
if (!Predicates)
return SE->getCouldNotCompute();
append_range(*Predicates, ENT.Predicates);
}
assert((isa<SCEVCouldNotCompute>(getConstantMax()) ||
isa<SCEVConstant>(getConstantMax())) &&
"No point in having a non-constant max backedge taken count!");
return getConstantMax();
}
const SCEV *ScalarEvolution::BackedgeTakenInfo::getSymbolicMax(
const Loop *L, ScalarEvolution *SE,
SmallVectorImpl<const SCEVPredicate *> *Predicates) {
if (!SymbolicMax) {
// Form an expression for the maximum exit count possible for this loop. We
// merge the max and exact information to approximate a version of
// getConstantMaxBackedgeTakenCount which isn't restricted to just
// constants.
SmallVector<const SCEV *, 4> ExitCounts;
for (const auto &ENT : ExitNotTaken) {
const SCEV *ExitCount = ENT.SymbolicMaxNotTaken;
if (!isa<SCEVCouldNotCompute>(ExitCount)) {
assert(SE->DT.dominates(ENT.ExitingBlock, L->getLoopLatch()) &&
"We should only have known counts for exiting blocks that "
"dominate latch!");
ExitCounts.push_back(ExitCount);
if (Predicates)
append_range(*Predicates, ENT.Predicates);
assert((Predicates || ENT.hasAlwaysTruePredicate()) &&
"Predicate should be always true!");
}
}
if (ExitCounts.empty())
SymbolicMax = SE->getCouldNotCompute();
else
SymbolicMax =
SE->getUMinFromMismatchedTypes(ExitCounts, /*Sequential*/ true);
}
return SymbolicMax;
}
bool ScalarEvolution::BackedgeTakenInfo::isConstantMaxOrZero(
ScalarEvolution *SE) const {
auto PredicateNotAlwaysTrue = [](const ExitNotTakenInfo &ENT) {
return !ENT.hasAlwaysTruePredicate();
};
return MaxOrZero && !any_of(ExitNotTaken, PredicateNotAlwaysTrue);
}
ScalarEvolution::ExitLimit::ExitLimit(const SCEV *E)
: ExitLimit(E, E, E, false) {}
ScalarEvolution::ExitLimit::ExitLimit(
const SCEV *E, const SCEV *ConstantMaxNotTaken,
const SCEV *SymbolicMaxNotTaken, bool MaxOrZero,
ArrayRef<ArrayRef<const SCEVPredicate *>> PredLists)
: ExactNotTaken(E), ConstantMaxNotTaken(ConstantMaxNotTaken),
SymbolicMaxNotTaken(SymbolicMaxNotTaken), MaxOrZero(MaxOrZero) {
// If we prove the max count is zero, so is the symbolic bound. This happens
// in practice due to differences in a) how context sensitive we've chosen
// to be and b) how we reason about bounds implied by UB.
if (ConstantMaxNotTaken->isZero()) {
this->ExactNotTaken = E = ConstantMaxNotTaken;
this->SymbolicMaxNotTaken = SymbolicMaxNotTaken = ConstantMaxNotTaken;
}
assert((isa<SCEVCouldNotCompute>(ExactNotTaken) ||
!isa<SCEVCouldNotCompute>(ConstantMaxNotTaken)) &&
"Exact is not allowed to be less precise than Constant Max");
assert((isa<SCEVCouldNotCompute>(ExactNotTaken) ||
!isa<SCEVCouldNotCompute>(SymbolicMaxNotTaken)) &&
"Exact is not allowed to be less precise than Symbolic Max");
assert((isa<SCEVCouldNotCompute>(SymbolicMaxNotTaken) ||
!isa<SCEVCouldNotCompute>(ConstantMaxNotTaken)) &&
"Symbolic Max is not allowed to be less precise than Constant Max");
assert((isa<SCEVCouldNotCompute>(ConstantMaxNotTaken) ||
isa<SCEVConstant>(ConstantMaxNotTaken)) &&
"No point in having a non-constant max backedge taken count!");
SmallPtrSet<const SCEVPredicate *, 4> SeenPreds;
for (const auto PredList : PredLists)
for (const auto *P : PredList) {
if (SeenPreds.contains(P))
continue;
assert(!isa<SCEVUnionPredicate>(P) && "Only add leaf predicates here!");
SeenPreds.insert(P);
Predicates.push_back(P);
}
assert((isa<SCEVCouldNotCompute>(E) || !E->getType()->isPointerTy()) &&
"Backedge count should be int");
assert((isa<SCEVCouldNotCompute>(ConstantMaxNotTaken) ||
!ConstantMaxNotTaken->getType()->isPointerTy()) &&
"Max backedge count should be int");
}
ScalarEvolution::ExitLimit::ExitLimit(const SCEV *E,
const SCEV *ConstantMaxNotTaken,
const SCEV *SymbolicMaxNotTaken,
bool MaxOrZero,
ArrayRef<const SCEVPredicate *> PredList)
: ExitLimit(E, ConstantMaxNotTaken, SymbolicMaxNotTaken, MaxOrZero,
ArrayRef({PredList})) {}
/// Allocate memory for BackedgeTakenInfo and copy the not-taken count of each
/// computable exit into a persistent ExitNotTakenInfo array.
ScalarEvolution::BackedgeTakenInfo::BackedgeTakenInfo(
ArrayRef<ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo> ExitCounts,
bool IsComplete, const SCEV *ConstantMax, bool MaxOrZero)
: ConstantMax(ConstantMax), IsComplete(IsComplete), MaxOrZero(MaxOrZero) {
using EdgeExitInfo = ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo;
ExitNotTaken.reserve(ExitCounts.size());
std::transform(ExitCounts.begin(), ExitCounts.end(),
std::back_inserter(ExitNotTaken),
[&](const EdgeExitInfo &EEI) {
BasicBlock *ExitBB = EEI.first;
const ExitLimit &EL = EEI.second;
return ExitNotTakenInfo(ExitBB, EL.ExactNotTaken,
EL.ConstantMaxNotTaken, EL.SymbolicMaxNotTaken,
EL.Predicates);
});
assert((isa<SCEVCouldNotCompute>(ConstantMax) ||
isa<SCEVConstant>(ConstantMax)) &&
"No point in having a non-constant max backedge taken count!");
}
/// Compute the number of times the backedge of the specified loop will execute.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::computeBackedgeTakenCount(const Loop *L,
bool AllowPredicates) {
SmallVector<BasicBlock *, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
using EdgeExitInfo = ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo;
SmallVector<EdgeExitInfo, 4> ExitCounts;
bool CouldComputeBECount = true;
BasicBlock *Latch = L->getLoopLatch(); // may be NULL.
const SCEV *MustExitMaxBECount = nullptr;
const SCEV *MayExitMaxBECount = nullptr;
bool MustExitMaxOrZero = false;
bool IsOnlyExit = ExitingBlocks.size() == 1;
// Compute the ExitLimit for each loop exit. Use this to populate ExitCounts
// and compute maxBECount.
// Do a union of all the predicates here.
for (BasicBlock *ExitBB : ExitingBlocks) {
// We canonicalize untaken exits to br (constant), ignore them so that
// proving an exit untaken doesn't negatively impact our ability to reason
// about the loop as whole.
if (auto *BI = dyn_cast<BranchInst>(ExitBB->getTerminator()))
if (auto *CI = dyn_cast<ConstantInt>(BI->getCondition())) {
bool ExitIfTrue = !L->contains(BI->getSuccessor(0));
if (ExitIfTrue == CI->isZero())
continue;
}
ExitLimit EL = computeExitLimit(L, ExitBB, IsOnlyExit, AllowPredicates);
assert((AllowPredicates || EL.Predicates.empty()) &&
"Predicated exit limit when predicates are not allowed!");
// 1. For each exit that can be computed, add an entry to ExitCounts.
// CouldComputeBECount is true only if all exits can be computed.
if (EL.ExactNotTaken != getCouldNotCompute())
++NumExitCountsComputed;
else
// We couldn't compute an exact value for this exit, so
// we won't be able to compute an exact value for the loop.
CouldComputeBECount = false;
// Remember exit count if either exact or symbolic is known. Because
// Exact always implies symbolic, only check symbolic.
if (EL.SymbolicMaxNotTaken != getCouldNotCompute())
ExitCounts.emplace_back(ExitBB, EL);
else {
assert(EL.ExactNotTaken == getCouldNotCompute() &&
"Exact is known but symbolic isn't?");
++NumExitCountsNotComputed;
}
// 2. Derive the loop's MaxBECount from each exit's max number of
// non-exiting iterations. Partition the loop exits into two kinds:
// LoopMustExits and LoopMayExits.
//
// If the exit dominates the loop latch, it is a LoopMustExit otherwise it
// is a LoopMayExit. If any computable LoopMustExit is found, then
// MaxBECount is the minimum EL.ConstantMaxNotTaken of computable
// LoopMustExits. Otherwise, MaxBECount is conservatively the maximum
// EL.ConstantMaxNotTaken, where CouldNotCompute is considered greater than
// any
// computable EL.ConstantMaxNotTaken.
if (EL.ConstantMaxNotTaken != getCouldNotCompute() && Latch &&
DT.dominates(ExitBB, Latch)) {
if (!MustExitMaxBECount) {
MustExitMaxBECount = EL.ConstantMaxNotTaken;
MustExitMaxOrZero = EL.MaxOrZero;
} else {
MustExitMaxBECount = getUMinFromMismatchedTypes(MustExitMaxBECount,
EL.ConstantMaxNotTaken);
}
} else if (MayExitMaxBECount != getCouldNotCompute()) {
if (!MayExitMaxBECount || EL.ConstantMaxNotTaken == getCouldNotCompute())
MayExitMaxBECount = EL.ConstantMaxNotTaken;
else {
MayExitMaxBECount = getUMaxFromMismatchedTypes(MayExitMaxBECount,
EL.ConstantMaxNotTaken);
}
}
}
const SCEV *MaxBECount = MustExitMaxBECount ? MustExitMaxBECount :
(MayExitMaxBECount ? MayExitMaxBECount : getCouldNotCompute());
// The loop backedge will be taken the maximum or zero times if there's
// a single exit that must be taken the maximum or zero times.
bool MaxOrZero = (MustExitMaxOrZero && ExitingBlocks.size() == 1);
// Remember which SCEVs are used in exit limits for invalidation purposes.
// We only care about non-constant SCEVs here, so we can ignore
// EL.ConstantMaxNotTaken
// and MaxBECount, which must be SCEVConstant.
for (const auto &Pair : ExitCounts) {
if (!isa<SCEVConstant>(Pair.second.ExactNotTaken))
BECountUsers[Pair.second.ExactNotTaken].insert({L, AllowPredicates});
if (!isa<SCEVConstant>(Pair.second.SymbolicMaxNotTaken))
BECountUsers[Pair.second.SymbolicMaxNotTaken].insert(
{L, AllowPredicates});
}
return BackedgeTakenInfo(std::move(ExitCounts), CouldComputeBECount,
MaxBECount, MaxOrZero);
}
ScalarEvolution::ExitLimit
ScalarEvolution::computeExitLimit(const Loop *L, BasicBlock *ExitingBlock,
bool IsOnlyExit, bool AllowPredicates) {
assert(L->contains(ExitingBlock) && "Exit count for non-loop block?");
// If our exiting block does not dominate the latch, then its connection with
// loop's exit limit may be far from trivial.
const BasicBlock *Latch = L->getLoopLatch();
if (!Latch || !DT.dominates(ExitingBlock, Latch))
return getCouldNotCompute();
Instruction *Term = ExitingBlock->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(Term)) {
assert(BI->isConditional() && "If unconditional, it can't be in loop!");
bool ExitIfTrue = !L->contains(BI->getSuccessor(0));
assert(ExitIfTrue == L->contains(BI->getSuccessor(1)) &&
"It should have one successor in loop and one exit block!");
// Proceed to the next level to examine the exit condition expression.
return computeExitLimitFromCond(L, BI->getCondition(), ExitIfTrue,
/*ControlsOnlyExit=*/IsOnlyExit,
AllowPredicates);
}
if (SwitchInst *SI = dyn_cast<SwitchInst>(Term)) {
// For switch, make sure that there is a single exit from the loop.
BasicBlock *Exit = nullptr;
for (auto *SBB : successors(ExitingBlock))
if (!L->contains(SBB)) {
if (Exit) // Multiple exit successors.
return getCouldNotCompute();
Exit = SBB;
}
assert(Exit && "Exiting block must have at least one exit");
return computeExitLimitFromSingleExitSwitch(
L, SI, Exit, /*ControlsOnlyExit=*/IsOnlyExit);
}
return getCouldNotCompute();
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCond(
const Loop *L, Value *ExitCond, bool ExitIfTrue, bool ControlsOnlyExit,
bool AllowPredicates) {
ScalarEvolution::ExitLimitCacheTy Cache(L, ExitIfTrue, AllowPredicates);
return computeExitLimitFromCondCached(Cache, L, ExitCond, ExitIfTrue,
ControlsOnlyExit, AllowPredicates);
}
std::optional<ScalarEvolution::ExitLimit>
ScalarEvolution::ExitLimitCache::find(const Loop *L, Value *ExitCond,
bool ExitIfTrue, bool ControlsOnlyExit,
bool AllowPredicates) {
(void)this->L;
(void)this->ExitIfTrue;
(void)this->AllowPredicates;
assert(this->L == L && this->ExitIfTrue == ExitIfTrue &&
this->AllowPredicates == AllowPredicates &&
"Variance in assumed invariant key components!");
auto Itr = TripCountMap.find({ExitCond, ControlsOnlyExit});
if (Itr == TripCountMap.end())
return std::nullopt;
return Itr->second;
}
void ScalarEvolution::ExitLimitCache::insert(const Loop *L, Value *ExitCond,
bool ExitIfTrue,
bool ControlsOnlyExit,
bool AllowPredicates,
const ExitLimit &EL) {
assert(this->L == L && this->ExitIfTrue == ExitIfTrue &&
this->AllowPredicates == AllowPredicates &&
"Variance in assumed invariant key components!");
auto InsertResult = TripCountMap.insert({{ExitCond, ControlsOnlyExit}, EL});
assert(InsertResult.second && "Expected successful insertion!");
(void)InsertResult;
(void)ExitIfTrue;
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCondCached(
ExitLimitCacheTy &Cache, const Loop *L, Value *ExitCond, bool ExitIfTrue,
bool ControlsOnlyExit, bool AllowPredicates) {
if (auto MaybeEL = Cache.find(L, ExitCond, ExitIfTrue, ControlsOnlyExit,
AllowPredicates))
return *MaybeEL;
ExitLimit EL = computeExitLimitFromCondImpl(
Cache, L, ExitCond, ExitIfTrue, ControlsOnlyExit, AllowPredicates);
Cache.insert(L, ExitCond, ExitIfTrue, ControlsOnlyExit, AllowPredicates, EL);
return EL;
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCondImpl(
ExitLimitCacheTy &Cache, const Loop *L, Value *ExitCond, bool ExitIfTrue,
bool ControlsOnlyExit, bool AllowPredicates) {
// Handle BinOp conditions (And, Or).
if (auto LimitFromBinOp = computeExitLimitFromCondFromBinOp(
Cache, L, ExitCond, ExitIfTrue, ControlsOnlyExit, AllowPredicates))
return *LimitFromBinOp;
// With an icmp, it may be feasible to compute an exact backedge-taken count.
// Proceed to the next level to examine the icmp.
if (ICmpInst *ExitCondICmp = dyn_cast<ICmpInst>(ExitCond)) {
ExitLimit EL =
computeExitLimitFromICmp(L, ExitCondICmp, ExitIfTrue, ControlsOnlyExit);
if (EL.hasFullInfo() || !AllowPredicates)
return EL;
// Try again, but use SCEV predicates this time.
return computeExitLimitFromICmp(L, ExitCondICmp, ExitIfTrue,
ControlsOnlyExit,
/*AllowPredicates=*/true);
}
// Check for a constant condition. These are normally stripped out by
// SimplifyCFG, but ScalarEvolution may be used by a pass which wishes to
// preserve the CFG and is temporarily leaving constant conditions
// in place.
if (ConstantInt *CI = dyn_cast<ConstantInt>(ExitCond)) {
if (ExitIfTrue == !CI->getZExtValue())
// The backedge is always taken.
return getCouldNotCompute();
// The backedge is never taken.
return getZero(CI->getType());
}
// If we're exiting based on the overflow flag of an x.with.overflow intrinsic
// with a constant step, we can form an equivalent icmp predicate and figure
// out how many iterations will be taken before we exit.
const WithOverflowInst *WO;
const APInt *C;
if (match(ExitCond, m_ExtractValue<1>(m_WithOverflowInst(WO))) &&
match(WO->getRHS(), m_APInt(C))) {
ConstantRange NWR =
ConstantRange::makeExactNoWrapRegion(WO->getBinaryOp(), *C,
WO->getNoWrapKind());
CmpInst::Predicate Pred;
APInt NewRHSC, Offset;
NWR.getEquivalentICmp(Pred, NewRHSC, Offset);
if (!ExitIfTrue)
Pred = ICmpInst::getInversePredicate(Pred);
auto *LHS = getSCEV(WO->getLHS());
if (Offset != 0)
LHS = getAddExpr(LHS, getConstant(Offset));
auto EL = computeExitLimitFromICmp(L, Pred, LHS, getConstant(NewRHSC),
ControlsOnlyExit, AllowPredicates);
if (EL.hasAnyInfo())
return EL;
}
// If it's not an integer or pointer comparison then compute it the hard way.
return computeExitCountExhaustively(L, ExitCond, ExitIfTrue);
}
std::optional<ScalarEvolution::ExitLimit>
ScalarEvolution::computeExitLimitFromCondFromBinOp(
ExitLimitCacheTy &Cache, const Loop *L, Value *ExitCond, bool ExitIfTrue,
bool ControlsOnlyExit, bool AllowPredicates) {
// Check if the controlling expression for this loop is an And or Or.
Value *Op0, *Op1;
bool IsAnd = false;
if (match(ExitCond, m_LogicalAnd(m_Value(Op0), m_Value(Op1))))
IsAnd = true;
else if (match(ExitCond, m_LogicalOr(m_Value(Op0), m_Value(Op1))))
IsAnd = false;
else
return std::nullopt;
// EitherMayExit is true in these two cases:
// br (and Op0 Op1), loop, exit
// br (or Op0 Op1), exit, loop
bool EitherMayExit = IsAnd ^ ExitIfTrue;
ExitLimit EL0 = computeExitLimitFromCondCached(
Cache, L, Op0, ExitIfTrue, ControlsOnlyExit && !EitherMayExit,
AllowPredicates);
ExitLimit EL1 = computeExitLimitFromCondCached(
Cache, L, Op1, ExitIfTrue, ControlsOnlyExit && !EitherMayExit,
AllowPredicates);
// Be robust against unsimplified IR for the form "op i1 X, NeutralElement"
const Constant *NeutralElement = ConstantInt::get(ExitCond->getType(), IsAnd);
if (isa<ConstantInt>(Op1))
return Op1 == NeutralElement ? EL0 : EL1;
if (isa<ConstantInt>(Op0))
return Op0 == NeutralElement ? EL1 : EL0;
const SCEV *BECount = getCouldNotCompute();
const SCEV *ConstantMaxBECount = getCouldNotCompute();
const SCEV *SymbolicMaxBECount = getCouldNotCompute();
if (EitherMayExit) {
bool UseSequentialUMin = !isa<BinaryOperator>(ExitCond);
// Both conditions must be same for the loop to continue executing.
// Choose the less conservative count.
if (EL0.ExactNotTaken != getCouldNotCompute() &&
EL1.ExactNotTaken != getCouldNotCompute()) {
BECount = getUMinFromMismatchedTypes(EL0.ExactNotTaken, EL1.ExactNotTaken,
UseSequentialUMin);
}
if (EL0.ConstantMaxNotTaken == getCouldNotCompute())
ConstantMaxBECount = EL1.ConstantMaxNotTaken;
else if (EL1.ConstantMaxNotTaken == getCouldNotCompute())
ConstantMaxBECount = EL0.ConstantMaxNotTaken;
else
ConstantMaxBECount = getUMinFromMismatchedTypes(EL0.ConstantMaxNotTaken,
EL1.ConstantMaxNotTaken);
if (EL0.SymbolicMaxNotTaken == getCouldNotCompute())
SymbolicMaxBECount = EL1.SymbolicMaxNotTaken;
else if (EL1.SymbolicMaxNotTaken == getCouldNotCompute())
SymbolicMaxBECount = EL0.SymbolicMaxNotTaken;
else
SymbolicMaxBECount = getUMinFromMismatchedTypes(
EL0.SymbolicMaxNotTaken, EL1.SymbolicMaxNotTaken, UseSequentialUMin);
} else {
// Both conditions must be same at the same time for the loop to exit.
// For now, be conservative.
if (EL0.ExactNotTaken == EL1.ExactNotTaken)
BECount = EL0.ExactNotTaken;
}
// There are cases (e.g. PR26207) where computeExitLimitFromCond is able
// to be more aggressive when computing BECount than when computing
// ConstantMaxBECount. In these cases it is possible for EL0.ExactNotTaken
// and
// EL1.ExactNotTaken to match, but for EL0.ConstantMaxNotTaken and
// EL1.ConstantMaxNotTaken to not.
if (isa<SCEVCouldNotCompute>(ConstantMaxBECount) &&
!isa<SCEVCouldNotCompute>(BECount))
ConstantMaxBECount = getConstant(getUnsignedRangeMax(BECount));
if (isa<SCEVCouldNotCompute>(SymbolicMaxBECount))
SymbolicMaxBECount =
isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, false,
{ArrayRef(EL0.Predicates), ArrayRef(EL1.Predicates)});
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromICmp(
const Loop *L, ICmpInst *ExitCond, bool ExitIfTrue, bool ControlsOnlyExit,
bool AllowPredicates) {
// If the condition was exit on true, convert the condition to exit on false
CmpPredicate Pred;
if (!ExitIfTrue)
Pred = ExitCond->getCmpPredicate();
else
Pred = ExitCond->getInverseCmpPredicate();
const ICmpInst::Predicate OriginalPred = Pred;
const SCEV *LHS = getSCEV(ExitCond->getOperand(0));
const SCEV *RHS = getSCEV(ExitCond->getOperand(1));
ExitLimit EL = computeExitLimitFromICmp(L, Pred, LHS, RHS, ControlsOnlyExit,
AllowPredicates);
if (EL.hasAnyInfo())
return EL;
auto *ExhaustiveCount =
computeExitCountExhaustively(L, ExitCond, ExitIfTrue);
if (!isa<SCEVCouldNotCompute>(ExhaustiveCount))
return ExhaustiveCount;
return computeShiftCompareExitLimit(ExitCond->getOperand(0),
ExitCond->getOperand(1), L, OriginalPred);
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromICmp(
const Loop *L, CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS,
bool ControlsOnlyExit, bool AllowPredicates) {
// Try to evaluate any dependencies out of the loop.
LHS = getSCEVAtScope(LHS, L);
RHS = getSCEVAtScope(RHS, L);
// At this point, we would like to compute how many iterations of the
// loop the predicate will return true for these inputs.
if (isLoopInvariant(LHS, L) && !isLoopInvariant(RHS, L)) {
// If there is a loop-invariant, force it into the RHS.
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
bool ControllingFiniteLoop = ControlsOnlyExit && loopHasNoAbnormalExits(L) &&
loopIsFiniteByAssumption(L);
// Simplify the operands before analyzing them.
(void)SimplifyICmpOperands(Pred, LHS, RHS, /*Depth=*/0);
// If we have a comparison of a chrec against a constant, try to use value
// ranges to answer this query.
if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS))
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(LHS))
if (AddRec->getLoop() == L) {
// Form the constant range.
ConstantRange CompRange =
ConstantRange::makeExactICmpRegion(Pred, RHSC->getAPInt());
const SCEV *Ret = AddRec->getNumIterationsInRange(CompRange, *this);
if (!isa<SCEVCouldNotCompute>(Ret)) return Ret;
}
// If this loop must exit based on this condition (or execute undefined
// behaviour), see if we can improve wrap flags. This is essentially
// a must execute style proof.
if (ControllingFiniteLoop && isLoopInvariant(RHS, L)) {
// If we can prove the test sequence produced must repeat the same values
// on self-wrap of the IV, then we can infer that IV doesn't self wrap
// because if it did, we'd have an infinite (undefined) loop.
// TODO: We can peel off any functions which are invertible *in L*. Loop
// invariant terms are effectively constants for our purposes here.
auto *InnerLHS = LHS;
if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS))
InnerLHS = ZExt->getOperand();
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(InnerLHS);
AR && !AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine() &&
isKnownToBeAPowerOfTwo(AR->getStepRecurrence(*this), /*OrZero=*/true,
/*OrNegative=*/true)) {
auto Flags = AR->getNoWrapFlags();
Flags = setFlags(Flags, SCEV::FlagNW);
SmallVector<const SCEV *> Operands{AR->operands()};
Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
}
// For a slt/ult condition with a positive step, can we prove nsw/nuw?
// From no-self-wrap, this follows trivially from the fact that every
// (un)signed-wrapped, but not self-wrapped value must be LT than the
// last value before (un)signed wrap. Since we know that last value
// didn't exit, nor will any smaller one.
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) {
auto WrapType = Pred == ICmpInst::ICMP_SLT ? SCEV::FlagNSW : SCEV::FlagNUW;
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS);
AR && AR->getLoop() == L && AR->isAffine() &&
!AR->getNoWrapFlags(WrapType) && AR->hasNoSelfWrap() &&
isKnownPositive(AR->getStepRecurrence(*this))) {
auto Flags = AR->getNoWrapFlags();
Flags = setFlags(Flags, WrapType);
SmallVector<const SCEV*> Operands{AR->operands()};
Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
}
}
}
switch (Pred) {
case ICmpInst::ICMP_NE: { // while (X != Y)
// Convert to: while (X-Y != 0)
if (LHS->getType()->isPointerTy()) {
LHS = getLosslessPtrToIntExpr(LHS);
if (isa<SCEVCouldNotCompute>(LHS))
return LHS;
}
if (RHS->getType()->isPointerTy()) {
RHS = getLosslessPtrToIntExpr(RHS);
if (isa<SCEVCouldNotCompute>(RHS))
return RHS;
}
ExitLimit EL = howFarToZero(getMinusSCEV(LHS, RHS), L, ControlsOnlyExit,
AllowPredicates);
if (EL.hasAnyInfo())
return EL;
break;
}
case ICmpInst::ICMP_EQ: { // while (X == Y)
// Convert to: while (X-Y == 0)
if (LHS->getType()->isPointerTy()) {
LHS = getLosslessPtrToIntExpr(LHS);
if (isa<SCEVCouldNotCompute>(LHS))
return LHS;
}
if (RHS->getType()->isPointerTy()) {
RHS = getLosslessPtrToIntExpr(RHS);
if (isa<SCEVCouldNotCompute>(RHS))
return RHS;
}
ExitLimit EL = howFarToNonZero(getMinusSCEV(LHS, RHS), L);
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULE:
// Since the loop is finite, an invariant RHS cannot include the boundary
// value, otherwise it would loop forever.
if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
!isLoopInvariant(RHS, L)) {
// Otherwise, perform the addition in a wider type, to avoid overflow.
// If the LHS is an addrec with the appropriate nowrap flag, the
// extension will be sunk into it and the exit count can be analyzed.
auto *OldType = dyn_cast<IntegerType>(LHS->getType());
if (!OldType)
break;
// Prefer doubling the bitwidth over adding a single bit to make it more
// likely that we use a legal type.
auto *NewType =
Type::getIntNTy(OldType->getContext(), OldType->getBitWidth() * 2);
if (ICmpInst::isSigned(Pred)) {
LHS = getSignExtendExpr(LHS, NewType);
RHS = getSignExtendExpr(RHS, NewType);
} else {
LHS = getZeroExtendExpr(LHS, NewType);
RHS = getZeroExtendExpr(RHS, NewType);
}
}
RHS = getAddExpr(getOne(RHS->getType()), RHS);
[[fallthrough]];
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_ULT: { // while (X < Y)
bool IsSigned = ICmpInst::isSigned(Pred);
ExitLimit EL = howManyLessThans(LHS, RHS, L, IsSigned, ControlsOnlyExit,
AllowPredicates);
if (EL.hasAnyInfo())
return EL;
break;
}
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGE:
// Since the loop is finite, an invariant RHS cannot include the boundary
// value, otherwise it would loop forever.
if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
!isLoopInvariant(RHS, L))
break;
RHS = getAddExpr(getMinusOne(RHS->getType()), RHS);
[[fallthrough]];
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_UGT: { // while (X > Y)
bool IsSigned = ICmpInst::isSigned(Pred);
ExitLimit EL = howManyGreaterThans(LHS, RHS, L, IsSigned, ControlsOnlyExit,
AllowPredicates);
if (EL.hasAnyInfo())
return EL;
break;
}
default:
break;
}
return getCouldNotCompute();
}
ScalarEvolution::ExitLimit
ScalarEvolution::computeExitLimitFromSingleExitSwitch(const Loop *L,
SwitchInst *Switch,
BasicBlock *ExitingBlock,
bool ControlsOnlyExit) {
assert(!L->contains(ExitingBlock) && "Not an exiting block!");
// Give up if the exit is the default dest of a switch.
if (Switch->getDefaultDest() == ExitingBlock)
return getCouldNotCompute();
assert(L->contains(Switch->getDefaultDest()) &&
"Default case must not exit the loop!");
const SCEV *LHS = getSCEVAtScope(Switch->getCondition(), L);
const SCEV *RHS = getConstant(Switch->findCaseDest(ExitingBlock));
// while (X != Y) --> while (X-Y != 0)
ExitLimit EL = howFarToZero(getMinusSCEV(LHS, RHS), L, ControlsOnlyExit);
if (EL.hasAnyInfo())
return EL;
return getCouldNotCompute();
}
static ConstantInt *
EvaluateConstantChrecAtConstant(const SCEVAddRecExpr *AddRec, ConstantInt *C,
ScalarEvolution &SE) {
const SCEV *InVal = SE.getConstant(C);
const SCEV *Val = AddRec->evaluateAtIteration(InVal, SE);
assert(isa<SCEVConstant>(Val) &&
"Evaluation of SCEV at constant didn't fold correctly?");
return cast<SCEVConstant>(Val)->getValue();
}
ScalarEvolution::ExitLimit ScalarEvolution::computeShiftCompareExitLimit(
Value *LHS, Value *RHSV, const Loop *L, ICmpInst::Predicate Pred) {
ConstantInt *RHS = dyn_cast<ConstantInt>(RHSV);
if (!RHS)
return getCouldNotCompute();
const BasicBlock *Latch = L->getLoopLatch();
if (!Latch)
return getCouldNotCompute();
const BasicBlock *Predecessor = L->getLoopPredecessor();
if (!Predecessor)
return getCouldNotCompute();
// Return true if V is of the form "LHS `shift_op` <positive constant>".
// Return LHS in OutLHS and shift_opt in OutOpCode.
auto MatchPositiveShift =
[](Value *V, Value *&OutLHS, Instruction::BinaryOps &OutOpCode) {
using namespace PatternMatch;
ConstantInt *ShiftAmt;
if (match(V, m_LShr(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
OutOpCode = Instruction::LShr;
else if (match(V, m_AShr(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
OutOpCode = Instruction::AShr;
else if (match(V, m_Shl(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
OutOpCode = Instruction::Shl;
else
return false;
return ShiftAmt->getValue().isStrictlyPositive();
};
// Recognize a "shift recurrence" either of the form %iv or of %iv.shifted in
//
// loop:
// %iv = phi i32 [ %iv.shifted, %loop ], [ %val, %preheader ]
// %iv.shifted = lshr i32 %iv, <positive constant>
//
// Return true on a successful match. Return the corresponding PHI node (%iv
// above) in PNOut and the opcode of the shift operation in OpCodeOut.
auto MatchShiftRecurrence =
[&](Value *V, PHINode *&PNOut, Instruction::BinaryOps &OpCodeOut) {
std::optional<Instruction::BinaryOps> PostShiftOpCode;
{
Instruction::BinaryOps OpC;
Value *V;
// If we encounter a shift instruction, "peel off" the shift operation,
// and remember that we did so. Later when we inspect %iv's backedge
// value, we will make sure that the backedge value uses the same
// operation.
//
// Note: the peeled shift operation does not have to be the same
// instruction as the one feeding into the PHI's backedge value. We only
// really care about it being the same *kind* of shift instruction --
// that's all that is required for our later inferences to hold.
if (MatchPositiveShift(LHS, V, OpC)) {
PostShiftOpCode = OpC;
LHS = V;
}
}
PNOut = dyn_cast<PHINode>(LHS);
if (!PNOut || PNOut->getParent() != L->getHeader())
return false;
Value *BEValue = PNOut->getIncomingValueForBlock(Latch);
Value *OpLHS;
return
// The backedge value for the PHI node must be a shift by a positive
// amount
MatchPositiveShift(BEValue, OpLHS, OpCodeOut) &&
// of the PHI node itself
OpLHS == PNOut &&
// and the kind of shift should be match the kind of shift we peeled
// off, if any.
(!PostShiftOpCode || *PostShiftOpCode == OpCodeOut);
};
PHINode *PN;
Instruction::BinaryOps OpCode;
if (!MatchShiftRecurrence(LHS, PN, OpCode))
return getCouldNotCompute();
const DataLayout &DL = getDataLayout();
// The key rationale for this optimization is that for some kinds of shift
// recurrences, the value of the recurrence "stabilizes" to either 0 or -1
// within a finite number of iterations. If the condition guarding the
// backedge (in the sense that the backedge is taken if the condition is true)
// is false for the value the shift recurrence stabilizes to, then we know
// that the backedge is taken only a finite number of times.
ConstantInt *StableValue = nullptr;
switch (OpCode) {
default:
llvm_unreachable("Impossible case!");
case Instruction::AShr: {
// {K,ashr,<positive-constant>} stabilizes to signum(K) in at most
// bitwidth(K) iterations.
Value *FirstValue = PN->getIncomingValueForBlock(Predecessor);
KnownBits Known = computeKnownBits(FirstValue, DL, 0, &AC,
Predecessor->getTerminator(), &DT);
auto *Ty = cast<IntegerType>(RHS->getType());
if (Known.isNonNegative())
StableValue = ConstantInt::get(Ty, 0);
else if (Known.isNegative())
StableValue = ConstantInt::get(Ty, -1, true);
else
return getCouldNotCompute();
break;
}
case Instruction::LShr:
case Instruction::Shl:
// Both {K,lshr,<positive-constant>} and {K,shl,<positive-constant>}
// stabilize to 0 in at most bitwidth(K) iterations.
