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//===-- SimplifyIndVar.cpp - Induction variable simplification ------------===//
//
// 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 implements induction variable simplification. It does
// not define any actual pass or policy, but provides a single function to
// simplify a loop's induction variables based on ScalarEvolution.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/SimplifyIndVar.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "indvars"
STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
STATISTIC(NumElimOperand, "Number of IV operands folded into a use");
STATISTIC(NumFoldedUser, "Number of IV users folded into a constant");
STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
STATISTIC(
NumSimplifiedSDiv,
"Number of IV signed division operations converted to unsigned division");
STATISTIC(
NumSimplifiedSRem,
"Number of IV signed remainder operations converted to unsigned remainder");
STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
namespace {
/// This is a utility for simplifying induction variables
/// based on ScalarEvolution. It is the primary instrument of the
/// IndvarSimplify pass, but it may also be directly invoked to cleanup after
/// other loop passes that preserve SCEV.
class SimplifyIndvar {
Loop *L;
LoopInfo *LI;
ScalarEvolution *SE;
DominatorTree *DT;
const TargetTransformInfo *TTI;
SCEVExpander &Rewriter;
SmallVectorImpl<WeakTrackingVH> &DeadInsts;
bool Changed = false;
bool RunUnswitching = false;
public:
SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, DominatorTree *DT,
LoopInfo *LI, const TargetTransformInfo *TTI,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakTrackingVH> &Dead)
: L(Loop), LI(LI), SE(SE), DT(DT), TTI(TTI), Rewriter(Rewriter),
DeadInsts(Dead) {
assert(LI && "IV simplification requires LoopInfo");
}
bool hasChanged() const { return Changed; }
bool runUnswitching() const { return RunUnswitching; }
/// Iteratively perform simplification on a worklist of users of the
/// specified induction variable. This is the top-level driver that applies
/// all simplifications to users of an IV.
void simplifyUsers(PHINode *CurrIV, IVVisitor *V = nullptr);
Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand);
bool eliminateIdentitySCEV(Instruction *UseInst, Instruction *IVOperand);
bool replaceIVUserWithLoopInvariant(Instruction *UseInst);
bool replaceFloatIVWithIntegerIV(Instruction *UseInst);
bool eliminateOverflowIntrinsic(WithOverflowInst *WO);
bool eliminateSaturatingIntrinsic(SaturatingInst *SI);
bool eliminateTrunc(TruncInst *TI);
bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
bool makeIVComparisonInvariant(ICmpInst *ICmp, Instruction *IVOperand);
void eliminateIVComparison(ICmpInst *ICmp, Instruction *IVOperand);
void simplifyIVRemainder(BinaryOperator *Rem, Instruction *IVOperand,
bool IsSigned);
void replaceRemWithNumerator(BinaryOperator *Rem);
void replaceRemWithNumeratorOrZero(BinaryOperator *Rem);
void replaceSRemWithURem(BinaryOperator *Rem);
bool eliminateSDiv(BinaryOperator *SDiv);
bool strengthenBinaryOp(BinaryOperator *BO, Instruction *IVOperand);
bool strengthenOverflowingOperation(BinaryOperator *OBO,
Instruction *IVOperand);
bool strengthenRightShift(BinaryOperator *BO, Instruction *IVOperand);
};
}
/// Find a point in code which dominates all given instructions. We can safely
/// assume that, whatever fact we can prove at the found point, this fact is
/// also true for each of the given instructions.
static Instruction *findCommonDominator(ArrayRef<Instruction *> Instructions,
DominatorTree &DT) {
Instruction *CommonDom = nullptr;
for (auto *Insn : Instructions)
CommonDom =
CommonDom ? DT.findNearestCommonDominator(CommonDom, Insn) : Insn;
assert(CommonDom && "Common dominator not found?");
return CommonDom;
}
/// Fold an IV operand into its use. This removes increments of an
/// aligned IV when used by a instruction that ignores the low bits.
///
/// IVOperand is guaranteed SCEVable, but UseInst may not be.
///
/// Return the operand of IVOperand for this induction variable if IVOperand can
/// be folded (in case more folding opportunities have been exposed).
/// Otherwise return null.
Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
Value *IVSrc = nullptr;
const unsigned OperIdx = 0;
const SCEV *FoldedExpr = nullptr;
bool MustDropExactFlag = false;
switch (UseInst->getOpcode()) {
default:
return nullptr;
case Instruction::UDiv:
case Instruction::LShr:
// We're only interested in the case where we know something about
// the numerator and have a constant denominator.
if (IVOperand != UseInst->getOperand(OperIdx) ||
!isa<ConstantInt>(UseInst->getOperand(1)))
return nullptr;
// Attempt to fold a binary operator with constant operand.
// e.g. ((I + 1) >> 2) => I >> 2
if (!isa<BinaryOperator>(IVOperand)
|| !isa<ConstantInt>(IVOperand->getOperand(1)))
return nullptr;
IVSrc = IVOperand->getOperand(0);
// IVSrc must be the (SCEVable) IV, since the other operand is const.
assert(SE->isSCEVable(IVSrc->getType()) && "Expect SCEVable IV operand");
ConstantInt *D = cast<ConstantInt>(UseInst->getOperand(1));
if (UseInst->getOpcode() == Instruction::LShr) {
// Get a constant for the divisor. See createSCEV.
uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
if (D->getValue().uge(BitWidth))
return nullptr;
D = ConstantInt::get(UseInst->getContext(),
APInt::getOneBitSet(BitWidth, D->getZExtValue()));
}
const auto *LHS = SE->getSCEV(IVSrc);
const auto *RHS = SE->getSCEV(D);
FoldedExpr = SE->getUDivExpr(LHS, RHS);
// We might have 'exact' flag set at this point which will no longer be
// correct after we make the replacement.
if (UseInst->isExact() && LHS != SE->getMulExpr(FoldedExpr, RHS))
MustDropExactFlag = true;
}
// We have something that might fold it's operand. Compare SCEVs.
if (!SE->isSCEVable(UseInst->getType()))
return nullptr;
// Bypass the operand if SCEV can prove it has no effect.
if (SE->getSCEV(UseInst) != FoldedExpr)
return nullptr;
LLVM_DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
<< " -> " << *UseInst << '\n');
UseInst->setOperand(OperIdx, IVSrc);
assert(SE->getSCEV(UseInst) == FoldedExpr && "bad SCEV with folded oper");
if (MustDropExactFlag)
UseInst->dropPoisonGeneratingFlags();
++NumElimOperand;
Changed = true;
if (IVOperand->use_empty())
DeadInsts.emplace_back(IVOperand);
return IVSrc;
}
bool SimplifyIndvar::makeIVComparisonInvariant(ICmpInst *ICmp,
Instruction *IVOperand) {
auto *Preheader = L->getLoopPreheader();
if (!Preheader)
return false;
unsigned IVOperIdx = 0;
ICmpInst::Predicate Pred = ICmp->getPredicate();
if (IVOperand != ICmp->getOperand(0)) {
// Swapped
assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
IVOperIdx = 1;
Pred = ICmpInst::getSwappedPredicate(Pred);
}
// Get the SCEVs for the ICmp operands (in the specific context of the
// current loop)
const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
const SCEV *S = SE->getSCEVAtScope(ICmp->getOperand(IVOperIdx), ICmpLoop);
const SCEV *X = SE->getSCEVAtScope(ICmp->getOperand(1 - IVOperIdx), ICmpLoop);
auto LIP = SE->getLoopInvariantPredicate(Pred, S, X, L, ICmp);
if (!LIP)
return false;
ICmpInst::Predicate InvariantPredicate = LIP->Pred;
const SCEV *InvariantLHS = LIP->LHS;
const SCEV *InvariantRHS = LIP->RHS;
// Do not generate something ridiculous.
auto *PHTerm = Preheader->getTerminator();
if (Rewriter.isHighCostExpansion({InvariantLHS, InvariantRHS}, L,
2 * SCEVCheapExpansionBudget, TTI, PHTerm) ||
!Rewriter.isSafeToExpandAt(InvariantLHS, PHTerm) ||
!Rewriter.isSafeToExpandAt(InvariantRHS, PHTerm))
return false;
auto *NewLHS =
Rewriter.expandCodeFor(InvariantLHS, IVOperand->getType(), PHTerm);
auto *NewRHS =
Rewriter.expandCodeFor(InvariantRHS, IVOperand->getType(), PHTerm);
LLVM_DEBUG(dbgs() << "INDVARS: Simplified comparison: " << *ICmp << '\n');
ICmp->setPredicate(InvariantPredicate);
ICmp->setOperand(0, NewLHS);
ICmp->setOperand(1, NewRHS);
RunUnswitching = true;
return true;
}
/// SimplifyIVUsers helper for eliminating useless
/// comparisons against an induction variable.
void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp,
Instruction *IVOperand) {
unsigned IVOperIdx = 0;
ICmpInst::Predicate Pred = ICmp->getPredicate();
ICmpInst::Predicate OriginalPred = Pred;
if (IVOperand != ICmp->getOperand(0)) {
// Swapped
assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
IVOperIdx = 1;
Pred = ICmpInst::getSwappedPredicate(Pred);
}
// Get the SCEVs for the ICmp operands (in the specific context of the
// current loop)
const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
const SCEV *S = SE->getSCEVAtScope(ICmp->getOperand(IVOperIdx), ICmpLoop);
const SCEV *X = SE->getSCEVAtScope(ICmp->getOperand(1 - IVOperIdx), ICmpLoop);
// If the condition is always true or always false in the given context,
// replace it with a constant value.
