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llvm / llvm-project / refs/heads/users/avillega/main.gsymdwarf-include-end_sequence-debug_line-rows-when-looking-up-addr-ranges / . / llvm / lib / Transforms / Scalar / ConstraintElimination.cpp
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//===-- ConstraintElimination.cpp - Eliminate conds using constraints. ----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Eliminate conditions based on constraints collected from dominating
// conditions.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/ConstraintElimination.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstraintSystem.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <cmath>
#include <optional>
#include <string>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "constraint-elimination"
STATISTIC(NumCondsRemoved, "Number of instructions removed");
DEBUG_COUNTER(EliminatedCounter, "conds-eliminated",
"Controls which conditions are eliminated");
static cl::opt<unsigned>
MaxRows("constraint-elimination-max-rows", cl::init(500), cl::Hidden,
cl::desc("Maximum number of rows to keep in constraint system"));
static cl::opt<bool> DumpReproducers(
"constraint-elimination-dump-reproducers", cl::init(false), cl::Hidden,
cl::desc("Dump IR to reproduce successful transformations."));
static int64_t MaxConstraintValue = std::numeric_limits<int64_t>::max();
static int64_t MinSignedConstraintValue = std::numeric_limits<int64_t>::min();
// A helper to multiply 2 signed integers where overflowing is allowed.
static int64_t multiplyWithOverflow(int64_t A, int64_t B) {
int64_t Result;
MulOverflow(A, B, Result);
return Result;
}
// A helper to add 2 signed integers where overflowing is allowed.
static int64_t addWithOverflow(int64_t A, int64_t B) {
int64_t Result;
AddOverflow(A, B, Result);
return Result;
}
static Instruction *getContextInstForUse(Use &U) {
Instruction *UserI = cast<Instruction>(U.getUser());
if (auto *Phi = dyn_cast<PHINode>(UserI))
UserI = Phi->getIncomingBlock(U)->getTerminator();
return UserI;
}
namespace {
/// Struct to express a condition of the form %Op0 Pred %Op1.
struct ConditionTy {
CmpInst::Predicate Pred;
Value *Op0;
Value *Op1;
ConditionTy()
: Pred(CmpInst::BAD_ICMP_PREDICATE), Op0(nullptr), Op1(nullptr) {}
ConditionTy(CmpInst::Predicate Pred, Value *Op0, Value *Op1)
: Pred(Pred), Op0(Op0), Op1(Op1) {}
};
/// Represents either
/// * a condition that holds on entry to a block (=condition fact)
/// * an assume (=assume fact)
/// * a use of a compare instruction to simplify.
/// It also tracks the Dominator DFS in and out numbers for each entry.
struct FactOrCheck {
enum class EntryTy {
ConditionFact, /// A condition that holds on entry to a block.
InstFact, /// A fact that holds after Inst executed (e.g. an assume or
/// min/mix intrinsic.
InstCheck, /// An instruction to simplify (e.g. an overflow math
/// intrinsics).
UseCheck /// An use of a compare instruction to simplify.
};
union {
Instruction *Inst;
Use *U;
ConditionTy Cond;
};
/// A pre-condition that must hold for the current fact to be added to the
/// system.