StableValue = ConstantInt::get(cast<IntegerType>(RHS->getType()), 0);
break;
}
auto *Result =
ConstantFoldCompareInstOperands(Pred, StableValue, RHS, DL, &TLI);
assert(Result->getType()->isIntegerTy(1) &&
"Otherwise cannot be an operand to a branch instruction");
if (Result->isZeroValue()) {
unsigned BitWidth = getTypeSizeInBits(RHS->getType());
const SCEV *UpperBound =
getConstant(getEffectiveSCEVType(RHS->getType()), BitWidth);
return ExitLimit(getCouldNotCompute(), UpperBound, UpperBound, false);
}
return getCouldNotCompute();
}
/// Return true if we can constant fold an instruction of the specified type,
/// assuming that all operands were constants.
static bool CanConstantFold(const Instruction *I) {
if (isa<BinaryOperator>(I) || isa<CmpInst>(I) ||
isa<SelectInst>(I) || isa<CastInst>(I) || isa<GetElementPtrInst>(I) ||
isa<LoadInst>(I) || isa<ExtractValueInst>(I))
return true;
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (const Function *F = CI->getCalledFunction())
return canConstantFoldCallTo(CI, F);
return false;
}
/// Determine whether this instruction can constant evolve within this loop
/// assuming its operands can all constant evolve.
static bool canConstantEvolve(Instruction *I, const Loop *L) {
// An instruction outside of the loop can't be derived from a loop PHI.
if (!L->contains(I)) return false;
if (isa<PHINode>(I)) {
// We don't currently keep track of the control flow needed to evaluate
// PHIs, so we cannot handle PHIs inside of loops.
return L->getHeader() == I->getParent();
}
// If we won't be able to constant fold this expression even if the operands
// are constants, bail early.
return CanConstantFold(I);
}
/// getConstantEvolvingPHIOperands - Implement getConstantEvolvingPHI by
/// recursing through each instruction operand until reaching a loop header phi.
static PHINode *
getConstantEvolvingPHIOperands(Instruction *UseInst, const Loop *L,
DenseMap<Instruction *, PHINode *> &PHIMap,
unsigned Depth) {
if (Depth > MaxConstantEvolvingDepth)
return nullptr;
// Otherwise, we can evaluate this instruction if all of its operands are
// constant or derived from a PHI node themselves.
PHINode *PHI = nullptr;
for (Value *Op : UseInst->operands()) {
if (isa<Constant>(Op)) continue;
Instruction *OpInst = dyn_cast<Instruction>(Op);
if (!OpInst || !canConstantEvolve(OpInst, L)) return nullptr;
PHINode *P = dyn_cast<PHINode>(OpInst);
if (!P)
// If this operand is already visited, reuse the prior result.
// We may have P != PHI if this is the deepest point at which the
// inconsistent paths meet.
P = PHIMap.lookup(OpInst);
if (!P) {
// Recurse and memoize the results, whether a phi is found or not.
// This recursive call invalidates pointers into PHIMap.
P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap, Depth + 1);
PHIMap[OpInst] = P;
}
if (!P)
return nullptr; // Not evolving from PHI
if (PHI && PHI != P)
return nullptr; // Evolving from multiple different PHIs.
PHI = P;
}
// This is a expression evolving from a constant PHI!
return PHI;
}
/// getConstantEvolvingPHI - Given an LLVM value and a loop, return a PHI node
/// in the loop that V is derived from. We allow arbitrary operations along the
/// way, but the operands of an operation must either be constants or a value
/// derived from a constant PHI. If this expression does not fit with these
/// constraints, return null.
static PHINode *getConstantEvolvingPHI(Value *V, const Loop *L) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !canConstantEvolve(I, L)) return nullptr;
if (PHINode *PN = dyn_cast<PHINode>(I))
return PN;
// Record non-constant instructions contained by the loop.
DenseMap<Instruction *, PHINode *> PHIMap;
return getConstantEvolvingPHIOperands(I, L, PHIMap, 0);
}
/// EvaluateExpression - Given an expression that passes the
/// getConstantEvolvingPHI predicate, evaluate its value assuming the PHI node
/// in the loop has the value PHIVal. If we can't fold this expression for some
/// reason, return null.
static Constant *EvaluateExpression(Value *V, const Loop *L,
DenseMap<Instruction *, Constant *> &Vals,
const DataLayout &DL,
const TargetLibraryInfo *TLI) {
// Convenient constant check, but redundant for recursive calls.
if (Constant *C = dyn_cast<Constant>(V)) return C;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return nullptr;
if (Constant *C = Vals.lookup(I)) return C;
// An instruction inside the loop depends on a value outside the loop that we
// weren't given a mapping for, or a value such as a call inside the loop.
if (!canConstantEvolve(I, L)) return nullptr;
// An unmapped PHI can be due to a branch or another loop inside this loop,
// or due to this not being the initial iteration through a loop where we
// couldn't compute the evolution of this particular PHI last time.
if (isa<PHINode>(I)) return nullptr;
std::vector<Constant*> Operands(I->getNumOperands());
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
Instruction *Operand = dyn_cast<Instruction>(I->getOperand(i));
if (!Operand) {
Operands[i] = dyn_cast<Constant>(I->getOperand(i));
if (!Operands[i]) return nullptr;
continue;
}
Constant *C = EvaluateExpression(Operand, L, Vals, DL, TLI);
Vals[Operand] = C;
if (!C) return nullptr;
Operands[i] = C;
}
return ConstantFoldInstOperands(I, Operands, DL, TLI,
/*AllowNonDeterministic=*/false);
}
// If every incoming value to PN except the one for BB is a specific Constant,
// return that, else return nullptr.
static Constant *getOtherIncomingValue(PHINode *PN, BasicBlock *BB) {
Constant *IncomingVal = nullptr;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (PN->getIncomingBlock(i) == BB)
continue;
auto *CurrentVal = dyn_cast<Constant>(PN->getIncomingValue(i));
if (!CurrentVal)
return nullptr;
if (IncomingVal != CurrentVal) {
if (IncomingVal)
return nullptr;
IncomingVal = CurrentVal;
}
}
return IncomingVal;
}
/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
/// in the header of its containing loop, we know the loop executes a
/// constant number of times, and the PHI node is just a recurrence
/// involving constants, fold it.
Constant *
ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
const APInt &BEs,
const Loop *L) {
auto [I, Inserted] = ConstantEvolutionLoopExitValue.try_emplace(PN);
if (!Inserted)
return I->second;
if (BEs.ugt(MaxBruteForceIterations))
return nullptr; // Not going to evaluate it.
Constant *&RetVal = I->second;
DenseMap<Instruction *, Constant *> CurrentIterVals;
BasicBlock *Header = L->getHeader();
assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
BasicBlock *Latch = L->getLoopLatch();
if (!Latch)
return nullptr;
for (PHINode &PHI : Header->phis()) {
if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
CurrentIterVals[&PHI] = StartCST;
}
if (!CurrentIterVals.count(PN))
return RetVal = nullptr;
Value *BEValue = PN->getIncomingValueForBlock(Latch);
// Execute the loop symbolically to determine the exit value.
assert(BEs.getActiveBits() < CHAR_BIT * sizeof(unsigned) &&
"BEs is <= MaxBruteForceIterations which is an 'unsigned'!");
unsigned NumIterations = BEs.getZExtValue(); // must be in range
unsigned IterationNum = 0;
const DataLayout &DL = getDataLayout();
for (; ; ++IterationNum) {
if (IterationNum == NumIterations)
return RetVal = CurrentIterVals[PN]; // Got exit value!
// Compute the value of the PHIs for the next iteration.
// EvaluateExpression adds non-phi values to the CurrentIterVals map.
DenseMap<Instruction *, Constant *> NextIterVals;
Constant *NextPHI =
EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
if (!NextPHI)
return nullptr; // Couldn't evaluate!
NextIterVals[PN] = NextPHI;
bool StoppedEvolving = NextPHI == CurrentIterVals[PN];
// Also evaluate the other PHI nodes. However, we don't get to stop if we
// cease to be able to evaluate one of them or if they stop evolving,
// because that doesn't necessarily prevent us from computing PN.
SmallVector<std::pair<PHINode *, Constant *>, 8> PHIsToCompute;
for (const auto &I : CurrentIterVals) {
PHINode *PHI = dyn_cast<PHINode>(I.first);
if (!PHI || PHI == PN || PHI->getParent() != Header) continue;
PHIsToCompute.emplace_back(PHI, I.second);
}
// We use two distinct loops because EvaluateExpression may invalidate any
// iterators into CurrentIterVals.
for (const auto &I : PHIsToCompute) {
PHINode *PHI = I.first;
Constant *&NextPHI = NextIterVals[PHI];
if (!NextPHI) { // Not already computed.
Value *BEValue = PHI->getIncomingValueForBlock(Latch);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
}
if (NextPHI != I.second)
StoppedEvolving = false;
}
// If all entries in CurrentIterVals == NextIterVals then we can stop
// iterating, the loop can't continue to change.
if (StoppedEvolving)
return RetVal = CurrentIterVals[PN];
CurrentIterVals.swap(NextIterVals);
}
}
const SCEV *ScalarEvolution::computeExitCountExhaustively(const Loop *L,
Value *Cond,
bool ExitWhen) {
PHINode *PN = getConstantEvolvingPHI(Cond, L);
if (!PN) return getCouldNotCompute();
// If the loop is canonicalized, the PHI will have exactly two entries.
// That's the only form we support here.
if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
DenseMap<Instruction *, Constant *> CurrentIterVals;
BasicBlock *Header = L->getHeader();
assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
BasicBlock *Latch = L->getLoopLatch();
assert(Latch && "Should follow from NumIncomingValues == 2!");
for (PHINode &PHI : Header->phis()) {
if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
CurrentIterVals[&PHI] = StartCST;
}
if (!CurrentIterVals.count(PN))
return getCouldNotCompute();
// Okay, we find a PHI node that defines the trip count of this loop. Execute
// the loop symbolically to determine when the condition gets a value of
// "ExitWhen".
unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis.
const DataLayout &DL = getDataLayout();
for (unsigned IterationNum = 0; IterationNum != MaxIterations;++IterationNum){
auto *CondVal = dyn_cast_or_null<ConstantInt>(
EvaluateExpression(Cond, L, CurrentIterVals, DL, &TLI));
// Couldn't symbolically evaluate.
if (!CondVal) return getCouldNotCompute();
if (CondVal->getValue() == uint64_t(ExitWhen)) {
++NumBruteForceTripCountsComputed;
return getConstant(Type::getInt32Ty(getContext()), IterationNum);
}
// Update all the PHI nodes for the next iteration.
DenseMap<Instruction *, Constant *> NextIterVals;
// Create a list of which PHIs we need to compute. We want to do this before
// calling EvaluateExpression on them because that may invalidate iterators
// into CurrentIterVals.
SmallVector<PHINode *, 8> PHIsToCompute;
for (const auto &I : CurrentIterVals) {
PHINode *PHI = dyn_cast<PHINode>(I.first);
if (!PHI || PHI->getParent() != Header) continue;
PHIsToCompute.push_back(PHI);
}
for (PHINode *PHI : PHIsToCompute) {
Constant *&NextPHI = NextIterVals[PHI];
if (NextPHI) continue; // Already computed!
Value *BEValue = PHI->getIncomingValueForBlock(Latch);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
}
CurrentIterVals.swap(NextIterVals);
}
// Too many iterations were needed to evaluate.
return getCouldNotCompute();
}
const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
SmallVector<std::pair<const Loop *, const SCEV *>, 2> &Values =
ValuesAtScopes[V];
// Check to see if we've folded this expression at this loop before.
for (auto &LS : Values)
if (LS.first == L)
return LS.second ? LS.second : V;
Values.emplace_back(L, nullptr);
// Otherwise compute it.
const SCEV *C = computeSCEVAtScope(V, L);
for (auto &LS : reverse(ValuesAtScopes[V]))
if (LS.first == L) {
LS.second = C;
if (!isa<SCEVConstant>(C))
ValuesAtScopesUsers[C].push_back({L, V});
break;
}
return C;
}
/// This builds up a Constant using the ConstantExpr interface. That way, we
/// will return Constants for objects which aren't represented by a
/// SCEVConstant, because SCEVConstant is restricted to ConstantInt.
/// Returns NULL if the SCEV isn't representable as a Constant.
static Constant *BuildConstantFromSCEV(const SCEV *V) {
switch (V->getSCEVType()) {
case scCouldNotCompute:
case scAddRecExpr:
case scVScale:
return nullptr;
case scConstant:
return cast<SCEVConstant>(V)->getValue();
case scUnknown:
return dyn_cast<Constant>(cast<SCEVUnknown>(V)->getValue());
case scPtrToInt: {
const SCEVPtrToIntExpr *P2I = cast<SCEVPtrToIntExpr>(V);
if (Constant *CastOp = BuildConstantFromSCEV(P2I->getOperand()))
return ConstantExpr::getPtrToInt(CastOp, P2I->getType());
return nullptr;
}
case scTruncate: {
const SCEVTruncateExpr *ST = cast<SCEVTruncateExpr>(V);
if (Constant *CastOp = BuildConstantFromSCEV(ST->getOperand()))
return ConstantExpr::getTrunc(CastOp, ST->getType());
return nullptr;
}
case scAddExpr: {
const SCEVAddExpr *SA = cast<SCEVAddExpr>(V);
Constant *C = nullptr;
for (const SCEV *Op : SA->operands()) {
Constant *OpC = BuildConstantFromSCEV(Op);
if (!OpC)
return nullptr;
if (!C) {
C = OpC;
continue;
}
assert(!C->getType()->isPointerTy() &&
"Can only have one pointer, and it must be last");
if (OpC->getType()->isPointerTy()) {
// The offsets have been converted to bytes. We can add bytes using
// an i8 GEP.
C = ConstantExpr::getGetElementPtr(Type::getInt8Ty(C->getContext()),
OpC, C);
} else {
C = ConstantExpr::getAdd(C, OpC);
}
}
return C;
}
case scMulExpr:
case scSignExtend:
case scZeroExtend:
case scUDivExpr:
case scSMaxExpr:
case scUMaxExpr:
case scSMinExpr:
case scUMinExpr:
case scSequentialUMinExpr:
return nullptr;
}
llvm_unreachable("Unknown SCEV kind!");
}
const SCEV *
ScalarEvolution::getWithOperands(const SCEV *S,
SmallVectorImpl<const SCEV *> &NewOps) {
switch (S->getSCEVType()) {
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
return getCastExpr(S->getSCEVType(), NewOps[0], S->getType());
case scAddRecExpr: {
auto *AddRec = cast<SCEVAddRecExpr>(S);
return getAddRecExpr(NewOps, AddRec->getLoop(), AddRec->getNoWrapFlags());
}
case scAddExpr:
return getAddExpr(NewOps, cast<SCEVAddExpr>(S)->getNoWrapFlags());
case scMulExpr:
return getMulExpr(NewOps, cast<SCEVMulExpr>(S)->getNoWrapFlags());
case scUDivExpr:
return getUDivExpr(NewOps[0], NewOps[1]);
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
return getMinMaxExpr(S->getSCEVType(), NewOps);
case scSequentialUMinExpr:
return getSequentialMinMaxExpr(S->getSCEVType(), NewOps);
case scConstant:
case scVScale:
case scUnknown:
return S;
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
switch (V->getSCEVType()) {
case scConstant:
case scVScale:
return V;
case scAddRecExpr: {
// If this is a loop recurrence for a loop that does not contain L, then we
// are dealing with the final value computed by the loop.
const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(V);
// First, attempt to evaluate each operand.
// Avoid performing the look-up in the common case where the specified
// expression has no loop-variant portions.
for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
const SCEV *OpAtScope = getSCEVAtScope(AddRec->getOperand(i), L);
if (OpAtScope == AddRec->getOperand(i))
continue;
// Okay, at least one of these operands is loop variant but might be
// foldable. Build a new instance of the folded commutative expression.
SmallVector<const SCEV *, 8> NewOps;
NewOps.reserve(AddRec->getNumOperands());
append_range(NewOps, AddRec->operands().take_front(i));
NewOps.push_back(OpAtScope);
for (++i; i != e; ++i)
NewOps.push_back(getSCEVAtScope(AddRec->getOperand(i), L));
const SCEV *FoldedRec = getAddRecExpr(
NewOps, AddRec->getLoop(), AddRec->getNoWrapFlags(SCEV::FlagNW));
AddRec = dyn_cast<SCEVAddRecExpr>(FoldedRec);
// The addrec may be folded to a nonrecurrence, for example, if the
// induction variable is multiplied by zero after constant folding. Go
// ahead and return the folded value.
if (!AddRec)
return FoldedRec;
break;
}
// If the scope is outside the addrec's loop, evaluate it by using the
// loop exit value of the addrec.
if (!AddRec->getLoop()->contains(L)) {
// To evaluate this recurrence, we need to know how many times the AddRec
// loop iterates. Compute this now.
const SCEV *BackedgeTakenCount = getBackedgeTakenCount(AddRec->getLoop());
if (BackedgeTakenCount == getCouldNotCompute())
return AddRec;
// Then, evaluate the AddRec.
return AddRec->evaluateAtIteration(BackedgeTakenCount, *this);
}
return AddRec;
}
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr: {
ArrayRef<const SCEV *> Ops = V->operands();
// Avoid performing the look-up in the common case where the specified
// expression has no loop-variant portions.
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
const SCEV *OpAtScope = getSCEVAtScope(Ops[i], L);
if (OpAtScope != Ops[i]) {
// Okay, at least one of these operands is loop variant but might be
// foldable. Build a new instance of the folded commutative expression.
SmallVector<const SCEV *, 8> NewOps;
NewOps.reserve(Ops.size());
append_range(NewOps, Ops.take_front(i));
NewOps.push_back(OpAtScope);
for (++i; i != e; ++i) {
OpAtScope = getSCEVAtScope(Ops[i], L);
NewOps.push_back(OpAtScope);
}
return getWithOperands(V, NewOps);
}
}
// If we got here, all operands are loop invariant.
return V;
}
case scUnknown: {
// If this instruction is evolved from a constant-evolving PHI, compute the
// exit value from the loop without using SCEVs.
const SCEVUnknown *SU = cast<SCEVUnknown>(V);
Instruction *I = dyn_cast<Instruction>(SU->getValue());
if (!I)
return V; // This is some other type of SCEVUnknown, just return it.
if (PHINode *PN = dyn_cast<PHINode>(I)) {
const Loop *CurrLoop = this->LI[I->getParent()];
// Looking for loop exit value.
if (CurrLoop && CurrLoop->getParentLoop() == L &&
PN->getParent() == CurrLoop->getHeader()) {
// Okay, there is no closed form solution for the PHI node. Check
// to see if the loop that contains it has a known backedge-taken
// count. If so, we may be able to force computation of the exit
// value.
const SCEV *BackedgeTakenCount = getBackedgeTakenCount(CurrLoop);
// This trivial case can show up in some degenerate cases where
// the incoming IR has not yet been fully simplified.
if (BackedgeTakenCount->isZero()) {
Value *InitValue = nullptr;
bool MultipleInitValues = false;
for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) {
if (!CurrLoop->contains(PN->getIncomingBlock(i))) {
if (!InitValue)
InitValue = PN->getIncomingValue(i);
else if (InitValue != PN->getIncomingValue(i)) {
MultipleInitValues = true;
break;
}
}
}
if (!MultipleInitValues && InitValue)
return getSCEV(InitValue);
}
// Do we have a loop invariant value flowing around the backedge
// for a loop which must execute the backedge?
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
isKnownNonZero(BackedgeTakenCount) &&
PN->getNumIncomingValues() == 2) {
unsigned InLoopPred =
CurrLoop->contains(PN->getIncomingBlock(0)) ? 0 : 1;
Value *BackedgeVal = PN->getIncomingValue(InLoopPred);
if (CurrLoop->isLoopInvariant(BackedgeVal))
return getSCEV(BackedgeVal);
}
if (auto *BTCC = dyn_cast<SCEVConstant>(BackedgeTakenCount)) {
// Okay, we know how many times the containing loop executes. If
// this is a constant evolving PHI node, get the final value at
// the specified iteration number.
Constant *RV =
getConstantEvolutionLoopExitValue(PN, BTCC->getAPInt(), CurrLoop);
if (RV)
return getSCEV(RV);
}
}
}
// Okay, this is an expression that we cannot symbolically evaluate
// into a SCEV. Check to see if it's possible to symbolically evaluate
// the arguments into constants, and if so, try to constant propagate the
// result. This is particularly useful for computing loop exit values.
if (!CanConstantFold(I))
return V; // This is some other type of SCEVUnknown, just return it.
SmallVector<Constant *, 4> Operands;
Operands.reserve(I->getNumOperands());
bool MadeImprovement = false;
for (Value *Op : I->operands()) {
if (Constant *C = dyn_cast<Constant>(Op)) {
Operands.push_back(C);
continue;
}
// If any of the operands is non-constant and if they are
// non-integer and non-pointer, don't even try to analyze them
// with scev techniques.
if (!isSCEVable(Op->getType()))
return V;
const SCEV *OrigV = getSCEV(Op);
const SCEV *OpV = getSCEVAtScope(OrigV, L);
MadeImprovement |= OrigV != OpV;
Constant *C = BuildConstantFromSCEV(OpV);
if (!C)
return V;
assert(C->getType() == Op->getType() && "Type mismatch");
Operands.push_back(C);
}
// Check to see if getSCEVAtScope actually made an improvement.
if (!MadeImprovement)
return V; // This is some other type of SCEVUnknown, just return it.
Constant *C = nullptr;
const DataLayout &DL = getDataLayout();
C = ConstantFoldInstOperands(I, Operands, DL, &TLI,
/*AllowNonDeterministic=*/false);
if (!C)
return V;
return getSCEV(C);
}
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV type!");
}
const SCEV *ScalarEvolution::getSCEVAtScope(Value *V, const Loop *L) {
return getSCEVAtScope(getSCEV(V), L);
}
const SCEV *ScalarEvolution::stripInjectiveFunctions(const SCEV *S) const {
if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S))
return stripInjectiveFunctions(ZExt->getOperand());
if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S))
return stripInjectiveFunctions(SExt->getOperand());
return S;
}
/// Finds the minimum unsigned root of the following equation:
///
/// A * X = B (mod N)
///
/// where N = 2^BW and BW is the common bit width of A and B. The signedness of
/// A and B isn't important.
///
/// If the equation does not have a solution, SCEVCouldNotCompute is returned.
static const SCEV *
SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
SmallVectorImpl<const SCEVPredicate *> *Predicates,
ScalarEvolution &SE) {
uint32_t BW = A.getBitWidth();
assert(BW == SE.getTypeSizeInBits(B->getType()));
assert(A != 0 && "A must be non-zero.");
// 1. D = gcd(A, N)
//
// The gcd of A and N may have only one prime factor: 2. The number of
// trailing zeros in A is its multiplicity
uint32_t Mult2 = A.countr_zero();
// D = 2^Mult2
// 2. Check if B is divisible by D.
//
// B is divisible by D if and only if the multiplicity of prime factor 2 for B
// is not less than multiplicity of this prime factor for D.
if (SE.getMinTrailingZeros(B) < Mult2) {
// Check if we can prove there's no remainder using URem.
const SCEV *URem =
SE.getURemExpr(B, SE.getConstant(APInt::getOneBitSet(BW, Mult2)));
const SCEV *Zero = SE.getZero(B->getType());
if (!SE.isKnownPredicate(CmpInst::ICMP_EQ, URem, Zero)) {
// Try to add a predicate ensuring B is a multiple of 1 << Mult2.
if (!Predicates)
return SE.getCouldNotCompute();
// Avoid adding a predicate that is known to be false.
if (SE.isKnownPredicate(CmpInst::ICMP_NE, URem, Zero))
return SE.getCouldNotCompute();
Predicates->push_back(SE.getEqualPredicate(URem, Zero));
}
}
// 3. Compute I: the multiplicative inverse of (A / D) in arithmetic
// modulo (N / D).
//
// If D == 1, (N / D) == N == 2^BW, so we need one extra bit to represent
// (N / D) in general. The inverse itself always fits into BW bits, though,
// so we immediately truncate it.
APInt AD = A.lshr(Mult2).trunc(BW - Mult2); // AD = A / D
APInt I = AD.multiplicativeInverse().zext(BW);
// 4. Compute the minimum unsigned root of the equation:
// I * (B / D) mod (N / D)
// To simplify the computation, we factor out the divide by D:
// (I * B mod N) / D
const SCEV *D = SE.getConstant(APInt::getOneBitSet(BW, Mult2));
return SE.getUDivExactExpr(SE.getMulExpr(B, SE.getConstant(I)), D);
}
/// For a given quadratic addrec, generate coefficients of the corresponding
/// quadratic equation, multiplied by a common value to ensure that they are
/// integers.
/// The returned value is a tuple { A, B, C, M, BitWidth }, where
/// Ax^2 + Bx + C is the quadratic function, M is the value that A, B and C
/// were multiplied by, and BitWidth is the bit width of the original addrec
/// coefficients.
/// This function returns std::nullopt if the addrec coefficients are not
/// compile- time constants.
static std::optional<std::tuple<APInt, APInt, APInt, APInt, unsigned>>
GetQuadraticEquation(const SCEVAddRecExpr *AddRec) {
assert(AddRec->getNumOperands() == 3 && "This is not a quadratic chrec!");
const SCEVConstant *LC = dyn_cast<SCEVConstant>(AddRec->getOperand(0));
const SCEVConstant *MC = dyn_cast<SCEVConstant>(AddRec->getOperand(1));
const SCEVConstant *NC = dyn_cast<SCEVConstant>(AddRec->getOperand(2));
LLVM_DEBUG(dbgs() << __func__ << ": analyzing quadratic addrec: "
<< *AddRec << '\n');
// We currently can only solve this if the coefficients are constants.
if (!LC || !MC || !NC) {
LLVM_DEBUG(dbgs() << __func__ << ": coefficients are not constant\n");
return std::nullopt;
}
APInt L = LC->getAPInt();
APInt M = MC->getAPInt();
APInt N = NC->getAPInt();
assert(!N.isZero() && "This is not a quadratic addrec");
unsigned BitWidth = LC->getAPInt().getBitWidth();
unsigned NewWidth = BitWidth + 1;
LLVM_DEBUG(dbgs() << __func__ << ": addrec coeff bw: "
<< BitWidth << '\n');
// The sign-extension (as opposed to a zero-extension) here matches the
// extension used in SolveQuadraticEquationWrap (with the same motivation).
N = N.sext(NewWidth);
M = M.sext(NewWidth);
L = L.sext(NewWidth);
// The increments are M, M+N, M+2N, ..., so the accumulated values are
// L+M, (L+M)+(M+N), (L+M)+(M+N)+(M+2N), ..., that is,
// L+M, L+2M+N, L+3M+3N, ...
// After n iterations the accumulated value Acc is L + nM + n(n-1)/2 N.
//
// The equation Acc = 0 is then
// L + nM + n(n-1)/2 N = 0, or 2L + 2M n + n(n-1) N = 0.
// In a quadratic form it becomes:
// N n^2 + (2M-N) n + 2L = 0.
APInt A = N;
APInt B = 2 * M - A;
APInt C = 2 * L;
APInt T = APInt(NewWidth, 2);
LLVM_DEBUG(dbgs() << __func__ << ": equation " << A << "x^2 + " << B
<< "x + " << C << ", coeff bw: " << NewWidth
<< ", multiplied by " << T << '\n');
return std::make_tuple(A, B, C, T, BitWidth);
}
/// Helper function to compare optional APInts:
/// (a) if X and Y both exist, return min(X, Y),
/// (b) if neither X nor Y exist, return std::nullopt,
/// (c) if exactly one of X and Y exists, return that value.
static std::optional<APInt> MinOptional(std::optional<APInt> X,
std::optional<APInt> Y) {
if (X && Y) {
unsigned W = std::max(X->getBitWidth(), Y->getBitWidth());
APInt XW = X->sext(W);
APInt YW = Y->sext(W);
return XW.slt(YW) ? *X : *Y;
}
if (!X && !Y)
return std::nullopt;
return X ? *X : *Y;
}
/// Helper function to truncate an optional APInt to a given BitWidth.
/// When solving addrec-related equations, it is preferable to return a value
/// that has the same bit width as the original addrec's coefficients. If the
/// solution fits in the original bit width, truncate it (except for i1).
/// Returning a value of a different bit width may inhibit some optimizations.
///
/// In general, a solution to a quadratic equation generated from an addrec
/// may require BW+1 bits, where BW is the bit width of the addrec's
/// coefficients. The reason is that the coefficients of the quadratic
/// equation are BW+1 bits wide (to avoid truncation when converting from
/// the addrec to the equation).
static std::optional<APInt> TruncIfPossible(std::optional<APInt> X,
unsigned BitWidth) {
if (!X)
return std::nullopt;
unsigned W = X->getBitWidth();
if (BitWidth > 1 && BitWidth < W && X->isIntN(BitWidth))
return X->trunc(BitWidth);
return X;
}
/// Let c(n) be the value of the quadratic chrec {L,+,M,+,N} after n
/// iterations. The values L, M, N are assumed to be signed, and they
/// should all have the same bit widths.
/// Find the least n >= 0 such that c(n) = 0 in the arithmetic modulo 2^BW,
/// where BW is the bit width of the addrec's coefficients.
/// If the calculated value is a BW-bit integer (for BW > 1), it will be
/// returned as such, otherwise the bit width of the returned value may
/// be greater than BW.
///
/// This function returns std::nullopt if
/// (a) the addrec coefficients are not constant, or
/// (b) SolveQuadraticEquationWrap was unable to find a solution. For cases
/// like x^2 = 5, no integer solutions exist, in other cases an integer
/// solution may exist, but SolveQuadraticEquationWrap may fail to find it.
static std::optional<APInt>
SolveQuadraticAddRecExact(const SCEVAddRecExpr *AddRec, ScalarEvolution &SE) {
APInt A, B, C, M;
unsigned BitWidth;
auto T = GetQuadraticEquation(AddRec);
if (!T)
return std::nullopt;
std::tie(A, B, C, M, BitWidth) = *T;
LLVM_DEBUG(dbgs() << __func__ << ": solving for unsigned overflow\n");
std::optional<APInt> X =
APIntOps::SolveQuadraticEquationWrap(A, B, C, BitWidth + 1);
if (!X)
return std::nullopt;
ConstantInt *CX = ConstantInt::get(SE.getContext(), *X);
ConstantInt *V = EvaluateConstantChrecAtConstant(AddRec, CX, SE);
if (!V->isZero())
return std::nullopt;
return TruncIfPossible(X, BitWidth);
}
/// Let c(n) be the value of the quadratic chrec {0,+,M,+,N} after n
/// iterations. The values M, N are assumed to be signed, and they
/// should all have the same bit widths.
/// Find the least n such that c(n) does not belong to the given range,
/// while c(n-1) does.
///
/// This function returns std::nullopt if
/// (a) the addrec coefficients are not constant, or
/// (b) SolveQuadraticEquationWrap was unable to find a solution for the
/// bounds of the range.
static std::optional<APInt>
SolveQuadraticAddRecRange(const SCEVAddRecExpr *AddRec,
const ConstantRange &Range, ScalarEvolution &SE) {
assert(AddRec->getOperand(0)->isZero() &&
"Starting value of addrec should be 0");
LLVM_DEBUG(dbgs() << __func__ << ": solving boundary crossing for range "
<< Range << ", addrec " << *AddRec << '\n');
// This case is handled in getNumIterationsInRange. Here we can assume that
// we start in the range.
assert(Range.contains(APInt(SE.getTypeSizeInBits(AddRec->getType()), 0)) &&
"Addrec's initial value should be in range");
APInt A, B, C, M;
unsigned BitWidth;
auto T = GetQuadraticEquation(AddRec);
if (!T)
return std::nullopt;
// Be careful about the return value: there can be two reasons for not
// returning an actual number. First, if no solutions to the equations
// were found, and second, if the solutions don't leave the given range.
// The first case means that the actual solution is "unknown", the second
// means that it's known, but not valid. If the solution is unknown, we
// cannot make any conclusions.
// Return a pair: the optional solution and a flag indicating if the
// solution was found.
auto SolveForBoundary =
[&](APInt Bound) -> std::pair<std::optional<APInt>, bool> {
// Solve for signed overflow and unsigned overflow, pick the lower
// solution.
LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: checking boundary "
<< Bound << " (before multiplying by " << M << ")\n");
Bound *= M; // The quadratic equation multiplier.
std::optional<APInt> SO;
if (BitWidth > 1) {
LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: solving for "
"signed overflow\n");
SO = APIntOps::SolveQuadraticEquationWrap(A, B, -Bound, BitWidth);
}
LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: solving for "
"unsigned overflow\n");
std::optional<APInt> UO =
APIntOps::SolveQuadraticEquationWrap(A, B, -Bound, BitWidth + 1);
auto LeavesRange = [&] (const APInt &X) {
ConstantInt *C0 = ConstantInt::get(SE.getContext(), X);
ConstantInt *V0 = EvaluateConstantChrecAtConstant(AddRec, C0, SE);
if (Range.contains(V0->getValue()))
return false;
// X should be at least 1, so X-1 is non-negative.
ConstantInt *C1 = ConstantInt::get(SE.getContext(), X-1);
ConstantInt *V1 = EvaluateConstantChrecAtConstant(AddRec, C1, SE);
if (Range.contains(V1->getValue()))
return true;
return false;
};
// If SolveQuadraticEquationWrap returns std::nullopt, it means that there
// can be a solution, but the function failed to find it. We cannot treat it
// as "no solution".
if (!SO || !UO)
return {std::nullopt, false};
// Check the smaller value first to see if it leaves the range.
// At this point, both SO and UO must have values.
std::optional<APInt> Min = MinOptional(SO, UO);
if (LeavesRange(*Min))
return { Min, true };
std::optional<APInt> Max = Min == SO ? UO : SO;
if (LeavesRange(*Max))
return { Max, true };
// Solutions were found, but were eliminated, hence the "true".
return {std::nullopt, true};
};
std::tie(A, B, C, M, BitWidth) = *T;
// Lower bound is inclusive, subtract 1 to represent the exiting value.
APInt Lower = Range.getLower().sext(A.getBitWidth()) - 1;
APInt Upper = Range.getUpper().sext(A.getBitWidth());
auto SL = SolveForBoundary(Lower);
auto SU = SolveForBoundary(Upper);
// If any of the solutions was unknown, no meaninigful conclusions can
// be made.
if (!SL.second || !SU.second)
return std::nullopt;
// Claim: The correct solution is not some value between Min and Max.