SmallVector<Instruction *, 4> Users;
for (auto *U : ICmp->users())
Users.push_back(cast<Instruction>(U));
const Instruction *CtxI = findCommonDominator(Users, *DT);
if (auto Ev = SE->evaluatePredicateAt(Pred, S, X, CtxI)) {
SE->forgetValue(ICmp);
ICmp->replaceAllUsesWith(ConstantInt::getBool(ICmp->getContext(), *Ev));
DeadInsts.emplace_back(ICmp);
LLVM_DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
} else if (makeIVComparisonInvariant(ICmp, IVOperand)) {
// fallthrough to end of function
} else if (ICmpInst::isSigned(OriginalPred) &&
SE->isKnownNonNegative(S) && SE->isKnownNonNegative(X)) {
// If we were unable to make anything above, all we can is to canonicalize
// the comparison hoping that it will open the doors for other
// optimizations. If we find out that we compare two non-negative values,
// we turn the instruction's predicate to its unsigned version. Note that
// we cannot rely on Pred here unless we check if we have swapped it.
assert(ICmp->getPredicate() == OriginalPred && "Predicate changed?");
LLVM_DEBUG(dbgs() << "INDVARS: Turn to unsigned comparison: " << *ICmp
<< '\n');
ICmp->setPredicate(ICmpInst::getUnsignedPredicate(OriginalPred));
} else
return;
++NumElimCmp;
Changed = true;
}
bool SimplifyIndvar::eliminateSDiv(BinaryOperator *SDiv) {
// Get the SCEVs for the ICmp operands.
auto *N = SE->getSCEV(SDiv->getOperand(0));
auto *D = SE->getSCEV(SDiv->getOperand(1));
// Simplify unnecessary loops away.
const Loop *L = LI->getLoopFor(SDiv->getParent());
N = SE->getSCEVAtScope(N, L);
D = SE->getSCEVAtScope(D, L);
// Replace sdiv by udiv if both of the operands are non-negative
if (SE->isKnownNonNegative(N) && SE->isKnownNonNegative(D)) {
auto *UDiv = BinaryOperator::Create(
BinaryOperator::UDiv, SDiv->getOperand(0), SDiv->getOperand(1),
SDiv->getName() + ".udiv", SDiv->getIterator());
UDiv->setIsExact(SDiv->isExact());
SDiv->replaceAllUsesWith(UDiv);
LLVM_DEBUG(dbgs() << "INDVARS: Simplified sdiv: " << *SDiv << '\n');
++NumSimplifiedSDiv;
Changed = true;
DeadInsts.push_back(SDiv);
return true;
}
return false;
}
// i %s n -> i %u n if i >= 0 and n >= 0
void SimplifyIndvar::replaceSRemWithURem(BinaryOperator *Rem) {
auto *N = Rem->getOperand(0), *D = Rem->getOperand(1);
auto *URem = BinaryOperator::Create(BinaryOperator::URem, N, D,
Rem->getName() + ".urem", Rem->getIterator());
Rem->replaceAllUsesWith(URem);
LLVM_DEBUG(dbgs() << "INDVARS: Simplified srem: " << *Rem << '\n');
++NumSimplifiedSRem;
Changed = true;
DeadInsts.emplace_back(Rem);
}
// i % n --> i if i is in [0,n).
void SimplifyIndvar::replaceRemWithNumerator(BinaryOperator *Rem) {
Rem->replaceAllUsesWith(Rem->getOperand(0));
LLVM_DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
DeadInsts.emplace_back(Rem);
}
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
void SimplifyIndvar::replaceRemWithNumeratorOrZero(BinaryOperator *Rem) {
auto *T = Rem->getType();
auto *N = Rem->getOperand(0), *D = Rem->getOperand(1);
ICmpInst *ICmp = new ICmpInst(Rem->getIterator(), ICmpInst::ICMP_EQ, N, D);
SelectInst *Sel =
SelectInst::Create(ICmp, ConstantInt::get(T, 0), N, "iv.rem", Rem->getIterator());
Rem->replaceAllUsesWith(Sel);
LLVM_DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
DeadInsts.emplace_back(Rem);
}
/// SimplifyIVUsers helper for eliminating useless remainder operations
/// operating on an induction variable or replacing srem by urem.
void SimplifyIndvar::simplifyIVRemainder(BinaryOperator *Rem,
Instruction *IVOperand,
bool IsSigned) {
auto *NValue = Rem->getOperand(0);
auto *DValue = Rem->getOperand(1);
// We're only interested in the case where we know something about
// the numerator, unless it is a srem, because we want to replace srem by urem
// in general.
bool UsedAsNumerator = IVOperand == NValue;
if (!UsedAsNumerator && !IsSigned)
return;
const SCEV *N = SE->getSCEV(NValue);
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
N = SE->getSCEVAtScope(N, ICmpLoop);
bool IsNumeratorNonNegative = !IsSigned || SE->isKnownNonNegative(N);
// Do not proceed if the Numerator may be negative
if (!IsNumeratorNonNegative)
return;
const SCEV *D = SE->getSCEV(DValue);
D = SE->getSCEVAtScope(D, ICmpLoop);
if (UsedAsNumerator) {
auto LT = IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
if (SE->isKnownPredicate(LT, N, D)) {
replaceRemWithNumerator(Rem);
return;
}
auto *T = Rem->getType();
const auto *NLessOne = SE->getMinusSCEV(N, SE->getOne(T));
if (SE->isKnownPredicate(LT, NLessOne, D)) {
replaceRemWithNumeratorOrZero(Rem);
return;
}
}
// Try to replace SRem with URem, if both N and D are known non-negative.
// Since we had already check N, we only need to check D now
if (!IsSigned || !SE->isKnownNonNegative(D))
return;
replaceSRemWithURem(Rem);
}
bool SimplifyIndvar::eliminateOverflowIntrinsic(WithOverflowInst *WO) {
const SCEV *LHS = SE->getSCEV(WO->getLHS());
const SCEV *RHS = SE->getSCEV(WO->getRHS());
if (!SE->willNotOverflow(WO->getBinaryOp(), WO->isSigned(), LHS, RHS))
return false;
// Proved no overflow, nuke the overflow check and, if possible, the overflow
// intrinsic as well.
BinaryOperator *NewResult = BinaryOperator::Create(
WO->getBinaryOp(), WO->getLHS(), WO->getRHS(), "", WO->getIterator());
if (WO->isSigned())
NewResult->setHasNoSignedWrap(true);
else
NewResult->setHasNoUnsignedWrap(true);
SmallVector<ExtractValueInst *, 4> ToDelete;
for (auto *U : WO->users()) {
if (auto *EVI = dyn_cast<ExtractValueInst>(U)) {
if (EVI->getIndices()[0] == 1)
EVI->replaceAllUsesWith(ConstantInt::getFalse(WO->getContext()));
else {
assert(EVI->getIndices()[0] == 0 && "Only two possibilities!");
EVI->replaceAllUsesWith(NewResult);
}
ToDelete.push_back(EVI);
}
}
for (auto *EVI : ToDelete)
EVI->eraseFromParent();
if (WO->use_empty())
WO->eraseFromParent();
Changed = true;
return true;
}
bool SimplifyIndvar::eliminateSaturatingIntrinsic(SaturatingInst *SI) {
const SCEV *LHS = SE->getSCEV(SI->getLHS());
const SCEV *RHS = SE->getSCEV(SI->getRHS());
if (!SE->willNotOverflow(SI->getBinaryOp(), SI->isSigned(), LHS, RHS))
return false;
BinaryOperator *BO = BinaryOperator::Create(
SI->getBinaryOp(), SI->getLHS(), SI->getRHS(), SI->getName(), SI->getIterator());
if (SI->isSigned())
BO->setHasNoSignedWrap();
else
BO->setHasNoUnsignedWrap();
SI->replaceAllUsesWith(BO);
DeadInsts.emplace_back(SI);
Changed = true;
return true;
}
bool SimplifyIndvar::eliminateTrunc(TruncInst *TI) {
// It is always legal to replace
// icmp <pred> i32 trunc(iv), n
// with
// icmp <pred> i64 sext(trunc(iv)), sext(n), if pred is signed predicate.
// Or with
// icmp <pred> i64 zext(trunc(iv)), zext(n), if pred is unsigned predicate.
// Or with either of these if pred is an equality predicate.
//
// If we can prove that iv == sext(trunc(iv)) or iv == zext(trunc(iv)) for
// every comparison which uses trunc, it means that we can replace each of
// them with comparison of iv against sext/zext(n). We no longer need trunc
// after that.
//
// TODO: Should we do this if we can widen *some* comparisons, but not all
// of them? Sometimes it is enough to enable other optimizations, but the
// trunc instruction will stay in the loop.
Value *IV = TI->getOperand(0);
Type *IVTy = IV->getType();
const SCEV *IVSCEV = SE->getSCEV(IV);
const SCEV *TISCEV = SE->getSCEV(TI);
// Check if iv == zext(trunc(iv)) and if iv == sext(trunc(iv)). If so, we can
// get rid of trunc
bool DoesSExtCollapse = false;
bool DoesZExtCollapse = false;
if (IVSCEV == SE->getSignExtendExpr(TISCEV, IVTy))
DoesSExtCollapse = true;
if (IVSCEV == SE->getZeroExtendExpr(TISCEV, IVTy))
DoesZExtCollapse = true;
// If neither sext nor zext does collapse, it is not profitable to do any
// transform. Bail.
if (!DoesSExtCollapse && !DoesZExtCollapse)
return false;
// Collect users of the trunc that look like comparisons against invariants.
// Bail if we find something different.
SmallVector<ICmpInst *, 4> ICmpUsers;
for (auto *U : TI->users()) {
// We don't care about users in unreachable blocks.
if (isa<Instruction>(U) &&
!DT->isReachableFromEntry(cast<Instruction>(U)->getParent()))
continue;
ICmpInst *ICI = dyn_cast<ICmpInst>(U);
if (!ICI) return false;
assert(L->contains(ICI->getParent()) && "LCSSA form broken?");
if (!(ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) &&
!(ICI->getOperand(1) == TI && L->isLoopInvariant(ICI->getOperand(0))))
return false;
// If we cannot get rid of trunc, bail.
if (ICI->isSigned() && !DoesSExtCollapse)
return false;
if (ICI->isUnsigned() && !DoesZExtCollapse)
return false;
// For equality, either signed or unsigned works.
ICmpUsers.push_back(ICI);
}
auto CanUseZExt = [&](ICmpInst *ICI) {
// Unsigned comparison can be widened as unsigned.
if (ICI->isUnsigned())
return true;
// Is it profitable to do zext?
if (!DoesZExtCollapse)
return false;
// For equality, we can safely zext both parts.
if (ICI->isEquality())
return true;
// Otherwise we can only use zext when comparing two non-negative or two
// negative values. But in practice, we will never pass DoesZExtCollapse
// check for a negative value, because zext(trunc(x)) is non-negative. So
// it only make sense to check for non-negativity here.
const SCEV *SCEVOP1 = SE->getSCEV(ICI->getOperand(0));
const SCEV *SCEVOP2 = SE->getSCEV(ICI->getOperand(1));
return SE->isKnownNonNegative(SCEVOP1) && SE->isKnownNonNegative(SCEVOP2);
};
// Replace all comparisons against trunc with comparisons against IV.
for (auto *ICI : ICmpUsers) {
bool IsSwapped = L->isLoopInvariant(ICI->getOperand(0));
auto *Op1 = IsSwapped ? ICI->getOperand(0) : ICI->getOperand(1);
IRBuilder<> Builder(ICI);
Value *Ext = nullptr;
// For signed/unsigned predicate, replace the old comparison with comparison
// of immediate IV against sext/zext of the invariant argument. If we can
// use either sext or zext (i.e. we are dealing with equality predicate),
// then prefer zext as a more canonical form.