ConditionTy DoesHold;
unsigned NumIn;
unsigned NumOut;
EntryTy Ty;
FactOrCheck(EntryTy Ty, DomTreeNode *DTN, Instruction *Inst)
: Inst(Inst), NumIn(DTN->getDFSNumIn()), NumOut(DTN->getDFSNumOut()),
Ty(Ty) {}
FactOrCheck(DomTreeNode *DTN, Use *U)
: U(U), DoesHold(CmpInst::BAD_ICMP_PREDICATE, nullptr, nullptr),
NumIn(DTN->getDFSNumIn()), NumOut(DTN->getDFSNumOut()),
Ty(EntryTy::UseCheck) {}
FactOrCheck(DomTreeNode *DTN, CmpInst::Predicate Pred, Value *Op0, Value *Op1,
ConditionTy Precond = ConditionTy())
: Cond(Pred, Op0, Op1), DoesHold(Precond), NumIn(DTN->getDFSNumIn()),
NumOut(DTN->getDFSNumOut()), Ty(EntryTy::ConditionFact) {}
static FactOrCheck getConditionFact(DomTreeNode *DTN, CmpInst::Predicate Pred,
Value *Op0, Value *Op1,
ConditionTy Precond = ConditionTy()) {
return FactOrCheck(DTN, Pred, Op0, Op1, Precond);
}
static FactOrCheck getInstFact(DomTreeNode *DTN, Instruction *Inst) {
return FactOrCheck(EntryTy::InstFact, DTN, Inst);
}
static FactOrCheck getCheck(DomTreeNode *DTN, Use *U) {
return FactOrCheck(DTN, U);
}
static FactOrCheck getCheck(DomTreeNode *DTN, CallInst *CI) {
return FactOrCheck(EntryTy::InstCheck, DTN, CI);
}
bool isCheck() const {
return Ty == EntryTy::InstCheck || Ty == EntryTy::UseCheck;
}
Instruction *getContextInst() const {
if (Ty == EntryTy::UseCheck)
return getContextInstForUse(*U);
return Inst;
}
Instruction *getInstructionToSimplify() const {
assert(isCheck());
if (Ty == EntryTy::InstCheck)
return Inst;
// The use may have been simplified to a constant already.
return dyn_cast<Instruction>(*U);
}
bool isConditionFact() const { return Ty == EntryTy::ConditionFact; }
};
/// Keep state required to build worklist.
struct State {
DominatorTree &DT;
LoopInfo &LI;
ScalarEvolution &SE;
SmallVector<FactOrCheck, 64> WorkList;
State(DominatorTree &DT, LoopInfo &LI, ScalarEvolution &SE)
: DT(DT), LI(LI), SE(SE) {}
/// Process block \p BB and add known facts to work-list.
void addInfoFor(BasicBlock &BB);
/// Try to add facts for loop inductions (AddRecs) in EQ/NE compares
/// controlling the loop header.
void addInfoForInductions(BasicBlock &BB);
/// Returns true if we can add a known condition from BB to its successor
/// block Succ.
bool canAddSuccessor(BasicBlock &BB, BasicBlock *Succ) const {
return DT.dominates(BasicBlockEdge(&BB, Succ), Succ);
}
};
class ConstraintInfo;
struct StackEntry {
unsigned NumIn;
unsigned NumOut;
bool IsSigned = false;
/// Variables that can be removed from the system once the stack entry gets
/// removed.
SmallVector<Value *, 2> ValuesToRelease;
StackEntry(unsigned NumIn, unsigned NumOut, bool IsSigned,
SmallVector<Value *, 2> ValuesToRelease)
: NumIn(NumIn), NumOut(NumOut), IsSigned(IsSigned),
ValuesToRelease(ValuesToRelease) {}
};
struct ConstraintTy {
SmallVector<int64_t, 8> Coefficients;
SmallVector<ConditionTy, 2> Preconditions;
SmallVector<SmallVector<int64_t, 8>> ExtraInfo;
bool IsSigned = false;
ConstraintTy() = default;
ConstraintTy(SmallVector<int64_t, 8> Coefficients, bool IsSigned, bool IsEq,
bool IsNe)
: Coefficients(std::move(Coefficients)), IsSigned(IsSigned), IsEq(IsEq),
IsNe(IsNe) {}
unsigned size() const { return Coefficients.size(); }
unsigned empty() const { return Coefficients.empty(); }
/// Returns true if all preconditions for this list of constraints are
/// satisfied given \p CS and the corresponding \p Value2Index mapping.
bool isValid(const ConstraintInfo &Info) const;
bool isEq() const { return IsEq; }
bool isNe() const { return IsNe; }
/// Check if the current constraint is implied by the given ConstraintSystem.