//
// Justification: Assuming that Min and Max are different values, one of
// them is when the first signed overflow happens, the other is when the
// first unsigned overflow happens. Crossing the range boundary is only
// possible via an overflow (treating 0 as a special case of it, modeling
// an overflow as crossing k*2^W for some k).
//
// The interesting case here is when Min was eliminated as an invalid
// solution, but Max was not. The argument is that if there was another
// overflow between Min and Max, it would also have been eliminated if
// it was considered.
//
// For a given boundary, it is possible to have two overflows of the same
// type (signed/unsigned) without having the other type in between: this
// can happen when the vertex of the parabola is between the iterations
// corresponding to the overflows. This is only possible when the two
// overflows cross k*2^W for the same k. In such case, if the second one
// left the range (and was the first one to do so), the first overflow
// would have to enter the range, which would mean that either we had left
// the range before or that we started outside of it. Both of these cases
// are contradictions.
//
// Claim: In the case where SolveForBoundary returns std::nullopt, the correct
// solution is not some value between the Max for this boundary and the
// Min of the other boundary.
//
// Justification: Assume that we had such Max_A and Min_B corresponding
// to range boundaries A and B and such that Max_A < Min_B. If there was
// a solution between Max_A and Min_B, it would have to be caused by an
// overflow corresponding to either A or B. It cannot correspond to B,
// since Min_B is the first occurrence of such an overflow. If it
// corresponded to A, it would have to be either a signed or an unsigned
// overflow that is larger than both eliminated overflows for A. But
// between the eliminated overflows and this overflow, the values would
// cover the entire value space, thus crossing the other boundary, which
// is a contradiction.
return TruncIfPossible(MinOptional(SL.first, SU.first), BitWidth);
}
ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
const Loop *L,
bool ControlsOnlyExit,
bool AllowPredicates) {
// This is only used for loops with a "x != y" exit test. The exit condition
// is now expressed as a single expression, V = x-y. So the exit test is
// effectively V != 0. We know and take advantage of the fact that this
// expression only being used in a comparison by zero context.
SmallVector<const SCEVPredicate *> Predicates;
// If the value is a constant
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) {
// If the value is already zero, the branch will execute zero times.
if (C->getValue()->isZero()) return C;
return getCouldNotCompute(); // Otherwise it will loop infinitely.
}
const SCEVAddRecExpr *AddRec =
dyn_cast<SCEVAddRecExpr>(stripInjectiveFunctions(V));
if (!AddRec && AllowPredicates)
// Try to make this an AddRec using runtime tests, in the first X
// iterations of this loop, where X is the SCEV expression found by the
// algorithm below.
AddRec = convertSCEVToAddRecWithPredicates(V, L, Predicates);
if (!AddRec || AddRec->getLoop() != L)
return getCouldNotCompute();
// If this is a quadratic (3-term) AddRec {L,+,M,+,N}, find the roots of
// the quadratic equation to solve it.
if (AddRec->isQuadratic() && AddRec->getType()->isIntegerTy()) {
// We can only use this value if the chrec ends up with an exact zero
// value at this index. When solving for "X*X != 5", for example, we
// should not accept a root of 2.
if (auto S = SolveQuadraticAddRecExact(AddRec, *this)) {
const auto *R = cast<SCEVConstant>(getConstant(*S));
return ExitLimit(R, R, R, false, Predicates);
}
return getCouldNotCompute();
}
// Otherwise we can only handle this if it is affine.
if (!AddRec->isAffine())
return getCouldNotCompute();
// If this is an affine expression, the execution count of this branch is
// the minimum unsigned root of the following equation:
//
// Start + Step*N = 0 (mod 2^BW)
//
// equivalent to:
//
// Step*N = -Start (mod 2^BW)
//
// where BW is the common bit width of Start and Step.
// Get the initial value for the loop.
const SCEV *Start = getSCEVAtScope(AddRec->getStart(), L->getParentLoop());
const SCEV *Step = getSCEVAtScope(AddRec->getOperand(1), L->getParentLoop());
if (!isLoopInvariant(Step, L))
return getCouldNotCompute();
LoopGuards Guards = LoopGuards::collect(L, *this);
// Specialize step for this loop so we get context sensitive facts below.
const SCEV *StepWLG = applyLoopGuards(Step, Guards);
// For positive steps (counting up until unsigned overflow):
// N = -Start/Step (as unsigned)
// For negative steps (counting down to zero):
// N = Start/-Step
// First compute the unsigned distance from zero in the direction of Step.
bool CountDown = isKnownNegative(StepWLG);
if (!CountDown && !isKnownNonNegative(StepWLG))
return getCouldNotCompute();
const SCEV *Distance = CountDown ? Start : getNegativeSCEV(Start);
// Handle unitary steps, which cannot wraparound.
// 1*N = -Start; -1*N = Start (mod 2^BW), so:
// N = Distance (as unsigned)
if (match(Step, m_CombineOr(m_scev_One(), m_scev_AllOnes()))) {
APInt MaxBECount = getUnsignedRangeMax(applyLoopGuards(Distance, Guards));
MaxBECount = APIntOps::umin(MaxBECount, getUnsignedRangeMax(Distance));
// When a loop like "for (int i = 0; i != n; ++i) { /* body */ }" is rotated,
// we end up with a loop whose backedge-taken count is n - 1. Detect this
// case, and see if we can improve the bound.
//
// Explicitly handling this here is necessary because getUnsignedRange
// isn't context-sensitive; it doesn't know that we only care about the
// range inside the loop.
const SCEV *Zero = getZero(Distance->getType());
const SCEV *One = getOne(Distance->getType());
const SCEV *DistancePlusOne = getAddExpr(Distance, One);
if (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, DistancePlusOne, Zero)) {
// If Distance + 1 doesn't overflow, we can compute the maximum distance
// as "unsigned_max(Distance + 1) - 1".
ConstantRange CR = getUnsignedRange(DistancePlusOne);
MaxBECount = APIntOps::umin(MaxBECount, CR.getUnsignedMax() - 1);
}
return ExitLimit(Distance, getConstant(MaxBECount), Distance, false,
Predicates);
}
// If the condition controls loop exit (the loop exits only if the expression
// is true) and the addition is no-wrap we can use unsigned divide to
// compute the backedge count. In this case, the step may not divide the
// distance, but we don't care because if the condition is "missed" the loop
// will have undefined behavior due to wrapping.
if (ControlsOnlyExit && AddRec->hasNoSelfWrap() &&
loopHasNoAbnormalExits(AddRec->getLoop())) {
// If the stride is zero and the start is non-zero, the loop must be
// infinite. In C++, most loops are finite by assumption, in which case the
// step being zero implies UB must execute if the loop is entered.
if (!(loopIsFiniteByAssumption(L) && isKnownNonZero(Start)) &&
!isKnownNonZero(StepWLG))
return getCouldNotCompute();
const SCEV *Exact =
getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
const SCEV *ConstantMax = getCouldNotCompute();
if (Exact != getCouldNotCompute()) {
APInt MaxInt = getUnsignedRangeMax(applyLoopGuards(Exact, Guards));
ConstantMax =
getConstant(APIntOps::umin(MaxInt, getUnsignedRangeMax(Exact)));
}
const SCEV *SymbolicMax =
isa<SCEVCouldNotCompute>(Exact) ? ConstantMax : Exact;
return ExitLimit(Exact, ConstantMax, SymbolicMax, false, Predicates);
}
// Solve the general equation.
const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
if (!StepC || StepC->getValue()->isZero())
return getCouldNotCompute();
const SCEV *E = SolveLinEquationWithOverflow(
StepC->getAPInt(), getNegativeSCEV(Start),
AllowPredicates ? &Predicates : nullptr, *this);
const SCEV *M = E;
if (E != getCouldNotCompute()) {
APInt MaxWithGuards = getUnsignedRangeMax(applyLoopGuards(E, Guards));
M = getConstant(APIntOps::umin(MaxWithGuards, getUnsignedRangeMax(E)));
}
auto *S = isa<SCEVCouldNotCompute>(E) ? M : E;
return ExitLimit(E, M, S, false, Predicates);
}
ScalarEvolution::ExitLimit
ScalarEvolution::howFarToNonZero(const SCEV *V, const Loop *L) {
// Loops that look like: while (X == 0) are very strange indeed. We don't
// handle them yet except for the trivial case. This could be expanded in the
// future as needed.
// If the value is a constant, check to see if it is known to be non-zero
// already. If so, the backedge will execute zero times.
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) {
if (!C->getValue()->isZero())
return getZero(C->getType());
return getCouldNotCompute(); // Otherwise it will loop infinitely.
}
// We could implement others, but I really doubt anyone writes loops like
// this, and if they did, they would already be constant folded.
return getCouldNotCompute();
}
std::pair<const BasicBlock *, const BasicBlock *>
ScalarEvolution::getPredecessorWithUniqueSuccessorForBB(const BasicBlock *BB)
const {
// If the block has a unique predecessor, then there is no path from the
// predecessor to the block that does not go through the direct edge
// from the predecessor to the block.
if (const BasicBlock *Pred = BB->getSinglePredecessor())
return {Pred, BB};
// A loop's header is defined to be a block that dominates the loop.
// If the header has a unique predecessor outside the loop, it must be
// a block that has exactly one successor that can reach the loop.
if (const Loop *L = LI.getLoopFor(BB))
return {L->getLoopPredecessor(), L->getHeader()};
return {nullptr, BB};
}
/// SCEV structural equivalence is usually sufficient for testing whether two
/// expressions are equal, however for the purposes of looking for a condition
/// guarding a loop, it can be useful to be a little more general, since a
/// front-end may have replicated the controlling expression.
static bool HasSameValue(const SCEV *A, const SCEV *B) {
// Quick check to see if they are the same SCEV.
if (A == B) return true;
auto ComputesEqualValues = [](const Instruction *A, const Instruction *B) {
// Not all instructions that are "identical" compute the same value. For
// instance, two distinct alloca instructions allocating the same type are
// identical and do not read memory; but compute distinct values.
return A->isIdenticalTo(B) && (isa<BinaryOperator>(A) || isa<GetElementPtrInst>(A));
};
// Otherwise, if they're both SCEVUnknown, it's possible that they hold
// two different instructions with the same value. Check for this case.
if (const SCEVUnknown *AU = dyn_cast<SCEVUnknown>(A))
if (const SCEVUnknown *BU = dyn_cast<SCEVUnknown>(B))
if (const Instruction *AI = dyn_cast<Instruction>(AU->getValue()))
if (const Instruction *BI = dyn_cast<Instruction>(BU->getValue()))
if (ComputesEqualValues(AI, BI))
return true;
// Otherwise assume they may have a different value.
return false;
}
static bool MatchBinarySub(const SCEV *S, const SCEV *&LHS, const SCEV *&RHS) {
const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S);
if (!Add || Add->getNumOperands() != 2)
return false;
if (auto *ME = dyn_cast<SCEVMulExpr>(Add->getOperand(0));
ME && ME->getNumOperands() == 2 && ME->getOperand(0)->isAllOnesValue()) {
LHS = Add->getOperand(1);
RHS = ME->getOperand(1);
return true;
}
if (auto *ME = dyn_cast<SCEVMulExpr>(Add->getOperand(1));
ME && ME->getNumOperands() == 2 && ME->getOperand(0)->isAllOnesValue()) {
LHS = Add->getOperand(0);
RHS = ME->getOperand(1);
return true;
}
return false;
}
bool ScalarEvolution::SimplifyICmpOperands(CmpPredicate &Pred, const SCEV *&LHS,
const SCEV *&RHS, unsigned Depth) {
bool Changed = false;
// Simplifies ICMP to trivial true or false by turning it into '0 == 0' or
// '0 != 0'.
auto TrivialCase = [&](bool TriviallyTrue) {
LHS = RHS = getConstant(ConstantInt::getFalse(getContext()));
Pred = TriviallyTrue ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE;
return true;
};
// If we hit the max recursion limit bail out.
if (Depth >= 3)
return false;
// Canonicalize a constant to the right side.
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
// Check for both operands constant.
if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
if (!ICmpInst::compare(LHSC->getAPInt(), RHSC->getAPInt(), Pred))
return TrivialCase(false);
return TrivialCase(true);
}
// Otherwise swap the operands to put the constant on the right.
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
Changed = true;
}
// If we're comparing an addrec with a value which is loop-invariant in the
// addrec's loop, put the addrec on the left. Also make a dominance check,
// as both operands could be addrecs loop-invariant in each other's loop.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS)) {
const Loop *L = AR->getLoop();
if (isLoopInvariant(LHS, L) && properlyDominates(LHS, L->getHeader())) {
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
Changed = true;
}
}
// If there's a constant operand, canonicalize comparisons with boundary
// cases, and canonicalize *-or-equal comparisons to regular comparisons.
if (const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS)) {
const APInt &RA = RC->getAPInt();
bool SimplifiedByConstantRange = false;
if (!ICmpInst::isEquality(Pred)) {
ConstantRange ExactCR = ConstantRange::makeExactICmpRegion(Pred, RA);
if (ExactCR.isFullSet())
return TrivialCase(true);
if (ExactCR.isEmptySet())
return TrivialCase(false);
APInt NewRHS;
CmpInst::Predicate NewPred;
if (ExactCR.getEquivalentICmp(NewPred, NewRHS) &&
ICmpInst::isEquality(NewPred)) {
// We were able to convert an inequality to an equality.
Pred = NewPred;
RHS = getConstant(NewRHS);
Changed = SimplifiedByConstantRange = true;
}
}
if (!SimplifiedByConstantRange) {
switch (Pred) {
default:
break;
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
// Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b.
if (RA.isZero() && MatchBinarySub(LHS, LHS, RHS))
Changed = true;
break;
// The "Should have been caught earlier!" messages refer to the fact
// that the ExactCR.isFullSet() or ExactCR.isEmptySet() check above
// should have fired on the corresponding cases, and canonicalized the
// check to trivial case.
case ICmpInst::ICMP_UGE:
assert(!RA.isMinValue() && "Should have been caught earlier!");
Pred = ICmpInst::ICMP_UGT;
RHS = getConstant(RA - 1);
Changed = true;
break;
case ICmpInst::ICMP_ULE:
assert(!RA.isMaxValue() && "Should have been caught earlier!");
Pred = ICmpInst::ICMP_ULT;
RHS = getConstant(RA + 1);
Changed = true;
break;
case ICmpInst::ICMP_SGE:
assert(!RA.isMinSignedValue() && "Should have been caught earlier!");
Pred = ICmpInst::ICMP_SGT;
RHS = getConstant(RA - 1);
Changed = true;
break;
case ICmpInst::ICMP_SLE:
assert(!RA.isMaxSignedValue() && "Should have been caught earlier!");
Pred = ICmpInst::ICMP_SLT;
RHS = getConstant(RA + 1);
Changed = true;
break;
}
}
}
// Check for obvious equality.
if (HasSameValue(LHS, RHS)) {
if (ICmpInst::isTrueWhenEqual(Pred))
return TrivialCase(true);
if (ICmpInst::isFalseWhenEqual(Pred))
return TrivialCase(false);
}
// If possible, canonicalize GE/LE comparisons to GT/LT comparisons, by
// adding or subtracting 1 from one of the operands.
switch (Pred) {
case ICmpInst::ICMP_SLE:
if (!getSignedRangeMax(RHS).isMaxSignedValue()) {
RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
SCEV::FlagNSW);
Pred = ICmpInst::ICMP_SLT;
Changed = true;
} else if (!getSignedRangeMin(LHS).isMinSignedValue()) {
LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS,
SCEV::FlagNSW);
Pred = ICmpInst::ICMP_SLT;
Changed = true;
}
break;
case ICmpInst::ICMP_SGE:
if (!getSignedRangeMin(RHS).isMinSignedValue()) {
RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS,
SCEV::FlagNSW);
Pred = ICmpInst::ICMP_SGT;
Changed = true;
} else if (!getSignedRangeMax(LHS).isMaxSignedValue()) {
LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
SCEV::FlagNSW);
Pred = ICmpInst::ICMP_SGT;
Changed = true;
}
break;
case ICmpInst::ICMP_ULE:
if (!getUnsignedRangeMax(RHS).isMaxValue()) {
RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
SCEV::FlagNUW);
Pred = ICmpInst::ICMP_ULT;
Changed = true;
} else if (!getUnsignedRangeMin(LHS).isMinValue()) {
LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS);
Pred = ICmpInst::ICMP_ULT;
Changed = true;
}
break;
case ICmpInst::ICMP_UGE:
if (!getUnsignedRangeMin(RHS).isMinValue()) {
RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS);
Pred = ICmpInst::ICMP_UGT;
Changed = true;
} else if (!getUnsignedRangeMax(LHS).isMaxValue()) {
LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
SCEV::FlagNUW);
Pred = ICmpInst::ICMP_UGT;
Changed = true;
}
break;
default:
break;
}
// TODO: More simplifications are possible here.
// Recursively simplify until we either hit a recursion limit or nothing
// changes.
if (Changed)
return SimplifyICmpOperands(Pred, LHS, RHS, Depth + 1);
return Changed;
}
bool ScalarEvolution::isKnownNegative(const SCEV *S) {
return getSignedRangeMax(S).isNegative();
}
bool ScalarEvolution::isKnownPositive(const SCEV *S) {
return getSignedRangeMin(S).isStrictlyPositive();
}
bool ScalarEvolution::isKnownNonNegative(const SCEV *S) {
return !getSignedRangeMin(S).isNegative();
}
bool ScalarEvolution::isKnownNonPositive(const SCEV *S) {
return !getSignedRangeMax(S).isStrictlyPositive();
}
bool ScalarEvolution::isKnownNonZero(const SCEV *S) {
// Query push down for cases where the unsigned range is
// less than sufficient.
if (const auto *SExt = dyn_cast<SCEVSignExtendExpr>(S))
return isKnownNonZero(SExt->getOperand(0));
return getUnsignedRangeMin(S) != 0;
}
bool ScalarEvolution::isKnownToBeAPowerOfTwo(const SCEV *S, bool OrZero,
bool OrNegative) {
auto NonRecursive = [this, OrNegative](const SCEV *S) {
if (auto *C = dyn_cast<SCEVConstant>(S))
return C->getAPInt().isPowerOf2() ||
(OrNegative && C->getAPInt().isNegatedPowerOf2());
// The vscale_range indicates vscale is a power-of-two.
return isa<SCEVVScale>(S) && F.hasFnAttribute(Attribute::VScaleRange);
};
if (NonRecursive(S))
return true;
auto *Mul = dyn_cast<SCEVMulExpr>(S);
if (!Mul)
return false;
return all_of(Mul->operands(), NonRecursive) && (OrZero || isKnownNonZero(S));
}
std::pair<const SCEV *, const SCEV *>
ScalarEvolution::SplitIntoInitAndPostInc(const Loop *L, const SCEV *S) {
// Compute SCEV on entry of loop L.
const SCEV *Start = SCEVInitRewriter::rewrite(S, L, *this);
if (Start == getCouldNotCompute())
return { Start, Start };
// Compute post increment SCEV for loop L.
const SCEV *PostInc = SCEVPostIncRewriter::rewrite(S, L, *this);
assert(PostInc != getCouldNotCompute() && "Unexpected could not compute");
return { Start, PostInc };
}
bool ScalarEvolution::isKnownViaInduction(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS) {
// First collect all loops.
SmallPtrSet<const Loop *, 8> LoopsUsed;
getUsedLoops(LHS, LoopsUsed);
getUsedLoops(RHS, LoopsUsed);
if (LoopsUsed.empty())
return false;
// Domination relationship must be a linear order on collected loops.
#ifndef NDEBUG
for (const auto *L1 : LoopsUsed)
for (const auto *L2 : LoopsUsed)
assert((DT.dominates(L1->getHeader(), L2->getHeader()) ||
DT.dominates(L2->getHeader(), L1->getHeader())) &&
"Domination relationship is not a linear order");
#endif
const Loop *MDL =
*llvm::max_element(LoopsUsed, [&](const Loop *L1, const Loop *L2) {
return DT.properlyDominates(L1->getHeader(), L2->getHeader());
});
// Get init and post increment value for LHS.
auto SplitLHS = SplitIntoInitAndPostInc(MDL, LHS);
// if LHS contains unknown non-invariant SCEV then bail out.
if (SplitLHS.first == getCouldNotCompute())
return false;
assert (SplitLHS.second != getCouldNotCompute() && "Unexpected CNC");
// Get init and post increment value for RHS.
auto SplitRHS = SplitIntoInitAndPostInc(MDL, RHS);
// if RHS contains unknown non-invariant SCEV then bail out.
if (SplitRHS.first == getCouldNotCompute())
return false;
assert (SplitRHS.second != getCouldNotCompute() && "Unexpected CNC");
// It is possible that init SCEV contains an invariant load but it does
// not dominate MDL and is not available at MDL loop entry, so we should
// check it here.
if (!isAvailableAtLoopEntry(SplitLHS.first, MDL) ||
!isAvailableAtLoopEntry(SplitRHS.first, MDL))
return false;
// It seems backedge guard check is faster than entry one so in some cases
// it can speed up whole estimation by short circuit
return isLoopBackedgeGuardedByCond(MDL, Pred, SplitLHS.second,
SplitRHS.second) &&
isLoopEntryGuardedByCond(MDL, Pred, SplitLHS.first, SplitRHS.first);
}
bool ScalarEvolution::isKnownPredicate(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS) {
// Canonicalize the inputs first.
(void)SimplifyICmpOperands(Pred, LHS, RHS);
if (isKnownViaInduction(Pred, LHS, RHS))
return true;
if (isKnownPredicateViaSplitting(Pred, LHS, RHS))
return true;
// Otherwise see what can be done with some simple reasoning.
return isKnownViaNonRecursiveReasoning(Pred, LHS, RHS);
}
std::optional<bool> ScalarEvolution::evaluatePredicate(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
if (isKnownPredicate(Pred, LHS, RHS))
return true;
if (isKnownPredicate(ICmpInst::getInverseCmpPredicate(Pred), LHS, RHS))
return false;
return std::nullopt;
}
bool ScalarEvolution::isKnownPredicateAt(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS,
const Instruction *CtxI) {
// TODO: Analyze guards and assumes from Context's block.
return isKnownPredicate(Pred, LHS, RHS) ||
isBasicBlockEntryGuardedByCond(CtxI->getParent(), Pred, LHS, RHS);
}
std::optional<bool>
ScalarEvolution::evaluatePredicateAt(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS, const Instruction *CtxI) {
std::optional<bool> KnownWithoutContext = evaluatePredicate(Pred, LHS, RHS);
if (KnownWithoutContext)
return KnownWithoutContext;
if (isBasicBlockEntryGuardedByCond(CtxI->getParent(), Pred, LHS, RHS))
return true;
if (isBasicBlockEntryGuardedByCond(
CtxI->getParent(), ICmpInst::getInverseCmpPredicate(Pred), LHS, RHS))
return false;
return std::nullopt;
}
bool ScalarEvolution::isKnownOnEveryIteration(CmpPredicate Pred,
const SCEVAddRecExpr *LHS,
const SCEV *RHS) {
const Loop *L = LHS->getLoop();
return isLoopEntryGuardedByCond(L, Pred, LHS->getStart(), RHS) &&
isLoopBackedgeGuardedByCond(L, Pred, LHS->getPostIncExpr(*this), RHS);
}
std::optional<ScalarEvolution::MonotonicPredicateType>
ScalarEvolution::getMonotonicPredicateType(const SCEVAddRecExpr *LHS,
ICmpInst::Predicate Pred) {
auto Result = getMonotonicPredicateTypeImpl(LHS, Pred);
#ifndef NDEBUG
// Verify an invariant: inverting the predicate should turn a monotonically
// increasing change to a monotonically decreasing one, and vice versa.
if (Result) {
auto ResultSwapped =
getMonotonicPredicateTypeImpl(LHS, ICmpInst::getSwappedPredicate(Pred));
assert(*ResultSwapped != *Result &&
"monotonicity should flip as we flip the predicate");
}
#endif
return Result;
}
std::optional<ScalarEvolution::MonotonicPredicateType>
ScalarEvolution::getMonotonicPredicateTypeImpl(const SCEVAddRecExpr *LHS,
ICmpInst::Predicate Pred) {
// A zero step value for LHS means the induction variable is essentially a
// loop invariant value. We don't really depend on the predicate actually
// flipping from false to true (for increasing predicates, and the other way
// around for decreasing predicates), all we care about is that *if* the
// predicate changes then it only changes from false to true.
//
// A zero step value in itself is not very useful, but there may be places
// where SCEV can prove X >= 0 but not prove X > 0, so it is helpful to be
// as general as possible.
// Only handle LE/LT/GE/GT predicates.
if (!ICmpInst::isRelational(Pred))
return std::nullopt;
bool IsGreater = ICmpInst::isGE(Pred) || ICmpInst::isGT(Pred);
assert((IsGreater || ICmpInst::isLE(Pred) || ICmpInst::isLT(Pred)) &&
"Should be greater or less!");
// Check that AR does not wrap.
if (ICmpInst::isUnsigned(Pred)) {
if (!LHS->hasNoUnsignedWrap())
return std::nullopt;
return IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
}
assert(ICmpInst::isSigned(Pred) &&
"Relational predicate is either signed or unsigned!");
if (!LHS->hasNoSignedWrap())
return std::nullopt;
const SCEV *Step = LHS->getStepRecurrence(*this);
if (isKnownNonNegative(Step))
return IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
if (isKnownNonPositive(Step))
return !IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
return std::nullopt;
}
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantPredicate(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS, const Loop *L,
const Instruction *CtxI) {
// If there is a loop-invariant, force it into the RHS, otherwise bail out.
if (!isLoopInvariant(RHS, L)) {
if (!isLoopInvariant(LHS, L))
return std::nullopt;
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
const SCEVAddRecExpr *ArLHS = dyn_cast<SCEVAddRecExpr>(LHS);
if (!ArLHS || ArLHS->getLoop() != L)
return std::nullopt;
auto MonotonicType = getMonotonicPredicateType(ArLHS, Pred);
if (!MonotonicType)
return std::nullopt;
// If the predicate "ArLHS `Pred` RHS" monotonically increases from false to
// true as the loop iterates, and the backedge is control dependent on
// "ArLHS `Pred` RHS" == true then we can reason as follows:
//
// * if the predicate was false in the first iteration then the predicate
// is never evaluated again, since the loop exits without taking the
// backedge.
// * if the predicate was true in the first iteration then it will
// continue to be true for all future iterations since it is
// monotonically increasing.
//
// For both the above possibilities, we can replace the loop varying
// predicate with its value on the first iteration of the loop (which is
// loop invariant).
//
// A similar reasoning applies for a monotonically decreasing predicate, by
// replacing true with false and false with true in the above two bullets.
bool Increasing = *MonotonicType == ScalarEvolution::MonotonicallyIncreasing;
auto P = Increasing ? Pred : ICmpInst::getInverseCmpPredicate(Pred);
if (isLoopBackedgeGuardedByCond(L, P, LHS, RHS))
return ScalarEvolution::LoopInvariantPredicate(Pred, ArLHS->getStart(),
RHS);
if (!CtxI)
return std::nullopt;
// Try to prove via context.
// TODO: Support other cases.
switch (Pred) {
default:
break;
case ICmpInst::ICMP_ULE:
case ICmpInst::ICMP_ULT: {
assert(ArLHS->hasNoUnsignedWrap() && "Is a requirement of monotonicity!");
// Given preconditions
// (1) ArLHS does not cross the border of positive and negative parts of
// range because of:
// - Positive step; (TODO: lift this limitation)
// - nuw - does not cross zero boundary;
// - nsw - does not cross SINT_MAX boundary;
// (2) ArLHS <s RHS
// (3) RHS >=s 0
// we can replace the loop variant ArLHS <u RHS condition with loop
// invariant Start(ArLHS) <u RHS.
//
// Because of (1) there are two options:
// - ArLHS is always negative. It means that ArLHS <u RHS is always false;
// - ArLHS is always non-negative. Because of (3) RHS is also non-negative.
// It means that ArLHS <s RHS <=> ArLHS <u RHS.
// Because of (2) ArLHS <u RHS is trivially true.
// All together it means that ArLHS <u RHS <=> Start(ArLHS) >=s 0.
// We can strengthen this to Start(ArLHS) <u RHS.
auto SignFlippedPred = ICmpInst::getFlippedSignednessPredicate(Pred);
if (ArLHS->hasNoSignedWrap() && ArLHS->isAffine() &&
isKnownPositive(ArLHS->getStepRecurrence(*this)) &&
isKnownNonNegative(RHS) &&
isKnownPredicateAt(SignFlippedPred, ArLHS, RHS, CtxI))
return ScalarEvolution::LoopInvariantPredicate(Pred, ArLHS->getStart(),
RHS);
}
}
return std::nullopt;
}
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantExitCondDuringFirstIterations(
CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
const Instruction *CtxI, const SCEV *MaxIter) {
if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
Pred, LHS, RHS, L, CtxI, MaxIter))
return LIP;
if (auto *UMin = dyn_cast<SCEVUMinExpr>(MaxIter))
// Number of iterations expressed as UMIN isn't always great for expressing
// the value on the last iteration. If the straightforward approach didn't
// work, try the following trick: if the a predicate is invariant for X, it
// is also invariant for umin(X, ...). So try to find something that works
// among subexpressions of MaxIter expressed as umin.
for (auto *Op : UMin->operands())
if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
Pred, LHS, RHS, L, CtxI, Op))
return LIP;
return std::nullopt;
}
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantExitCondDuringFirstIterationsImpl(
CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
const Instruction *CtxI, const SCEV *MaxIter) {
// Try to prove the following set of facts:
// - The predicate is monotonic in the iteration space.
// - If the check does not fail on the 1st iteration:
// - No overflow will happen during first MaxIter iterations;
// - It will not fail on the MaxIter'th iteration.
// If the check does fail on the 1st iteration, we leave the loop and no
// other checks matter.
// If there is a loop-invariant, force it into the RHS, otherwise bail out.
if (!isLoopInvariant(RHS, L)) {
if (!isLoopInvariant(LHS, L))
return std::nullopt;
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
auto *AR = dyn_cast<SCEVAddRecExpr>(LHS);
if (!AR || AR->getLoop() != L)
return std::nullopt;
// The predicate must be relational (i.e. <, <=, >=, >).
if (!ICmpInst::isRelational(Pred))
return std::nullopt;
// TODO: Support steps other than +/- 1.
const SCEV *Step = AR->getStepRecurrence(*this);
auto *One = getOne(Step->getType());
auto *MinusOne = getNegativeSCEV(One);
if (Step != One && Step != MinusOne)
return std::nullopt;
// Type mismatch here means that MaxIter is potentially larger than max
// unsigned value in start type, which mean we cannot prove no wrap for the
// indvar.
if (AR->getType() != MaxIter->getType())
return std::nullopt;
// Value of IV on suggested last iteration.
const SCEV *Last = AR->evaluateAtIteration(MaxIter, *this);
// Does it still meet the requirement?
if (!isLoopBackedgeGuardedByCond(L, Pred, Last, RHS))
return std::nullopt;
// Because step is +/- 1 and MaxIter has same type as Start (i.e. it does
// not exceed max unsigned value of this type), this effectively proves
// that there is no wrap during the iteration. To prove that there is no
// signed/unsigned wrap, we need to check that
// Start <= Last for step = 1 or Start >= Last for step = -1.
ICmpInst::Predicate NoOverflowPred =
CmpInst::isSigned(Pred) ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
if (Step == MinusOne)
NoOverflowPred = ICmpInst::getSwappedCmpPredicate(NoOverflowPred);
const SCEV *Start = AR->getStart();
if (!isKnownPredicateAt(NoOverflowPred, Start, Last, CtxI))
return std::nullopt;
// Everything is fine.
return ScalarEvolution::LoopInvariantPredicate(Pred, Start, RHS);
}
bool ScalarEvolution::isKnownPredicateViaConstantRanges(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
if (HasSameValue(LHS, RHS))
return ICmpInst::isTrueWhenEqual(Pred);
// This code is split out from isKnownPredicate because it is called from
// within isLoopEntryGuardedByCond.
auto CheckRanges = [&](const ConstantRange &RangeLHS,
const ConstantRange &RangeRHS) {
return RangeLHS.icmp(Pred, RangeRHS);
};
// The check at the top of the function catches the case where the values are
// known to be equal.
if (Pred == CmpInst::ICMP_EQ)
return false;
if (Pred == CmpInst::ICMP_NE) {
auto SL = getSignedRange(LHS);
auto SR = getSignedRange(RHS);
if (CheckRanges(SL, SR))
return true;
auto UL = getUnsignedRange(LHS);
auto UR = getUnsignedRange(RHS);
if (CheckRanges(UL, UR))
return true;
auto *Diff = getMinusSCEV(LHS, RHS);
return !isa<SCEVCouldNotCompute>(Diff) && isKnownNonZero(Diff);
}
if (CmpInst::isSigned(Pred)) {
auto SL = getSignedRange(LHS);
auto SR = getSignedRange(RHS);
return CheckRanges(SL, SR);
}
auto UL = getUnsignedRange(LHS);
auto UR = getUnsignedRange(RHS);
return CheckRanges(UL, UR);
}
bool ScalarEvolution::isKnownPredicateViaNoOverflow(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
// Match X to (A + C1)<ExpectedFlags> and Y to (A + C2)<ExpectedFlags>, where
// C1 and C2 are constant integers. If either X or Y are not add expressions,
// consider them as X + 0 and Y + 0 respectively. C1 and C2 are returned via
// OutC1 and OutC2.
auto MatchBinaryAddToConst = [this](const SCEV *X, const SCEV *Y,
APInt &OutC1, APInt &OutC2,
SCEV::NoWrapFlags ExpectedFlags) {
const SCEV *XNonConstOp, *XConstOp;
const SCEV *YNonConstOp, *YConstOp;
SCEV::NoWrapFlags XFlagsPresent;
SCEV::NoWrapFlags YFlagsPresent;
if (!splitBinaryAdd(X, XConstOp, XNonConstOp, XFlagsPresent)) {
XConstOp = getZero(X->getType());
XNonConstOp = X;
XFlagsPresent = ExpectedFlags;
}
if (!isa<SCEVConstant>(XConstOp) ||
(XFlagsPresent & ExpectedFlags) != ExpectedFlags)
return false;
if (!splitBinaryAdd(Y, YConstOp, YNonConstOp, YFlagsPresent)) {
YConstOp = getZero(Y->getType());
YNonConstOp = Y;
YFlagsPresent = ExpectedFlags;
}
if (!isa<SCEVConstant>(YConstOp) ||
(YFlagsPresent & ExpectedFlags) != ExpectedFlags)
return false;
if (YNonConstOp != XNonConstOp)
return false;
OutC1 = cast<SCEVConstant>(XConstOp)->getAPInt();
OutC2 = cast<SCEVConstant>(YConstOp)->getAPInt();
return true;
};
APInt C1;
APInt C2;
switch (Pred) {
default:
break;
case ICmpInst::ICMP_SGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_SLE:
// (X + C1)<nsw> s<= (X + C2)<nsw> if C1 s<= C2.
if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNSW) && C1.sle(C2))
return true;
break;
case ICmpInst::ICMP_SGT:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_SLT:
// (X + C1)<nsw> s< (X + C2)<nsw> if C1 s< C2.
if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNSW) && C1.slt(C2))
return true;
break;
case ICmpInst::ICMP_UGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_ULE:
// (X + C1)<nuw> u<= (X + C2)<nuw> for C1 u<= C2.
if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNUW) && C1.ule(C2))
return true;
break;
case ICmpInst::ICMP_UGT:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_ULT:
// (X + C1)<nuw> u< (X + C2)<nuw> if C1 u< C2.
if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNUW) && C1.ult(C2))
return true;
break;
}
return false;
}
bool ScalarEvolution::isKnownPredicateViaSplitting(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
if (Pred != ICmpInst::ICMP_ULT || ProvingSplitPredicate)
return false;
// Allowing arbitrary number of activations of isKnownPredicateViaSplitting on
// the stack can result in exponential time complexity.