// TODO: If we see a signed comparison which can be turned into unsigned,
// we can do it here for canonicalization purposes.
ICmpInst::Predicate Pred = ICI->getPredicate();
if (IsSwapped) Pred = ICmpInst::getSwappedPredicate(Pred);
if (CanUseZExt(ICI)) {
assert(DoesZExtCollapse && "Unprofitable zext?");
Ext = Builder.CreateZExt(Op1, IVTy, "zext");
Pred = ICmpInst::getUnsignedPredicate(Pred);
} else {
assert(DoesSExtCollapse && "Unprofitable sext?");
Ext = Builder.CreateSExt(Op1, IVTy, "sext");
assert(Pred == ICmpInst::getSignedPredicate(Pred) && "Must be signed!");
}
bool Changed;
L->makeLoopInvariant(Ext, Changed);
(void)Changed;
auto *NewCmp = Builder.CreateICmp(Pred, IV, Ext);
ICI->replaceAllUsesWith(NewCmp);
DeadInsts.emplace_back(ICI);
}
// Trunc no longer needed.
TI->replaceAllUsesWith(PoisonValue::get(TI->getType()));
DeadInsts.emplace_back(TI);
return true;
}
/// Eliminate an operation that consumes a simple IV and has no observable
/// side-effect given the range of IV values. IVOperand is guaranteed SCEVable,
/// but UseInst may not be.
bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst,
Instruction *IVOperand) {
if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
eliminateIVComparison(ICmp, IVOperand);
return true;
}
if (BinaryOperator *Bin = dyn_cast<BinaryOperator>(UseInst)) {
bool IsSRem = Bin->getOpcode() == Instruction::SRem;
if (IsSRem || Bin->getOpcode() == Instruction::URem) {
simplifyIVRemainder(Bin, IVOperand, IsSRem);
return true;
}
if (Bin->getOpcode() == Instruction::SDiv)
return eliminateSDiv(Bin);
}
if (auto *WO = dyn_cast<WithOverflowInst>(UseInst))
if (eliminateOverflowIntrinsic(WO))
return true;
if (auto *SI = dyn_cast<SaturatingInst>(UseInst))
if (eliminateSaturatingIntrinsic(SI))
return true;
if (auto *TI = dyn_cast<TruncInst>(UseInst))
if (eliminateTrunc(TI))
return true;
if (eliminateIdentitySCEV(UseInst, IVOperand))
return true;
return false;
}
static Instruction *GetLoopInvariantInsertPosition(Loop *L, Instruction *Hint) {
if (auto *BB = L->getLoopPreheader())
return BB->getTerminator();
return Hint;
}
/// Replace the UseInst with a loop invariant expression if it is safe.
bool SimplifyIndvar::replaceIVUserWithLoopInvariant(Instruction *I) {
if (!SE->isSCEVable(I->getType()))
return false;
// Get the symbolic expression for this instruction.
const SCEV *S = SE->getSCEV(I);
if (!SE->isLoopInvariant(S, L))
return false;
// Do not generate something ridiculous even if S is loop invariant.
if (Rewriter.isHighCostExpansion(S, L, SCEVCheapExpansionBudget, TTI, I))
return false;
auto *IP = GetLoopInvariantInsertPosition(L, I);
if (!Rewriter.isSafeToExpandAt(S, IP)) {
LLVM_DEBUG(dbgs() << "INDVARS: Can not replace IV user: " << *I
<< " with non-speculable loop invariant: " << *S << '\n');
return false;
}
auto *Invariant = Rewriter.expandCodeFor(S, I->getType(), IP);
bool NeedToEmitLCSSAPhis = false;
if (!LI->replacementPreservesLCSSAForm(I, Invariant))
NeedToEmitLCSSAPhis = true;
I->replaceAllUsesWith(Invariant);
LLVM_DEBUG(dbgs() << "INDVARS: Replace IV user: " << *I
<< " with loop invariant: " << *S << '\n');
if (NeedToEmitLCSSAPhis) {
SmallVector<Instruction *, 1> NeedsLCSSAPhis;
NeedsLCSSAPhis.push_back(cast<Instruction>(Invariant));
formLCSSAForInstructions(NeedsLCSSAPhis, *DT, *LI, SE);
LLVM_DEBUG(dbgs() << " INDVARS: Replacement breaks LCSSA form"
<< " inserting LCSSA Phis" << '\n');
}
++NumFoldedUser;
Changed = true;
DeadInsts.emplace_back(I);
return true;
}
/// Eliminate redundant type cast between integer and float.
bool SimplifyIndvar::replaceFloatIVWithIntegerIV(Instruction *UseInst) {
if (UseInst->getOpcode() != CastInst::SIToFP &&
UseInst->getOpcode() != CastInst::UIToFP)
return false;
Instruction *IVOperand = cast<Instruction>(UseInst->getOperand(0));
// Get the symbolic expression for this instruction.
const SCEV *IV = SE->getSCEV(IVOperand);
int MaskBits;
if (UseInst->getOpcode() == CastInst::SIToFP)
MaskBits = (int)SE->getSignedRange(IV).getMinSignedBits();
else
MaskBits = (int)SE->getUnsignedRange(IV).getActiveBits();
int DestNumSigBits = UseInst->getType()->getFPMantissaWidth();
if (MaskBits <= DestNumSigBits) {
for (User *U : UseInst->users()) {
// Match for fptosi/fptoui of sitofp and with same type.
auto *CI = dyn_cast<CastInst>(U);
if (!CI)
continue;
CastInst::CastOps Opcode = CI->getOpcode();
if (Opcode != CastInst::FPToSI && Opcode != CastInst::FPToUI)
continue;
Value *Conv = nullptr;
if (IVOperand->getType() != CI->getType()) {
IRBuilder<> Builder(CI);
StringRef Name = IVOperand->getName();
// To match InstCombine logic, we only need sext if both fptosi and
// sitofp are used. If one of them is unsigned, then we can use zext.
if (SE->getTypeSizeInBits(IVOperand->getType()) >
SE->getTypeSizeInBits(CI->getType())) {
Conv = Builder.CreateTrunc(IVOperand, CI->getType(), Name + ".trunc");
} else if (Opcode == CastInst::FPToUI ||
UseInst->getOpcode() == CastInst::UIToFP) {
Conv = Builder.CreateZExt(IVOperand, CI->getType(), Name + ".zext");
} else {
Conv = Builder.CreateSExt(IVOperand, CI->getType(), Name + ".sext");
}
} else
Conv = IVOperand;
CI->replaceAllUsesWith(Conv);
DeadInsts.push_back(CI);
LLVM_DEBUG(dbgs() << "INDVARS: Replace IV user: " << *CI
<< " with: " << *Conv << '\n');
++NumFoldedUser;
Changed = true;
}
}
return Changed;
}
/// Eliminate any operation that SCEV can prove is an identity function.
bool SimplifyIndvar::eliminateIdentitySCEV(Instruction *UseInst,
Instruction *IVOperand) {
if (!SE->isSCEVable(UseInst->getType()) ||
UseInst->getType() != IVOperand->getType())
return false;
const SCEV *UseSCEV = SE->getSCEV(UseInst);
if (UseSCEV != SE->getSCEV(IVOperand))
return false;
// getSCEV(X) == getSCEV(Y) does not guarantee that X and Y are related in the
// dominator tree, even if X is an operand to Y. For instance, in
//
// %iv = phi i32 {0,+,1}
// br %cond, label %left, label %merge
//
// left:
// %X = add i32 %iv, 0
// br label %merge
//
// merge:
// %M = phi (%X, %iv)
//
// getSCEV(%M) == getSCEV(%X) == {0,+,1}, but %X does not dominate %M, and
// %M.replaceAllUsesWith(%X) would be incorrect.
if (isa<PHINode>(UseInst))
// If UseInst is not a PHI node then we know that IVOperand dominates
// UseInst directly from the legality of SSA.
if (!DT || !DT->dominates(IVOperand, UseInst))
return false;
if (!LI->replacementPreservesLCSSAForm(UseInst, IVOperand))
return false;
// Make sure the operand is not more poisonous than the instruction.
if (!impliesPoison(IVOperand, UseInst)) {
SmallVector<Instruction *> DropPoisonGeneratingInsts;
if (!SE->canReuseInstruction(UseSCEV, IVOperand, DropPoisonGeneratingInsts))
return false;
for (Instruction *I : DropPoisonGeneratingInsts)
I->dropPoisonGeneratingAnnotations();
}
LLVM_DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
SE->forgetValue(UseInst);
UseInst->replaceAllUsesWith(IVOperand);
++NumElimIdentity;
Changed = true;
DeadInsts.emplace_back(UseInst);
return true;
}
bool SimplifyIndvar::strengthenBinaryOp(BinaryOperator *BO,
Instruction *IVOperand) {
return (isa<OverflowingBinaryOperator>(BO) &&
strengthenOverflowingOperation(BO, IVOperand)) ||
(isa<ShlOperator>(BO) && strengthenRightShift(BO, IVOperand));
}
/// Annotate BO with nsw / nuw if it provably does not signed-overflow /
/// unsigned-overflow. Returns true if anything changed, false otherwise.
bool SimplifyIndvar::strengthenOverflowingOperation(BinaryOperator *BO,
Instruction *IVOperand) {
auto Flags = SE->getStrengthenedNoWrapFlagsFromBinOp(
cast<OverflowingBinaryOperator>(BO));
if (!Flags)
return false;
BO->setHasNoUnsignedWrap(ScalarEvolution::maskFlags(*Flags, SCEV::FlagNUW) ==
SCEV::FlagNUW);
BO->setHasNoSignedWrap(ScalarEvolution::maskFlags(*Flags, SCEV::FlagNSW) ==
SCEV::FlagNSW);
// The getStrengthenedNoWrapFlagsFromBinOp() check inferred additional nowrap
// flags on addrecs while performing zero/sign extensions. We could call
// forgetValue() here to make sure those flags also propagate to any other
// SCEV expressions based on the addrec. However, this can have pathological
// compile-time impact, see https://bugs.llvm.org/show_bug.cgi?id=50384.
return true;
}
/// Annotate the Shr in (X << IVOperand) >> C as exact using the
/// information from the IV's range. Returns true if anything changed, false
/// otherwise.
bool SimplifyIndvar::strengthenRightShift(BinaryOperator *BO,
Instruction *IVOperand) {
if (BO->getOpcode() == Instruction::Shl) {
bool Changed = false;
ConstantRange IVRange = SE->getUnsignedRange(SE->getSCEV(IVOperand));
for (auto *U : BO->users()) {
const APInt *C;
if (match(U,
m_AShr(m_Shl(m_Value(), m_Specific(IVOperand)), m_APInt(C))) ||
match(U,
m_LShr(m_Shl(m_Value(), m_Specific(IVOperand)), m_APInt(C)))) {
BinaryOperator *Shr = cast<BinaryOperator>(U);
if (!Shr->isExact() && IVRange.getUnsignedMin().uge(*C)) {
Shr->setIsExact(true);
Changed = true;
}
}
}
return Changed;
}
return false;
}
/// Add all uses of Def to the current IV's worklist.
static void pushIVUsers(
Instruction *Def, Loop *L,
SmallPtrSet<Instruction*,16> &Simplified,
SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
for (User *U : Def->users()) {
Instruction *UI = cast<Instruction>(U);
// Avoid infinite or exponential worklist processing.