///
/// \return true or false if the constraint is proven to be respectively true,
/// or false. When the constraint cannot be proven to be either true or false,
/// std::nullopt is returned.
std::optional<bool> isImpliedBy(const ConstraintSystem &CS) const;
private:
bool IsEq = false;
bool IsNe = false;
};
/// Wrapper encapsulating separate constraint systems and corresponding value
/// mappings for both unsigned and signed information. Facts are added to and
/// conditions are checked against the corresponding system depending on the
/// signed-ness of their predicates. While the information is kept separate
/// based on signed-ness, certain conditions can be transferred between the two
/// systems.
class ConstraintInfo {
ConstraintSystem UnsignedCS;
ConstraintSystem SignedCS;
const DataLayout &DL;
public:
ConstraintInfo(const DataLayout &DL, ArrayRef<Value *> FunctionArgs)
: UnsignedCS(FunctionArgs), SignedCS(FunctionArgs), DL(DL) {
auto &Value2Index = getValue2Index(false);
// Add Arg > -1 constraints to unsigned system for all function arguments.
for (Value *Arg : FunctionArgs) {
ConstraintTy VarPos(SmallVector<int64_t, 8>(Value2Index.size() + 1, 0),
false, false, false);
VarPos.Coefficients[Value2Index[Arg]] = -1;
UnsignedCS.addVariableRow(VarPos.Coefficients);
}
}
DenseMap<Value *, unsigned> &getValue2Index(bool Signed) {
return Signed ? SignedCS.getValue2Index() : UnsignedCS.getValue2Index();
}
const DenseMap<Value *, unsigned> &getValue2Index(bool Signed) const {
return Signed ? SignedCS.getValue2Index() : UnsignedCS.getValue2Index();
}
ConstraintSystem &getCS(bool Signed) {
return Signed ? SignedCS : UnsignedCS;
}
const ConstraintSystem &getCS(bool Signed) const {
return Signed ? SignedCS : UnsignedCS;
}
void popLastConstraint(bool Signed) { getCS(Signed).popLastConstraint(); }
void popLastNVariables(bool Signed, unsigned N) {
getCS(Signed).popLastNVariables(N);
}
bool doesHold(CmpInst::Predicate Pred, Value *A, Value *B) const;
void addFact(CmpInst::Predicate Pred, Value *A, Value *B, unsigned NumIn,
unsigned NumOut, SmallVectorImpl<StackEntry> &DFSInStack);
/// Turn a comparison of the form \p Op0 \p Pred \p Op1 into a vector of
/// constraints, using indices from the corresponding constraint system.
/// New variables that need to be added to the system are collected in
/// \p NewVariables.
ConstraintTy getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
SmallVectorImpl<Value *> &NewVariables) const;
/// Turns a comparison of the form \p Op0 \p Pred \p Op1 into a vector of
/// constraints using getConstraint. Returns an empty constraint if the result
/// cannot be used to query the existing constraint system, e.g. because it
/// would require adding new variables. Also tries to convert signed
/// predicates to unsigned ones if possible to allow using the unsigned system
/// which increases the effectiveness of the signed <-> unsigned transfer
/// logic.
ConstraintTy getConstraintForSolving(CmpInst::Predicate Pred, Value *Op0,
Value *Op1) const;
/// Try to add information from \p A \p Pred \p B to the unsigned/signed
/// system if \p Pred is signed/unsigned.
void transferToOtherSystem(CmpInst::Predicate Pred, Value *A, Value *B,
unsigned NumIn, unsigned NumOut,
SmallVectorImpl<StackEntry> &DFSInStack);
};
/// Represents a (Coefficient * Variable) entry after IR decomposition.
struct DecompEntry {
int64_t Coefficient;
Value *Variable;
/// True if the variable is known positive in the current constraint.
bool IsKnownNonNegative;
DecompEntry(int64_t Coefficient, Value *Variable,
bool IsKnownNonNegative = false)
: Coefficient(Coefficient), Variable(Variable),
IsKnownNonNegative(IsKnownNonNegative) {}
};
/// Represents an Offset + Coefficient1 * Variable1 + ... decomposition.
struct Decomposition {
int64_t Offset = 0;
SmallVector<DecompEntry, 3> Vars;
Decomposition(int64_t Offset) : Offset(Offset) {}
Decomposition(Value *V, bool IsKnownNonNegative = false) {
Vars.emplace_back(1, V, IsKnownNonNegative);
}
Decomposition(int64_t Offset, ArrayRef<DecompEntry> Vars)
: Offset(Offset), Vars(Vars) {}
void add(int64_t OtherOffset) {
Offset = addWithOverflow(Offset, OtherOffset);
}
void add(const Decomposition &Other) {
add(Other.Offset);
append_range(Vars, Other.Vars);
}
void sub(const Decomposition &Other) {
Decomposition Tmp = Other;
Tmp.mul(-1);
add(Tmp.Offset);
append_range(Vars, Tmp.Vars);
}
void mul(int64_t Factor) {
Offset = multiplyWithOverflow(Offset, Factor);
for (auto &Var : Vars)
Var.Coefficient = multiplyWithOverflow(Var.Coefficient, Factor);
}
};
// Variable and constant offsets for a chain of GEPs, with base pointer BasePtr.