SaveAndRestore Restore(ProvingSplitPredicate, true);
// If L >= 0 then I `ult` L <=> I >= 0 && I `slt` L
//
// To prove L >= 0 we use isKnownNonNegative whereas to prove I >= 0 we use
// isKnownPredicate. isKnownPredicate is more powerful, but also more
// expensive; and using isKnownNonNegative(RHS) is sufficient for most of the
// interesting cases seen in practice. We can consider "upgrading" L >= 0 to
// use isKnownPredicate later if needed.
return isKnownNonNegative(RHS) &&
isKnownPredicate(CmpInst::ICMP_SGE, LHS, getZero(LHS->getType())) &&
isKnownPredicate(CmpInst::ICMP_SLT, LHS, RHS);
}
bool ScalarEvolution::isImpliedViaGuard(const BasicBlock *BB, CmpPredicate Pred,
const SCEV *LHS, const SCEV *RHS) {
// No need to even try if we know the module has no guards.
if (!HasGuards)
return false;
return any_of(*BB, [&](const Instruction &I) {
using namespace llvm::PatternMatch;
Value *Condition;
return match(&I, m_Intrinsic<Intrinsic::experimental_guard>(
m_Value(Condition))) &&
isImpliedCond(Pred, LHS, RHS, Condition, false);
});
}
/// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is
/// protected by a conditional between LHS and RHS. This is used to
/// to eliminate casts.
bool ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
// Interpret a null as meaning no loop, where there is obviously no guard
// (interprocedural conditions notwithstanding). Do not bother about
// unreachable loops.
if (!L || !DT.isReachableFromEntry(L->getHeader()))
return true;
if (VerifyIR)
assert(!verifyFunction(*L->getHeader()->getParent(), &dbgs()) &&
"This cannot be done on broken IR!");
if (isKnownViaNonRecursiveReasoning(Pred, LHS, RHS))
return true;
BasicBlock *Latch = L->getLoopLatch();
if (!Latch)
return false;
BranchInst *LoopContinuePredicate =
dyn_cast<BranchInst>(Latch->getTerminator());
if (LoopContinuePredicate && LoopContinuePredicate->isConditional() &&
isImpliedCond(Pred, LHS, RHS,
LoopContinuePredicate->getCondition(),
LoopContinuePredicate->getSuccessor(0) != L->getHeader()))
return true;
// We don't want more than one activation of the following loops on the stack
// -- that can lead to O(n!) time complexity.
if (WalkingBEDominatingConds)
return false;
SaveAndRestore ClearOnExit(WalkingBEDominatingConds, true);
// See if we can exploit a trip count to prove the predicate.
const auto &BETakenInfo = getBackedgeTakenInfo(L);
const SCEV *LatchBECount = BETakenInfo.getExact(Latch, this);
if (LatchBECount != getCouldNotCompute()) {
// We know that Latch branches back to the loop header exactly
// LatchBECount times. This means the backdege condition at Latch is
// equivalent to "{0,+,1} u< LatchBECount".
Type *Ty = LatchBECount->getType();
auto NoWrapFlags = SCEV::NoWrapFlags(SCEV::FlagNUW | SCEV::FlagNW);
const SCEV *LoopCounter =
getAddRecExpr(getZero(Ty), getOne(Ty), L, NoWrapFlags);
if (isImpliedCond(Pred, LHS, RHS, ICmpInst::ICMP_ULT, LoopCounter,
LatchBECount))
return true;
}
// Check conditions due to any @llvm.assume intrinsics.
for (auto &AssumeVH : AC.assumptions()) {
if (!AssumeVH)
continue;
auto *CI = cast<CallInst>(AssumeVH);
if (!DT.dominates(CI, Latch->getTerminator()))
continue;
if (isImpliedCond(Pred, LHS, RHS, CI->getArgOperand(0), false))
return true;
}
if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
return true;
for (DomTreeNode *DTN = DT[Latch], *HeaderDTN = DT[L->getHeader()];
DTN != HeaderDTN; DTN = DTN->getIDom()) {
assert(DTN && "should reach the loop header before reaching the root!");
BasicBlock *BB = DTN->getBlock();
if (isImpliedViaGuard(BB, Pred, LHS, RHS))
return true;
BasicBlock *PBB = BB->getSinglePredecessor();
if (!PBB)
continue;
BranchInst *ContinuePredicate = dyn_cast<BranchInst>(PBB->getTerminator());
if (!ContinuePredicate || !ContinuePredicate->isConditional())
continue;
Value *Condition = ContinuePredicate->getCondition();
// If we have an edge `E` within the loop body that dominates the only
// latch, the condition guarding `E` also guards the backedge. This
// reasoning works only for loops with a single latch.
BasicBlockEdge DominatingEdge(PBB, BB);
if (DominatingEdge.isSingleEdge()) {
// We're constructively (and conservatively) enumerating edges within the
// loop body that dominate the latch. The dominator tree better agree
// with us on this:
assert(DT.dominates(DominatingEdge, Latch) && "should be!");
if (isImpliedCond(Pred, LHS, RHS, Condition,
BB != ContinuePredicate->getSuccessor(0)))
return true;
}
}
return false;
}
bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
// Do not bother proving facts for unreachable code.
if (!DT.isReachableFromEntry(BB))
return true;
if (VerifyIR)
assert(!verifyFunction(*BB->getParent(), &dbgs()) &&
"This cannot be done on broken IR!");
// If we cannot prove strict comparison (e.g. a > b), maybe we can prove
// the facts (a >= b && a != b) separately. A typical situation is when the
// non-strict comparison is known from ranges and non-equality is known from
// dominating predicates. If we are proving strict comparison, we always try
// to prove non-equality and non-strict comparison separately.
CmpPredicate NonStrictPredicate = ICmpInst::getNonStrictCmpPredicate(Pred);
const bool ProvingStrictComparison =
Pred != NonStrictPredicate.dropSameSign();
bool ProvedNonStrictComparison = false;
bool ProvedNonEquality = false;
auto SplitAndProve = [&](std::function<bool(CmpPredicate)> Fn) -> bool {
if (!ProvedNonStrictComparison)
ProvedNonStrictComparison = Fn(NonStrictPredicate);
if (!ProvedNonEquality)
ProvedNonEquality = Fn(ICmpInst::ICMP_NE);
if (ProvedNonStrictComparison && ProvedNonEquality)
return true;
return false;
};
if (ProvingStrictComparison) {
auto ProofFn = [&](CmpPredicate P) {
return isKnownViaNonRecursiveReasoning(P, LHS, RHS);
};
if (SplitAndProve(ProofFn))
return true;
}
// Try to prove (Pred, LHS, RHS) using isImpliedCond.
auto ProveViaCond = [&](const Value *Condition, bool Inverse) {
const Instruction *CtxI = &BB->front();
if (isImpliedCond(Pred, LHS, RHS, Condition, Inverse, CtxI))
return true;
if (ProvingStrictComparison) {
auto ProofFn = [&](CmpPredicate P) {
return isImpliedCond(P, LHS, RHS, Condition, Inverse, CtxI);
};
if (SplitAndProve(ProofFn))
return true;
}
return false;
};
// Starting at the block's predecessor, climb up the predecessor chain, as long
// as there are predecessors that can be found that have unique successors
// leading to the original block.
const Loop *ContainingLoop = LI.getLoopFor(BB);
const BasicBlock *PredBB;
if (ContainingLoop && ContainingLoop->getHeader() == BB)
PredBB = ContainingLoop->getLoopPredecessor();
else
PredBB = BB->getSinglePredecessor();
for (std::pair<const BasicBlock *, const BasicBlock *> Pair(PredBB, BB);
Pair.first; Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
const BranchInst *BlockEntryPredicate =
dyn_cast<BranchInst>(Pair.first->getTerminator());
if (!BlockEntryPredicate || BlockEntryPredicate->isUnconditional())
continue;
if (ProveViaCond(BlockEntryPredicate->getCondition(),
BlockEntryPredicate->getSuccessor(0) != Pair.second))
return true;
}
// Check conditions due to any @llvm.assume intrinsics.
for (auto &AssumeVH : AC.assumptions()) {
if (!AssumeVH)
continue;
auto *CI = cast<CallInst>(AssumeVH);
if (!DT.dominates(CI, BB))
continue;
if (ProveViaCond(CI->getArgOperand(0), false))
return true;
}
// Check conditions due to any @llvm.experimental.guard intrinsics.
auto *GuardDecl = Intrinsic::getDeclarationIfExists(
F.getParent(), Intrinsic::experimental_guard);
if (GuardDecl)
for (const auto *GU : GuardDecl->users())
if (const auto *Guard = dyn_cast<IntrinsicInst>(GU))
if (Guard->getFunction() == BB->getParent() && DT.dominates(Guard, BB))
if (ProveViaCond(Guard->getArgOperand(0), false))
return true;
return false;
}
bool ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L, CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
// Interpret a null as meaning no loop, where there is obviously no guard
// (interprocedural conditions notwithstanding).
if (!L)
return false;
// Both LHS and RHS must be available at loop entry.
assert(isAvailableAtLoopEntry(LHS, L) &&
"LHS is not available at Loop Entry");
assert(isAvailableAtLoopEntry(RHS, L) &&
"RHS is not available at Loop Entry");
if (isKnownViaNonRecursiveReasoning(Pred, LHS, RHS))
return true;
return isBasicBlockEntryGuardedByCond(L->getHeader(), Pred, LHS, RHS);
}
bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS,
const Value *FoundCondValue, bool Inverse,
const Instruction *CtxI) {
// False conditions implies anything. Do not bother analyzing it further.
if (FoundCondValue ==
ConstantInt::getBool(FoundCondValue->getContext(), Inverse))
return true;
if (!PendingLoopPredicates.insert(FoundCondValue).second)
return false;
auto ClearOnExit =
make_scope_exit([&]() { PendingLoopPredicates.erase(FoundCondValue); });
// Recursively handle And and Or conditions.
const Value *Op0, *Op1;
if (match(FoundCondValue, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
if (!Inverse)
return isImpliedCond(Pred, LHS, RHS, Op0, Inverse, CtxI) ||
isImpliedCond(Pred, LHS, RHS, Op1, Inverse, CtxI);
} else if (match(FoundCondValue, m_LogicalOr(m_Value(Op0), m_Value(Op1)))) {
if (Inverse)
return isImpliedCond(Pred, LHS, RHS, Op0, Inverse, CtxI) ||
isImpliedCond(Pred, LHS, RHS, Op1, Inverse, CtxI);
}
const ICmpInst *ICI = dyn_cast<ICmpInst>(FoundCondValue);
if (!ICI) return false;
// Now that we found a conditional branch that dominates the loop or controls
// the loop latch. Check to see if it is the comparison we are looking for.
CmpPredicate FoundPred;
if (Inverse)
FoundPred = ICI->getInverseCmpPredicate();
else
FoundPred = ICI->getCmpPredicate();
const SCEV *FoundLHS = getSCEV(ICI->getOperand(0));
const SCEV *FoundRHS = getSCEV(ICI->getOperand(1));
return isImpliedCond(Pred, LHS, RHS, FoundPred, FoundLHS, FoundRHS, CtxI);
}
bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS, CmpPredicate FoundPred,
const SCEV *FoundLHS, const SCEV *FoundRHS,
const Instruction *CtxI) {
// Balance the types.
if (getTypeSizeInBits(LHS->getType()) <
getTypeSizeInBits(FoundLHS->getType())) {
// For unsigned and equality predicates, try to prove that both found
// operands fit into narrow unsigned range. If so, try to prove facts in
// narrow types.
if (!CmpInst::isSigned(FoundPred) && !FoundLHS->getType()->isPointerTy() &&
!FoundRHS->getType()->isPointerTy()) {
auto *NarrowType = LHS->getType();
auto *WideType = FoundLHS->getType();
auto BitWidth = getTypeSizeInBits(NarrowType);
const SCEV *MaxValue = getZeroExtendExpr(
getConstant(APInt::getMaxValue(BitWidth)), WideType);
if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundLHS,
MaxValue) &&
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundRHS,
MaxValue)) {
const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
// We cannot preserve samesign after truncation.
if (isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred.dropSameSign(),
TruncFoundLHS, TruncFoundRHS, CtxI))
return true;
}
}
if (LHS->getType()->isPointerTy() || RHS->getType()->isPointerTy())
return false;
if (CmpInst::isSigned(Pred)) {
LHS = getSignExtendExpr(LHS, FoundLHS->getType());
RHS = getSignExtendExpr(RHS, FoundLHS->getType());
} else {
LHS = getZeroExtendExpr(LHS, FoundLHS->getType());
RHS = getZeroExtendExpr(RHS, FoundLHS->getType());
}
} else if (getTypeSizeInBits(LHS->getType()) >
getTypeSizeInBits(FoundLHS->getType())) {
if (FoundLHS->getType()->isPointerTy() || FoundRHS->getType()->isPointerTy())
return false;
if (CmpInst::isSigned(FoundPred)) {
FoundLHS = getSignExtendExpr(FoundLHS, LHS->getType());
FoundRHS = getSignExtendExpr(FoundRHS, LHS->getType());
} else {
FoundLHS = getZeroExtendExpr(FoundLHS, LHS->getType());
FoundRHS = getZeroExtendExpr(FoundRHS, LHS->getType());
}
}
return isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred, FoundLHS,
FoundRHS, CtxI);
}
bool ScalarEvolution::isImpliedCondBalancedTypes(
CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, CmpPredicate FoundPred,
const SCEV *FoundLHS, const SCEV *FoundRHS, const Instruction *CtxI) {
assert(getTypeSizeInBits(LHS->getType()) ==
getTypeSizeInBits(FoundLHS->getType()) &&
"Types should be balanced!");
// Canonicalize the query to match the way instcombine will have
// canonicalized the comparison.
if (SimplifyICmpOperands(Pred, LHS, RHS))
if (LHS == RHS)
return CmpInst::isTrueWhenEqual(Pred);
if (SimplifyICmpOperands(FoundPred, FoundLHS, FoundRHS))
if (FoundLHS == FoundRHS)
return CmpInst::isFalseWhenEqual(FoundPred);
// Check to see if we can make the LHS or RHS match.
if (LHS == FoundRHS || RHS == FoundLHS) {
if (isa<SCEVConstant>(RHS)) {
std::swap(FoundLHS, FoundRHS);
FoundPred = ICmpInst::getSwappedCmpPredicate(FoundPred);
} else {
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
}
// Check whether the found predicate is the same as the desired predicate.
if (auto P = CmpPredicate::getMatching(FoundPred, Pred))
return isImpliedCondOperands(*P, LHS, RHS, FoundLHS, FoundRHS, CtxI);
// Check whether swapping the found predicate makes it the same as the
// desired predicate.
if (auto P = CmpPredicate::getMatching(
ICmpInst::getSwappedCmpPredicate(FoundPred), Pred)) {
// We can write the implication
// 0. LHS Pred RHS <- FoundLHS SwapPred FoundRHS
// using one of the following ways:
// 1. LHS Pred RHS <- FoundRHS Pred FoundLHS
// 2. RHS SwapPred LHS <- FoundLHS SwapPred FoundRHS
// 3. LHS Pred RHS <- ~FoundLHS Pred ~FoundRHS
// 4. ~LHS SwapPred ~RHS <- FoundLHS SwapPred FoundRHS
// Forms 1. and 2. require swapping the operands of one condition. Don't
// do this if it would break canonical constant/addrec ordering.
if (!isa<SCEVConstant>(RHS) && !isa<SCEVAddRecExpr>(LHS))
return isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(*P), RHS,
LHS, FoundLHS, FoundRHS, CtxI);
if (!isa<SCEVConstant>(FoundRHS) && !isa<SCEVAddRecExpr>(FoundLHS))
return isImpliedCondOperands(*P, LHS, RHS, FoundRHS, FoundLHS, CtxI);
// There's no clear preference between forms 3. and 4., try both. Avoid
// forming getNotSCEV of pointer values as the resulting subtract is
// not legal.
if (!LHS->getType()->isPointerTy() && !RHS->getType()->isPointerTy() &&
isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(*P),
getNotSCEV(LHS), getNotSCEV(RHS), FoundLHS,
FoundRHS, CtxI))
return true;
if (!FoundLHS->getType()->isPointerTy() &&
!FoundRHS->getType()->isPointerTy() &&
isImpliedCondOperands(*P, LHS, RHS, getNotSCEV(FoundLHS),
getNotSCEV(FoundRHS), CtxI))
return true;
return false;
}
auto IsSignFlippedPredicate = [](CmpInst::Predicate P1,
CmpInst::Predicate P2) {
assert(P1 != P2 && "Handled earlier!");
return CmpInst::isRelational(P2) &&
P1 == ICmpInst::getFlippedSignednessPredicate(P2);
};
if (IsSignFlippedPredicate(Pred, FoundPred)) {
// Unsigned comparison is the same as signed comparison when both the
// operands are non-negative or negative.
if ((isKnownNonNegative(FoundLHS) && isKnownNonNegative(FoundRHS)) ||
(isKnownNegative(FoundLHS) && isKnownNegative(FoundRHS)))
return isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS, CtxI);
// Create local copies that we can freely swap and canonicalize our
// conditions to "le/lt".
CmpPredicate CanonicalPred = Pred, CanonicalFoundPred = FoundPred;
const SCEV *CanonicalLHS = LHS, *CanonicalRHS = RHS,
*CanonicalFoundLHS = FoundLHS, *CanonicalFoundRHS = FoundRHS;
if (ICmpInst::isGT(CanonicalPred) || ICmpInst::isGE(CanonicalPred)) {
CanonicalPred = ICmpInst::getSwappedCmpPredicate(CanonicalPred);
CanonicalFoundPred = ICmpInst::getSwappedCmpPredicate(CanonicalFoundPred);
std::swap(CanonicalLHS, CanonicalRHS);
std::swap(CanonicalFoundLHS, CanonicalFoundRHS);
}
assert((ICmpInst::isLT(CanonicalPred) || ICmpInst::isLE(CanonicalPred)) &&
"Must be!");
assert((ICmpInst::isLT(CanonicalFoundPred) ||
ICmpInst::isLE(CanonicalFoundPred)) &&
"Must be!");
if (ICmpInst::isSigned(CanonicalPred) && isKnownNonNegative(CanonicalRHS))
// Use implication:
// x <u y && y >=s 0 --> x <s y.
// If we can prove the left part, the right part is also proven.
return isImpliedCondOperands(CanonicalFoundPred, CanonicalLHS,
CanonicalRHS, CanonicalFoundLHS,
CanonicalFoundRHS);
if (ICmpInst::isUnsigned(CanonicalPred) && isKnownNegative(CanonicalRHS))
// Use implication:
// x <s y && y <s 0 --> x <u y.
// If we can prove the left part, the right part is also proven.
return isImpliedCondOperands(CanonicalFoundPred, CanonicalLHS,
CanonicalRHS, CanonicalFoundLHS,
CanonicalFoundRHS);
}
// Check if we can make progress by sharpening ranges.
if (FoundPred == ICmpInst::ICMP_NE &&
(isa<SCEVConstant>(FoundLHS) || isa<SCEVConstant>(FoundRHS))) {
const SCEVConstant *C = nullptr;
const SCEV *V = nullptr;
if (isa<SCEVConstant>(FoundLHS)) {
C = cast<SCEVConstant>(FoundLHS);
V = FoundRHS;
} else {
C = cast<SCEVConstant>(FoundRHS);
V = FoundLHS;
}
// The guarding predicate tells us that C != V. If the known range
// of V is [C, t), we can sharpen the range to [C + 1, t). The
// range we consider has to correspond to same signedness as the
// predicate we're interested in folding.
APInt Min = ICmpInst::isSigned(Pred) ?
getSignedRangeMin(V) : getUnsignedRangeMin(V);
if (Min == C->getAPInt()) {
// Given (V >= Min && V != Min) we conclude V >= (Min + 1).
// This is true even if (Min + 1) wraps around -- in case of
// wraparound, (Min + 1) < Min, so (V >= Min => V >= (Min + 1)).
APInt SharperMin = Min + 1;
switch (Pred) {
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGE:
// We know V `Pred` SharperMin. If this implies LHS `Pred`
// RHS, we're done.
if (isImpliedCondOperands(Pred, LHS, RHS, V, getConstant(SharperMin),
CtxI))
return true;
[[fallthrough]];
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_UGT:
// We know from the range information that (V `Pred` Min ||
// V == Min). We know from the guarding condition that !(V
// == Min). This gives us
//
// V `Pred` Min || V == Min && !(V == Min)
// => V `Pred` Min
//
// If V `Pred` Min implies LHS `Pred` RHS, we're done.
if (isImpliedCondOperands(Pred, LHS, RHS, V, getConstant(Min), CtxI))
return true;
break;
// `LHS < RHS` and `LHS <= RHS` are handled in the same way as `RHS > LHS` and `RHS >= LHS` respectively.
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULE:
if (isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(Pred), RHS,
LHS, V, getConstant(SharperMin), CtxI))
return true;
[[fallthrough]];
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_ULT:
if (isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(Pred), RHS,
LHS, V, getConstant(Min), CtxI))
return true;
break;
default:
// No change
break;
}
}
}
// Check whether the actual condition is beyond sufficient.
if (FoundPred == ICmpInst::ICMP_EQ)
if (ICmpInst::isTrueWhenEqual(Pred))
if (isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
return true;
if (Pred == ICmpInst::ICMP_NE)
if (!ICmpInst::isTrueWhenEqual(FoundPred))
if (isImpliedCondOperands(FoundPred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
return true;
if (isImpliedCondOperandsViaRanges(Pred, LHS, RHS, FoundPred, FoundLHS, FoundRHS))
return true;
// Otherwise assume the worst.
return false;
}
bool ScalarEvolution::splitBinaryAdd(const SCEV *Expr,
const SCEV *&L, const SCEV *&R,
SCEV::NoWrapFlags &Flags) {
const auto *AE = dyn_cast<SCEVAddExpr>(Expr);
if (!AE || AE->getNumOperands() != 2)
return false;
L = AE->getOperand(0);
R = AE->getOperand(1);
Flags = AE->getNoWrapFlags();
return true;
}
std::optional<APInt>
ScalarEvolution::computeConstantDifference(const SCEV *More, const SCEV *Less) {
// We avoid subtracting expressions here because this function is usually
// fairly deep in the call stack (i.e. is called many times).
unsigned BW = getTypeSizeInBits(More->getType());
APInt Diff(BW, 0);
APInt DiffMul(BW, 1);
// Try various simplifications to reduce the difference to a constant. Limit
// the number of allowed simplifications to keep compile-time low.
for (unsigned I = 0; I < 8; ++I) {
if (More == Less)
return Diff;
// Reduce addrecs with identical steps to their start value.
if (isa<SCEVAddRecExpr>(Less) && isa<SCEVAddRecExpr>(More)) {
const auto *LAR = cast<SCEVAddRecExpr>(Less);
const auto *MAR = cast<SCEVAddRecExpr>(More);
if (LAR->getLoop() != MAR->getLoop())
return std::nullopt;
// We look at affine expressions only; not for correctness but to keep
// getStepRecurrence cheap.
if (!LAR->isAffine() || !MAR->isAffine())
return std::nullopt;
if (LAR->getStepRecurrence(*this) != MAR->getStepRecurrence(*this))
return std::nullopt;
Less = LAR->getStart();
More = MAR->getStart();
continue;
}
// Try to match a common constant multiply.
auto MatchConstMul =
[](const SCEV *S) -> std::optional<std::pair<const SCEV *, APInt>> {
auto *M = dyn_cast<SCEVMulExpr>(S);
if (!M || M->getNumOperands() != 2 ||
!isa<SCEVConstant>(M->getOperand(0)))
return std::nullopt;
return {
{M->getOperand(1), cast<SCEVConstant>(M->getOperand(0))->getAPInt()}};
};
if (auto MatchedMore = MatchConstMul(More)) {
if (auto MatchedLess = MatchConstMul(Less)) {
if (MatchedMore->second == MatchedLess->second) {
More = MatchedMore->first;
Less = MatchedLess->first;
DiffMul *= MatchedMore->second;
continue;
}
}
}
// Try to cancel out common factors in two add expressions.
SmallDenseMap<const SCEV *, int, 8> Multiplicity;
auto Add = [&](const SCEV *S, int Mul) {
if (auto *C = dyn_cast<SCEVConstant>(S)) {
if (Mul == 1) {
Diff += C->getAPInt() * DiffMul;
} else {
assert(Mul == -1);
Diff -= C->getAPInt() * DiffMul;
}
} else
Multiplicity[S] += Mul;
};
auto Decompose = [&](const SCEV *S, int Mul) {
if (isa<SCEVAddExpr>(S)) {
for (const SCEV *Op : S->operands())
Add(Op, Mul);
} else
Add(S, Mul);
};
Decompose(More, 1);
Decompose(Less, -1);
// Check whether all the non-constants cancel out, or reduce to new
// More/Less values.
const SCEV *NewMore = nullptr, *NewLess = nullptr;
for (const auto &[S, Mul] : Multiplicity) {
if (Mul == 0)
continue;
if (Mul == 1) {
if (NewMore)
return std::nullopt;
NewMore = S;
} else if (Mul == -1) {
if (NewLess)
return std::nullopt;
NewLess = S;
} else
return std::nullopt;
}
// Values stayed the same, no point in trying further.
if (NewMore == More || NewLess == Less)
return std::nullopt;
More = NewMore;
Less = NewLess;
// Reduced to constant.
if (!More && !Less)
return Diff;
// Left with variable on only one side, bail out.
if (!More || !Less)
return std::nullopt;
}
// Did not reduce to constant.
return std::nullopt;
}
bool ScalarEvolution::isImpliedCondOperandsViaAddRecStart(
CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const SCEV *FoundLHS,
const SCEV *FoundRHS, const Instruction *CtxI) {
// Try to recognize the following pattern:
//
// FoundRHS = ...
// ...
// loop:
// FoundLHS = {Start,+,W}
// context_bb: // Basic block from the same loop
// known(Pred, FoundLHS, FoundRHS)
//
// If some predicate is known in the context of a loop, it is also known on
// each iteration of this loop, including the first iteration. Therefore, in
// this case, `FoundLHS Pred FoundRHS` implies `Start Pred FoundRHS`. Try to
// prove the original pred using this fact.
if (!CtxI)
return false;
const BasicBlock *ContextBB = CtxI->getParent();
// Make sure AR varies in the context block.
if (auto *AR = dyn_cast<SCEVAddRecExpr>(FoundLHS)) {
const Loop *L = AR->getLoop();
// Make sure that context belongs to the loop and executes on 1st iteration
// (if it ever executes at all).
if (!L->contains(ContextBB) || !DT.dominates(ContextBB, L->getLoopLatch()))
return false;
if (!isAvailableAtLoopEntry(FoundRHS, AR->getLoop()))
return false;
return isImpliedCondOperands(Pred, LHS, RHS, AR->getStart(), FoundRHS);
}
if (auto *AR = dyn_cast<SCEVAddRecExpr>(FoundRHS)) {
const Loop *L = AR->getLoop();
// Make sure that context belongs to the loop and executes on 1st iteration
// (if it ever executes at all).
if (!L->contains(ContextBB) || !DT.dominates(ContextBB, L->getLoopLatch()))
return false;
if (!isAvailableAtLoopEntry(FoundLHS, AR->getLoop()))
return false;
return isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, AR->getStart());
}
return false;
}
bool ScalarEvolution::isImpliedCondOperandsViaNoOverflow(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS,
const SCEV *FoundLHS,
const SCEV *FoundRHS) {
if (Pred != CmpInst::ICMP_SLT && Pred != CmpInst::ICMP_ULT)
return false;
const auto *AddRecLHS = dyn_cast<SCEVAddRecExpr>(LHS);
if (!AddRecLHS)
return false;
const auto *AddRecFoundLHS = dyn_cast<SCEVAddRecExpr>(FoundLHS);
if (!AddRecFoundLHS)
return false;
// We'd like to let SCEV reason about control dependencies, so we constrain
// both the inequalities to be about add recurrences on the same loop. This
// way we can use isLoopEntryGuardedByCond later.
const Loop *L = AddRecFoundLHS->getLoop();
if (L != AddRecLHS->getLoop())
return false;
// FoundLHS u< FoundRHS u< -C => (FoundLHS + C) u< (FoundRHS + C) ... (1)
//
// FoundLHS s< FoundRHS s< INT_MIN - C => (FoundLHS + C) s< (FoundRHS + C)
// ... (2)
//
// Informal proof for (2), assuming (1) [*]:
//
// We'll also assume (A s< B) <=> ((A + INT_MIN) u< (B + INT_MIN)) ... (3)[**]
//
// Then
//
// FoundLHS s< FoundRHS s< INT_MIN - C
// <=> (FoundLHS + INT_MIN) u< (FoundRHS + INT_MIN) u< -C [ using (3) ]
// <=> (FoundLHS + INT_MIN + C) u< (FoundRHS + INT_MIN + C) [ using (1) ]
// <=> (FoundLHS + INT_MIN + C + INT_MIN) s<
// (FoundRHS + INT_MIN + C + INT_MIN) [ using (3) ]
// <=> FoundLHS + C s< FoundRHS + C
//
// [*]: (1) can be proved by ruling out overflow.
//
// [**]: This can be proved by analyzing all the four possibilities:
// (A s< 0, B s< 0), (A s< 0, B s>= 0), (A s>= 0, B s< 0) and
// (A s>= 0, B s>= 0).
//
// Note:
// Despite (2), "FoundRHS s< INT_MIN - C" does not mean that "FoundRHS + C"
// will not sign underflow. For instance, say FoundLHS = (i8 -128), FoundRHS
// = (i8 -127) and C = (i8 -100). Then INT_MIN - C = (i8 -28), and FoundRHS
// s< (INT_MIN - C). Lack of sign overflow / underflow in "FoundRHS + C" is
// neither necessary nor sufficient to prove "(FoundLHS + C) s< (FoundRHS +
// C)".
std::optional<APInt> LDiff = computeConstantDifference(LHS, FoundLHS);
if (!LDiff)
return false;
std::optional<APInt> RDiff = computeConstantDifference(RHS, FoundRHS);
if (!RDiff || *LDiff != *RDiff)
return false;
if (LDiff->isMinValue())
return true;
APInt FoundRHSLimit;
if (Pred == CmpInst::ICMP_ULT) {
FoundRHSLimit = -(*RDiff);
} else {
assert(Pred == CmpInst::ICMP_SLT && "Checked above!");
FoundRHSLimit = APInt::getSignedMinValue(getTypeSizeInBits(RHS->getType())) - *RDiff;
}
// Try to prove (1) or (2), as needed.
return isAvailableAtLoopEntry(FoundRHS, L) &&
isLoopEntryGuardedByCond(L, Pred, FoundRHS,
getConstant(FoundRHSLimit));
}
bool ScalarEvolution::isImpliedViaMerge(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS, const SCEV *FoundLHS,
const SCEV *FoundRHS, unsigned Depth) {
const PHINode *LPhi = nullptr, *RPhi = nullptr;
auto ClearOnExit = make_scope_exit([&]() {
if (LPhi) {
bool Erased = PendingMerges.erase(LPhi);
assert(Erased && "Failed to erase LPhi!");
(void)Erased;
}
if (RPhi) {
bool Erased = PendingMerges.erase(RPhi);
assert(Erased && "Failed to erase RPhi!");
(void)Erased;
}
});
// Find respective Phis and check that they are not being pending.
if (const SCEVUnknown *LU = dyn_cast<SCEVUnknown>(LHS))
if (auto *Phi = dyn_cast<PHINode>(LU->getValue())) {
if (!PendingMerges.insert(Phi).second)
return false;
LPhi = Phi;
}
if (const SCEVUnknown *RU = dyn_cast<SCEVUnknown>(RHS))
if (auto *Phi = dyn_cast<PHINode>(RU->getValue())) {
// If we detect a loop of Phi nodes being processed by this method, for
// example:
//
// %a = phi i32 [ %some1, %preheader ], [ %b, %latch ]
// %b = phi i32 [ %some2, %preheader ], [ %a, %latch ]
//
// we don't want to deal with a case that complex, so return conservative
// answer false.
if (!PendingMerges.insert(Phi).second)
return false;
RPhi = Phi;
}
// If none of LHS, RHS is a Phi, nothing to do here.
if (!LPhi && !RPhi)
return false;
// If there is a SCEVUnknown Phi we are interested in, make it left.
if (!LPhi) {
std::swap(LHS, RHS);
std::swap(FoundLHS, FoundRHS);
std::swap(LPhi, RPhi);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
assert(LPhi && "LPhi should definitely be a SCEVUnknown Phi!");
const BasicBlock *LBB = LPhi->getParent();
const SCEVAddRecExpr *RAR = dyn_cast<SCEVAddRecExpr>(RHS);
auto ProvedEasily = [&](const SCEV *S1, const SCEV *S2) {
return isKnownViaNonRecursiveReasoning(Pred, S1, S2) ||
isImpliedCondOperandsViaRanges(Pred, S1, S2, Pred, FoundLHS, FoundRHS) ||
isImpliedViaOperations(Pred, S1, S2, FoundLHS, FoundRHS, Depth);
};
if (RPhi && RPhi->getParent() == LBB) {
// Case one: RHS is also a SCEVUnknown Phi from the same basic block.