// Also ensure unique worklist users.
// If Def is a LoopPhi, it may not be in the Simplified set, so check for
// self edges first.
if (UI == Def)
continue;
// Only change the current Loop, do not change the other parts (e.g. other
// Loops).
if (!L->contains(UI))
continue;
// Do not push the same instruction more than once.
if (!Simplified.insert(UI).second)
continue;
SimpleIVUsers.push_back(std::make_pair(UI, Def));
}
}
/// Return true if this instruction generates a simple SCEV
/// expression in terms of that IV.
///
/// This is similar to IVUsers' isInteresting() but processes each instruction
/// non-recursively when the operand is already known to be a simpleIVUser.
///
static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) {
if (!SE->isSCEVable(I->getType()))
return false;
// Get the symbolic expression for this instruction.
const SCEV *S = SE->getSCEV(I);
// Only consider affine recurrences.
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
if (AR && AR->getLoop() == L)
return true;
return false;
}
/// Iteratively perform simplification on a worklist of users
/// of the specified induction variable. Each successive simplification may push
/// more users which may themselves be candidates for simplification.
///
/// This algorithm does not require IVUsers analysis. Instead, it simplifies
/// instructions in-place during analysis. Rather than rewriting induction
/// variables bottom-up from their users, it transforms a chain of IVUsers
/// top-down, updating the IR only when it encounters a clear optimization
/// opportunity.
///
/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
///
void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
if (!SE->isSCEVable(CurrIV->getType()))
return;
// Instructions processed by SimplifyIndvar for CurrIV.
SmallPtrSet<Instruction*,16> Simplified;
// Use-def pairs if IV users waiting to be processed for CurrIV.
SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
// Push users of the current LoopPhi. In rare cases, pushIVUsers may be
// called multiple times for the same LoopPhi. This is the proper thing to
// do for loop header phis that use each other.
pushIVUsers(CurrIV, L, Simplified, SimpleIVUsers);
while (!SimpleIVUsers.empty()) {
std::pair<Instruction*, Instruction*> UseOper =
SimpleIVUsers.pop_back_val();
Instruction *UseInst = UseOper.first;
// If a user of the IndVar is trivially dead, we prefer just to mark it dead
// rather than try to do some complex analysis or transformation (such as
// widening) basing on it.
// TODO: Propagate TLI and pass it here to handle more cases.
if (isInstructionTriviallyDead(UseInst, /* TLI */ nullptr)) {
DeadInsts.emplace_back(UseInst);
continue;
}
// Bypass back edges to avoid extra work.
if (UseInst == CurrIV) continue;
// Try to replace UseInst with a loop invariant before any other
// simplifications.
if (replaceIVUserWithLoopInvariant(UseInst))
continue;
// Go further for the bitcast 'prtoint ptr to i64' or if the cast is done
// by truncation
if ((isa<PtrToIntInst>(UseInst)) || (isa<TruncInst>(UseInst)))
for (Use &U : UseInst->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
if (replaceIVUserWithLoopInvariant(User))
break; // done replacing
}
Instruction *IVOperand = UseOper.second;
for (unsigned N = 0; IVOperand; ++N) {
assert(N <= Simplified.size() && "runaway iteration");
(void) N;
Value *NewOper = foldIVUser(UseInst, IVOperand);
if (!NewOper)
break; // done folding
IVOperand = dyn_cast<Instruction>(NewOper);
}
if (!IVOperand)
continue;
if (eliminateIVUser(UseInst, IVOperand)) {
pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
continue;
}
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(UseInst)) {
if (strengthenBinaryOp(BO, IVOperand)) {
// re-queue uses of the now modified binary operator and fall
// through to the checks that remain.
pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
}
}
// Try to use integer induction for FPToSI of float induction directly.
if (replaceFloatIVWithIntegerIV(UseInst)) {
// Re-queue the potentially new direct uses of IVOperand.
pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
continue;
}
CastInst *Cast = dyn_cast<CastInst>(UseInst);
if (V && Cast) {
V->visitCast(Cast);
continue;
}
if (isSimpleIVUser(UseInst, L, SE)) {
pushIVUsers(UseInst, L, Simplified, SimpleIVUsers);
}
}
}
namespace llvm {
void IVVisitor::anchor() { }
/// Simplify instructions that use this induction variable
/// by using ScalarEvolution to analyze the IV's recurrence.
/// Returns a pair where the first entry indicates that the function makes
/// changes and the second entry indicates that it introduced new opportunities
/// for loop unswitching.
std::pair<bool, bool> simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE,
DominatorTree *DT, LoopInfo *LI,
const TargetTransformInfo *TTI,
SmallVectorImpl<WeakTrackingVH> &Dead,
SCEVExpander &Rewriter, IVVisitor *V) {
SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, DT, LI, TTI,
Rewriter, Dead);
SIV.simplifyUsers(CurrIV, V);
return {SIV.hasChanged(), SIV.runUnswitching()};
}
/// Simplify users of induction variables within this
/// loop. This does not actually change or add IVs.
bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, DominatorTree *DT,
LoopInfo *LI, const TargetTransformInfo *TTI,
SmallVectorImpl<WeakTrackingVH> &Dead) {
SCEVExpander Rewriter(*SE, SE->getDataLayout(), "indvars");
#ifndef NDEBUG
Rewriter.setDebugType(DEBUG_TYPE);
#endif
bool Changed = false;
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
const auto &[C, _] =
simplifyUsersOfIV(cast<PHINode>(I), SE, DT, LI, TTI, Dead, Rewriter);
Changed |= C;
}
return Changed;
}
} // namespace llvm
namespace {
//===----------------------------------------------------------------------===//
// Widen Induction Variables - Extend the width of an IV to cover its
// widest uses.
//===----------------------------------------------------------------------===//
class WidenIV {
// Parameters
PHINode *OrigPhi;
Type *WideType;
// Context
LoopInfo *LI;
Loop *L;
ScalarEvolution *SE;
DominatorTree *DT;
// Does the module have any calls to the llvm.experimental.guard intrinsic
// at all? If not we can avoid scanning instructions looking for guards.
bool HasGuards;
bool UsePostIncrementRanges;
// Statistics
unsigned NumElimExt = 0;
unsigned NumWidened = 0;
// Result
PHINode *WidePhi = nullptr;
Instruction *WideInc = nullptr;
const SCEV *WideIncExpr = nullptr;
SmallVectorImpl<WeakTrackingVH> &DeadInsts;
SmallPtrSet<Instruction *,16> Widened;
enum class ExtendKind { Zero, Sign, Unknown };
// A map tracking the kind of extension used to widen each narrow IV
// and narrow IV user.
// Key: pointer to a narrow IV or IV user.
// Value: the kind of extension used to widen this Instruction.
DenseMap<AssertingVH<Instruction>, ExtendKind> ExtendKindMap;
using DefUserPair = std::pair<AssertingVH<Value>, AssertingVH<Instruction>>;
// A map with control-dependent ranges for post increment IV uses. The key is
// a pair of IV def and a use of this def denoting the context. The value is
// a ConstantRange representing possible values of the def at the given
// context.
DenseMap<DefUserPair, ConstantRange> PostIncRangeInfos;
std::optional<ConstantRange> getPostIncRangeInfo(Value *Def,
Instruction *UseI) {
DefUserPair Key(Def, UseI);
auto It = PostIncRangeInfos.find(Key);
return It == PostIncRangeInfos.end()
? std::optional<ConstantRange>(std::nullopt)
: std::optional<ConstantRange>(It->second);
}
void calculatePostIncRanges(PHINode *OrigPhi);
void calculatePostIncRange(Instruction *NarrowDef, Instruction *NarrowUser);
void updatePostIncRangeInfo(Value *Def, Instruction *UseI, ConstantRange R) {
DefUserPair Key(Def, UseI);
auto It = PostIncRangeInfos.find(Key);
if (It == PostIncRangeInfos.end())
PostIncRangeInfos.insert({Key, R});
else
It->second = R.intersectWith(It->second);
}
public:
/// Record a link in the Narrow IV def-use chain along with the WideIV that
/// computes the same value as the Narrow IV def. This avoids caching Use*
/// pointers.
struct NarrowIVDefUse {
Instruction *NarrowDef = nullptr;
Instruction *NarrowUse = nullptr;
Instruction *WideDef = nullptr;
// True if the narrow def is never negative. Tracking this information lets
// us use a sign extension instead of a zero extension or vice versa, when
// profitable and legal.
bool NeverNegative = false;
NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD,
bool NeverNegative)
: NarrowDef(ND), NarrowUse(NU), WideDef(WD),
NeverNegative(NeverNegative) {}
};
WidenIV(const WideIVInfo &WI, LoopInfo *LInfo, ScalarEvolution *SEv,
DominatorTree *DTree, SmallVectorImpl<WeakTrackingVH> &DI,
bool HasGuards, bool UsePostIncrementRanges = true);
PHINode *createWideIV(SCEVExpander &Rewriter);
unsigned getNumElimExt() { return NumElimExt; };
unsigned getNumWidened() { return NumWidened; };
protected:
Value *createExtendInst(Value *NarrowOper, Type *WideType, bool IsSigned,
Instruction *Use);
Instruction *cloneIVUser(NarrowIVDefUse DU, const SCEVAddRecExpr *WideAR);
Instruction *cloneArithmeticIVUser(NarrowIVDefUse DU,
const SCEVAddRecExpr *WideAR);
Instruction *cloneBitwiseIVUser(NarrowIVDefUse DU);
ExtendKind getExtendKind(Instruction *I);
using WidenedRecTy = std::pair<const SCEVAddRecExpr *, ExtendKind>;
WidenedRecTy getWideRecurrence(NarrowIVDefUse DU);
WidenedRecTy getExtendedOperandRecurrence(NarrowIVDefUse DU);
const SCEV *getSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
unsigned OpCode) const;
Instruction *widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter,
PHINode *OrigPhi, PHINode *WidePhi);
void truncateIVUse(NarrowIVDefUse DU);
bool widenLoopCompare(NarrowIVDefUse DU);
bool widenWithVariantUse(NarrowIVDefUse DU);
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
private:
SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
};
} // namespace
/// Determine the insertion point for this user. By default, insert immediately
/// before the user. SCEVExpander or LICM will hoist loop invariants out of the
/// loop. For PHI nodes, there may be multiple uses, so compute the nearest
/// common dominator for the incoming blocks. A nullptr can be returned if no
/// viable location is found: it may happen if User is a PHI and Def only comes
/// to this PHI from unreachable blocks.