struct OffsetResult {
Value *BasePtr;
APInt ConstantOffset;
MapVector<Value *, APInt> VariableOffsets;
bool AllInbounds;
OffsetResult() : BasePtr(nullptr), ConstantOffset(0, uint64_t(0)) {}
OffsetResult(GEPOperator &GEP, const DataLayout &DL)
: BasePtr(GEP.getPointerOperand()), AllInbounds(GEP.isInBounds()) {
ConstantOffset = APInt(DL.getIndexTypeSizeInBits(BasePtr->getType()), 0);
}
};
} // namespace
// Try to collect variable and constant offsets for \p GEP, partly traversing
// nested GEPs. Returns an OffsetResult with nullptr as BasePtr of collecting
// the offset fails.
static OffsetResult collectOffsets(GEPOperator &GEP, const DataLayout &DL) {
OffsetResult Result(GEP, DL);
unsigned BitWidth = Result.ConstantOffset.getBitWidth();
if (!GEP.collectOffset(DL, BitWidth, Result.VariableOffsets,
Result.ConstantOffset))
return {};
// If we have a nested GEP, check if we can combine the constant offset of the
// inner GEP with the outer GEP.
if (auto *InnerGEP = dyn_cast<GetElementPtrInst>(Result.BasePtr)) {
MapVector<Value *, APInt> VariableOffsets2;
APInt ConstantOffset2(BitWidth, 0);
bool CanCollectInner = InnerGEP->collectOffset(
DL, BitWidth, VariableOffsets2, ConstantOffset2);
// TODO: Support cases with more than 1 variable offset.
if (!CanCollectInner || Result.VariableOffsets.size() > 1 ||
VariableOffsets2.size() > 1 ||
(Result.VariableOffsets.size() >= 1 && VariableOffsets2.size() >= 1)) {
// More than 1 variable index, use outer result.
return Result;
}
Result.BasePtr = InnerGEP->getPointerOperand();
Result.ConstantOffset += ConstantOffset2;
if (Result.VariableOffsets.size() == 0 && VariableOffsets2.size() == 1)
Result.VariableOffsets = VariableOffsets2;
Result.AllInbounds &= InnerGEP->isInBounds();
}
return Result;
}
static Decomposition decompose(Value *V,
SmallVectorImpl<ConditionTy> &Preconditions,
bool IsSigned, const DataLayout &DL);
static bool canUseSExt(ConstantInt *CI) {
const APInt &Val = CI->getValue();
return Val.sgt(MinSignedConstraintValue) && Val.slt(MaxConstraintValue);
}
static Decomposition decomposeGEP(GEPOperator &GEP,
SmallVectorImpl<ConditionTy> &Preconditions,
bool IsSigned, const DataLayout &DL) {
// Do not reason about pointers where the index size is larger than 64 bits,
// as the coefficients used to encode constraints are 64 bit integers.
if (DL.getIndexTypeSizeInBits(GEP.getPointerOperand()->getType()) > 64)
return &GEP;
assert(!IsSigned && "The logic below only supports decomposition for "
"unsigned predicates at the moment.");
const auto &[BasePtr, ConstantOffset, VariableOffsets, AllInbounds] =
collectOffsets(GEP, DL);
if (!BasePtr || !AllInbounds)
return &GEP;
Decomposition Result(ConstantOffset.getSExtValue(), DecompEntry(1, BasePtr));
for (auto [Index, Scale] : VariableOffsets) {
auto IdxResult = decompose(Index, Preconditions, IsSigned, DL);
IdxResult.mul(Scale.getSExtValue());
Result.add(IdxResult);
// If Op0 is signed non-negative, the GEP is increasing monotonically and
// can be de-composed.