// If we compare two Phis from the same block, and for each entry block
// the predicate is true for incoming values from this block, then the
// predicate is also true for the Phis.
for (const BasicBlock *IncBB : predecessors(LBB)) {
const SCEV *L = getSCEV(LPhi->getIncomingValueForBlock(IncBB));
const SCEV *R = getSCEV(RPhi->getIncomingValueForBlock(IncBB));
if (!ProvedEasily(L, R))
return false;
}
} else if (RAR && RAR->getLoop()->getHeader() == LBB) {
// Case two: RHS is also a Phi from the same basic block, and it is an
// AddRec. It means that there is a loop which has both AddRec and Unknown
// PHIs, for it we can compare incoming values of AddRec from above the loop
// and latch with their respective incoming values of LPhi.
// TODO: Generalize to handle loops with many inputs in a header.
if (LPhi->getNumIncomingValues() != 2) return false;
auto *RLoop = RAR->getLoop();
auto *Predecessor = RLoop->getLoopPredecessor();
assert(Predecessor && "Loop with AddRec with no predecessor?");
const SCEV *L1 = getSCEV(LPhi->getIncomingValueForBlock(Predecessor));
if (!ProvedEasily(L1, RAR->getStart()))
return false;
auto *Latch = RLoop->getLoopLatch();
assert(Latch && "Loop with AddRec with no latch?");
const SCEV *L2 = getSCEV(LPhi->getIncomingValueForBlock(Latch));
if (!ProvedEasily(L2, RAR->getPostIncExpr(*this)))
return false;
} else {
// In all other cases go over inputs of LHS and compare each of them to RHS,
// the predicate is true for (LHS, RHS) if it is true for all such pairs.
// At this point RHS is either a non-Phi, or it is a Phi from some block
// different from LBB.
for (const BasicBlock *IncBB : predecessors(LBB)) {
// Check that RHS is available in this block.
if (!dominates(RHS, IncBB))
return false;
const SCEV *L = getSCEV(LPhi->getIncomingValueForBlock(IncBB));
// Make sure L does not refer to a value from a potentially previous
// iteration of a loop.
if (!properlyDominates(L, LBB))
return false;
// Addrecs are considered to properly dominate their loop, so are missed
// by the previous check. Discard any values that have computable
// evolution in this loop.
if (auto *Loop = LI.getLoopFor(LBB))
if (hasComputableLoopEvolution(L, Loop))
return false;
if (!ProvedEasily(L, RHS))
return false;
}
}
return true;
}
bool ScalarEvolution::isImpliedCondOperandsViaShift(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS,
const SCEV *FoundLHS,
const SCEV *FoundRHS) {
// We want to imply LHS < RHS from LHS < (RHS >> shiftvalue). First, make
// sure that we are dealing with same LHS.
if (RHS == FoundRHS) {
std::swap(LHS, RHS);
std::swap(FoundLHS, FoundRHS);
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
}
if (LHS != FoundLHS)
return false;
auto *SUFoundRHS = dyn_cast<SCEVUnknown>(FoundRHS);
if (!SUFoundRHS)
return false;
Value *Shiftee, *ShiftValue;
using namespace PatternMatch;
if (match(SUFoundRHS->getValue(),
m_LShr(m_Value(Shiftee), m_Value(ShiftValue)))) {
auto *ShifteeS = getSCEV(Shiftee);
// Prove one of the following:
// LHS <u (shiftee >> shiftvalue) && shiftee <=u RHS ---> LHS <u RHS
// LHS <=u (shiftee >> shiftvalue) && shiftee <=u RHS ---> LHS <=u RHS
// LHS <s (shiftee >> shiftvalue) && shiftee <=s RHS && shiftee >=s 0
// ---> LHS <s RHS
// LHS <=s (shiftee >> shiftvalue) && shiftee <=s RHS && shiftee >=s 0
// ---> LHS <=s RHS
if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE)
return isKnownPredicate(ICmpInst::ICMP_ULE, ShifteeS, RHS);
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
if (isKnownNonNegative(ShifteeS))
return isKnownPredicate(ICmpInst::ICMP_SLE, ShifteeS, RHS);
}
return false;
}
bool ScalarEvolution::isImpliedCondOperands(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS,
const SCEV *FoundLHS,
const SCEV *FoundRHS,
const Instruction *CtxI) {
if (isImpliedCondOperandsViaRanges(Pred, LHS, RHS, Pred, FoundLHS, FoundRHS))
return true;
if (isImpliedCondOperandsViaNoOverflow(Pred, LHS, RHS, FoundLHS, FoundRHS))
return true;
if (isImpliedCondOperandsViaShift(Pred, LHS, RHS, FoundLHS, FoundRHS))
return true;
if (isImpliedCondOperandsViaAddRecStart(Pred, LHS, RHS, FoundLHS, FoundRHS,
CtxI))
return true;
return isImpliedCondOperandsHelper(Pred, LHS, RHS,
FoundLHS, FoundRHS);
}
/// Is MaybeMinMaxExpr an (U|S)(Min|Max) of Candidate and some other values?
template <typename MinMaxExprType>
static bool IsMinMaxConsistingOf(const SCEV *MaybeMinMaxExpr,
const SCEV *Candidate) {
const MinMaxExprType *MinMaxExpr = dyn_cast<MinMaxExprType>(MaybeMinMaxExpr);
if (!MinMaxExpr)
return false;
return is_contained(MinMaxExpr->operands(), Candidate);
}
static bool IsKnownPredicateViaAddRecStart(ScalarEvolution &SE,
CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS) {
// If both sides are affine addrecs for the same loop, with equal
// steps, and we know the recurrences don't wrap, then we only
// need to check the predicate on the starting values.
if (!ICmpInst::isRelational(Pred))
return false;
const SCEVAddRecExpr *LAR = dyn_cast<SCEVAddRecExpr>(LHS);
if (!LAR)
return false;
const SCEVAddRecExpr *RAR = dyn_cast<SCEVAddRecExpr>(RHS);
if (!RAR)
return false;
if (LAR->getLoop() != RAR->getLoop())
return false;
if (!LAR->isAffine() || !RAR->isAffine())
return false;
if (LAR->getStepRecurrence(SE) != RAR->getStepRecurrence(SE))
return false;
SCEV::NoWrapFlags NW = ICmpInst::isSigned(Pred) ?
SCEV::FlagNSW : SCEV::FlagNUW;
if (!LAR->getNoWrapFlags(NW) || !RAR->getNoWrapFlags(NW))
return false;
return SE.isKnownPredicate(Pred, LAR->getStart(), RAR->getStart());
}
/// Is LHS `Pred` RHS true on the virtue of LHS or RHS being a Min or Max
/// expression?
static bool IsKnownPredicateViaMinOrMax(ScalarEvolution &SE, CmpPredicate Pred,
const SCEV *LHS, const SCEV *RHS) {
switch (Pred) {
default:
return false;
case ICmpInst::ICMP_SGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_SLE:
return
// min(A, ...) <= A
IsMinMaxConsistingOf<SCEVSMinExpr>(LHS, RHS) ||
// A <= max(A, ...)
IsMinMaxConsistingOf<SCEVSMaxExpr>(RHS, LHS);
case ICmpInst::ICMP_UGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_ULE:
return
// min(A, ...) <= A
// FIXME: what about umin_seq?
IsMinMaxConsistingOf<SCEVUMinExpr>(LHS, RHS) ||
// A <= max(A, ...)
IsMinMaxConsistingOf<SCEVUMaxExpr>(RHS, LHS);
}
llvm_unreachable("covered switch fell through?!");
}
bool ScalarEvolution::isImpliedViaOperations(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS,
const SCEV *FoundLHS,
const SCEV *FoundRHS,
unsigned Depth) {
assert(getTypeSizeInBits(LHS->getType()) ==
getTypeSizeInBits(RHS->getType()) &&
"LHS and RHS have different sizes?");
assert(getTypeSizeInBits(FoundLHS->getType()) ==
getTypeSizeInBits(FoundRHS->getType()) &&
"FoundLHS and FoundRHS have different sizes?");
// We want to avoid hurting the compile time with analysis of too big trees.
if (Depth > MaxSCEVOperationsImplicationDepth)
return false;
// We only want to work with GT comparison so far.
if (ICmpInst::isLT(Pred)) {
Pred = ICmpInst::getSwappedCmpPredicate(Pred);
std::swap(LHS, RHS);
std::swap(FoundLHS, FoundRHS);
}
CmpInst::Predicate P = Pred.getPreferredSignedPredicate();
// For unsigned, try to reduce it to corresponding signed comparison.
if (P == ICmpInst::ICMP_UGT)
// We can replace unsigned predicate with its signed counterpart if all
// involved values are non-negative.
// TODO: We could have better support for unsigned.
if (isKnownNonNegative(FoundLHS) && isKnownNonNegative(FoundRHS)) {
// Knowing that both FoundLHS and FoundRHS are non-negative, and knowing
// FoundLHS >u FoundRHS, we also know that FoundLHS >s FoundRHS. Let us
// use this fact to prove that LHS and RHS are non-negative.
const SCEV *MinusOne = getMinusOne(LHS->getType());
if (isImpliedCondOperands(ICmpInst::ICMP_SGT, LHS, MinusOne, FoundLHS,
FoundRHS) &&
isImpliedCondOperands(ICmpInst::ICMP_SGT, RHS, MinusOne, FoundLHS,
FoundRHS))
P = ICmpInst::ICMP_SGT;
}
if (P != ICmpInst::ICMP_SGT)
return false;
auto GetOpFromSExt = [&](const SCEV *S) {
if (auto *Ext = dyn_cast<SCEVSignExtendExpr>(S))
return Ext->getOperand();
// TODO: If S is a SCEVConstant then you can cheaply "strip" the sext off
// the constant in some cases.
return S;
};
// Acquire values from extensions.
auto *OrigLHS = LHS;
auto *OrigFoundLHS = FoundLHS;
LHS = GetOpFromSExt(LHS);
FoundLHS = GetOpFromSExt(FoundLHS);
// Is the SGT predicate can be proved trivially or using the found context.
auto IsSGTViaContext = [&](const SCEV *S1, const SCEV *S2) {
return isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGT, S1, S2) ||
isImpliedViaOperations(ICmpInst::ICMP_SGT, S1, S2, OrigFoundLHS,
FoundRHS, Depth + 1);
};
if (auto *LHSAddExpr = dyn_cast<SCEVAddExpr>(LHS)) {
// We want to avoid creation of any new non-constant SCEV. Since we are
// going to compare the operands to RHS, we should be certain that we don't
// need any size extensions for this. So let's decline all cases when the
// sizes of types of LHS and RHS do not match.
// TODO: Maybe try to get RHS from sext to catch more cases?
if (getTypeSizeInBits(LHS->getType()) != getTypeSizeInBits(RHS->getType()))
return false;
// Should not overflow.
if (!LHSAddExpr->hasNoSignedWrap())
return false;
auto *LL = LHSAddExpr->getOperand(0);
auto *LR = LHSAddExpr->getOperand(1);
auto *MinusOne = getMinusOne(RHS->getType());
// Checks that S1 >= 0 && S2 > RHS, trivially or using the found context.
auto IsSumGreaterThanRHS = [&](const SCEV *S1, const SCEV *S2) {
return IsSGTViaContext(S1, MinusOne) && IsSGTViaContext(S2, RHS);
};
// Try to prove the following rule:
// (LHS = LL + LR) && (LL >= 0) && (LR > RHS) => (LHS > RHS).
// (LHS = LL + LR) && (LR >= 0) && (LL > RHS) => (LHS > RHS).
if (IsSumGreaterThanRHS(LL, LR) || IsSumGreaterThanRHS(LR, LL))
return true;
} else if (auto *LHSUnknownExpr = dyn_cast<SCEVUnknown>(LHS)) {
Value *LL, *LR;
// FIXME: Once we have SDiv implemented, we can get rid of this matching.
using namespace llvm::PatternMatch;
if (match(LHSUnknownExpr->getValue(), m_SDiv(m_Value(LL), m_Value(LR)))) {
// Rules for division.
// We are going to perform some comparisons with Denominator and its
// derivative expressions. In general case, creating a SCEV for it may
// lead to a complex analysis of the entire graph, and in particular it
// can request trip count recalculation for the same loop. This would
// cache as SCEVCouldNotCompute to avoid the infinite recursion. To avoid
// this, we only want to create SCEVs that are constants in this section.
// So we bail if Denominator is not a constant.
if (!isa<ConstantInt>(LR))
return false;
auto *Denominator = cast<SCEVConstant>(getSCEV(LR));
// We want to make sure that LHS = FoundLHS / Denominator. If it is so,
// then a SCEV for the numerator already exists and matches with FoundLHS.
auto *Numerator = getExistingSCEV(LL);
if (!Numerator || Numerator->getType() != FoundLHS->getType())
return false;
// Make sure that the numerator matches with FoundLHS and the denominator
// is positive.
if (!HasSameValue(Numerator, FoundLHS) || !isKnownPositive(Denominator))
return false;
auto *DTy = Denominator->getType();
auto *FRHSTy = FoundRHS->getType();
if (DTy->isPointerTy() != FRHSTy->isPointerTy())
// One of types is a pointer and another one is not. We cannot extend
// them properly to a wider type, so let us just reject this case.
// TODO: Usage of getEffectiveSCEVType for DTy, FRHSTy etc should help
// to avoid this check.
return false;
// Given that:
// FoundLHS > FoundRHS, LHS = FoundLHS / Denominator, Denominator > 0.
auto *WTy = getWiderType(DTy, FRHSTy);
auto *DenominatorExt = getNoopOrSignExtend(Denominator, WTy);
auto *FoundRHSExt = getNoopOrSignExtend(FoundRHS, WTy);
// Try to prove the following rule:
// (FoundRHS > Denominator - 2) && (RHS <= 0) => (LHS > RHS).
// For example, given that FoundLHS > 2. It means that FoundLHS is at
// least 3. If we divide it by Denominator < 4, we will have at least 1.
auto *DenomMinusTwo = getMinusSCEV(DenominatorExt, getConstant(WTy, 2));
if (isKnownNonPositive(RHS) &&
IsSGTViaContext(FoundRHSExt, DenomMinusTwo))
return true;
// Try to prove the following rule:
// (FoundRHS > -1 - Denominator) && (RHS < 0) => (LHS > RHS).
// For example, given that FoundLHS > -3. Then FoundLHS is at least -2.
// If we divide it by Denominator > 2, then:
// 1. If FoundLHS is negative, then the result is 0.
// 2. If FoundLHS is non-negative, then the result is non-negative.
// Anyways, the result is non-negative.
auto *MinusOne = getMinusOne(WTy);
auto *NegDenomMinusOne = getMinusSCEV(MinusOne, DenominatorExt);
if (isKnownNegative(RHS) &&
IsSGTViaContext(FoundRHSExt, NegDenomMinusOne))
return true;
}
}
// If our expression contained SCEVUnknown Phis, and we split it down and now
// need to prove something for them, try to prove the predicate for every
// possible incoming values of those Phis.
if (isImpliedViaMerge(Pred, OrigLHS, RHS, OrigFoundLHS, FoundRHS, Depth + 1))
return true;
return false;
}
static bool isKnownPredicateExtendIdiom(CmpPredicate Pred, const SCEV *LHS,
const SCEV *RHS) {
// zext x u<= sext x, sext x s<= zext x
const SCEV *Op;
switch (Pred) {
case ICmpInst::ICMP_SGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_SLE: {
// If operand >=s 0 then ZExt == SExt. If operand <s 0 then SExt <s ZExt.
return match(LHS, m_scev_SExt(m_SCEV(Op))) &&
match(RHS, m_scev_ZExt(m_Specific(Op)));
}
case ICmpInst::ICMP_UGE:
std::swap(LHS, RHS);
[[fallthrough]];
case ICmpInst::ICMP_ULE: {
// If operand >=u 0 then ZExt == SExt. If operand <u 0 then ZExt <u SExt.
return match(LHS, m_scev_ZExt(m_SCEV(Op))) &&
match(RHS, m_scev_SExt(m_Specific(Op)));
}
default:
return false;
};
llvm_unreachable("unhandled case");
}
bool ScalarEvolution::isKnownViaNonRecursiveReasoning(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS) {
return isKnownPredicateExtendIdiom(Pred, LHS, RHS) ||
isKnownPredicateViaConstantRanges(Pred, LHS, RHS) ||
IsKnownPredicateViaMinOrMax(*this, Pred, LHS, RHS) ||
IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS) ||
isKnownPredicateViaNoOverflow(Pred, LHS, RHS);
}
bool ScalarEvolution::isImpliedCondOperandsHelper(CmpPredicate Pred,
const SCEV *LHS,
const SCEV *RHS,
const SCEV *FoundLHS,
const SCEV *FoundRHS) {
switch (Pred) {
default:
llvm_unreachable("Unexpected CmpPredicate value!");
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
if (HasSameValue(LHS, FoundLHS) && HasSameValue(RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE:
if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE:
if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SLE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE:
if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_UGE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE:
if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, RHS, FoundRHS))
return true;
break;
}
// Maybe it can be proved via operations?
if (isImpliedViaOperations(Pred, LHS, RHS, FoundLHS, FoundRHS))
return true;
return false;
}
bool ScalarEvolution::isImpliedCondOperandsViaRanges(
CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, CmpPredicate FoundPred,
const SCEV *FoundLHS, const SCEV *FoundRHS) {
if (!isa<SCEVConstant>(RHS) || !isa<SCEVConstant>(FoundRHS))
// The restriction on `FoundRHS` be lifted easily -- it exists only to
// reduce the compile time impact of this optimization.
return false;
std::optional<APInt> Addend = computeConstantDifference(LHS, FoundLHS);
if (!Addend)
return false;
const APInt &ConstFoundRHS = cast<SCEVConstant>(FoundRHS)->getAPInt();
// `FoundLHSRange` is the range we know `FoundLHS` to be in by virtue of the
// antecedent "`FoundLHS` `FoundPred` `FoundRHS`".
ConstantRange FoundLHSRange =
ConstantRange::makeExactICmpRegion(FoundPred, ConstFoundRHS);
// Since `LHS` is `FoundLHS` + `Addend`, we can compute a range for `LHS`:
ConstantRange LHSRange = FoundLHSRange.add(ConstantRange(*Addend));
// We can also compute the range of values for `LHS` that satisfy the
// consequent, "`LHS` `Pred` `RHS`":
const APInt &ConstRHS = cast<SCEVConstant>(RHS)->getAPInt();
// The antecedent implies the consequent if every value of `LHS` that
// satisfies the antecedent also satisfies the consequent.
return LHSRange.icmp(Pred, ConstRHS);
}
bool ScalarEvolution::canIVOverflowOnLT(const SCEV *RHS, const SCEV *Stride,
bool IsSigned) {
assert(isKnownPositive(Stride) && "Positive stride expected!");
unsigned BitWidth = getTypeSizeInBits(RHS->getType());
const SCEV *One = getOne(Stride->getType());
if (IsSigned) {
APInt MaxRHS = getSignedRangeMax(RHS);
APInt MaxValue = APInt::getSignedMaxValue(BitWidth);
APInt MaxStrideMinusOne = getSignedRangeMax(getMinusSCEV(Stride, One));
// SMaxRHS + SMaxStrideMinusOne > SMaxValue => overflow!
return (std::move(MaxValue) - MaxStrideMinusOne).slt(MaxRHS);
}
APInt MaxRHS = getUnsignedRangeMax(RHS);
APInt MaxValue = APInt::getMaxValue(BitWidth);
APInt MaxStrideMinusOne = getUnsignedRangeMax(getMinusSCEV(Stride, One));
// UMaxRHS + UMaxStrideMinusOne > UMaxValue => overflow!
return (std::move(MaxValue) - MaxStrideMinusOne).ult(MaxRHS);
}
bool ScalarEvolution::canIVOverflowOnGT(const SCEV *RHS, const SCEV *Stride,
bool IsSigned) {
unsigned BitWidth = getTypeSizeInBits(RHS->getType());
const SCEV *One = getOne(Stride->getType());
if (IsSigned) {
APInt MinRHS = getSignedRangeMin(RHS);
APInt MinValue = APInt::getSignedMinValue(BitWidth);
APInt MaxStrideMinusOne = getSignedRangeMax(getMinusSCEV(Stride, One));
// SMinRHS - SMaxStrideMinusOne < SMinValue => overflow!
return (std::move(MinValue) + MaxStrideMinusOne).sgt(MinRHS);
}
APInt MinRHS = getUnsignedRangeMin(RHS);
APInt MinValue = APInt::getMinValue(BitWidth);
APInt MaxStrideMinusOne = getUnsignedRangeMax(getMinusSCEV(Stride, One));
// UMinRHS - UMaxStrideMinusOne < UMinValue => overflow!
return (std::move(MinValue) + MaxStrideMinusOne).ugt(MinRHS);
}
const SCEV *ScalarEvolution::getUDivCeilSCEV(const SCEV *N, const SCEV *D) {
// umin(N, 1) + floor((N - umin(N, 1)) / D)
// This is equivalent to "1 + floor((N - 1) / D)" for N != 0. The umin
// expression fixes the case of N=0.
const SCEV *MinNOne = getUMinExpr(N, getOne(N->getType()));
const SCEV *NMinusOne = getMinusSCEV(N, MinNOne);
return getAddExpr(MinNOne, getUDivExpr(NMinusOne, D));
}
const SCEV *ScalarEvolution::computeMaxBECountForLT(const SCEV *Start,
const SCEV *Stride,
const SCEV *End,
unsigned BitWidth,
bool IsSigned) {
// The logic in this function assumes we can represent a positive stride.
// If we can't, the backedge-taken count must be zero.
if (IsSigned && BitWidth == 1)
return getZero(Stride->getType());
// This code below only been closely audited for negative strides in the
// unsigned comparison case, it may be correct for signed comparison, but
// that needs to be established.
if (IsSigned && isKnownNegative(Stride))
return getCouldNotCompute();
// Calculate the maximum backedge count based on the range of values
// permitted by Start, End, and Stride.
APInt MinStart =
IsSigned ? getSignedRangeMin(Start) : getUnsignedRangeMin(Start);
APInt MinStride =
IsSigned ? getSignedRangeMin(Stride) : getUnsignedRangeMin(Stride);
// We assume either the stride is positive, or the backedge-taken count
// is zero. So force StrideForMaxBECount to be at least one.
APInt One(BitWidth, 1);
APInt StrideForMaxBECount = IsSigned ? APIntOps::smax(One, MinStride)
: APIntOps::umax(One, MinStride);
APInt MaxValue = IsSigned ? APInt::getSignedMaxValue(BitWidth)
: APInt::getMaxValue(BitWidth);
APInt Limit = MaxValue - (StrideForMaxBECount - 1);
// Although End can be a MAX expression we estimate MaxEnd considering only
// the case End = RHS of the loop termination condition. This is safe because
// in the other case (End - Start) is zero, leading to a zero maximum backedge
// taken count.
APInt MaxEnd = IsSigned ? APIntOps::smin(getSignedRangeMax(End), Limit)
: APIntOps::umin(getUnsignedRangeMax(End), Limit);
// MaxBECount = ceil((max(MaxEnd, MinStart) - MinStart) / Stride)
MaxEnd = IsSigned ? APIntOps::smax(MaxEnd, MinStart)
: APIntOps::umax(MaxEnd, MinStart);
return getUDivCeilSCEV(getConstant(MaxEnd - MinStart) /* Delta */,
getConstant(StrideForMaxBECount) /* Step */);
}
ScalarEvolution::ExitLimit
ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
const Loop *L, bool IsSigned,
bool ControlsOnlyExit, bool AllowPredicates) {
SmallVector<const SCEVPredicate *> Predicates;
const SCEVAddRecExpr *IV = dyn_cast<SCEVAddRecExpr>(LHS);
bool PredicatedIV = false;
if (!IV) {
if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS)) {
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(ZExt->getOperand());
if (AR && AR->getLoop() == L && AR->isAffine()) {
auto canProveNUW = [&]() {
// We can use the comparison to infer no-wrap flags only if it fully
// controls the loop exit.
if (!ControlsOnlyExit)
return false;
if (!isLoopInvariant(RHS, L))
return false;
if (!isKnownNonZero(AR->getStepRecurrence(*this)))
// We need the sequence defined by AR to strictly increase in the
// unsigned integer domain for the logic below to hold.
return false;
const unsigned InnerBitWidth = getTypeSizeInBits(AR->getType());
const unsigned OuterBitWidth = getTypeSizeInBits(RHS->getType());
// If RHS <=u Limit, then there must exist a value V in the sequence
// defined by AR (e.g. {Start,+,Step}) such that V >u RHS, and
// V <=u UINT_MAX. Thus, we must exit the loop before unsigned
// overflow occurs. This limit also implies that a signed comparison
// (in the wide bitwidth) is equivalent to an unsigned comparison as
// the high bits on both sides must be zero.
APInt StrideMax = getUnsignedRangeMax(AR->getStepRecurrence(*this));
APInt Limit = APInt::getMaxValue(InnerBitWidth) - (StrideMax - 1);
Limit = Limit.zext(OuterBitWidth);
return getUnsignedRangeMax(applyLoopGuards(RHS, L)).ule(Limit);
};
auto Flags = AR->getNoWrapFlags();
if (!hasFlags(Flags, SCEV::FlagNUW) && canProveNUW())
Flags = setFlags(Flags, SCEV::FlagNUW);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
if (AR->hasNoUnsignedWrap()) {
// Emulate what getZeroExtendExpr would have done during construction
// if we'd been able to infer the fact just above at that time.
const SCEV *Step = AR->getStepRecurrence(*this);
Type *Ty = ZExt->getType();
auto *S = getAddRecExpr(
getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, 0),
getZeroExtendExpr(Step, Ty, 0), L, AR->getNoWrapFlags());
IV = dyn_cast<SCEVAddRecExpr>(S);
}
}
}
}
if (!IV && AllowPredicates) {
// Try to make this an AddRec using runtime tests, in the first X
// iterations of this loop, where X is the SCEV expression found by the
// algorithm below.
IV = convertSCEVToAddRecWithPredicates(LHS, L, Predicates);
PredicatedIV = true;
}
// Avoid weird loops
if (!IV || IV->getLoop() != L || !IV->isAffine())
return getCouldNotCompute();
// A precondition of this method is that the condition being analyzed
// reaches an exiting branch which dominates the latch. Given that, we can
// assume that an increment which violates the nowrap specification and
// produces poison must cause undefined behavior when the resulting poison
// value is branched upon and thus we can conclude that the backedge is
// taken no more often than would be required to produce that poison value.
// Note that a well defined loop can exit on the iteration which violates
// the nowrap specification if there is another exit (either explicit or
// implicit/exceptional) which causes the loop to execute before the
// exiting instruction we're analyzing would trigger UB.
auto WrapType = IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW;
bool NoWrap = ControlsOnlyExit && IV->getNoWrapFlags(WrapType);
ICmpInst::Predicate Cond = IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
const SCEV *Stride = IV->getStepRecurrence(*this);
bool PositiveStride = isKnownPositive(Stride);
// Avoid negative or zero stride values.
if (!PositiveStride) {
// We can compute the correct backedge taken count for loops with unknown
// strides if we can prove that the loop is not an infinite loop with side
// effects. Here's the loop structure we are trying to handle -
//
// i = start
// do {
// A[i] = i;
// i += s;
// } while (i < end);
//
// The backedge taken count for such loops is evaluated as -
// (max(end, start + stride) - start - 1) /u stride
//
// The additional preconditions that we need to check to prove correctness
// of the above formula is as follows -
//
// a) IV is either nuw or nsw depending upon signedness (indicated by the
// NoWrap flag).
// b) the loop is guaranteed to be finite (e.g. is mustprogress and has
// no side effects within the loop)
// c) loop has a single static exit (with no abnormal exits)
//
// Precondition a) implies that if the stride is negative, this is a single
// trip loop. The backedge taken count formula reduces to zero in this case.
//
// Precondition b) and c) combine to imply that if rhs is invariant in L,
// then a zero stride means the backedge can't be taken without executing
// undefined behavior.
//
// The positive stride case is the same as isKnownPositive(Stride) returning
// true (original behavior of the function).
//
if (PredicatedIV || !NoWrap || !loopIsFiniteByAssumption(L) ||
!loopHasNoAbnormalExits(L))
return getCouldNotCompute();
if (!isKnownNonZero(Stride)) {
// If we have a step of zero, and RHS isn't invariant in L, we don't know
// if it might eventually be greater than start and if so, on which
// iteration. We can't even produce a useful upper bound.
if (!isLoopInvariant(RHS, L))
return getCouldNotCompute();
// We allow a potentially zero stride, but we need to divide by stride
// below. Since the loop can't be infinite and this check must control
// the sole exit, we can infer the exit must be taken on the first
// iteration (e.g. backedge count = 0) if the stride is zero. Given that,
// we know the numerator in the divides below must be zero, so we can
// pick an arbitrary non-zero value for the denominator (e.g. stride)
// and produce the right result.
// FIXME: Handle the case where Stride is poison?
auto wouldZeroStrideBeUB = [&]() {
// Proof by contradiction. Suppose the stride were zero. If we can
// prove that the backedge *is* taken on the first iteration, then since
// we know this condition controls the sole exit, we must have an
// infinite loop. We can't have a (well defined) infinite loop per
// check just above.
// Note: The (Start - Stride) term is used to get the start' term from
// (start' + stride,+,stride). Remember that we only care about the
// result of this expression when stride == 0 at runtime.
auto *StartIfZero = getMinusSCEV(IV->getStart(), Stride);
return isLoopEntryGuardedByCond(L, Cond, StartIfZero, RHS);
};
if (!wouldZeroStrideBeUB()) {
Stride = getUMaxExpr(Stride, getOne(Stride->getType()));
}
}
} else if (!NoWrap) {
// Avoid proven overflow cases: this will ensure that the backedge taken
// count will not generate any unsigned overflow.
if (canIVOverflowOnLT(RHS, Stride, IsSigned))
return getCouldNotCompute();
}
// On all paths just preceeding, we established the following invariant:
// IV can be assumed not to overflow up to and including the exiting
// iteration. We proved this in one of two ways:
// 1) We can show overflow doesn't occur before the exiting iteration
// 1a) canIVOverflowOnLT, and b) step of one
// 2) We can show that if overflow occurs, the loop must execute UB
// before any possible exit.
// Note that we have not yet proved RHS invariant (in general).
const SCEV *Start = IV->getStart();
// Preserve pointer-typed Start/RHS to pass to isLoopEntryGuardedByCond.
// If we convert to integers, isLoopEntryGuardedByCond will miss some cases.
// Use integer-typed versions for actual computation; we can't subtract
// pointers in general.
const SCEV *OrigStart = Start;
const SCEV *OrigRHS = RHS;
if (Start->getType()->isPointerTy()) {
Start = getLosslessPtrToIntExpr(Start);
if (isa<SCEVCouldNotCompute>(Start))
return Start;
}
if (RHS->getType()->isPointerTy()) {
RHS = getLosslessPtrToIntExpr(RHS);
if (isa<SCEVCouldNotCompute>(RHS))
return RHS;
}
const SCEV *End = nullptr, *BECount = nullptr,
*BECountIfBackedgeTaken = nullptr;
if (!isLoopInvariant(RHS, L)) {
const auto *RHSAddRec = dyn_cast<SCEVAddRecExpr>(RHS);
if (PositiveStride && RHSAddRec != nullptr && RHSAddRec->getLoop() == L &&
RHSAddRec->getNoWrapFlags()) {
// The structure of loop we are trying to calculate backedge count of:
//
// left = left_start
// right = right_start
//
// while(left < right){
// ... do something here ...
// left += s1; // stride of left is s1 (s1 > 0)
// right += s2; // stride of right is s2 (s2 < 0)
// }
//
const SCEV *RHSStart = RHSAddRec->getStart();
const SCEV *RHSStride = RHSAddRec->getStepRecurrence(*this);
// If Stride - RHSStride is positive and does not overflow, we can write
// backedge count as ->
// ceil((End - Start) /u (Stride - RHSStride))
// Where, End = max(RHSStart, Start)
// Check if RHSStride < 0 and Stride - RHSStride will not overflow.
if (isKnownNegative(RHSStride) &&
willNotOverflow(Instruction::Sub, /*Signed=*/true, Stride,
RHSStride)) {
const SCEV *Denominator = getMinusSCEV(Stride, RHSStride);
if (isKnownPositive(Denominator)) {
End = IsSigned ? getSMaxExpr(RHSStart, Start)
: getUMaxExpr(RHSStart, Start);
// We can do this because End >= Start, as End = max(RHSStart, Start)
const SCEV *Delta = getMinusSCEV(End, Start);
BECount = getUDivCeilSCEV(Delta, Denominator);
BECountIfBackedgeTaken =
getUDivCeilSCEV(getMinusSCEV(RHSStart, Start), Denominator);
}
}
}
if (BECount == nullptr) {
// If we cannot calculate ExactBECount, we can calculate the MaxBECount,
// given the start, stride and max value for the end bound of the
// loop (RHS), and the fact that IV does not overflow (which is
// checked above).
const SCEV *MaxBECount = computeMaxBECountForLT(
Start, Stride, RHS, getTypeSizeInBits(LHS->getType()), IsSigned);
return ExitLimit(getCouldNotCompute() /* ExactNotTaken */, MaxBECount,
MaxBECount, false /*MaxOrZero*/, Predicates);
}
} else {
// We use the expression (max(End,Start)-Start)/Stride to describe the
// backedge count, as if the backedge is taken at least once
// max(End,Start) is End and so the result is as above, and if not
// max(End,Start) is Start so we get a backedge count of zero.
auto *OrigStartMinusStride = getMinusSCEV(OrigStart, Stride);
assert(isAvailableAtLoopEntry(OrigStartMinusStride, L) && "Must be!");
assert(isAvailableAtLoopEntry(OrigStart, L) && "Must be!");
assert(isAvailableAtLoopEntry(OrigRHS, L) && "Must be!");
// Can we prove (max(RHS,Start) > Start - Stride?
if (isLoopEntryGuardedByCond(L, Cond, OrigStartMinusStride, OrigStart) &&
isLoopEntryGuardedByCond(L, Cond, OrigStartMinusStride, OrigRHS)) {
// In this case, we can use a refined formula for computing backedge
// taken count. The general formula remains:
// "End-Start /uceiling Stride" where "End = max(RHS,Start)"
// We want to use the alternate formula:
// "((End - 1) - (Start - Stride)) /u Stride"
// Let's do a quick case analysis to show these are equivalent under
// our precondition that max(RHS,Start) > Start - Stride.
// * For RHS <= Start, the backedge-taken count must be zero.
// "((End - 1) - (Start - Stride)) /u Stride" reduces to
// "((Start - 1) - (Start - Stride)) /u Stride" which simplies to
// "Stride - 1 /u Stride" which is indeed zero for all non-zero values
// of Stride. For 0 stride, we've use umin(1,Stride) above,
// reducing this to the stride of 1 case.