static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
DominatorTree *DT, LoopInfo *LI) {
PHINode *PHI = dyn_cast<PHINode>(User);
if (!PHI)
return User;
Instruction *InsertPt = nullptr;
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
if (PHI->getIncomingValue(i) != Def)
continue;
BasicBlock *InsertBB = PHI->getIncomingBlock(i);
if (!DT->isReachableFromEntry(InsertBB))
continue;
if (!InsertPt) {
InsertPt = InsertBB->getTerminator();
continue;
}
InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
InsertPt = InsertBB->getTerminator();
}
// If we have skipped all inputs, it means that Def only comes to Phi from
// unreachable blocks.
if (!InsertPt)
return nullptr;
auto *DefI = dyn_cast<Instruction>(Def);
if (!DefI)
return InsertPt;
assert(DT->dominates(DefI, InsertPt) && "def does not dominate all uses");
auto *L = LI->getLoopFor(DefI->getParent());
assert(!L || L->contains(LI->getLoopFor(InsertPt->getParent())));
for (auto *DTN = (*DT)[InsertPt->getParent()]; DTN; DTN = DTN->getIDom())
if (LI->getLoopFor(DTN->getBlock()) == L)
return DTN->getBlock()->getTerminator();
llvm_unreachable("DefI dominates InsertPt!");
}
WidenIV::WidenIV(const WideIVInfo &WI, LoopInfo *LInfo, ScalarEvolution *SEv,
DominatorTree *DTree, SmallVectorImpl<WeakTrackingVH> &DI,
bool HasGuards, bool UsePostIncrementRanges)
: OrigPhi(WI.NarrowIV), WideType(WI.WidestNativeType), LI(LInfo),
L(LI->getLoopFor(OrigPhi->getParent())), SE(SEv), DT(DTree),
HasGuards(HasGuards), UsePostIncrementRanges(UsePostIncrementRanges),
DeadInsts(DI) {
assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
ExtendKindMap[OrigPhi] = WI.IsSigned ? ExtendKind::Sign : ExtendKind::Zero;
}
Value *WidenIV::createExtendInst(Value *NarrowOper, Type *WideType,
bool IsSigned, Instruction *Use) {
// Set the debug location and conservative insertion point.
IRBuilder<> Builder(Use);
// Hoist the insertion point into loop preheaders as far as possible.
for (const Loop *L = LI->getLoopFor(Use->getParent());
L && L->getLoopPreheader() && L->isLoopInvariant(NarrowOper);
L = L->getParentLoop())
Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
Builder.CreateZExt(NarrowOper, WideType);
}
/// Instantiate a wide operation to replace a narrow operation. This only needs
/// to handle operations that can evaluation to SCEVAddRec. It can safely return
/// 0 for any operation we decide not to clone.
Instruction *WidenIV::cloneIVUser(WidenIV::NarrowIVDefUse DU,
const SCEVAddRecExpr *WideAR) {
unsigned Opcode = DU.NarrowUse->getOpcode();
switch (Opcode) {
default:
return nullptr;
case Instruction::Add:
case Instruction::Mul:
case Instruction::UDiv:
case Instruction::Sub:
return cloneArithmeticIVUser(DU, WideAR);
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
return cloneBitwiseIVUser(DU);
}
}
Instruction *WidenIV::cloneBitwiseIVUser(WidenIV::NarrowIVDefUse DU) {
Instruction *NarrowUse = DU.NarrowUse;
Instruction *NarrowDef = DU.NarrowDef;
Instruction *WideDef = DU.WideDef;
LLVM_DEBUG(dbgs() << "Cloning bitwise IVUser: " << *NarrowUse << "\n");
// Replace NarrowDef operands with WideDef. Otherwise, we don't know anything
// about the narrow operand yet so must insert a [sz]ext. It is probably loop
// invariant and will be folded or hoisted. If it actually comes from a
// widened IV, it should be removed during a future call to widenIVUse.
bool IsSigned = getExtendKind(NarrowDef) == ExtendKind::Sign;
Value *LHS = (NarrowUse->getOperand(0) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(0), WideType,
IsSigned, NarrowUse);
Value *RHS = (NarrowUse->getOperand(1) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(1), WideType,
IsSigned, NarrowUse);
auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
NarrowBO->getName());
IRBuilder<> Builder(NarrowUse);
Builder.Insert(WideBO);
WideBO->copyIRFlags(NarrowBO);
return WideBO;
}
Instruction *WidenIV::cloneArithmeticIVUser(WidenIV::NarrowIVDefUse DU,
const SCEVAddRecExpr *WideAR) {
Instruction *NarrowUse = DU.NarrowUse;
Instruction *NarrowDef = DU.NarrowDef;
Instruction *WideDef = DU.WideDef;
LLVM_DEBUG(dbgs() << "Cloning arithmetic IVUser: " << *NarrowUse << "\n");
unsigned IVOpIdx = (NarrowUse->getOperand(0) == NarrowDef) ? 0 : 1;
// We're trying to find X such that
//
// Widen(NarrowDef `op` NonIVNarrowDef) == WideAR == WideDef `op.wide` X
//
// We guess two solutions to X, sext(NonIVNarrowDef) and zext(NonIVNarrowDef),
// and check using SCEV if any of them are correct.
// Returns true if extending NonIVNarrowDef according to `SignExt` is a
// correct solution to X.
auto GuessNonIVOperand = [&](bool SignExt) {
const SCEV *WideLHS;
const SCEV *WideRHS;
auto GetExtend = [this, SignExt](const SCEV *S, Type *Ty) {
if (SignExt)
return SE->getSignExtendExpr(S, Ty);
return SE->getZeroExtendExpr(S, Ty);
};
if (IVOpIdx == 0) {
WideLHS = SE->getSCEV(WideDef);
const SCEV *NarrowRHS = SE->getSCEV(NarrowUse->getOperand(1));
WideRHS = GetExtend(NarrowRHS, WideType);
} else {
const SCEV *NarrowLHS = SE->getSCEV(NarrowUse->getOperand(0));
WideLHS = GetExtend(NarrowLHS, WideType);
WideRHS = SE->getSCEV(WideDef);
}
// WideUse is "WideDef `op.wide` X" as described in the comment.
const SCEV *WideUse =
getSCEVByOpCode(WideLHS, WideRHS, NarrowUse->getOpcode());
return WideUse == WideAR;
};
bool SignExtend = getExtendKind(NarrowDef) == ExtendKind::Sign;
if (!GuessNonIVOperand(SignExtend)) {
SignExtend = !SignExtend;
if (!GuessNonIVOperand(SignExtend))
return nullptr;
}
Value *LHS = (NarrowUse->getOperand(0) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(0), WideType,
SignExtend, NarrowUse);
Value *RHS = (NarrowUse->getOperand(1) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(1), WideType,
SignExtend, NarrowUse);
auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
NarrowBO->getName());
IRBuilder<> Builder(NarrowUse);
Builder.Insert(WideBO);
WideBO->copyIRFlags(NarrowBO);
return WideBO;
}
WidenIV::ExtendKind WidenIV::getExtendKind(Instruction *I) {
auto It = ExtendKindMap.find(I);
assert(It != ExtendKindMap.end() && "Instruction not yet extended!");
return It->second;
}
const SCEV *WidenIV::getSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
unsigned OpCode) const {
switch (OpCode) {
case Instruction::Add:
return SE->getAddExpr(LHS, RHS);
case Instruction::Sub:
return SE->getMinusSCEV(LHS, RHS);
case Instruction::Mul:
return SE->getMulExpr(LHS, RHS);
case Instruction::UDiv:
return SE->getUDivExpr(LHS, RHS);
default:
llvm_unreachable("Unsupported opcode.");
};
}
namespace {
// Represents a interesting integer binary operation for
// getExtendedOperandRecurrence. This may be a shl that is being treated as a
// multiply or a 'or disjoint' that is being treated as 'add nsw nuw'.
struct BinaryOp {
unsigned Opcode;
std::array<Value *, 2> Operands;
bool IsNSW = false;
bool IsNUW = false;
explicit BinaryOp(Instruction *Op)
: Opcode(Op->getOpcode()),
Operands({Op->getOperand(0), Op->getOperand(1)}) {
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(Op)) {
IsNSW = OBO->hasNoSignedWrap();
IsNUW = OBO->hasNoUnsignedWrap();
}
}
explicit BinaryOp(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS,
bool IsNSW = false, bool IsNUW = false)
: Opcode(Opcode), Operands({LHS, RHS}), IsNSW(IsNSW), IsNUW(IsNUW) {}
};
} // end anonymous namespace
static std::optional<BinaryOp> matchBinaryOp(Instruction *Op) {
switch (Op->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
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);
break;
}
case Instruction::Shl: {
if (ConstantInt *SA = dyn_cast<ConstantInt>(Op->getOperand(1))) {
unsigned 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().ult(BitWidth)) {
// 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.
bool IsNUW = Op->hasNoUnsignedWrap();
bool IsNSW = Op->hasNoSignedWrap() &&
(IsNUW || SA->getValue().ult(BitWidth - 1));
ConstantInt *X =
ConstantInt::get(Op->getContext(),
APInt::getOneBitSet(BitWidth, SA->getZExtValue()));
return BinaryOp(Instruction::Mul, Op->getOperand(0), X, IsNSW, IsNUW);
}
}
break;
}
}
return std::nullopt;
}
/// No-wrap operations can transfer sign extension of their result to their
/// operands. Generate the SCEV value for the widened operation without
/// actually modifying the IR yet. If the expression after extending the
/// operands is an AddRec for this loop, return the AddRec and the kind of
/// extension used.
WidenIV::WidenedRecTy
WidenIV::getExtendedOperandRecurrence(WidenIV::NarrowIVDefUse DU) {
auto Op = matchBinaryOp(DU.NarrowUse);
if (!Op)
return {nullptr, ExtendKind::Unknown};
assert((Op->Opcode == Instruction::Add || Op->Opcode == Instruction::Sub ||
Op->Opcode == Instruction::Mul) &&
"Unexpected opcode");
// One operand (NarrowDef) has already been extended to WideDef. Now determine
// if extending the other will lead to a recurrence.
const unsigned ExtendOperIdx = Op->Operands[0] == DU.NarrowDef ? 1 : 0;
assert(Op->Operands[1 - ExtendOperIdx] == DU.NarrowDef && "bad DU");
ExtendKind ExtKind = getExtendKind(DU.NarrowDef);
if (!(ExtKind == ExtendKind::Sign && Op->IsNSW) &&
!(ExtKind == ExtendKind::Zero && Op->IsNUW)) {
ExtKind = ExtendKind::Unknown;
// For a non-negative NarrowDef, we can choose either type of
// extension. We want to use the current extend kind if legal
// (see above), and we only hit this code if we need to check
// the opposite case.
if (DU.NeverNegative) {
if (Op->IsNSW) {
ExtKind = ExtendKind::Sign;
} else if (Op->IsNUW) {
ExtKind = ExtendKind::Zero;
}
}
}
const SCEV *ExtendOperExpr = SE->getSCEV(Op->Operands[ExtendOperIdx]);
if (ExtKind == ExtendKind::Sign)
ExtendOperExpr = SE->getSignExtendExpr(ExtendOperExpr, WideType);
else if (ExtKind == ExtendKind::Zero)
ExtendOperExpr = SE->getZeroExtendExpr(ExtendOperExpr, WideType);
else
return {nullptr, ExtendKind::Unknown};
// When creating this SCEV expr, don't apply the current operations NSW or NUW
// flags. This instruction may be guarded by control flow that the no-wrap
// behavior depends on. Non-control-equivalent instructions can be mapped to
// the same SCEV expression, and it would be incorrect to transfer NSW/NUW
// semantics to those operations.
const SCEV *lhs = SE->getSCEV(DU.WideDef);
const SCEV *rhs = ExtendOperExpr;
// Let's swap operands to the initial order for the case of non-commutative
// operations, like SUB. See PR21014.
if (ExtendOperIdx == 0)
std::swap(lhs, rhs);
const SCEVAddRecExpr *AddRec =
dyn_cast<SCEVAddRecExpr>(getSCEVByOpCode(lhs, rhs, Op->Opcode));
if (!AddRec || AddRec->getLoop() != L)
return {nullptr, ExtendKind::Unknown};
return {AddRec, ExtKind};
}
/// Is this instruction potentially interesting for further simplification after
/// widening it's type? In other words, can the extend be safely hoisted out of
/// the loop with SCEV reducing the value to a recurrence on the same loop. If
/// so, return the extended recurrence and the kind of extension used. Otherwise
/// return {nullptr, ExtendKind::Unknown}.
WidenIV::WidenedRecTy WidenIV::getWideRecurrence(WidenIV::NarrowIVDefUse DU) {
if (!DU.NarrowUse->getType()->isIntegerTy())
return {nullptr, ExtendKind::Unknown};
const SCEV *NarrowExpr = SE->getSCEV(DU.NarrowUse);
if (SE->getTypeSizeInBits(NarrowExpr->getType()) >=
SE->getTypeSizeInBits(WideType)) {
// NarrowUse implicitly widens its operand. e.g. a gep with a narrow
// index. So don't follow this use.
return {nullptr, ExtendKind::Unknown};
}
const SCEV *WideExpr;
ExtendKind ExtKind;
if (DU.NeverNegative) {
WideExpr = SE->getSignExtendExpr(NarrowExpr, WideType);
if (isa<SCEVAddRecExpr>(WideExpr))
ExtKind = ExtendKind::Sign;
else {
WideExpr = SE->getZeroExtendExpr(NarrowExpr, WideType);
ExtKind = ExtendKind::Zero;
}
} else if (getExtendKind(DU.NarrowDef) == ExtendKind::Sign) {
WideExpr = SE->getSignExtendExpr(NarrowExpr, WideType);
ExtKind = ExtendKind::Sign;
} else {
WideExpr = SE->getZeroExtendExpr(NarrowExpr, WideType);
ExtKind = ExtendKind::Zero;
}
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
if (!AddRec || AddRec->getLoop() != L)
return {nullptr, ExtendKind::Unknown};
return {AddRec, ExtKind};
}
/// This IV user cannot be widened. Replace this use of the original narrow IV
/// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
void WidenIV::truncateIVUse(NarrowIVDefUse DU) {
auto *InsertPt = getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI);
if (!InsertPt)
return;
LLVM_DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef << " for user "
<< *DU.NarrowUse << "\n");
ExtendKind ExtKind = getExtendKind(DU.NarrowDef);
IRBuilder<> Builder(InsertPt);
Value *Trunc =
Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType(), "",
DU.NeverNegative || ExtKind == ExtendKind::Zero,
DU.NeverNegative || ExtKind == ExtendKind::Sign);
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
}
/// If the narrow use is a compare instruction, then widen the compare
// (and possibly the other operand). The extend operation is hoisted into the
// loop preheader as far as possible.
bool WidenIV::widenLoopCompare(WidenIV::NarrowIVDefUse DU) {
ICmpInst *Cmp = dyn_cast<ICmpInst>(DU.NarrowUse);
if (!Cmp)
return false;
// We can legally widen the comparison in the following two cases:
//
// - The signedness of the IV extension and comparison match
//
// - The narrow IV is always positive (and thus its sign extension is equal
// to its zero extension). For instance, let's say we're zero extending
// %narrow for the following use
//
// icmp slt i32 %narrow, %val ... (A)
//
// and %narrow is always positive. Then
//
// (A) == icmp slt i32 sext(%narrow), sext(%val)
// == icmp slt i32 zext(%narrow), sext(%val)
bool IsSigned = getExtendKind(DU.NarrowDef) == ExtendKind::Sign;
if (!(DU.NeverNegative || IsSigned == Cmp->isSigned()))
return false;
Value *Op = Cmp->getOperand(Cmp->getOperand(0) == DU.NarrowDef ? 1 : 0);
unsigned CastWidth = SE->getTypeSizeInBits(Op->getType());
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
assert(CastWidth <= IVWidth && "Unexpected width while widening compare.");
// Widen the compare instruction.
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
// Widen the other operand of the compare, if necessary.
if (CastWidth < IVWidth) {
Value *ExtOp = createExtendInst(Op, WideType, Cmp->isSigned(), Cmp);
DU.NarrowUse->replaceUsesOfWith(Op, ExtOp);
}
return true;
}
// The widenIVUse avoids generating trunc by evaluating the use as AddRec, this
// will not work when:
// 1) SCEV traces back to an instruction inside the loop that SCEV can not
// expand, eg. add %indvar, (load %addr)
// 2) SCEV finds a loop variant, eg. add %indvar, %loopvariant
// While SCEV fails to avoid trunc, we can still try to use instruction
// combining approach to prove trunc is not required. This can be further
// extended with other instruction combining checks, but for now we handle the
// following case (sub can be "add" and "mul", "nsw + sext" can be "nus + zext")
//
// Src:
// %c = sub nsw %b, %indvar
// %d = sext %c to i64
// Dst:
// %indvar.ext1 = sext %indvar to i64
// %m = sext %b to i64
// %d = sub nsw i64 %m, %indvar.ext1
// Therefore, as long as the result of add/sub/mul is extended to wide type, no
// trunc is required regardless of how %b is generated. This pattern is common
// when calculating address in 64 bit architecture
bool WidenIV::widenWithVariantUse(WidenIV::NarrowIVDefUse DU) {
Instruction *NarrowUse = DU.NarrowUse;
Instruction *NarrowDef = DU.NarrowDef;
Instruction *WideDef = DU.WideDef;
// Handle the common case of add<nsw/nuw>
const unsigned OpCode = NarrowUse->getOpcode();
// Only Add/Sub/Mul instructions are supported.
if (OpCode != Instruction::Add && OpCode != Instruction::Sub &&
OpCode != Instruction::Mul)
return false;
// The operand that is not defined by NarrowDef of DU. Let's call it the
// other operand.
assert((NarrowUse->getOperand(0) == NarrowDef ||
NarrowUse->getOperand(1) == NarrowDef) &&
"bad DU");
const OverflowingBinaryOperator *OBO =
cast<OverflowingBinaryOperator>(NarrowUse);
ExtendKind ExtKind = getExtendKind(NarrowDef);
bool CanSignExtend = ExtKind == ExtendKind::Sign && OBO->hasNoSignedWrap();
bool CanZeroExtend = ExtKind == ExtendKind::Zero && OBO->hasNoUnsignedWrap();
auto AnotherOpExtKind = ExtKind;
// Check that all uses are either:
// - narrow def (in case of we are widening the IV increment);
// - single-input LCSSA Phis;
// - comparison of the chosen type;
// - extend of the chosen type (raison d'etre).
SmallVector<Instruction *, 4> ExtUsers;
SmallVector<PHINode *, 4> LCSSAPhiUsers;
SmallVector<ICmpInst *, 4> ICmpUsers;
for (Use &U : NarrowUse->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
if (User == NarrowDef)
continue;
if (!L->contains(User)) {
auto *LCSSAPhi = cast<PHINode>(User);
// Make sure there is only 1 input, so that we don't have to split
// critical edges.
if (LCSSAPhi->getNumOperands() != 1)
return false;
LCSSAPhiUsers.push_back(LCSSAPhi);
continue;
}
if (auto *ICmp = dyn_cast<ICmpInst>(User)) {
auto Pred = ICmp->getPredicate();
// We have 3 types of predicates: signed, unsigned and equality
// predicates. For equality, it's legal to widen icmp for either sign and
// zero extend. For sign extend, we can also do so for signed predicates,
// likeweise for zero extend we can widen icmp for unsigned predicates.
if (ExtKind == ExtendKind::Zero && ICmpInst::isSigned(Pred))
return false;
if (ExtKind == ExtendKind::Sign && ICmpInst::isUnsigned(Pred))
return false;
ICmpUsers.push_back(ICmp);
continue;
}
if (ExtKind == ExtendKind::Sign)
User = dyn_cast<SExtInst>(User);
else
User = dyn_cast<ZExtInst>(User);
if (!User || User->getType() != WideType)
return false;
ExtUsers.push_back(User);
}
if (ExtUsers.empty()) {
DeadInsts.emplace_back(NarrowUse);
return true;
}
// We'll prove some facts that should be true in the context of ext users. If
// there is no users, we are done now. If there are some, pick their common
// dominator as context.
const Instruction *CtxI = findCommonDominator(ExtUsers, *DT);
if (!CanSignExtend && !CanZeroExtend) {
// Because InstCombine turns 'sub nuw' to 'add' losing the no-wrap flag, we
// will most likely not see it. Let's try to prove it.
if (OpCode != Instruction::Add)
return false;
if (ExtKind != ExtendKind::Zero)
return false;
const SCEV *LHS = SE->getSCEV(OBO->getOperand(0));
const SCEV *RHS = SE->getSCEV(OBO->getOperand(1));
// TODO: Support case for NarrowDef = NarrowUse->getOperand(1).
if (NarrowUse->getOperand(0) != NarrowDef)
return false;
if (!SE->isKnownNegative(RHS))
return false;
bool ProvedSubNUW = SE->isKnownPredicateAt(ICmpInst::ICMP_UGE, LHS,
SE->getNegativeSCEV(RHS), CtxI);
if (!ProvedSubNUW)
return false;
// In fact, our 'add' is 'sub nuw'. We will need to widen the 2nd operand as
// neg(zext(neg(op))), which is basically sext(op).