// * For RHS >= Start, the backedge count must be "RHS-Start /uceil
// Stride".
// "((End - 1) - (Start - Stride)) /u Stride" reduces to
// "((RHS - 1) - (Start - Stride)) /u Stride" reassociates to
// "((RHS - (Start - Stride) - 1) /u Stride".
// Our preconditions trivially imply no overflow in that form.
const SCEV *MinusOne = getMinusOne(Stride->getType());
const SCEV *Numerator =
getMinusSCEV(getAddExpr(RHS, MinusOne), getMinusSCEV(Start, Stride));
BECount = getUDivExpr(Numerator, Stride);
}
if (!BECount) {
auto canProveRHSGreaterThanEqualStart = [&]() {
auto CondGE = IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
const SCEV *GuardedRHS = applyLoopGuards(OrigRHS, L);
const SCEV *GuardedStart = applyLoopGuards(OrigStart, L);
if (isLoopEntryGuardedByCond(L, CondGE, OrigRHS, OrigStart) ||
isKnownPredicate(CondGE, GuardedRHS, GuardedStart))
return true;
// (RHS > Start - 1) implies RHS >= Start.
// * "RHS >= Start" is trivially equivalent to "RHS > Start - 1" if
// "Start - 1" doesn't overflow.
// * For signed comparison, if Start - 1 does overflow, it's equal
// to INT_MAX, and "RHS >s INT_MAX" is trivially false.
// * For unsigned comparison, if Start - 1 does overflow, it's equal
// to UINT_MAX, and "RHS >u UINT_MAX" is trivially false.
//
// FIXME: Should isLoopEntryGuardedByCond do this for us?
auto CondGT = IsSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
auto *StartMinusOne =
getAddExpr(OrigStart, getMinusOne(OrigStart->getType()));
return isLoopEntryGuardedByCond(L, CondGT, OrigRHS, StartMinusOne);
};
// If we know that RHS >= Start in the context of loop, then we know
// that max(RHS, Start) = RHS at this point.
if (canProveRHSGreaterThanEqualStart()) {
End = RHS;
} else {
// If RHS < Start, the backedge will be taken zero times. So in
// general, we can write the backedge-taken count as:
//
// RHS >= Start ? ceil(RHS - Start) / Stride : 0
//
// We convert it to the following to make it more convenient for SCEV:
//
// ceil(max(RHS, Start) - Start) / Stride
End = IsSigned ? getSMaxExpr(RHS, Start) : getUMaxExpr(RHS, Start);
// See what would happen if we assume the backedge is taken. This is
// used to compute MaxBECount.
BECountIfBackedgeTaken =
getUDivCeilSCEV(getMinusSCEV(RHS, Start), Stride);
}
// At this point, we know:
//
// 1. If IsSigned, Start <=s End; otherwise, Start <=u End
// 2. The index variable doesn't overflow.
//
// Therefore, we know N exists such that
// (Start + Stride * N) >= End, and computing "(Start + Stride * N)"
// doesn't overflow.
//
// Using this information, try to prove whether the addition in
// "(Start - End) + (Stride - 1)" has unsigned overflow.
const SCEV *One = getOne(Stride->getType());
bool MayAddOverflow = [&] {
if (isKnownToBeAPowerOfTwo(Stride)) {
// Suppose Stride is a power of two, and Start/End are unsigned
// integers. Let UMAX be the largest representable unsigned
// integer.
//
// By the preconditions of this function, we know
// "(Start + Stride * N) >= End", and this doesn't overflow.
// As a formula:
//
// End <= (Start + Stride * N) <= UMAX
//
// Subtracting Start from all the terms:
//
// End - Start <= Stride * N <= UMAX - Start
//
// Since Start is unsigned, UMAX - Start <= UMAX. Therefore:
//
// End - Start <= Stride * N <= UMAX
//
// Stride * N is a multiple of Stride. Therefore,
//
// End - Start <= Stride * N <= UMAX - (UMAX mod Stride)
//
// Since Stride is a power of two, UMAX + 1 is divisible by
// Stride. Therefore, UMAX mod Stride == Stride - 1. So we can
// write:
//
// End - Start <= Stride * N <= UMAX - Stride - 1
//
// Dropping the middle term:
//
// End - Start <= UMAX - Stride - 1
//
// Adding Stride - 1 to both sides:
//
// (End - Start) + (Stride - 1) <= UMAX
//
// In other words, the addition doesn't have unsigned overflow.
//
// A similar proof works if we treat Start/End as signed values.
// Just rewrite steps before "End - Start <= Stride * N <= UMAX"
// to use signed max instead of unsigned max. Note that we're
// trying to prove a lack of unsigned overflow in either case.
return false;
}
if (Start == Stride || Start == getMinusSCEV(Stride, One)) {
// If Start is equal to Stride, (End - Start) + (Stride - 1) == End
// - 1. If !IsSigned, 0 <u Stride == Start <=u End; so 0 <u End - 1
// <u End. If IsSigned, 0 <s Stride == Start <=s End; so 0 <s End -
// 1 <s End.
//
// If Start is equal to Stride - 1, (End - Start) + Stride - 1 ==
// End.
return false;
}
return true;
}();
const SCEV *Delta = getMinusSCEV(End, Start);
if (!MayAddOverflow) {
// floor((D + (S - 1)) / S)
// We prefer this formulation if it's legal because it's fewer
// operations.
BECount =
getUDivExpr(getAddExpr(Delta, getMinusSCEV(Stride, One)), Stride);
} else {
BECount = getUDivCeilSCEV(Delta, Stride);
}
}
}
const SCEV *ConstantMaxBECount;
bool MaxOrZero = false;
if (isa<SCEVConstant>(BECount)) {
ConstantMaxBECount = BECount;
} else if (BECountIfBackedgeTaken &&
isa<SCEVConstant>(BECountIfBackedgeTaken)) {
// If we know exactly how many times the backedge will be taken if it's
// taken at least once, then the backedge count will either be that or
// zero.
ConstantMaxBECount = BECountIfBackedgeTaken;
MaxOrZero = true;
} else {
ConstantMaxBECount = computeMaxBECountForLT(
Start, Stride, RHS, getTypeSizeInBits(LHS->getType()), IsSigned);
}
if (isa<SCEVCouldNotCompute>(ConstantMaxBECount) &&
!isa<SCEVCouldNotCompute>(BECount))
ConstantMaxBECount = getConstant(getUnsignedRangeMax(BECount));
const SCEV *SymbolicMaxBECount =
isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, MaxOrZero,
Predicates);
}
ScalarEvolution::ExitLimit ScalarEvolution::howManyGreaterThans(
const SCEV *LHS, const SCEV *RHS, const Loop *L, bool IsSigned,
bool ControlsOnlyExit, bool AllowPredicates) {
SmallVector<const SCEVPredicate *> Predicates;
// We handle only IV > Invariant
if (!isLoopInvariant(RHS, L))
return getCouldNotCompute();
const SCEVAddRecExpr *IV = dyn_cast<SCEVAddRecExpr>(LHS);
if (!IV && AllowPredicates)
// Try to make this an AddRec using runtime tests, in the first X
// iterations of this loop, where X is the SCEV expression found by the
// algorithm below.
IV = convertSCEVToAddRecWithPredicates(LHS, L, Predicates);
// Avoid weird loops
if (!IV || IV->getLoop() != L || !IV->isAffine())
return getCouldNotCompute();
auto WrapType = IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW;
bool NoWrap = ControlsOnlyExit && IV->getNoWrapFlags(WrapType);
ICmpInst::Predicate Cond = IsSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
const SCEV *Stride = getNegativeSCEV(IV->getStepRecurrence(*this));
// Avoid negative or zero stride values
if (!isKnownPositive(Stride))
return getCouldNotCompute();
// Avoid proven overflow cases: this will ensure that the backedge taken count
// will not generate any unsigned overflow. Relaxed no-overflow conditions
// exploit NoWrapFlags, allowing to optimize in presence of undefined
// behaviors like the case of C language.
if (!Stride->isOne() && !NoWrap)
if (canIVOverflowOnGT(RHS, Stride, IsSigned))
return getCouldNotCompute();
const SCEV *Start = IV->getStart();
const SCEV *End = RHS;
if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS)) {
// If we know that Start >= RHS in the context of loop, then we know that
// min(RHS, Start) = RHS at this point.
if (isLoopEntryGuardedByCond(
L, IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE, Start, RHS))
End = RHS;
else
End = IsSigned ? getSMinExpr(RHS, Start) : getUMinExpr(RHS, Start);
}
if (Start->getType()->isPointerTy()) {
Start = getLosslessPtrToIntExpr(Start);
if (isa<SCEVCouldNotCompute>(Start))
return Start;
}
if (End->getType()->isPointerTy()) {
End = getLosslessPtrToIntExpr(End);
if (isa<SCEVCouldNotCompute>(End))
return End;
}
// Compute ((Start - End) + (Stride - 1)) / Stride.
// FIXME: This can overflow. Holding off on fixing this for now;
// howManyGreaterThans will hopefully be gone soon.
const SCEV *One = getOne(Stride->getType());
const SCEV *BECount = getUDivExpr(
getAddExpr(getMinusSCEV(Start, End), getMinusSCEV(Stride, One)), Stride);
APInt MaxStart = IsSigned ? getSignedRangeMax(Start)
: getUnsignedRangeMax(Start);
APInt MinStride = IsSigned ? getSignedRangeMin(Stride)
: getUnsignedRangeMin(Stride);
unsigned BitWidth = getTypeSizeInBits(LHS->getType());
APInt Limit = IsSigned ? APInt::getSignedMinValue(BitWidth) + (MinStride - 1)
: APInt::getMinValue(BitWidth) + (MinStride - 1);
// Although End can be a MIN expression we estimate MinEnd considering only
// the case End = RHS. This is safe because in the other case (Start - End)
// is zero, leading to a zero maximum backedge taken count.
APInt MinEnd =
IsSigned ? APIntOps::smax(getSignedRangeMin(RHS), Limit)
: APIntOps::umax(getUnsignedRangeMin(RHS), Limit);
const SCEV *ConstantMaxBECount =
isa<SCEVConstant>(BECount)
? BECount
: getUDivCeilSCEV(getConstant(MaxStart - MinEnd),
getConstant(MinStride));
if (isa<SCEVCouldNotCompute>(ConstantMaxBECount))
ConstantMaxBECount = BECount;
const SCEV *SymbolicMaxBECount =
isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, false,
Predicates);
}
const SCEV *SCEVAddRecExpr::getNumIterationsInRange(const ConstantRange &Range,
ScalarEvolution &SE) const {
if (Range.isFullSet()) // Infinite loop.
return SE.getCouldNotCompute();
// If the start is a non-zero constant, shift the range to simplify things.
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(getStart()))
if (!SC->getValue()->isZero()) {
SmallVector<const SCEV *, 4> Operands(operands());
Operands[0] = SE.getZero(SC->getType());
const SCEV *Shifted = SE.getAddRecExpr(Operands, getLoop(),
getNoWrapFlags(FlagNW));
if (const auto *ShiftedAddRec = dyn_cast<SCEVAddRecExpr>(Shifted))
return ShiftedAddRec->getNumIterationsInRange(
Range.subtract(SC->getAPInt()), SE);
// This is strange and shouldn't happen.
return SE.getCouldNotCompute();
}
// The only time we can solve this is when we have all constant indices.
// Otherwise, we cannot determine the overflow conditions.
if (any_of(operands(), [](const SCEV *Op) { return !isa<SCEVConstant>(Op); }))
return SE.getCouldNotCompute();
// Okay at this point we know that all elements of the chrec are constants and
// that the start element is zero.
// First check to see if the range contains zero. If not, the first
// iteration exits.
unsigned BitWidth = SE.getTypeSizeInBits(getType());
if (!Range.contains(APInt(BitWidth, 0)))
return SE.getZero(getType());
if (isAffine()) {
// If this is an affine expression then we have this situation:
// Solve {0,+,A} in Range === Ax in Range
// We know that zero is in the range. If A is positive then we know that
// the upper value of the range must be the first possible exit value.
// If A is negative then the lower of the range is the last possible loop
// value. Also note that we already checked for a full range.
APInt A = cast<SCEVConstant>(getOperand(1))->getAPInt();
APInt End = A.sge(1) ? (Range.getUpper() - 1) : Range.getLower();
// The exit value should be (End+A)/A.
APInt ExitVal = (End + A).udiv(A);
ConstantInt *ExitValue = ConstantInt::get(SE.getContext(), ExitVal);
// Evaluate at the exit value. If we really did fall out of the valid
// range, then we computed our trip count, otherwise wrap around or other
// things must have happened.
ConstantInt *Val = EvaluateConstantChrecAtConstant(this, ExitValue, SE);
if (Range.contains(Val->getValue()))
return SE.getCouldNotCompute(); // Something strange happened
// Ensure that the previous value is in the range.
assert(Range.contains(
EvaluateConstantChrecAtConstant(this,
ConstantInt::get(SE.getContext(), ExitVal - 1), SE)->getValue()) &&
"Linear scev computation is off in a bad way!");
return SE.getConstant(ExitValue);
}
if (isQuadratic()) {
if (auto S = SolveQuadraticAddRecRange(this, Range, SE))
return SE.getConstant(*S);
}
return SE.getCouldNotCompute();
}
const SCEVAddRecExpr *
SCEVAddRecExpr::getPostIncExpr(ScalarEvolution &SE) const {
assert(getNumOperands() > 1 && "AddRec with zero step?");
// There is a temptation to just call getAddExpr(this, getStepRecurrence(SE)),
// but in this case we cannot guarantee that the value returned will be an
// AddRec because SCEV does not have a fixed point where it stops
// simplification: it is legal to return ({rec1} + {rec2}). For example, it
// may happen if we reach arithmetic depth limit while simplifying. So we
// construct the returned value explicitly.
SmallVector<const SCEV *, 3> Ops;
// If this is {A,+,B,+,C,...,+,N}, then its step is {B,+,C,+,...,+,N}, and
// (this + Step) is {A+B,+,B+C,+...,+,N}.
for (unsigned i = 0, e = getNumOperands() - 1; i < e; ++i)
Ops.push_back(SE.getAddExpr(getOperand(i), getOperand(i + 1)));
// We know that the last operand is not a constant zero (otherwise it would
// have been popped out earlier). This guarantees us that if the result has
// the same last operand, then it will also not be popped out, meaning that
// the returned value will be an AddRec.
const SCEV *Last = getOperand(getNumOperands() - 1);
assert(!Last->isZero() && "Recurrency with zero step?");
Ops.push_back(Last);
return cast<SCEVAddRecExpr>(SE.getAddRecExpr(Ops, getLoop(),
SCEV::FlagAnyWrap));
}
// Return true when S contains at least an undef value.
bool ScalarEvolution::containsUndefs(const SCEV *S) const {
return SCEVExprContains(S, [](const SCEV *S) {
if (const auto *SU = dyn_cast<SCEVUnknown>(S))
return isa<UndefValue>(SU->getValue());
return false;
});
}
// Return true when S contains a value that is a nullptr.
bool ScalarEvolution::containsErasedValue(const SCEV *S) const {
return SCEVExprContains(S, [](const SCEV *S) {
if (const auto *SU = dyn_cast<SCEVUnknown>(S))
return SU->getValue() == nullptr;
return false;
});
}
/// Return the size of an element read or written by Inst.
const SCEV *ScalarEvolution::getElementSize(Instruction *Inst) {
Type *Ty;
if (StoreInst *Store = dyn_cast<StoreInst>(Inst))
Ty = Store->getValueOperand()->getType();
else if (LoadInst *Load = dyn_cast<LoadInst>(Inst))
Ty = Load->getType();
else
return nullptr;
Type *ETy = getEffectiveSCEVType(PointerType::getUnqual(Inst->getContext()));
return getSizeOfExpr(ETy, Ty);
}
//===----------------------------------------------------------------------===//
// SCEVCallbackVH Class Implementation
//===----------------------------------------------------------------------===//
void ScalarEvolution::SCEVCallbackVH::deleted() {
assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
if (PHINode *PN = dyn_cast<PHINode>(getValPtr()))
SE->ConstantEvolutionLoopExitValue.erase(PN);
SE->eraseValueFromMap(getValPtr());
// this now dangles!
}
void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *V) {
assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
// Forget all the expressions associated with users of the old value,
// so that future queries will recompute the expressions using the new
// value.
SE->forgetValue(getValPtr());
// this now dangles!
}
ScalarEvolution::SCEVCallbackVH::SCEVCallbackVH(Value *V, ScalarEvolution *se)
: CallbackVH(V), SE(se) {}
//===----------------------------------------------------------------------===//
// ScalarEvolution Class Implementation
//===----------------------------------------------------------------------===//
ScalarEvolution::ScalarEvolution(Function &F, TargetLibraryInfo &TLI,
AssumptionCache &AC, DominatorTree &DT,
LoopInfo &LI)
: F(F), DL(F.getDataLayout()), TLI(TLI), AC(AC), DT(DT), LI(LI),
CouldNotCompute(new SCEVCouldNotCompute()), ValuesAtScopes(64),
LoopDispositions(64), BlockDispositions(64) {
// To use guards for proving predicates, we need to scan every instruction in
// relevant basic blocks, and not just terminators. Doing this is a waste of
// time if the IR does not actually contain any calls to
// @llvm.experimental.guard, so do a quick check and remember this beforehand.
//
// This pessimizes the case where a pass that preserves ScalarEvolution wants
// to _add_ guards to the module when there weren't any before, and wants
// ScalarEvolution to optimize based on those guards. For now we prefer to be
// efficient in lieu of being smart in that rather obscure case.
auto *GuardDecl = Intrinsic::getDeclarationIfExists(
F.getParent(), Intrinsic::experimental_guard);
HasGuards = GuardDecl && !GuardDecl->use_empty();
}
ScalarEvolution::ScalarEvolution(ScalarEvolution &&Arg)
: F(Arg.F), DL(Arg.DL), HasGuards(Arg.HasGuards), TLI(Arg.TLI), AC(Arg.AC),
DT(Arg.DT), LI(Arg.LI), CouldNotCompute(std::move(Arg.CouldNotCompute)),
ValueExprMap(std::move(Arg.ValueExprMap)),
PendingLoopPredicates(std::move(Arg.PendingLoopPredicates)),
PendingPhiRanges(std::move(Arg.PendingPhiRanges)),
PendingMerges(std::move(Arg.PendingMerges)),
ConstantMultipleCache(std::move(Arg.ConstantMultipleCache)),
BackedgeTakenCounts(std::move(Arg.BackedgeTakenCounts)),
PredicatedBackedgeTakenCounts(
std::move(Arg.PredicatedBackedgeTakenCounts)),
BECountUsers(std::move(Arg.BECountUsers)),
ConstantEvolutionLoopExitValue(
std::move(Arg.ConstantEvolutionLoopExitValue)),
ValuesAtScopes(std::move(Arg.ValuesAtScopes)),
ValuesAtScopesUsers(std::move(Arg.ValuesAtScopesUsers)),
LoopDispositions(std::move(Arg.LoopDispositions)),
LoopPropertiesCache(std::move(Arg.LoopPropertiesCache)),
BlockDispositions(std::move(Arg.BlockDispositions)),
SCEVUsers(std::move(Arg.SCEVUsers)),
UnsignedRanges(std::move(Arg.UnsignedRanges)),
SignedRanges(std::move(Arg.SignedRanges)),
UniqueSCEVs(std::move(Arg.UniqueSCEVs)),
UniquePreds(std::move(Arg.UniquePreds)),
SCEVAllocator(std::move(Arg.SCEVAllocator)),
LoopUsers(std::move(Arg.LoopUsers)),
PredicatedSCEVRewrites(std::move(Arg.PredicatedSCEVRewrites)),
FirstUnknown(Arg.FirstUnknown) {
Arg.FirstUnknown = nullptr;
}
ScalarEvolution::~ScalarEvolution() {
// Iterate through all the SCEVUnknown instances and call their
// destructors, so that they release their references to their values.
for (SCEVUnknown *U = FirstUnknown; U;) {
SCEVUnknown *Tmp = U;
U = U->Next;
Tmp->~SCEVUnknown();
}
FirstUnknown = nullptr;
ExprValueMap.clear();
ValueExprMap.clear();
HasRecMap.clear();
BackedgeTakenCounts.clear();
PredicatedBackedgeTakenCounts.clear();
assert(PendingLoopPredicates.empty() && "isImpliedCond garbage");
assert(PendingPhiRanges.empty() && "getRangeRef garbage");
assert(PendingMerges.empty() && "isImpliedViaMerge garbage");
assert(!WalkingBEDominatingConds && "isLoopBackedgeGuardedByCond garbage!");
assert(!ProvingSplitPredicate && "ProvingSplitPredicate garbage!");
}
bool ScalarEvolution::hasLoopInvariantBackedgeTakenCount(const Loop *L) {
return !isa<SCEVCouldNotCompute>(getBackedgeTakenCount(L));
}
/// When printing a top-level SCEV for trip counts, it's helpful to include
/// a type for constants which are otherwise hard to disambiguate.
static void PrintSCEVWithTypeHint(raw_ostream &OS, const SCEV* S) {
if (isa<SCEVConstant>(S))
OS << *S->getType() << " ";
OS << *S;
}
static void PrintLoopInfo(raw_ostream &OS, ScalarEvolution *SE,
const Loop *L) {
// Print all inner loops first
for (Loop *I : *L)
PrintLoopInfo(OS, SE, I);
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
SmallVector<BasicBlock *, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
if (ExitingBlocks.size() != 1)
OS << "<multiple exits> ";
auto *BTC = SE->getBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(BTC)) {
OS << "backedge-taken count is ";
PrintSCEVWithTypeHint(OS, BTC);
} else
OS << "Unpredictable backedge-taken count.";
OS << "\n";
if (ExitingBlocks.size() > 1)
for (BasicBlock *ExitingBlock : ExitingBlocks) {
OS << " exit count for " << ExitingBlock->getName() << ": ";
const SCEV *EC = SE->getExitCount(L, ExitingBlock);
PrintSCEVWithTypeHint(OS, EC);
if (isa<SCEVCouldNotCompute>(EC)) {
// Retry with predicates.
SmallVector<const SCEVPredicate *> Predicates;
EC = SE->getPredicatedExitCount(L, ExitingBlock, &Predicates);
if (!isa<SCEVCouldNotCompute>(EC)) {
OS << "\n predicated exit count for " << ExitingBlock->getName()
<< ": ";
PrintSCEVWithTypeHint(OS, EC);
OS << "\n Predicates:\n";
for (const auto *P : Predicates)
P->print(OS, 4);
}
}
OS << "\n";
}
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
auto *ConstantBTC = SE->getConstantMaxBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(ConstantBTC)) {
OS << "constant max backedge-taken count is ";
PrintSCEVWithTypeHint(OS, ConstantBTC);
if (SE->isBackedgeTakenCountMaxOrZero(L))
OS << ", actual taken count either this or zero.";
} else {
OS << "Unpredictable constant max backedge-taken count. ";
}
OS << "\n"
"Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
auto *SymbolicBTC = SE->getSymbolicMaxBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(SymbolicBTC)) {
OS << "symbolic max backedge-taken count is ";
PrintSCEVWithTypeHint(OS, SymbolicBTC);
if (SE->isBackedgeTakenCountMaxOrZero(L))
OS << ", actual taken count either this or zero.";
} else {
OS << "Unpredictable symbolic max backedge-taken count. ";
}
OS << "\n";
if (ExitingBlocks.size() > 1)
for (BasicBlock *ExitingBlock : ExitingBlocks) {
OS << " symbolic max exit count for " << ExitingBlock->getName() << ": ";
auto *ExitBTC = SE->getExitCount(L, ExitingBlock,
ScalarEvolution::SymbolicMaximum);
PrintSCEVWithTypeHint(OS, ExitBTC);
if (isa<SCEVCouldNotCompute>(ExitBTC)) {
// Retry with predicates.
SmallVector<const SCEVPredicate *> Predicates;
ExitBTC = SE->getPredicatedExitCount(L, ExitingBlock, &Predicates,
ScalarEvolution::SymbolicMaximum);
if (!isa<SCEVCouldNotCompute>(ExitBTC)) {
OS << "\n predicated symbolic max exit count for "
<< ExitingBlock->getName() << ": ";
PrintSCEVWithTypeHint(OS, ExitBTC);
OS << "\n Predicates:\n";
for (const auto *P : Predicates)
P->print(OS, 4);
}
}
OS << "\n";
}
SmallVector<const SCEVPredicate *, 4> Preds;
auto *PBT = SE->getPredicatedBackedgeTakenCount(L, Preds);
if (PBT != BTC) {
assert(!Preds.empty() && "Different predicated BTC, but no predicates");
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
if (!isa<SCEVCouldNotCompute>(PBT)) {
OS << "Predicated backedge-taken count is ";
PrintSCEVWithTypeHint(OS, PBT);
} else
OS << "Unpredictable predicated backedge-taken count.";
OS << "\n";
OS << " Predicates:\n";
for (const auto *P : Preds)
P->print(OS, 4);
}
Preds.clear();
auto *PredConstantMax =
SE->getPredicatedConstantMaxBackedgeTakenCount(L, Preds);
if (PredConstantMax != ConstantBTC) {
assert(!Preds.empty() &&
"different predicated constant max BTC but no predicates");
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
if (!isa<SCEVCouldNotCompute>(PredConstantMax)) {
OS << "Predicated constant max backedge-taken count is ";
PrintSCEVWithTypeHint(OS, PredConstantMax);
} else
OS << "Unpredictable predicated constant max backedge-taken count.";
OS << "\n";
OS << " Predicates:\n";
for (const auto *P : Preds)
P->print(OS, 4);
}
Preds.clear();
auto *PredSymbolicMax =
SE->getPredicatedSymbolicMaxBackedgeTakenCount(L, Preds);
if (SymbolicBTC != PredSymbolicMax) {
assert(!Preds.empty() &&
"Different predicated symbolic max BTC, but no predicates");
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
if (!isa<SCEVCouldNotCompute>(PredSymbolicMax)) {
OS << "Predicated symbolic max backedge-taken count is ";
PrintSCEVWithTypeHint(OS, PredSymbolicMax);
} else
OS << "Unpredictable predicated symbolic max backedge-taken count.";
OS << "\n";
OS << " Predicates:\n";
for (const auto *P : Preds)
P->print(OS, 4);
}
if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
OS << "Loop ";
L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": ";
OS << "Trip multiple is " << SE->getSmallConstantTripMultiple(L) << "\n";
}
}
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, ScalarEvolution::LoopDisposition LD) {
switch (LD) {
case ScalarEvolution::LoopVariant:
OS << "Variant";
break;
case ScalarEvolution::LoopInvariant:
OS << "Invariant";
break;
case ScalarEvolution::LoopComputable:
OS << "Computable";
break;
}
return OS;
}
raw_ostream &operator<<(raw_ostream &OS, ScalarEvolution::BlockDisposition BD) {
switch (BD) {
case ScalarEvolution::DoesNotDominateBlock:
OS << "DoesNotDominate";
break;
case ScalarEvolution::DominatesBlock:
OS << "Dominates";
break;
case ScalarEvolution::ProperlyDominatesBlock:
OS << "ProperlyDominates";
break;
}
return OS;
}
} // namespace llvm
void ScalarEvolution::print(raw_ostream &OS) const {
// ScalarEvolution's implementation of the print method is to print
// out SCEV values of all instructions that are interesting. Doing
// this potentially causes it to create new SCEV objects though,
// which technically conflicts with the const qualifier. This isn't
// observable from outside the class though, so casting away the
// const isn't dangerous.
ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this);
if (ClassifyExpressions) {
OS << "Classifying expressions for: ";
F.printAsOperand(OS, /*PrintType=*/false);
OS << "\n";
for (Instruction &I : instructions(F))
if (isSCEVable(I.getType()) && !isa<CmpInst>(I)) {
OS << I << '\n';
OS << " --> ";
const SCEV *SV = SE.getSCEV(&I);
SV->print(OS);
if (!isa<SCEVCouldNotCompute>(SV)) {
OS << " U: ";
SE.getUnsignedRange(SV).print(OS);
OS << " S: ";
SE.getSignedRange(SV).print(OS);
}
const Loop *L = LI.getLoopFor(I.getParent());
const SCEV *AtUse = SE.getSCEVAtScope(SV, L);
if (AtUse != SV) {
OS << " --> ";
AtUse->print(OS);
if (!isa<SCEVCouldNotCompute>(AtUse)) {
OS << " U: ";
SE.getUnsignedRange(AtUse).print(OS);
OS << " S: ";
SE.getSignedRange(AtUse).print(OS);
}
}
if (L) {
OS << "\t\t" "Exits: ";
const SCEV *ExitValue = SE.getSCEVAtScope(SV, L->getParentLoop());
if (!SE.isLoopInvariant(ExitValue, L)) {
OS << "<<Unknown>>";
} else {
OS << *ExitValue;
}
bool First = true;
for (const auto *Iter = L; Iter; Iter = Iter->getParentLoop()) {
if (First) {
OS << "\t\t" "LoopDispositions: { ";
First = false;
} else {
OS << ", ";
}
Iter->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": " << SE.getLoopDisposition(SV, Iter);
}
for (const auto *InnerL : depth_first(L)) {
if (InnerL == L)
continue;
if (First) {
OS << "\t\t" "LoopDispositions: { ";
First = false;
} else {
OS << ", ";
}
InnerL->getHeader()->printAsOperand(OS, /*PrintType=*/false);
OS << ": " << SE.getLoopDisposition(SV, InnerL);
}
OS << " }";
}
OS << "\n";
}
}
OS << "Determining loop execution counts for: ";
F.printAsOperand(OS, /*PrintType=*/false);
OS << "\n";
for (Loop *I : LI)
PrintLoopInfo(OS, &SE, I);
}
ScalarEvolution::LoopDisposition
ScalarEvolution::getLoopDisposition(const SCEV *S, const Loop *L) {
auto &Values = LoopDispositions[S];
for (auto &V : Values) {
if (V.getPointer() == L)
return V.getInt();
}
Values.emplace_back(L, LoopVariant);
LoopDisposition D = computeLoopDisposition(S, L);
auto &Values2 = LoopDispositions[S];
for (auto &V : llvm::reverse(Values2)) {
if (V.getPointer() == L) {
V.setInt(D);
break;
}
}
return D;
}
ScalarEvolution::LoopDisposition
ScalarEvolution::computeLoopDisposition(const SCEV *S, const Loop *L) {
switch (S->getSCEVType()) {
case scConstant:
case scVScale:
return LoopInvariant;
case scAddRecExpr: {
const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S);
// If L is the addrec's loop, it's computable.
if (AR->getLoop() == L)
return LoopComputable;
// Add recurrences are never invariant in the function-body (null loop).
if (!L)
return LoopVariant;
// Everything that is not defined at loop entry is variant.
if (DT.dominates(L->getHeader(), AR->getLoop()->getHeader()))
return LoopVariant;
assert(!L->contains(AR->getLoop()) && "Containing loop's header does not"
" dominate the contained loop's header?");
// This recurrence is invariant w.r.t. L if AR's loop contains L.
if (AR->getLoop()->contains(L))
return LoopInvariant;
// This recurrence is variant w.r.t. L if any of its operands
// are variant.
for (const auto *Op : AR->operands())
if (!isLoopInvariant(Op, L))
return LoopVariant;
// Otherwise it's loop-invariant.
return LoopInvariant;
}
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr: {
bool HasVarying = false;
for (const auto *Op : S->operands()) {
LoopDisposition D = getLoopDisposition(Op, L);
if (D == LoopVariant)
return LoopVariant;
if (D == LoopComputable)
HasVarying = true;
}
return HasVarying ? LoopComputable : LoopInvariant;
}
case scUnknown:
// All non-instruction values are loop invariant. All instructions are loop
// invariant if they are not contained in the specified loop.
// Instructions are never considered invariant in the function body
// (null loop) because they are defined within the "loop".
if (auto *I = dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue()))
return (L && !L->contains(I)) ? LoopInvariant : LoopVariant;
return LoopInvariant;
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
bool ScalarEvolution::isLoopInvariant(const SCEV *S, const Loop *L) {
return getLoopDisposition(S, L) == LoopInvariant;
}
bool ScalarEvolution::hasComputableLoopEvolution(const SCEV *S, const Loop *L) {
return getLoopDisposition(S, L) == LoopComputable;
}
ScalarEvolution::BlockDisposition
ScalarEvolution::getBlockDisposition(const SCEV *S, const BasicBlock *BB) {
auto &Values = BlockDispositions[S];
for (auto &V : Values) {
if (V.getPointer() == BB)
return V.getInt();
}
Values.emplace_back(BB, DoesNotDominateBlock);
BlockDisposition D = computeBlockDisposition(S, BB);
auto &Values2 = BlockDispositions[S];
for (auto &V : llvm::reverse(Values2)) {
if (V.getPointer() == BB) {
V.setInt(D);
break;
}
}
return D;
}
ScalarEvolution::BlockDisposition
ScalarEvolution::computeBlockDisposition(const SCEV *S, const BasicBlock *BB) {
switch (S->getSCEVType()) {
case scConstant:
case scVScale:
return ProperlyDominatesBlock;
case scAddRecExpr: {
// This uses a "dominates" query instead of "properly dominates" query
// to test for proper dominance too, because the instruction which
// produces the addrec's value is a PHI, and a PHI effectively properly
// dominates its entire containing block.
const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S);
if (!DT.dominates(AR->getLoop()->getHeader(), BB))
return DoesNotDominateBlock;
// Fall through into SCEVNAryExpr handling.
[[fallthrough]];
}
case scTruncate:
case scZeroExtend:
case scSignExtend:
case scPtrToInt:
case scAddExpr:
case scMulExpr:
case scUDivExpr:
case scUMaxExpr:
case scSMaxExpr:
case scUMinExpr:
case scSMinExpr:
case scSequentialUMinExpr: {
bool Proper = true;
for (const SCEV *NAryOp : S->operands()) {
BlockDisposition D = getBlockDisposition(NAryOp, BB);
if (D == DoesNotDominateBlock)
return DoesNotDominateBlock;
if (D == DominatesBlock)
Proper = false;
}
return Proper ? ProperlyDominatesBlock : DominatesBlock;
}
case scUnknown:
if (Instruction *I =
dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue())) {
if (I->getParent() == BB)
return DominatesBlock;
if (DT.properlyDominates(I->getParent(), BB))
return ProperlyDominatesBlock;
return DoesNotDominateBlock;
}
return ProperlyDominatesBlock;
case scCouldNotCompute:
llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
}
llvm_unreachable("Unknown SCEV kind!");
}
bool ScalarEvolution::dominates(const SCEV *S, const BasicBlock *BB) {
return getBlockDisposition(S, BB) >= DominatesBlock;
}
bool ScalarEvolution::properlyDominates(const SCEV *S, const BasicBlock *BB) {
return getBlockDisposition(S, BB) == ProperlyDominatesBlock;
}
bool ScalarEvolution::hasOperand(const SCEV *S, const SCEV *Op) const {
return SCEVExprContains(S, [&](const SCEV *Expr) { return Expr == Op; });
}
void ScalarEvolution::forgetBackedgeTakenCounts(const Loop *L,
bool Predicated) {
auto &BECounts =
Predicated ? PredicatedBackedgeTakenCounts : BackedgeTakenCounts;
auto It = BECounts.find(L);
if (It != BECounts.end()) {
for (const ExitNotTakenInfo &ENT : It->second.ExitNotTaken) {
for (const SCEV *S : {ENT.ExactNotTaken, ENT.SymbolicMaxNotTaken}) {
if (!isa<SCEVConstant>(S)) {
auto UserIt = BECountUsers.find(S);
assert(UserIt != BECountUsers.end());
UserIt->second.erase({L, Predicated});
}
}
}
BECounts.erase(It);
}
}
void ScalarEvolution::forgetMemoizedResults(ArrayRef<const SCEV *> SCEVs) {
SmallPtrSet<const SCEV *, 8> ToForget(llvm::from_range, SCEVs);
SmallVector<const SCEV *, 8> Worklist(ToForget.begin(), ToForget.end());
while (!Worklist.empty()) {
const SCEV *Curr = Worklist.pop_back_val();
auto Users = SCEVUsers.find(Curr);
if (Users != SCEVUsers.end())
for (const auto *User : Users->second)
if (ToForget.insert(User).second)
Worklist.push_back(User);
}
for (const auto *S : ToForget)
forgetMemoizedResultsImpl(S);
for (auto I = PredicatedSCEVRewrites.begin();
I != PredicatedSCEVRewrites.end();) {
std::pair<const SCEV *, const Loop *> Entry = I->first;
if (ToForget.count(Entry.first))
PredicatedSCEVRewrites.erase(I++);
else
++I;
}
}
void ScalarEvolution::forgetMemoizedResultsImpl(const SCEV *S) {
LoopDispositions.erase(S);
BlockDispositions.erase(S);
UnsignedRanges.erase(S);
SignedRanges.erase(S);
HasRecMap.erase(S);
ConstantMultipleCache.erase(S);
if (auto *AR = dyn_cast<SCEVAddRecExpr>(S)) {
UnsignedWrapViaInductionTried.erase(AR);
SignedWrapViaInductionTried.erase(AR);
}
auto ExprIt = ExprValueMap.find(S);
if (ExprIt != ExprValueMap.end()) {
for (Value *V : ExprIt->second) {
auto ValueIt = ValueExprMap.find_as(V);
if (ValueIt != ValueExprMap.end())
ValueExprMap.erase(ValueIt);
}
ExprValueMap.erase(ExprIt);
}
auto ScopeIt = ValuesAtScopes.find(S);
if (ScopeIt != ValuesAtScopes.end()) {
for (const auto &Pair : ScopeIt->second)
if (!isa_and_nonnull<SCEVConstant>(Pair.second))
llvm::erase(ValuesAtScopesUsers[Pair.second],
std::make_pair(Pair.first, S));
ValuesAtScopes.erase(ScopeIt);
}
auto ScopeUserIt = ValuesAtScopesUsers.find(S);
if (ScopeUserIt != ValuesAtScopesUsers.end()) {
for (const auto &Pair : ScopeUserIt->second)
llvm::erase(ValuesAtScopes[Pair.second], std::make_pair(Pair.first, S));
ValuesAtScopesUsers.erase(ScopeUserIt);
}
auto BEUsersIt = BECountUsers.find(S);
if (BEUsersIt != BECountUsers.end()) {
// Work on a copy, as forgetBackedgeTakenCounts() will modify the original.
auto Copy = BEUsersIt->second;
for (const auto &Pair : Copy)
forgetBackedgeTakenCounts(Pair.getPointer(), Pair.getInt());
BECountUsers.erase(BEUsersIt);
}
auto FoldUser = FoldCacheUser.find(S);
if (FoldUser != FoldCacheUser.end())
for (auto &KV : FoldUser->second)
FoldCache.erase(KV);
FoldCacheUser.erase(S);
}
void
ScalarEvolution::getUsedLoops(const SCEV *S,
SmallPtrSetImpl<const Loop *> &LoopsUsed) {
struct FindUsedLoops {
FindUsedLoops(SmallPtrSetImpl<const Loop *> &LoopsUsed)
: LoopsUsed(LoopsUsed) {}
SmallPtrSetImpl<const Loop *> &LoopsUsed;
bool follow(const SCEV *S) {
if (auto *AR = dyn_cast<SCEVAddRecExpr>(S))
LoopsUsed.insert(AR->getLoop());
return true;
}
bool isDone() const { return false; }
};
FindUsedLoops F(LoopsUsed);
SCEVTraversal<FindUsedLoops>(F).visitAll(S);
}
void ScalarEvolution::getReachableBlocks(
SmallPtrSetImpl<BasicBlock *> &Reachable, Function &F) {
SmallVector<BasicBlock *> Worklist;
Worklist.push_back(&F.getEntryBlock());
while (!Worklist.empty()) {
BasicBlock *BB = Worklist.pop_back_val();
if (!Reachable.insert(BB).second)
continue;
Value *Cond;
BasicBlock *TrueBB, *FalseBB;
if (match(BB->getTerminator(), m_Br(m_Value(Cond), m_BasicBlock(TrueBB),
m_BasicBlock(FalseBB)))) {
if (auto *C = dyn_cast<ConstantInt>(Cond)) {
Worklist.push_back(C->isOne() ? TrueBB : FalseBB);
continue;
}
if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
const SCEV *L = getSCEV(Cmp->getOperand(0));
const SCEV *R = getSCEV(Cmp->getOperand(1));
if (isKnownPredicateViaConstantRanges(Cmp->getCmpPredicate(), L, R)) {
Worklist.push_back(TrueBB);
continue;
}
if (isKnownPredicateViaConstantRanges(Cmp->getInverseCmpPredicate(), L,
R)) {
Worklist.push_back(FalseBB);
continue;
}
}
}
append_range(Worklist, successors(BB));
}
}
void ScalarEvolution::verify() const {
ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this);
ScalarEvolution SE2(F, TLI, AC, DT, LI);
SmallVector<Loop *, 8> LoopStack(LI.begin(), LI.end());
// Map's SCEV expressions from one ScalarEvolution "universe" to another.
struct SCEVMapper : public SCEVRewriteVisitor<SCEVMapper> {
SCEVMapper(ScalarEvolution &SE) : SCEVRewriteVisitor<SCEVMapper>(SE) {}
const SCEV *visitConstant(const SCEVConstant *Constant) {
return SE.getConstant(Constant->getAPInt());
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
return SE.getUnknown(Expr->getValue());
}
const SCEV *visitCouldNotCompute(const SCEVCouldNotCompute *Expr) {
return SE.getCouldNotCompute();
}
};
SCEVMapper SCM(SE2);
SmallPtrSet<BasicBlock *, 16> ReachableBlocks;
SE2.getReachableBlocks(ReachableBlocks, F);
auto GetDelta = [&](const SCEV *Old, const SCEV *New) -> const SCEV * {
if (containsUndefs(Old) || containsUndefs(New)) {
// SCEV treats "undef" as an unknown but consistent value (i.e. it does
// not propagate undef aggressively). This means we can (and do) fail
// verification in cases where a transform makes a value go from "undef"
// to "undef+1" (say). The transform is fine, since in both cases the
// result is "undef", but SCEV thinks the value increased by 1.
return nullptr;
}
// Unless VerifySCEVStrict is set, we only compare constant deltas.
const SCEV *Delta = SE2.getMinusSCEV(Old, New);
if (!VerifySCEVStrict && !isa<SCEVConstant>(Delta))
return nullptr;
return Delta;
};
while (!LoopStack.empty()) {
auto *L = LoopStack.pop_back_val();
llvm::append_range(LoopStack, *L);
// Only verify BECounts in reachable loops. For an unreachable loop,
// any BECount is legal.
if (!ReachableBlocks.contains(L->getHeader()))
continue;
// Only verify cached BECounts. Computing new BECounts may change the
// results of subsequent SCEV uses.
auto It = BackedgeTakenCounts.find(L);
if (It == BackedgeTakenCounts.end())
continue;
auto *CurBECount =
SCM.visit(It->second.getExact(L, const_cast<ScalarEvolution *>(this)));
auto *NewBECount = SE2.getBackedgeTakenCount(L);
if (CurBECount == SE2.getCouldNotCompute() ||
NewBECount == SE2.getCouldNotCompute()) {
// NB! This situation is legal, but is very suspicious -- whatever pass
// change the loop to make a trip count go from could not compute to
// computable or vice-versa *should have* invalidated SCEV. However, we
// choose not to assert here (for now) since we don't want false
// positives.
continue;
}
if (SE.getTypeSizeInBits(CurBECount->getType()) >
SE.getTypeSizeInBits(NewBECount->getType()))
NewBECount = SE2.getZeroExtendExpr(NewBECount, CurBECount->getType());
else if (SE.getTypeSizeInBits(CurBECount->getType()) <
SE.getTypeSizeInBits(NewBECount->getType()))
CurBECount = SE2.getZeroExtendExpr(CurBECount, NewBECount->getType());
const SCEV *Delta = GetDelta(CurBECount, NewBECount);
if (Delta && !Delta->isZero()) {
dbgs() << "Trip Count for " << *L << " Changed!\n";
dbgs() << "Old: " << *CurBECount << "\n";
dbgs() << "New: " << *NewBECount << "\n";
dbgs() << "Delta: " << *Delta << "\n";
std::abort();
}
}
// Collect all valid loops currently in LoopInfo.
SmallPtrSet<Loop *, 32> ValidLoops;
SmallVector<Loop *, 32> Worklist(LI.begin(), LI.end());
while (!Worklist.empty()) {
Loop *L = Worklist.pop_back_val();
if (ValidLoops.insert(L).second)
Worklist.append(L->begin(), L->end());
}
for (const auto &KV : ValueExprMap) {
#ifndef NDEBUG
// Check for SCEV expressions referencing invalid/deleted loops.
if (auto *AR = dyn_cast<SCEVAddRecExpr>(KV.second)) {
assert(ValidLoops.contains(AR->getLoop()) &&
"AddRec references invalid loop");
}
#endif
// Check that the value is also part of the reverse map.
auto It = ExprValueMap.find(KV.second);
if (It == ExprValueMap.end() || !It->second.contains(KV.first)) {
dbgs() << "Value " << *KV.first
<< " is in ValueExprMap but not in ExprValueMap\n";
std::abort();
}
if (auto *I = dyn_cast<Instruction>(&*KV.first)) {
if (!ReachableBlocks.contains(I->getParent()))
continue;
const SCEV *OldSCEV = SCM.visit(KV.second);
const SCEV *NewSCEV = SE2.getSCEV(I);
const SCEV *Delta = GetDelta(OldSCEV, NewSCEV);
if (Delta && !Delta->isZero()) {
dbgs() << "SCEV for value " << *I << " changed!\n"
<< "Old: " << *OldSCEV << "\n"
<< "New: " << *NewSCEV << "\n"
<< "Delta: " << *Delta << "\n";
std::abort();
}
}
}
for (const auto &KV : ExprValueMap) {
for (Value *V : KV.second) {
auto It = ValueExprMap.find_as(V);
if (It == ValueExprMap.end()) {
dbgs() << "Value " << *V
<< " is in ExprValueMap but not in ValueExprMap\n";
std::abort();
}
if (It->second != KV.first) {
dbgs() << "Value " << *V << " mapped to " << *It->second
<< " rather than " << *KV.first << "\n";
std::abort();
}
}
}
// Verify integrity of SCEV users.
for (const auto &S : UniqueSCEVs) {
for (const auto *Op : S.operands()) {
// We do not store dependencies of constants.
if (isa<SCEVConstant>(Op))
continue;
auto It = SCEVUsers.find(Op);
if (It != SCEVUsers.end() && It->second.count(&S))
continue;
dbgs() << "Use of operand " << *Op << " by user " << S
<< " is not being tracked!\n";
std::abort();
}
}
// Verify integrity of ValuesAtScopes users.
for (const auto &ValueAndVec : ValuesAtScopes) {
const SCEV *Value = ValueAndVec.first;
for (const auto &LoopAndValueAtScope : ValueAndVec.second) {
const Loop *L = LoopAndValueAtScope.first;
const SCEV *ValueAtScope = LoopAndValueAtScope.second;
if (!isa<SCEVConstant>(ValueAtScope)) {
auto It = ValuesAtScopesUsers.find(ValueAtScope);
if (It != ValuesAtScopesUsers.end() &&
is_contained(It->second, std::make_pair(L, Value)))
continue;
dbgs() << "Value: " << *Value << ", Loop: " << *L << ", ValueAtScope: "
<< *ValueAtScope << " missing in ValuesAtScopesUsers\n";
std::abort();
}
}
}
for (const auto &ValueAtScopeAndVec : ValuesAtScopesUsers) {
const SCEV *ValueAtScope = ValueAtScopeAndVec.first;
for (const auto &LoopAndValue : ValueAtScopeAndVec.second) {
const Loop *L = LoopAndValue.first;
const SCEV *Value = LoopAndValue.second;
assert(!isa<SCEVConstant>(Value));
auto It = ValuesAtScopes.find(Value);
if (It != ValuesAtScopes.end() &&
is_contained(It->second, std::make_pair(L, ValueAtScope)))
continue;
dbgs() << "Value: " << *Value << ", Loop: " << *L << ", ValueAtScope: "
<< *ValueAtScope << " missing in ValuesAtScopes\n";
std::abort();
}
}
// Verify integrity of BECountUsers.
auto VerifyBECountUsers = [&](bool Predicated) {
auto &BECounts =
Predicated ? PredicatedBackedgeTakenCounts : BackedgeTakenCounts;
for (const auto &LoopAndBEInfo : BECounts) {
for (const ExitNotTakenInfo &ENT : LoopAndBEInfo.second.ExitNotTaken) {
for (const SCEV *S : {ENT.ExactNotTaken, ENT.SymbolicMaxNotTaken}) {
if (!isa<SCEVConstant>(S)) {
auto UserIt = BECountUsers.find(S);
if (UserIt != BECountUsers.end() &&
UserIt->second.contains({ LoopAndBEInfo.first, Predicated }))
continue;
dbgs() << "Value " << *S << " for loop " << *LoopAndBEInfo.first
<< " missing from BECountUsers\n";
std::abort();
}
}
}
}
};
VerifyBECountUsers(/* Predicated */ false);
VerifyBECountUsers(/* Predicated */ true);
// Verify intergity of loop disposition cache.
for (auto &[S, Values] : LoopDispositions) {
for (auto [Loop, CachedDisposition] : Values) {
const auto RecomputedDisposition = SE2.getLoopDisposition(S, Loop);
if (CachedDisposition != RecomputedDisposition) {
dbgs() << "Cached disposition of " << *S << " for loop " << *Loop
<< " is incorrect: cached " << CachedDisposition << ", actual "
<< RecomputedDisposition << "\n";
std::abort();
}
}
}
// Verify integrity of the block disposition cache.
for (auto &[S, Values] : BlockDispositions) {
for (auto [BB, CachedDisposition] : Values) {
const auto RecomputedDisposition = SE2.getBlockDisposition(S, BB);
if (CachedDisposition != RecomputedDisposition) {
dbgs() << "Cached disposition of " << *S << " for block %"
<< BB->getName() << " is incorrect: cached " << CachedDisposition
<< ", actual " << RecomputedDisposition << "\n";
std::abort();
}
}
}
// Verify FoldCache/FoldCacheUser caches.
for (auto [FoldID, Expr] : FoldCache) {
auto I = FoldCacheUser.find(Expr);
if (I == FoldCacheUser.end()) {
dbgs() << "Missing entry in FoldCacheUser for cached expression " << *Expr
<< "!\n";
std::abort();
}
if (!is_contained(I->second, FoldID)) {
dbgs() << "Missing FoldID in cached users of " << *Expr << "!\n";
std::abort();
}
}
for (auto [Expr, IDs] : FoldCacheUser) {
for (auto &FoldID : IDs) {
auto I = FoldCache.find(FoldID);
if (I == FoldCache.end()) {
dbgs() << "Missing entry in FoldCache for expression " << *Expr
<< "!\n";
std::abort();
}
if (I->second != Expr) {
dbgs() << "Entry in FoldCache doesn't match FoldCacheUser: "
<< *I->second << " != " << *Expr << "!\n";
std::abort();
}
}
}
// Verify that ConstantMultipleCache computations are correct. We check that
// cached multiples and recomputed multiples are multiples of each other to
// verify correctness. It is possible that a recomputed multiple is different
// from the cached multiple due to strengthened no wrap flags or changes in
// KnownBits computations.
for (auto [S, Multiple] : ConstantMultipleCache) {
APInt RecomputedMultiple = SE2.getConstantMultiple(S);
if ((Multiple != 0 && RecomputedMultiple != 0 &&
Multiple.urem(RecomputedMultiple) != 0 &&
RecomputedMultiple.urem(Multiple) != 0)) {
dbgs() << "Incorrect cached computation in ConstantMultipleCache for "
<< *S << " : Computed " << RecomputedMultiple
<< " but cache contains " << Multiple << "!\n";
std::abort();
}
}
}
bool ScalarEvolution::invalidate(
Function &F, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &Inv) {
// Invalidate the ScalarEvolution object whenever it isn't preserved or one
// of its dependencies is invalidated.
auto PAC = PA.getChecker<ScalarEvolutionAnalysis>();
return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()) ||
Inv.invalidate<AssumptionAnalysis>(F, PA) ||
Inv.invalidate<DominatorTreeAnalysis>(F, PA) ||
Inv.invalidate<LoopAnalysis>(F, PA);
}
AnalysisKey ScalarEvolutionAnalysis::Key;
ScalarEvolution ScalarEvolutionAnalysis::run(Function &F,
FunctionAnalysisManager &AM) {
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &LI = AM.getResult<LoopAnalysis>(F);
return ScalarEvolution(F, TLI, AC, DT, LI);
}
PreservedAnalyses
ScalarEvolutionVerifierPass::run(Function &F, FunctionAnalysisManager &AM) {
AM.getResult<ScalarEvolutionAnalysis>(F).verify();
return PreservedAnalyses::all();
}
PreservedAnalyses
ScalarEvolutionPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
// For compatibility with opt's -analyze feature under legacy pass manager
// which was not ported to NPM. This keeps tests using
// update_analyze_test_checks.py working.
OS << "Printing analysis 'Scalar Evolution Analysis' for function '"
<< F.getName() << "':\n";
AM.getResult<ScalarEvolutionAnalysis>(F).print(OS);
return PreservedAnalyses::all();
}
INITIALIZE_PASS_BEGIN(ScalarEvolutionWrapperPass, "scalar-evolution",
"Scalar Evolution Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(ScalarEvolutionWrapperPass, "scalar-evolution",
"Scalar Evolution Analysis", false, true)
char ScalarEvolutionWrapperPass::ID = 0;
ScalarEvolutionWrapperPass::ScalarEvolutionWrapperPass() : FunctionPass(ID) {
initializeScalarEvolutionWrapperPassPass(*PassRegistry::getPassRegistry());
}
bool ScalarEvolutionWrapperPass::runOnFunction(Function &F) {
SE.reset(new ScalarEvolution(
F, getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F),
getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
getAnalysis<LoopInfoWrapperPass>().getLoopInfo()));
return false;
}
void ScalarEvolutionWrapperPass::releaseMemory() { SE.reset(); }
void ScalarEvolutionWrapperPass::print(raw_ostream &OS, const Module *) const {
SE->print(OS);
}
void ScalarEvolutionWrapperPass::verifyAnalysis() const {
if (!VerifySCEV)
return;
SE->verify();
}
void ScalarEvolutionWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequiredTransitive<AssumptionCacheTracker>();
AU.addRequiredTransitive<LoopInfoWrapperPass>();
AU.addRequiredTransitive<DominatorTreeWrapperPass>();
AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
}
const SCEVPredicate *ScalarEvolution::getEqualPredicate(const SCEV *LHS,
const SCEV *RHS) {
return getComparePredicate(ICmpInst::ICMP_EQ, LHS, RHS);
}
const SCEVPredicate *
ScalarEvolution::getComparePredicate(const ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS) {
FoldingSetNodeID ID;
assert(LHS->getType() == RHS->getType() &&
"Type mismatch between LHS and RHS");
// Unique this node based on the arguments
ID.AddInteger(SCEVPredicate::P_Compare);
ID.AddInteger(Pred);
ID.AddPointer(LHS);
ID.AddPointer(RHS);
void *IP = nullptr;
if (const auto *S = UniquePreds.FindNodeOrInsertPos(ID, IP))
return S;
SCEVComparePredicate *Eq = new (SCEVAllocator)
SCEVComparePredicate(ID.Intern(SCEVAllocator), Pred, LHS, RHS);
UniquePreds.InsertNode(Eq, IP);
return Eq;
}
const SCEVPredicate *ScalarEvolution::getWrapPredicate(
const SCEVAddRecExpr *AR,
SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
FoldingSetNodeID ID;
// Unique this node based on the arguments
ID.AddInteger(SCEVPredicate::P_Wrap);
ID.AddPointer(AR);
ID.AddInteger(AddedFlags);
void *IP = nullptr;
if (const auto *S = UniquePreds.FindNodeOrInsertPos(ID, IP))
return S;
auto *OF = new (SCEVAllocator)
SCEVWrapPredicate(ID.Intern(SCEVAllocator), AR, AddedFlags);
UniquePreds.InsertNode(OF, IP);
return OF;
}
namespace {
class SCEVPredicateRewriter : public SCEVRewriteVisitor<SCEVPredicateRewriter> {
public:
/// Rewrites \p S in the context of a loop L and the SCEV predication
/// infrastructure.
///
/// If \p Pred is non-null, the SCEV expression is rewritten to respect the
/// equivalences present in \p Pred.
///
/// If \p NewPreds is non-null, rewrite is free to add further predicates to
/// \p NewPreds such that the result will be an AddRecExpr.
static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE,
SmallVectorImpl<const SCEVPredicate *> *NewPreds,
const SCEVPredicate *Pred) {
SCEVPredicateRewriter Rewriter(L, SE, NewPreds, Pred);
return Rewriter.visit(S);
}
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
if (Pred) {
if (auto *U = dyn_cast<SCEVUnionPredicate>(Pred)) {
for (const auto *Pred : U->getPredicates())
if (const auto *IPred = dyn_cast<SCEVComparePredicate>(Pred))
if (IPred->getLHS() == Expr &&
IPred->getPredicate() == ICmpInst::ICMP_EQ)
return IPred->getRHS();
} else if (const auto *IPred = dyn_cast<SCEVComparePredicate>(Pred)) {
if (IPred->getLHS() == Expr &&
IPred->getPredicate() == ICmpInst::ICMP_EQ)
return IPred->getRHS();
}
}
return convertToAddRecWithPreds(Expr);
}
const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
const SCEV *Operand = visit(Expr->getOperand());
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Operand);
if (AR && AR->getLoop() == L && AR->isAffine()) {
// This couldn't be folded because the operand didn't have the nuw
// flag. Add the nusw flag as an assumption that we could make.
const SCEV *Step = AR->getStepRecurrence(SE);
Type *Ty = Expr->getType();
if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNUSW))
return SE.getAddRecExpr(SE.getZeroExtendExpr(AR->getStart(), Ty),
SE.getSignExtendExpr(Step, Ty), L,
AR->getNoWrapFlags());
}
return SE.getZeroExtendExpr(Operand, Expr->getType());
}
const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
const SCEV *Operand = visit(Expr->getOperand());
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Operand);
if (AR && AR->getLoop() == L && AR->isAffine()) {
// This couldn't be folded because the operand didn't have the nsw
// flag. Add the nssw flag as an assumption that we could make.
const SCEV *Step = AR->getStepRecurrence(SE);
Type *Ty = Expr->getType();
if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNSSW))
return SE.getAddRecExpr(SE.getSignExtendExpr(AR->getStart(), Ty),
SE.getSignExtendExpr(Step, Ty), L,
AR->getNoWrapFlags());
}
return SE.getSignExtendExpr(Operand, Expr->getType());
}
private:
explicit SCEVPredicateRewriter(
const Loop *L, ScalarEvolution &SE,
SmallVectorImpl<const SCEVPredicate *> *NewPreds,
const SCEVPredicate *Pred)
: SCEVRewriteVisitor(SE), NewPreds(NewPreds), Pred(Pred), L(L) {}
bool addOverflowAssumption(const SCEVPredicate *P) {
if (!NewPreds) {
// Check if we've already made this assumption.
return Pred && Pred->implies(P, SE);
}
NewPreds->push_back(P);
return true;
}
bool addOverflowAssumption(const SCEVAddRecExpr *AR,
SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
auto *A = SE.getWrapPredicate(AR, AddedFlags);
return addOverflowAssumption(A);
}
// If \p Expr represents a PHINode, we try to see if it can be represented
// as an AddRec, possibly under a predicate (PHISCEVPred). If it is possible
// to add this predicate as a runtime overflow check, we return the AddRec.
// If \p Expr does not meet these conditions (is not a PHI node, or we
// couldn't create an AddRec for it, or couldn't add the predicate), we just
// return \p Expr.
const SCEV *convertToAddRecWithPreds(const SCEVUnknown *Expr) {
if (!isa<PHINode>(Expr->getValue()))
return Expr;
std::optional<
std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
PredicatedRewrite = SE.createAddRecFromPHIWithCasts(Expr);
if (!PredicatedRewrite)
return Expr;
for (const auto *P : PredicatedRewrite->second){
// Wrap predicates from outer loops are not supported.
if (auto *WP = dyn_cast<const SCEVWrapPredicate>(P)) {
if (L != WP->getExpr()->getLoop())
return Expr;
}
if (!addOverflowAssumption(P))
return Expr;
}
return PredicatedRewrite->first;
}
SmallVectorImpl<const SCEVPredicate *> *NewPreds;
const SCEVPredicate *Pred;
const Loop *L;
};
} // end anonymous namespace
const SCEV *
ScalarEvolution::rewriteUsingPredicate(const SCEV *S, const Loop *L,
const SCEVPredicate &Preds) {
return SCEVPredicateRewriter::rewrite(S, L, *this, nullptr, &Preds);
}
const SCEVAddRecExpr *ScalarEvolution::convertSCEVToAddRecWithPredicates(
const SCEV *S, const Loop *L,
SmallVectorImpl<const SCEVPredicate *> &Preds) {
SmallVector<const SCEVPredicate *> TransformPreds;
S = SCEVPredicateRewriter::rewrite(S, L, *this, &TransformPreds, nullptr);
auto *AddRec = dyn_cast<SCEVAddRecExpr>(S);
if (!AddRec)
return nullptr;
// Since the transformation was successful, we can now transfer the SCEV
// predicates.
Preds.append(TransformPreds.begin(), TransformPreds.end());
return AddRec;
}
/// SCEV predicates
SCEVPredicate::SCEVPredicate(const FoldingSetNodeIDRef ID,
SCEVPredicateKind Kind)
: FastID(ID), Kind(Kind) {}
SCEVComparePredicate::SCEVComparePredicate(const FoldingSetNodeIDRef ID,
const ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS)
: SCEVPredicate(ID, P_Compare), Pred(Pred), LHS(LHS), RHS(RHS) {
assert(LHS->getType() == RHS->getType() && "LHS and RHS types don't match");
assert(LHS != RHS && "LHS and RHS are the same SCEV");
}
bool SCEVComparePredicate::implies(const SCEVPredicate *N,
ScalarEvolution &SE) const {
const auto *Op = dyn_cast<SCEVComparePredicate>(N);
if (!Op)
return false;
if (Pred != ICmpInst::ICMP_EQ)
return false;
return Op->LHS == LHS && Op->RHS == RHS;
}
bool SCEVComparePredicate::isAlwaysTrue() const { return false; }
void SCEVComparePredicate::print(raw_ostream &OS, unsigned Depth) const {
if (Pred == ICmpInst::ICMP_EQ)
OS.indent(Depth) << "Equal predicate: " << *LHS << " == " << *RHS << "\n";
else
OS.indent(Depth) << "Compare predicate: " << *LHS << " " << Pred << ") "
<< *RHS << "\n";
}
SCEVWrapPredicate::SCEVWrapPredicate(const FoldingSetNodeIDRef ID,
const SCEVAddRecExpr *AR,
IncrementWrapFlags Flags)
: SCEVPredicate(ID, P_Wrap), AR(AR), Flags(Flags) {}
const SCEVAddRecExpr *SCEVWrapPredicate::getExpr() const { return AR; }
bool SCEVWrapPredicate::implies(const SCEVPredicate *N,
ScalarEvolution &SE) const {
const auto *Op = dyn_cast<SCEVWrapPredicate>(N);
if (!Op || setFlags(Flags, Op->Flags) != Flags)
return false;
if (Op->AR == AR)
return true;
if (Flags != SCEVWrapPredicate::IncrementNSSW &&
Flags != SCEVWrapPredicate::IncrementNUSW)
return false;
const SCEV *Start = AR->getStart();
const SCEV *OpStart = Op->AR->getStart();
if (Start->getType()->isPointerTy() != OpStart->getType()->isPointerTy())
return false;
const SCEV *Step = AR->getStepRecurrence(SE);
const SCEV *OpStep = Op->AR->getStepRecurrence(SE);
if (!SE.isKnownPositive(Step) || !SE.isKnownPositive(OpStep))
return false;
// If both steps are positive, this implies N, if N's start and step are
// ULE/SLE (for NSUW/NSSW) than this'.
Type *WiderTy = SE.getWiderType(Step->getType(), OpStep->getType());
Step = SE.getNoopOrZeroExtend(Step, WiderTy);
OpStep = SE.getNoopOrZeroExtend(OpStep, WiderTy);
bool IsNUW = Flags == SCEVWrapPredicate::IncrementNUSW;
OpStart = IsNUW ? SE.getNoopOrZeroExtend(OpStart, WiderTy)
: SE.getNoopOrSignExtend(OpStart, WiderTy);
Start = IsNUW ? SE.getNoopOrZeroExtend(Start, WiderTy)
: SE.getNoopOrSignExtend(Start, WiderTy);
CmpInst::Predicate Pred = IsNUW ? CmpInst::ICMP_ULE : CmpInst::ICMP_SLE;
return SE.isKnownPredicate(Pred, OpStep, Step) &&
SE.isKnownPredicate(Pred, OpStart, Start);
}
bool SCEVWrapPredicate::isAlwaysTrue() const {
SCEV::NoWrapFlags ScevFlags = AR->getNoWrapFlags();
IncrementWrapFlags IFlags = Flags;
if (ScalarEvolution::setFlags(ScevFlags, SCEV::FlagNSW) == ScevFlags)
IFlags = clearFlags(IFlags, IncrementNSSW);
return IFlags == IncrementAnyWrap;
}
void SCEVWrapPredicate::print(raw_ostream &OS, unsigned Depth) const {
OS.indent(Depth) << *getExpr() << " Added Flags: ";
if (SCEVWrapPredicate::IncrementNUSW & getFlags())
OS << "<nusw>";
if (SCEVWrapPredicate::IncrementNSSW & getFlags())
OS << "<nssw>";
OS << "\n";
}
SCEVWrapPredicate::IncrementWrapFlags
SCEVWrapPredicate::getImpliedFlags(const SCEVAddRecExpr *AR,
ScalarEvolution &SE) {
IncrementWrapFlags ImpliedFlags = IncrementAnyWrap;
SCEV::NoWrapFlags StaticFlags = AR->getNoWrapFlags();
// We can safely transfer the NSW flag as NSSW.
if (ScalarEvolution::setFlags(StaticFlags, SCEV::FlagNSW) == StaticFlags)
ImpliedFlags = IncrementNSSW;
if (ScalarEvolution::setFlags(StaticFlags, SCEV::FlagNUW) == StaticFlags) {
// If the increment is positive, the SCEV NUW flag will also imply the
// WrapPredicate NUSW flag.
if (const auto *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
if (Step->getValue()->getValue().isNonNegative())
ImpliedFlags = setFlags(ImpliedFlags, IncrementNUSW);
}
return ImpliedFlags;
}
/// Union predicates don't get cached so create a dummy set ID for it.
SCEVUnionPredicate::SCEVUnionPredicate(ArrayRef<const SCEVPredicate *> Preds,
ScalarEvolution &SE)
: SCEVPredicate(FoldingSetNodeIDRef(nullptr, 0), P_Union) {
for (const auto *P : Preds)
add(P, SE);
}
bool SCEVUnionPredicate::isAlwaysTrue() const {
return all_of(Preds,
[](const SCEVPredicate *I) { return I->isAlwaysTrue(); });
}
bool SCEVUnionPredicate::implies(const SCEVPredicate *N,
ScalarEvolution &SE) const {
if (const auto *Set = dyn_cast<SCEVUnionPredicate>(N))
return all_of(Set->Preds, [this, &SE](const SCEVPredicate *I) {
return this->implies(I, SE);
});
return any_of(Preds,
[N, &SE](const SCEVPredicate *I) { return I->implies(N, SE); });
}
void SCEVUnionPredicate::print(raw_ostream &OS, unsigned Depth) const {
for (const auto *Pred : Preds)
Pred->print(OS, Depth);
}
void SCEVUnionPredicate::add(const SCEVPredicate *N, ScalarEvolution &SE) {
if (const auto *Set = dyn_cast<SCEVUnionPredicate>(N)) {
for (const auto *Pred : Set->Preds)
add(Pred, SE);
return;
}
// Only add predicate if it is not already implied by this union predicate.
if (implies(N, SE))
return;
// Build a new vector containing the current predicates, except the ones that
// are implied by the new predicate N.