AnotherOpExtKind = ExtendKind::Sign;
}
// Verifying that Defining operand is an AddRec
const SCEV *Op1 = SE->getSCEV(WideDef);
const SCEVAddRecExpr *AddRecOp1 = dyn_cast<SCEVAddRecExpr>(Op1);
if (!AddRecOp1 || AddRecOp1->getLoop() != L)
return false;
LLVM_DEBUG(dbgs() << "Cloning arithmetic IVUser: " << *NarrowUse << "\n");
// Generating a widening use instruction.
Value *LHS =
(NarrowUse->getOperand(0) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(0), WideType,
AnotherOpExtKind == ExtendKind::Sign, NarrowUse);
Value *RHS =
(NarrowUse->getOperand(1) == NarrowDef)
? WideDef
: createExtendInst(NarrowUse->getOperand(1), WideType,
AnotherOpExtKind == ExtendKind::Sign, NarrowUse);
auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
NarrowBO->getName());
IRBuilder<> Builder(NarrowUse);
Builder.Insert(WideBO);
WideBO->copyIRFlags(NarrowBO);
ExtendKindMap[NarrowUse] = ExtKind;
for (Instruction *User : ExtUsers) {
assert(User->getType() == WideType && "Checked before!");
LLVM_DEBUG(dbgs() << "INDVARS: eliminating " << *User << " replaced by "
<< *WideBO << "\n");
++NumElimExt;
User->replaceAllUsesWith(WideBO);
DeadInsts.emplace_back(User);
}
for (PHINode *User : LCSSAPhiUsers) {
assert(User->getNumOperands() == 1 && "Checked before!");
Builder.SetInsertPoint(User);
auto *WidePN =
Builder.CreatePHI(WideBO->getType(), 1, User->getName() + ".wide");
BasicBlock *LoopExitingBlock = User->getParent()->getSinglePredecessor();
assert(LoopExitingBlock && L->contains(LoopExitingBlock) &&
"Not a LCSSA Phi?");
WidePN->addIncoming(WideBO, LoopExitingBlock);
Builder.SetInsertPoint(User->getParent(),
User->getParent()->getFirstInsertionPt());
auto *TruncPN = Builder.CreateTrunc(WidePN, User->getType());
User->replaceAllUsesWith(TruncPN);
DeadInsts.emplace_back(User);
}
for (ICmpInst *User : ICmpUsers) {
Builder.SetInsertPoint(User);
auto ExtendedOp = [&](Value * V)->Value * {
if (V == NarrowUse)
return WideBO;
if (ExtKind == ExtendKind::Zero)
return Builder.CreateZExt(V, WideBO->getType());
else
return Builder.CreateSExt(V, WideBO->getType());
};
auto Pred = User->getPredicate();
auto *LHS = ExtendedOp(User->getOperand(0));
auto *RHS = ExtendedOp(User->getOperand(1));
auto *WideCmp =
Builder.CreateICmp(Pred, LHS, RHS, User->getName() + ".wide");
User->replaceAllUsesWith(WideCmp);
DeadInsts.emplace_back(User);
}
return true;
}
/// Determine whether an individual user of the narrow IV can be widened. If so,
/// return the wide clone of the user.
Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU,
SCEVExpander &Rewriter, PHINode *OrigPhi,
PHINode *WidePhi) {
assert(ExtendKindMap.count(DU.NarrowDef) &&
"Should already know the kind of extension used to widen NarrowDef");
// This narrow use can be widened by a sext if it's non-negative or its narrow
// def was widened by a sext. Same for zext.
bool CanWidenBySExt =
DU.NeverNegative || getExtendKind(DU.NarrowDef) == ExtendKind::Sign;
bool CanWidenByZExt =
DU.NeverNegative || getExtendKind(DU.NarrowDef) == ExtendKind::Zero;
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
if (PHINode *UsePhi = dyn_cast<PHINode>(DU.NarrowUse)) {
if (LI->getLoopFor(UsePhi->getParent()) != L) {
// For LCSSA phis, sink the truncate outside the loop.
// After SimplifyCFG most loop exit targets have a single predecessor.
// Otherwise fall back to a truncate within the loop.
if (UsePhi->getNumOperands() != 1)
truncateIVUse(DU);
else {
// Widening the PHI requires us to insert a trunc. The logical place
// for this trunc is in the same BB as the PHI. This is not possible if
// the BB is terminated by a catchswitch.
if (isa<CatchSwitchInst>(UsePhi->getParent()->getTerminator()))
return nullptr;
PHINode *WidePhi =
PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide",
UsePhi->getIterator());
WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
BasicBlock *WidePhiBB = WidePhi->getParent();
IRBuilder<> Builder(WidePhiBB, WidePhiBB->getFirstInsertionPt());
Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType(), "",
CanWidenByZExt, CanWidenBySExt);
UsePhi->replaceAllUsesWith(Trunc);
DeadInsts.emplace_back(UsePhi);
LLVM_DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi << " to "
<< *WidePhi << "\n");
}
return nullptr;
}
}
// Our raison d'etre! Eliminate sign and zero extension.
if ((match(DU.NarrowUse, m_SExtLike(m_Value())) && CanWidenBySExt) ||
(isa<ZExtInst>(DU.NarrowUse) && CanWidenByZExt)) {
Value *NewDef = DU.WideDef;
if (DU.NarrowUse->getType() != WideType) {
unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
if (CastWidth < IVWidth) {
// The cast isn't as wide as the IV, so insert a Trunc.
IRBuilder<> Builder(DU.NarrowUse);
NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType(), "",
CanWidenByZExt, CanWidenBySExt);
}
else {
// A wider extend was hidden behind a narrower one. This may induce
// another round of IV widening in which the intermediate IV becomes
// dead. It should be very rare.
LLVM_DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
<< " not wide enough to subsume " << *DU.NarrowUse
<< "\n");
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
NewDef = DU.NarrowUse;
}
}
if (NewDef != DU.NarrowUse) {
LLVM_DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
<< " replaced by " << *DU.WideDef << "\n");
++NumElimExt;
DU.NarrowUse->replaceAllUsesWith(NewDef);
DeadInsts.emplace_back(DU.NarrowUse);
}
// Now that the extend is gone, we want to expose it's uses for potential
// further simplification. We don't need to directly inform SimplifyIVUsers
// of the new users, because their parent IV will be processed later as a
// new loop phi. If we preserved IVUsers analysis, we would also want to
// push the uses of WideDef here.
// No further widening is needed. The deceased [sz]ext had done it for us.
return nullptr;
}
auto tryAddRecExpansion = [&]() -> Instruction* {
// Does this user itself evaluate to a recurrence after widening?
WidenedRecTy WideAddRec = getExtendedOperandRecurrence(DU);
if (!WideAddRec.first)
WideAddRec = getWideRecurrence(DU);
assert((WideAddRec.first == nullptr) ==
(WideAddRec.second == ExtendKind::Unknown));
if (!WideAddRec.first)
return nullptr;
// Reuse the IV increment that SCEVExpander created. Recompute flags, unless
// the flags for both increments agree and it is safe to use the ones from
// the original inc. In that case, the new use of the wide increment won't
// be more poisonous.
bool NeedToRecomputeFlags =
!SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
DU.NarrowUse, WideInc) ||
DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
Instruction *WideUse = nullptr;
if (WideAddRec.first == WideIncExpr &&
Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags))
WideUse = WideInc;
else {
WideUse = cloneIVUser(DU, WideAddRec.first);
if (!WideUse)
return nullptr;
}
// Evaluation of WideAddRec ensured that the narrow expression could be
// extended outside the loop without overflow. This suggests that the wide use
// evaluates to the same expression as the extended narrow use, but doesn't
// absolutely guarantee it. Hence the following failsafe check. In rare cases
// where it fails, we simply throw away the newly created wide use.
if (WideAddRec.first != SE->getSCEV(WideUse)) {
LLVM_DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse << ": "
<< *SE->getSCEV(WideUse) << " != " << *WideAddRec.first
<< "\n");
DeadInsts.emplace_back(WideUse);
return nullptr;
};
// if we reached this point then we are going to replace
// DU.NarrowUse with WideUse. Reattach DbgValue then.
replaceAllDbgUsesWith(*DU.NarrowUse, *WideUse, *WideUse, *DT);
ExtendKindMap[DU.NarrowUse] = WideAddRec.second;
// Returning WideUse pushes it on the worklist.
return WideUse;
};
if (auto *I = tryAddRecExpansion())
return I;
// If use is a loop condition, try to promote the condition instead of
// truncating the IV first.
if (widenLoopCompare(DU))
return nullptr;
// We are here about to generate a truncate instruction that may hurt
// performance because the scalar evolution expression computed earlier
// in WideAddRec.first does not indicate a polynomial induction expression.