SmallVector<const SCEVPredicate *> PrunedPreds;
for (auto *P : Preds) {
if (N->implies(P, SE))
continue;
PrunedPreds.push_back(P);
}
Preds = std::move(PrunedPreds);
Preds.push_back(N);
}
PredicatedScalarEvolution::PredicatedScalarEvolution(ScalarEvolution &SE,
Loop &L)
: SE(SE), L(L) {
SmallVector<const SCEVPredicate*, 4> Empty;
Preds = std::make_unique<SCEVUnionPredicate>(Empty, SE);
}
void ScalarEvolution::registerUser(const SCEV *User,
ArrayRef<const SCEV *> Ops) {
for (const auto *Op : Ops)
// We do not expect that forgetting cached data for SCEVConstants will ever
// open any prospects for sharpening or introduce any correctness issues,
// so we don't bother storing their dependencies.
if (!isa<SCEVConstant>(Op))
SCEVUsers[Op].insert(User);
}
const SCEV *PredicatedScalarEvolution::getSCEV(Value *V) {
const SCEV *Expr = SE.getSCEV(V);
RewriteEntry &Entry = RewriteMap[Expr];
// If we already have an entry and the version matches, return it.
if (Entry.second && Generation == Entry.first)
return Entry.second;
// We found an entry but it's stale. Rewrite the stale entry
// according to the current predicate.
if (Entry.second)
Expr = Entry.second;
const SCEV *NewSCEV = SE.rewriteUsingPredicate(Expr, &L, *Preds);
Entry = {Generation, NewSCEV};
return NewSCEV;
}
const SCEV *PredicatedScalarEvolution::getBackedgeTakenCount() {
if (!BackedgeCount) {
SmallVector<const SCEVPredicate *, 4> Preds;
BackedgeCount = SE.getPredicatedBackedgeTakenCount(&L, Preds);
for (const auto *P : Preds)
addPredicate(*P);
}
return BackedgeCount;
}
const SCEV *PredicatedScalarEvolution::getSymbolicMaxBackedgeTakenCount() {
if (!SymbolicMaxBackedgeCount) {
SmallVector<const SCEVPredicate *, 4> Preds;
SymbolicMaxBackedgeCount =
SE.getPredicatedSymbolicMaxBackedgeTakenCount(&L, Preds);
for (const auto *P : Preds)
addPredicate(*P);
}
return SymbolicMaxBackedgeCount;
}
unsigned PredicatedScalarEvolution::getSmallConstantMaxTripCount() {
if (!SmallConstantMaxTripCount) {
SmallVector<const SCEVPredicate *, 4> Preds;
SmallConstantMaxTripCount = SE.getSmallConstantMaxTripCount(&L, &Preds);
for (const auto *P : Preds)
addPredicate(*P);
}
return *SmallConstantMaxTripCount;
}
void PredicatedScalarEvolution::addPredicate(const SCEVPredicate &Pred) {
if (Preds->implies(&Pred, SE))
return;
SmallVector<const SCEVPredicate *, 4> NewPreds(Preds->getPredicates());
NewPreds.push_back(&Pred);
Preds = std::make_unique<SCEVUnionPredicate>(NewPreds, SE);
updateGeneration();
}
const SCEVPredicate &PredicatedScalarEvolution::getPredicate() const {
return *Preds;
}
void PredicatedScalarEvolution::updateGeneration() {
// If the generation number wrapped recompute everything.
if (++Generation == 0) {
for (auto &II : RewriteMap) {
const SCEV *Rewritten = II.second.second;
II.second = {Generation, SE.rewriteUsingPredicate(Rewritten, &L, *Preds)};
}
}
}
void PredicatedScalarEvolution::setNoOverflow(
Value *V, SCEVWrapPredicate::IncrementWrapFlags Flags) {
const SCEV *Expr = getSCEV(V);
const auto *AR = cast<SCEVAddRecExpr>(Expr);
auto ImpliedFlags = SCEVWrapPredicate::getImpliedFlags(AR, SE);
// Clear the statically implied flags.
Flags = SCEVWrapPredicate::clearFlags(Flags, ImpliedFlags);
addPredicate(*SE.getWrapPredicate(AR, Flags));
auto II = FlagsMap.insert({V, Flags});
if (!II.second)
II.first->second = SCEVWrapPredicate::setFlags(Flags, II.first->second);
}
bool PredicatedScalarEvolution::hasNoOverflow(
Value *V, SCEVWrapPredicate::IncrementWrapFlags Flags) {
const SCEV *Expr = getSCEV(V);
const auto *AR = cast<SCEVAddRecExpr>(Expr);
Flags = SCEVWrapPredicate::clearFlags(
Flags, SCEVWrapPredicate::getImpliedFlags(AR, SE));
auto II = FlagsMap.find(V);
if (II != FlagsMap.end())
Flags = SCEVWrapPredicate::clearFlags(Flags, II->second);
return Flags == SCEVWrapPredicate::IncrementAnyWrap;
}
const SCEVAddRecExpr *PredicatedScalarEvolution::getAsAddRec(Value *V) {
const SCEV *Expr = this->getSCEV(V);
SmallVector<const SCEVPredicate *, 4> NewPreds;
auto *New = SE.convertSCEVToAddRecWithPredicates(Expr, &L, NewPreds);
if (!New)
return nullptr;
for (const auto *P : NewPreds)
addPredicate(*P);
RewriteMap[SE.getSCEV(V)] = {Generation, New};
return New;
}
PredicatedScalarEvolution::PredicatedScalarEvolution(
const PredicatedScalarEvolution &Init)
: RewriteMap(Init.RewriteMap), SE(Init.SE), L(Init.L),
Preds(std::make_unique<SCEVUnionPredicate>(Init.Preds->getPredicates(),
SE)),
Generation(Init.Generation), BackedgeCount(Init.BackedgeCount) {
for (auto I : Init.FlagsMap)
FlagsMap.insert(I);
}
void PredicatedScalarEvolution::print(raw_ostream &OS, unsigned Depth) const {
// For each block.
for (auto *BB : L.getBlocks())
for (auto &I : *BB) {
if (!SE.isSCEVable(I.getType()))
continue;
auto *Expr = SE.getSCEV(&I);
auto II = RewriteMap.find(Expr);
if (II == RewriteMap.end())
continue;
// Don't print things that are not interesting.
if (II->second.second == Expr)
continue;
OS.indent(Depth) << "[PSE]" << I << ":\n";
OS.indent(Depth + 2) << *Expr << "\n";
OS.indent(Depth + 2) << "--> " << *II->second.second << "\n";
}
}
// Match the mathematical pattern A - (A / B) * B, where A and B can be
// arbitrary expressions. Also match zext (trunc A to iB) to iY, which is used
// for URem with constant power-of-2 second operands.
// It's not always easy, as A and B can be folded (imagine A is X / 2, and B is
// 4, A / B becomes X / 8).
bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
const SCEV *&RHS) {
if (Expr->getType()->isPointerTy())
return false;
// Try to match 'zext (trunc A to iB) to iY', which is used
// for URem with constant power-of-2 second operands. Make sure the size of
// the operand A matches the size of the whole expressions.
if (const auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(Expr))
if (const auto *Trunc = dyn_cast<SCEVTruncateExpr>(ZExt->getOperand(0))) {
LHS = Trunc->getOperand();
// Bail out if the type of the LHS is larger than the type of the
// expression for now.
if (getTypeSizeInBits(LHS->getType()) >
getTypeSizeInBits(Expr->getType()))
return false;
if (LHS->getType() != Expr->getType())
LHS = getZeroExtendExpr(LHS, Expr->getType());
RHS = getConstant(APInt(getTypeSizeInBits(Expr->getType()), 1)
<< getTypeSizeInBits(Trunc->getType()));
return true;
}
const auto *Add = dyn_cast<SCEVAddExpr>(Expr);
if (Add == nullptr || Add->getNumOperands() != 2)
return false;
const SCEV *A = Add->getOperand(1);
const auto *Mul = dyn_cast<SCEVMulExpr>(Add->getOperand(0));
if (Mul == nullptr)
return false;
const auto MatchURemWithDivisor = [&](const SCEV *B) {
// (SomeExpr + (-(SomeExpr / B) * B)).
if (Expr == getURemExpr(A, B)) {
LHS = A;
RHS = B;
return true;
}
return false;
};
// (SomeExpr + (-1 * (SomeExpr / B) * B)).
if (Mul->getNumOperands() == 3 && isa<SCEVConstant>(Mul->getOperand(0)))
return MatchURemWithDivisor(Mul->getOperand(1)) ||
MatchURemWithDivisor(Mul->getOperand(2));
// (SomeExpr + ((-SomeExpr / B) * B)) or (SomeExpr + ((SomeExpr / B) * -B)).
if (Mul->getNumOperands() == 2)
return MatchURemWithDivisor(Mul->getOperand(1)) ||
MatchURemWithDivisor(Mul->getOperand(0)) ||
MatchURemWithDivisor(getNegativeSCEV(Mul->getOperand(1))) ||
MatchURemWithDivisor(getNegativeSCEV(Mul->getOperand(0)));
return false;
}
ScalarEvolution::LoopGuards
ScalarEvolution::LoopGuards::collect(const Loop *L, ScalarEvolution &SE) {
BasicBlock *Header = L->getHeader();
BasicBlock *Pred = L->getLoopPredecessor();
LoopGuards Guards(SE);
if (!Pred)
return Guards;
SmallPtrSet<const BasicBlock *, 8> VisitedBlocks;
collectFromBlock(SE, Guards, Header, Pred, VisitedBlocks);
return Guards;
}
void ScalarEvolution::LoopGuards::collectFromPHI(
ScalarEvolution &SE, ScalarEvolution::LoopGuards &Guards,
const PHINode &Phi, SmallPtrSetImpl<const BasicBlock *> &VisitedBlocks,
SmallDenseMap<const BasicBlock *, LoopGuards> &IncomingGuards,
unsigned Depth) {
if (!SE.isSCEVable(Phi.getType()))
return;
using MinMaxPattern = std::pair<const SCEVConstant *, SCEVTypes>;
auto GetMinMaxConst = [&](unsigned IncomingIdx) -> MinMaxPattern {
const BasicBlock *InBlock = Phi.getIncomingBlock(IncomingIdx);
if (!VisitedBlocks.insert(InBlock).second)
return {nullptr, scCouldNotCompute};
auto [G, Inserted] = IncomingGuards.try_emplace(InBlock, LoopGuards(SE));
if (Inserted)
collectFromBlock(SE, G->second, Phi.getParent(), InBlock, VisitedBlocks,
Depth + 1);
auto &RewriteMap = G->second.RewriteMap;
if (RewriteMap.empty())
return {nullptr, scCouldNotCompute};
auto S = RewriteMap.find(SE.getSCEV(Phi.getIncomingValue(IncomingIdx)));
if (S == RewriteMap.end())
return {nullptr, scCouldNotCompute};
auto *SM = dyn_cast_if_present<SCEVMinMaxExpr>(S->second);
if (!SM)
return {nullptr, scCouldNotCompute};
if (const SCEVConstant *C0 = dyn_cast<SCEVConstant>(SM->getOperand(0)))
return {C0, SM->getSCEVType()};
return {nullptr, scCouldNotCompute};
};
auto MergeMinMaxConst = [](MinMaxPattern P1,
MinMaxPattern P2) -> MinMaxPattern {
auto [C1, T1] = P1;
auto [C2, T2] = P2;
if (!C1 || !C2 || T1 != T2)
return {nullptr, scCouldNotCompute};
switch (T1) {
case scUMaxExpr:
return {C1->getAPInt().ult(C2->getAPInt()) ? C1 : C2, T1};
case scSMaxExpr:
return {C1->getAPInt().slt(C2->getAPInt()) ? C1 : C2, T1};
case scUMinExpr:
return {C1->getAPInt().ugt(C2->getAPInt()) ? C1 : C2, T1};
case scSMinExpr:
return {C1->getAPInt().sgt(C2->getAPInt()) ? C1 : C2, T1};
default:
llvm_unreachable("Trying to merge non-MinMaxExpr SCEVs.");
}
};
auto P = GetMinMaxConst(0);
for (unsigned int In = 1; In < Phi.getNumIncomingValues(); In++) {
if (!P.first)
break;
P = MergeMinMaxConst(P, GetMinMaxConst(In));
}
if (P.first) {
const SCEV *LHS = SE.getSCEV(const_cast<PHINode *>(&Phi));
SmallVector<const SCEV *, 2> Ops({P.first, LHS});
const SCEV *RHS = SE.getMinMaxExpr(P.second, Ops);
Guards.RewriteMap.insert({LHS, RHS});
}
}
void ScalarEvolution::LoopGuards::collectFromBlock(
ScalarEvolution &SE, ScalarEvolution::LoopGuards &Guards,
const BasicBlock *Block, const BasicBlock *Pred,
SmallPtrSetImpl<const BasicBlock *> &VisitedBlocks, unsigned Depth) {
SmallVector<const SCEV *> ExprsToRewrite;
auto CollectCondition = [&](ICmpInst::Predicate Predicate, const SCEV *LHS,
const SCEV *RHS,
DenseMap<const SCEV *, const SCEV *>
&RewriteMap) {
// WARNING: It is generally unsound to apply any wrap flags to the proposed
// replacement SCEV which isn't directly implied by the structure of that
// SCEV. In particular, using contextual facts to imply flags is *NOT*
// legal. See the scoping rules for flags in the header to understand why.
// If LHS is a constant, apply information to the other expression.
if (isa<SCEVConstant>(LHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
// Check for a condition of the form (-C1 + X < C2). InstCombine will
// create this form when combining two checks of the form (X u< C2 + C1) and
// (X >=u C1).
auto MatchRangeCheckIdiom = [&SE, Predicate, LHS, RHS, &RewriteMap,
&ExprsToRewrite]() {
const SCEVConstant *C1;
const SCEVUnknown *LHSUnknown;
auto *C2 = dyn_cast<SCEVConstant>(RHS);
if (!match(LHS,
m_scev_Add(m_SCEVConstant(C1), m_SCEVUnknown(LHSUnknown))) ||
!C2)
return false;
auto ExactRegion =
ConstantRange::makeExactICmpRegion(Predicate, C2->getAPInt())
.sub(C1->getAPInt());
// Bail out, unless we have a non-wrapping, monotonic range.
if (ExactRegion.isWrappedSet() || ExactRegion.isFullSet())
return false;
auto [I, Inserted] = RewriteMap.try_emplace(LHSUnknown);
const SCEV *RewrittenLHS = Inserted ? LHSUnknown : I->second;
I->second = SE.getUMaxExpr(
SE.getConstant(ExactRegion.getUnsignedMin()),
SE.getUMinExpr(RewrittenLHS,
SE.getConstant(ExactRegion.getUnsignedMax())));
ExprsToRewrite.push_back(LHSUnknown);
return true;
};
if (MatchRangeCheckIdiom())
return;
// Return true if \p Expr is a MinMax SCEV expression with a non-negative
// constant operand. If so, return in \p SCTy the SCEV type and in \p RHS
// the non-constant operand and in \p LHS the constant operand.
auto IsMinMaxSCEVWithNonNegativeConstant =
[&](const SCEV *Expr, SCEVTypes &SCTy, const SCEV *&LHS,
const SCEV *&RHS) {
if (auto *MinMax = dyn_cast<SCEVMinMaxExpr>(Expr)) {
if (MinMax->getNumOperands() != 2)
return false;
if (auto *C = dyn_cast<SCEVConstant>(MinMax->getOperand(0))) {
if (C->getAPInt().isNegative())
return false;
SCTy = MinMax->getSCEVType();
LHS = MinMax->getOperand(0);
RHS = MinMax->getOperand(1);
return true;
}
}
return false;
};
// Checks whether Expr is a non-negative constant, and Divisor is a positive
// constant, and returns their APInt in ExprVal and in DivisorVal.
auto GetNonNegExprAndPosDivisor = [&](const SCEV *Expr, const SCEV *Divisor,
APInt &ExprVal, APInt &DivisorVal) {
auto *ConstExpr = dyn_cast<SCEVConstant>(Expr);
auto *ConstDivisor = dyn_cast<SCEVConstant>(Divisor);
if (!ConstExpr || !ConstDivisor)
return false;
ExprVal = ConstExpr->getAPInt();
DivisorVal = ConstDivisor->getAPInt();
return ExprVal.isNonNegative() && !DivisorVal.isNonPositive();
};
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and greater or equal than Expr.
// For now, only handle constant Expr and Divisor.
auto GetNextSCEVDividesByDivisor = [&](const SCEV *Expr,
const SCEV *Divisor) {
APInt ExprVal;
APInt DivisorVal;
if (!GetNonNegExprAndPosDivisor(Expr, Divisor, ExprVal, DivisorVal))
return Expr;
APInt Rem = ExprVal.urem(DivisorVal);
if (!Rem.isZero())
// return the SCEV: Expr + Divisor - Expr % Divisor
return SE.getConstant(ExprVal + DivisorVal - Rem);
return Expr;
};
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and less or equal than Expr.
// For now, only handle constant Expr and Divisor.
auto GetPreviousSCEVDividesByDivisor = [&](const SCEV *Expr,
const SCEV *Divisor) {
APInt ExprVal;
APInt DivisorVal;
if (!GetNonNegExprAndPosDivisor(Expr, Divisor, ExprVal, DivisorVal))
return Expr;
APInt Rem = ExprVal.urem(DivisorVal);
// return the SCEV: Expr - Expr % Divisor
return SE.getConstant(ExprVal - Rem);
};
// Apply divisibilty by \p Divisor on MinMaxExpr with constant values,
// recursively. This is done by aligning up/down the constant value to the
// Divisor.
std::function<const SCEV *(const SCEV *, const SCEV *)>
ApplyDivisibiltyOnMinMaxExpr = [&](const SCEV *MinMaxExpr,
const SCEV *Divisor) {
const SCEV *MinMaxLHS = nullptr, *MinMaxRHS = nullptr;
SCEVTypes SCTy;
if (!IsMinMaxSCEVWithNonNegativeConstant(MinMaxExpr, SCTy, MinMaxLHS,
MinMaxRHS))
return MinMaxExpr;
auto IsMin =
isa<SCEVSMinExpr>(MinMaxExpr) || isa<SCEVUMinExpr>(MinMaxExpr);
assert(SE.isKnownNonNegative(MinMaxLHS) &&
"Expected non-negative operand!");
auto *DivisibleExpr =
IsMin ? GetPreviousSCEVDividesByDivisor(MinMaxLHS, Divisor)
: GetNextSCEVDividesByDivisor(MinMaxLHS, Divisor);
SmallVector<const SCEV *> Ops = {
ApplyDivisibiltyOnMinMaxExpr(MinMaxRHS, Divisor), DivisibleExpr};
return SE.getMinMaxExpr(SCTy, Ops);
};
// If we have LHS == 0, check if LHS is computing a property of some unknown
// SCEV %v which we can rewrite %v to express explicitly.
if (Predicate == CmpInst::ICMP_EQ && match(RHS, m_scev_Zero())) {
// If LHS is A % B, i.e. A % B == 0, rewrite A to (A /u B) * B to
// explicitly express that.
const SCEV *URemLHS = nullptr;
const SCEV *URemRHS = nullptr;
if (SE.matchURem(LHS, URemLHS, URemRHS)) {
if (const SCEVUnknown *LHSUnknown = dyn_cast<SCEVUnknown>(URemLHS)) {
auto I = RewriteMap.find(LHSUnknown);
const SCEV *RewrittenLHS =
I != RewriteMap.end() ? I->second : LHSUnknown;
RewrittenLHS = ApplyDivisibiltyOnMinMaxExpr(RewrittenLHS, URemRHS);
const auto *Multiple =
SE.getMulExpr(SE.getUDivExpr(RewrittenLHS, URemRHS), URemRHS);
RewriteMap[LHSUnknown] = Multiple;
ExprsToRewrite.push_back(LHSUnknown);
return;
}
}
}
// Do not apply information for constants or if RHS contains an AddRec.
if (isa<SCEVConstant>(LHS) || SE.containsAddRecurrence(RHS))
return;
// If RHS is SCEVUnknown, make sure the information is applied to it.
if (!isa<SCEVUnknown>(LHS) && isa<SCEVUnknown>(RHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
// Puts rewrite rule \p From -> \p To into the rewrite map. Also if \p From
// and \p FromRewritten are the same (i.e. there has been no rewrite
// registered for \p From), then puts this value in the list of rewritten
// expressions.
auto AddRewrite = [&](const SCEV *From, const SCEV *FromRewritten,
const SCEV *To) {
if (From == FromRewritten)
ExprsToRewrite.push_back(From);
RewriteMap[From] = To;
};
// Checks whether \p S has already been rewritten. In that case returns the
// existing rewrite because we want to chain further rewrites onto the
// already rewritten value. Otherwise returns \p S.
auto GetMaybeRewritten = [&](const SCEV *S) {
auto I = RewriteMap.find(S);
return I != RewriteMap.end() ? I->second : S;
};
// Check for the SCEV expression (A /u B) * B while B is a constant, inside
// \p Expr. The check is done recuresively on \p Expr, which is assumed to
// be a composition of Min/Max SCEVs. Return whether the SCEV expression (A
// /u B) * B was found, and return the divisor B in \p DividesBy. For
// example, if Expr = umin (umax ((A /u 8) * 8, 16), 64), return true since
// (A /u 8) * 8 matched the pattern, and return the constant SCEV 8 in \p
// DividesBy.
std::function<bool(const SCEV *, const SCEV *&)> HasDivisibiltyInfo =
[&](const SCEV *Expr, const SCEV *&DividesBy) {
if (auto *Mul = dyn_cast<SCEVMulExpr>(Expr)) {
if (Mul->getNumOperands() != 2)
return false;
auto *MulLHS = Mul->getOperand(0);
auto *MulRHS = Mul->getOperand(1);
if (isa<SCEVConstant>(MulLHS))
std::swap(MulLHS, MulRHS);
if (auto *Div = dyn_cast<SCEVUDivExpr>(MulLHS))
if (Div->getOperand(1) == MulRHS) {
DividesBy = MulRHS;
return true;
}
}
if (auto *MinMax = dyn_cast<SCEVMinMaxExpr>(Expr))
return HasDivisibiltyInfo(MinMax->getOperand(0), DividesBy) ||
HasDivisibiltyInfo(MinMax->getOperand(1), DividesBy);
return false;
};
// Return true if Expr known to divide by \p DividesBy.
std::function<bool(const SCEV *, const SCEV *&)> IsKnownToDivideBy =
[&](const SCEV *Expr, const SCEV *DividesBy) {
if (SE.getURemExpr(Expr, DividesBy)->isZero())
return true;
if (auto *MinMax = dyn_cast<SCEVMinMaxExpr>(Expr))
return IsKnownToDivideBy(MinMax->getOperand(0), DividesBy) &&
IsKnownToDivideBy(MinMax->getOperand(1), DividesBy);
return false;
};
const SCEV *RewrittenLHS = GetMaybeRewritten(LHS);
const SCEV *DividesBy = nullptr;
if (HasDivisibiltyInfo(RewrittenLHS, DividesBy))
// Check that the whole expression is divided by DividesBy
DividesBy =
IsKnownToDivideBy(RewrittenLHS, DividesBy) ? DividesBy : nullptr;
// Collect rewrites for LHS and its transitive operands based on the
// condition.
// For min/max expressions, also apply the guard to its operands:
// 'min(a, b) >= c' -> '(a >= c) and (b >= c)',
// 'min(a, b) > c' -> '(a > c) and (b > c)',
// 'max(a, b) <= c' -> '(a <= c) and (b <= c)',
// 'max(a, b) < c' -> '(a < c) and (b < c)'.
// We cannot express strict predicates in SCEV, so instead we replace them
// with non-strict ones against plus or minus one of RHS depending on the
// predicate.
const SCEV *One = SE.getOne(RHS->getType());
switch (Predicate) {
case CmpInst::ICMP_ULT:
if (RHS->getType()->isPointerTy())
return;
RHS = SE.getUMaxExpr(RHS, One);
[[fallthrough]];
case CmpInst::ICMP_SLT: {
RHS = SE.getMinusSCEV(RHS, One);
RHS = DividesBy ? GetPreviousSCEVDividesByDivisor(RHS, DividesBy) : RHS;
break;
}
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_SGT:
RHS = SE.getAddExpr(RHS, One);
RHS = DividesBy ? GetNextSCEVDividesByDivisor(RHS, DividesBy) : RHS;
break;
case CmpInst::ICMP_ULE:
case CmpInst::ICMP_SLE:
RHS = DividesBy ? GetPreviousSCEVDividesByDivisor(RHS, DividesBy) : RHS;
break;
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_SGE:
RHS = DividesBy ? GetNextSCEVDividesByDivisor(RHS, DividesBy) : RHS;
break;
default:
break;
}
SmallVector<const SCEV *, 16> Worklist(1, LHS);
SmallPtrSet<const SCEV *, 16> Visited;
auto EnqueueOperands = [&Worklist](const SCEVNAryExpr *S) {
append_range(Worklist, S->operands());
};
while (!Worklist.empty()) {
const SCEV *From = Worklist.pop_back_val();
if (isa<SCEVConstant>(From))
continue;
if (!Visited.insert(From).second)
continue;
const SCEV *FromRewritten = GetMaybeRewritten(From);
const SCEV *To = nullptr;
switch (Predicate) {
case CmpInst::ICMP_ULT:
case CmpInst::ICMP_ULE:
To = SE.getUMinExpr(FromRewritten, RHS);
if (auto *UMax = dyn_cast<SCEVUMaxExpr>(FromRewritten))
EnqueueOperands(UMax);
break;
case CmpInst::ICMP_SLT:
case CmpInst::ICMP_SLE:
To = SE.getSMinExpr(FromRewritten, RHS);
if (auto *SMax = dyn_cast<SCEVSMaxExpr>(FromRewritten))
EnqueueOperands(SMax);
break;
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_UGE:
To = SE.getUMaxExpr(FromRewritten, RHS);
if (auto *UMin = dyn_cast<SCEVUMinExpr>(FromRewritten))
EnqueueOperands(UMin);
break;
case CmpInst::ICMP_SGT:
case CmpInst::ICMP_SGE:
To = SE.getSMaxExpr(FromRewritten, RHS);
if (auto *SMin = dyn_cast<SCEVSMinExpr>(FromRewritten))
EnqueueOperands(SMin);
break;
case CmpInst::ICMP_EQ:
if (isa<SCEVConstant>(RHS))
To = RHS;
break;
case CmpInst::ICMP_NE:
if (match(RHS, m_scev_Zero())) {
const SCEV *OneAlignedUp =
DividesBy ? GetNextSCEVDividesByDivisor(One, DividesBy) : One;
To = SE.getUMaxExpr(FromRewritten, OneAlignedUp);
}
break;
default:
break;
}
if (To)
AddRewrite(From, FromRewritten, To);
}
};
SmallVector<PointerIntPair<Value *, 1, bool>> Terms;
// First, collect information from assumptions dominating the loop.
for (auto &AssumeVH : SE.AC.assumptions()) {
if (!AssumeVH)
continue;
auto *AssumeI = cast<CallInst>(AssumeVH);
if (!SE.DT.dominates(AssumeI, Block))
continue;
Terms.emplace_back(AssumeI->getOperand(0), true);
}
// Second, collect information from llvm.experimental.guards dominating the loop.
auto *GuardDecl = Intrinsic::getDeclarationIfExists(
SE.F.getParent(), Intrinsic::experimental_guard);
if (GuardDecl)
for (const auto *GU : GuardDecl->users())
if (const auto *Guard = dyn_cast<IntrinsicInst>(GU))
if (Guard->getFunction() == Block->getParent() &&
SE.DT.dominates(Guard, Block))
Terms.emplace_back(Guard->getArgOperand(0), true);
// Third, collect conditions from dominating branches. Starting at the loop
// predecessor, climb up the predecessor chain, as long as there are
// predecessors that can be found that have unique successors leading to the
// original header.
// TODO: share this logic with isLoopEntryGuardedByCond.
unsigned NumCollectedConditions = 0;
VisitedBlocks.insert(Block);
std::pair<const BasicBlock *, const BasicBlock *> Pair(Pred, Block);
for (; Pair.first;
Pair = SE.getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
VisitedBlocks.insert(Pair.second);
const BranchInst *LoopEntryPredicate =
dyn_cast<BranchInst>(Pair.first->getTerminator());
if (!LoopEntryPredicate || LoopEntryPredicate->isUnconditional())
continue;
Terms.emplace_back(LoopEntryPredicate->getCondition(),
LoopEntryPredicate->getSuccessor(0) == Pair.second);
NumCollectedConditions++;
// If we are recursively collecting guards stop after 2
// conditions to limit compile-time impact for now.
if (Depth > 0 && NumCollectedConditions == 2)
break;
}
// Finally, if we stopped climbing the predecessor chain because
// there wasn't a unique one to continue, try to collect conditions
// for PHINodes by recursively following all of their incoming
// blocks and try to merge the found conditions to build a new one
// for the Phi.
if (Pair.second->hasNPredecessorsOrMore(2) &&
Depth < MaxLoopGuardCollectionDepth) {
SmallDenseMap<const BasicBlock *, LoopGuards> IncomingGuards;
for (auto &Phi : Pair.second->phis())
collectFromPHI(SE, Guards, Phi, VisitedBlocks, IncomingGuards, Depth);
}
// Now apply the information from the collected conditions to
// Guards.RewriteMap. Conditions are processed in reverse order, so the
// earliest conditions is processed first. This ensures the SCEVs with the
// shortest dependency chains are constructed first.
for (auto [Term, EnterIfTrue] : reverse(Terms)) {
SmallVector<Value *, 8> Worklist;
SmallPtrSet<Value *, 8> Visited;
Worklist.push_back(Term);
while (!Worklist.empty()) {
Value *Cond = Worklist.pop_back_val();
if (!Visited.insert(Cond).second)
continue;
if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
auto Predicate =
EnterIfTrue ? Cmp->getPredicate() : Cmp->getInversePredicate();
const auto *LHS = SE.getSCEV(Cmp->getOperand(0));
const auto *RHS = SE.getSCEV(Cmp->getOperand(1));
CollectCondition(Predicate, LHS, RHS, Guards.RewriteMap);
continue;
}
Value *L, *R;
if (EnterIfTrue ? match(Cond, m_LogicalAnd(m_Value(L), m_Value(R)))
: match(Cond, m_LogicalOr(m_Value(L), m_Value(R)))) {
Worklist.push_back(L);
Worklist.push_back(R);
}
}
}
// Let the rewriter preserve NUW/NSW flags if the unsigned/signed ranges of
// the replacement expressions are contained in the ranges of the replaced
// expressions.
Guards.PreserveNUW = true;
Guards.PreserveNSW = true;
for (const SCEV *Expr : ExprsToRewrite) {
const SCEV *RewriteTo = Guards.RewriteMap[Expr];
Guards.PreserveNUW &=
SE.getUnsignedRange(Expr).contains(SE.getUnsignedRange(RewriteTo));
Guards.PreserveNSW &=
SE.getSignedRange(Expr).contains(SE.getSignedRange(RewriteTo));
}
// Now that all rewrite information is collect, rewrite the collected
// expressions with the information in the map. This applies information to
// sub-expressions.
if (ExprsToRewrite.size() > 1) {
for (const SCEV *Expr : ExprsToRewrite) {
const SCEV *RewriteTo = Guards.RewriteMap[Expr];
Guards.RewriteMap.erase(Expr);
Guards.RewriteMap.insert({Expr, Guards.rewrite(RewriteTo)});
}
}
}
const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
/// A rewriter to replace SCEV expressions in Map with the corresponding entry
/// in the map. It skips AddRecExpr because we cannot guarantee that the
/// replacement is loop invariant in the loop of the AddRec.
class SCEVLoopGuardRewriter
: public SCEVRewriteVisitor<SCEVLoopGuardRewriter> {
const DenseMap<const SCEV *, const SCEV *> &Map;
SCEV::NoWrapFlags FlagMask = SCEV::FlagAnyWrap;
public:
SCEVLoopGuardRewriter(ScalarEvolution &SE,
const ScalarEvolution::LoopGuards &Guards)
: SCEVRewriteVisitor(SE), Map(Guards.RewriteMap) {
if (Guards.PreserveNUW)
FlagMask = ScalarEvolution::setFlags(FlagMask, SCEV::FlagNUW);
if (Guards.PreserveNSW)
FlagMask = ScalarEvolution::setFlags(FlagMask, SCEV::FlagNSW);
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) { return Expr; }
const SCEV *visitUnknown(const SCEVUnknown *Expr) {
auto I = Map.find(Expr);
if (I == Map.end())
return Expr;
return I->second;
}
const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
auto I = Map.find(Expr);
if (I == Map.end()) {
// If we didn't find the extact ZExt expr in the map, check if there's
// an entry for a smaller ZExt we can use instead.
Type *Ty = Expr->getType();
const SCEV *Op = Expr->getOperand(0);
unsigned Bitwidth = Ty->getScalarSizeInBits() / 2;
while (Bitwidth % 8 == 0 && Bitwidth >= 8 &&
Bitwidth > Op->getType()->getScalarSizeInBits()) {
Type *NarrowTy = IntegerType::get(SE.getContext(), Bitwidth);
auto *NarrowExt = SE.getZeroExtendExpr(Op, NarrowTy);
auto I = Map.find(NarrowExt);
if (I != Map.end())
return SE.getZeroExtendExpr(I->second, Ty);
Bitwidth = Bitwidth / 2;
}
return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitZeroExtendExpr(
Expr);
}
return I->second;
}
const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
auto I = Map.find(Expr);
if (I == Map.end())
return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSignExtendExpr(
Expr);
return I->second;
}
const SCEV *visitUMinExpr(const SCEVUMinExpr *Expr) {
auto I = Map.find(Expr);
if (I == Map.end())
return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitUMinExpr(Expr);
return I->second;
}
const SCEV *visitSMinExpr(const SCEVSMinExpr *Expr) {
auto I = Map.find(Expr);
if (I == Map.end())
return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSMinExpr(Expr);
return I->second;
}
const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
SmallVector<const SCEV *, 2> Operands;
bool Changed = false;
for (const auto *Op : Expr->operands()) {
Operands.push_back(
SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visit(Op));
Changed |= Op != Operands.back();
}
// We are only replacing operands with equivalent values, so transfer the
// flags from the original expression.
return !Changed ? Expr
: SE.getAddExpr(Operands,
ScalarEvolution::maskFlags(
Expr->getNoWrapFlags(), FlagMask));
}
const SCEV *visitMulExpr(const SCEVMulExpr *Expr) {
SmallVector<const SCEV *, 2> Operands;
bool Changed = false;
for (const auto *Op : Expr->operands()) {
Operands.push_back(
SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visit(Op));
Changed |= Op != Operands.back();
}
// We are only replacing operands with equivalent values, so transfer the
// flags from the original expression.
return !Changed ? Expr
: SE.getMulExpr(Operands,
ScalarEvolution::maskFlags(
Expr->getNoWrapFlags(), FlagMask));
}
};
if (RewriteMap.empty())
return Expr;
SCEVLoopGuardRewriter Rewriter(SE, *this);
return Rewriter.visit(Expr);
}
const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
return applyLoopGuards(Expr, LoopGuards::collect(L, *this));
}
const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr,
const LoopGuards &Guards) {
return Guards.rewrite(Expr);
}