// In that case, look at the operands of the use instruction to determine
// if we can still widen the use instead of truncating its operand.
if (widenWithVariantUse(DU))
return nullptr;
// This user does not evaluate to a recurrence after widening, so don't
// follow it. Instead insert a Trunc to kill off the original use,
// eventually isolating the original narrow IV so it can be removed.
truncateIVUse(DU);
return nullptr;
}
/// Add eligible users of NarrowDef to NarrowIVUsers.
void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
const SCEV *NarrowSCEV = SE->getSCEV(NarrowDef);
bool NonNegativeDef =
SE->isKnownPredicate(ICmpInst::ICMP_SGE, NarrowSCEV,
SE->getZero(NarrowSCEV->getType()));
for (User *U : NarrowDef->users()) {
Instruction *NarrowUser = cast<Instruction>(U);
// Handle data flow merges and bizarre phi cycles.
if (!Widened.insert(NarrowUser).second)
continue;
bool NonNegativeUse = false;
if (!NonNegativeDef) {
// We might have a control-dependent range information for this context.
if (auto RangeInfo = getPostIncRangeInfo(NarrowDef, NarrowUser))
NonNegativeUse = RangeInfo->getSignedMin().isNonNegative();
}
NarrowIVUsers.emplace_back(NarrowDef, NarrowUser, WideDef,
NonNegativeDef || NonNegativeUse);
}
}
/// Process a single induction variable. First use the SCEVExpander to create a
/// wide induction variable that evaluates to the same recurrence as the
/// original narrow IV. Then use a worklist to forward traverse the narrow IV's
/// def-use chain. After widenIVUse has processed all interesting IV users, the
/// narrow IV will be isolated for removal by DeleteDeadPHIs.
///
/// It would be simpler to delete uses as they are processed, but we must avoid
/// invalidating SCEV expressions.
PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
// Is this phi an induction variable?
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
if (!AddRec)
return nullptr;
// Widen the induction variable expression.
const SCEV *WideIVExpr = getExtendKind(OrigPhi) == ExtendKind::Sign
? SE->getSignExtendExpr(AddRec, WideType)
: SE->getZeroExtendExpr(AddRec, WideType);
assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
"Expect the new IV expression to preserve its type");
// Can the IV be extended outside the loop without overflow?
AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
if (!AddRec || AddRec->getLoop() != L)
return nullptr;
// An AddRec must have loop-invariant operands. Since this AddRec is
// materialized by a loop header phi, the expression cannot have any post-loop
// operands, so they must dominate the loop header.
assert(
SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader()) &&
"Loop header phi recurrence inputs do not dominate the loop");
// Iterate over IV uses (including transitive ones) looking for IV increments
// of the form 'add nsw %iv, <const>'. For each increment and each use of
// the increment calculate control-dependent range information basing on
// dominating conditions inside of the loop (e.g. a range check inside of the
// loop). Calculated ranges are stored in PostIncRangeInfos map.
//
// Control-dependent range information is later used to prove that a narrow
// definition is not negative (see pushNarrowIVUsers). It's difficult to do
// this on demand because when pushNarrowIVUsers needs this information some
// of the dominating conditions might be already widened.
if (UsePostIncrementRanges)
calculatePostIncRanges(OrigPhi);
// The rewriter provides a value for the desired IV expression. This may
// either find an existing phi or materialize a new one. Either way, we
// expect a well-formed cyclic phi-with-increments. i.e. any operand not part
// of the phi-SCC dominates the loop entry.
Instruction *InsertPt = &*L->getHeader()->getFirstInsertionPt();
Value *ExpandInst = Rewriter.expandCodeFor(AddRec, WideType, InsertPt);
// If the wide phi is not a phi node, for example a cast node, like bitcast,
// inttoptr, ptrtoint, just skip for now.
if (!(WidePhi = dyn_cast<PHINode>(ExpandInst))) {
// if the cast node is an inserted instruction without any user, we should
// remove it to make sure the pass don't touch the function as we can not
// wide the phi.
if (ExpandInst->hasNUses(0) &&
Rewriter.isInsertedInstruction(cast<Instruction>(ExpandInst)))
DeadInsts.emplace_back(ExpandInst);
return nullptr;
}
// Remembering the WideIV increment generated by SCEVExpander allows
// widenIVUse to reuse it when widening the narrow IV's increment. We don't
// employ a general reuse mechanism because the call above is the only call to
// SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
if (BasicBlock *LatchBlock = L->getLoopLatch()) {
WideInc =
dyn_cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
if (WideInc) {
WideIncExpr = SE->getSCEV(WideInc);
// Propagate the debug location associated with the original loop
// increment to the new (widened) increment.
auto *OrigInc =
cast<Instruction>(OrigPhi->getIncomingValueForBlock(LatchBlock));
WideInc->setDebugLoc(OrigInc->getDebugLoc());
// We are replacing a narrow IV increment with a wider IV increment. If
// the original (narrow) increment did not wrap, the wider increment one
// should not wrap either. Set the flags to be the union of both wide
// increment and original increment; this ensures we preserve flags SCEV
// could infer for the wider increment. Limit this only to cases where
// both increments directly increment the corresponding PHI nodes and have
// the same opcode. It is not safe to re-use the flags from the original
// increment, if it is more complex and SCEV expansion may have yielded a
// more simplified wider increment.
if (SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
OrigInc, WideInc) &&
isa<OverflowingBinaryOperator>(OrigInc) &&
isa<OverflowingBinaryOperator>(WideInc)) {
WideInc->setHasNoUnsignedWrap(WideInc->hasNoUnsignedWrap() ||
OrigInc->hasNoUnsignedWrap());
WideInc->setHasNoSignedWrap(WideInc->hasNoSignedWrap() ||
OrigInc->hasNoSignedWrap());
}
}
}
LLVM_DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
++NumWidened;
// Traverse the def-use chain using a worklist starting at the original IV.
assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
Widened.insert(OrigPhi);
pushNarrowIVUsers(OrigPhi, WidePhi);
while (!NarrowIVUsers.empty()) {
WidenIV::NarrowIVDefUse DU = NarrowIVUsers.pop_back_val();
// Process a def-use edge. This may replace the use, so don't hold a
// use_iterator across it.
Instruction *WideUse = widenIVUse(DU, Rewriter, OrigPhi, WidePhi);
// Follow all def-use edges from the previous narrow use.
if (WideUse)
pushNarrowIVUsers(DU.NarrowUse, WideUse);
// widenIVUse may have removed the def-use edge.
if (DU.NarrowDef->use_empty())
DeadInsts.emplace_back(DU.NarrowDef);
}
// Attach any debug information to the new PHI.
replaceAllDbgUsesWith(*OrigPhi, *WidePhi, *WidePhi, *DT);
return WidePhi;
}
/// Calculates control-dependent range for the given def at the given context
/// by looking at dominating conditions inside of the loop
void WidenIV::calculatePostIncRange(Instruction *NarrowDef,
Instruction *NarrowUser) {
Value *NarrowDefLHS;
const APInt *NarrowDefRHS;
if (!match(NarrowDef, m_NSWAdd(m_Value(NarrowDefLHS),
m_APInt(NarrowDefRHS))) ||
!NarrowDefRHS->isNonNegative())
return;
auto UpdateRangeFromCondition = [&] (Value *Condition,
bool TrueDest) {
CmpInst::Predicate Pred;
Value *CmpRHS;
if (!match(Condition, m_ICmp(Pred, m_Specific(NarrowDefLHS),
m_Value(CmpRHS))))
return;
CmpInst::Predicate P =
TrueDest ? Pred : CmpInst::getInversePredicate(Pred);
auto CmpRHSRange = SE->getSignedRange(SE->getSCEV(CmpRHS));
auto CmpConstrainedLHSRange =
ConstantRange::makeAllowedICmpRegion(P, CmpRHSRange);
auto NarrowDefRange = CmpConstrainedLHSRange.addWithNoWrap(
*NarrowDefRHS, OverflowingBinaryOperator::NoSignedWrap);
updatePostIncRangeInfo(NarrowDef, NarrowUser, NarrowDefRange);
};
auto UpdateRangeFromGuards = [&](Instruction *Ctx) {
if (!HasGuards)
return;
for (Instruction &I : make_range(Ctx->getIterator().getReverse(),
Ctx->getParent()->rend())) {
Value *C = nullptr;
if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>(m_Value(C))))
UpdateRangeFromCondition(C, /*TrueDest=*/true);
}
};
UpdateRangeFromGuards(NarrowUser);
BasicBlock *NarrowUserBB = NarrowUser->getParent();
// If NarrowUserBB is statically unreachable asking dominator queries may
// yield surprising results. (e.g. the block may not have a dom tree node)
if (!DT->isReachableFromEntry(NarrowUserBB))
return;
for (auto *DTB = (*DT)[NarrowUserBB]->getIDom();
L->contains(DTB->getBlock());
DTB = DTB->getIDom()) {
auto *BB = DTB->getBlock();
auto *TI = BB->getTerminator();
UpdateRangeFromGuards(TI);
auto *BI = dyn_cast<BranchInst>(TI);
if (!BI || !BI->isConditional())
continue;
auto *TrueSuccessor = BI->getSuccessor(0);
auto *FalseSuccessor = BI->getSuccessor(1);
auto DominatesNarrowUser = [this, NarrowUser] (BasicBlockEdge BBE) {
return BBE.isSingleEdge() &&
DT->dominates(BBE, NarrowUser->getParent());
};
if (DominatesNarrowUser(BasicBlockEdge(BB, TrueSuccessor)))
UpdateRangeFromCondition(BI->getCondition(), /*TrueDest=*/true);
if (DominatesNarrowUser(BasicBlockEdge(BB, FalseSuccessor)))
UpdateRangeFromCondition(BI->getCondition(), /*TrueDest=*/false);
}
}
/// Calculates PostIncRangeInfos map for the given IV
void WidenIV::calculatePostIncRanges(PHINode *OrigPhi) {
SmallPtrSet<Instruction *, 16> Visited;
SmallVector<Instruction *, 6> Worklist;
Worklist.push_back(OrigPhi);
Visited.insert(OrigPhi);
while (!Worklist.empty()) {
Instruction *NarrowDef = Worklist.pop_back_val();
for (Use &U : NarrowDef->uses()) {
auto *NarrowUser = cast<Instruction>(U.getUser());
// Don't go looking outside the current loop.
auto *NarrowUserLoop = (*LI)[NarrowUser->getParent()];
if (!NarrowUserLoop || !L->contains(NarrowUserLoop))
continue;
if (!Visited.insert(NarrowUser).second)
continue;
Worklist.push_back(NarrowUser);
calculatePostIncRange(NarrowDef, NarrowUser);
}
}
}
PHINode *llvm::createWideIV(const WideIVInfo &WI,
LoopInfo *LI, ScalarEvolution *SE, SCEVExpander &Rewriter,
DominatorTree *DT, SmallVectorImpl<WeakTrackingVH> &DeadInsts,
unsigned &NumElimExt, unsigned &NumWidened,
bool HasGuards, bool UsePostIncrementRanges) {
WidenIV Widener(WI, LI, SE, DT, DeadInsts, HasGuards, UsePostIncrementRanges);
PHINode *WidePHI = Widener.createWideIV(Rewriter);
NumElimExt = Widener.getNumElimExt();
NumWidened = Widener.getNumWidened();
return WidePHI;
}