if (!isKnownNonNegative(Index, DL))
Preconditions.emplace_back(CmpInst::ICMP_SGE, Index,
ConstantInt::get(Index->getType(), 0));
}
return Result;
}
// Decomposes \p V into a constant offset + list of pairs { Coefficient,
// Variable } where Coefficient * Variable. The sum of the constant offset and
// pairs equals \p V.
static Decomposition decompose(Value *V,
SmallVectorImpl<ConditionTy> &Preconditions,
bool IsSigned, const DataLayout &DL) {
auto MergeResults = [&Preconditions, IsSigned, &DL](Value *A, Value *B,
bool IsSignedB) {
auto ResA = decompose(A, Preconditions, IsSigned, DL);
auto ResB = decompose(B, Preconditions, IsSignedB, DL);
ResA.add(ResB);
return ResA;
};
Type *Ty = V->getType()->getScalarType();
if (Ty->isPointerTy() && !IsSigned) {
if (auto *GEP = dyn_cast<GEPOperator>(V))
return decomposeGEP(*GEP, Preconditions, IsSigned, DL);
if (isa<ConstantPointerNull>(V))
return int64_t(0);
return V;
}
// Don't handle integers > 64 bit. Our coefficients are 64-bit large, so
// coefficient add/mul may wrap, while the operation in the full bit width
// would not.
if (!Ty->isIntegerTy() || Ty->getIntegerBitWidth() > 64)
return V;
bool IsKnownNonNegative = false;
// Decompose \p V used with a signed predicate.
if (IsSigned) {
if (auto *CI = dyn_cast<ConstantInt>(V)) {
if (canUseSExt(CI))
return CI->getSExtValue();
}
Value *Op0;
Value *Op1;
if (match(V, m_SExt(m_Value(Op0))))
V = Op0;
else if (match(V, m_NNegZExt(m_Value(Op0)))) {
V = Op0;
IsKnownNonNegative = true;
}
if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1))))
return MergeResults(Op0, Op1, IsSigned);
ConstantInt *CI;
if (match(V, m_NSWMul(m_Value(Op0), m_ConstantInt(CI))) && canUseSExt(CI)) {
auto Result = decompose(Op0, Preconditions, IsSigned, DL);
Result.mul(CI->getSExtValue());
return Result;
}
// (shl nsw x, shift) is (mul nsw x, (1<<shift)), with the exception of
// shift == bw-1.
if (match(V, m_NSWShl(m_Value(Op0), m_ConstantInt(CI)))) {
uint64_t Shift = CI->getValue().getLimitedValue();
if (Shift < Ty->getIntegerBitWidth() - 1) {
assert(Shift < 64 && "Would overflow");
auto Result = decompose(Op0, Preconditions, IsSigned, DL);
Result.mul(int64_t(1) << Shift);
return Result;
}
}
return {V, IsKnownNonNegative};
}
if (auto *CI = dyn_cast<ConstantInt>(V)) {
if (CI->uge(MaxConstraintValue))
return V;
return int64_t(CI->getZExtValue());
}
Value *Op0;
if (match(V, m_ZExt(m_Value(Op0)))) {
IsKnownNonNegative = true;
V = Op0;
}
Value *Op1;
ConstantInt *CI;
if (match(V, m_NUWAdd(m_Value(Op0), m_Value(Op1)))) {
return MergeResults(Op0, Op1, IsSigned);
}
if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1)))) {
if (!isKnownNonNegative(Op0, DL))
Preconditions.emplace_back(CmpInst::ICMP_SGE, Op0,
ConstantInt::get(Op0->getType(), 0));
if (!isKnownNonNegative(Op1, DL))
Preconditions.emplace_back(CmpInst::ICMP_SGE, Op1,
ConstantInt::get(Op1->getType(), 0));
return MergeResults(Op0, Op1, IsSigned);
}
if (match(V, m_Add(m_Value(Op0), m_ConstantInt(CI))) && CI->isNegative() &&
canUseSExt(CI)) {
Preconditions.emplace_back(
CmpInst::ICMP_UGE, Op0,
ConstantInt::get(Op0->getType(), CI->getSExtValue() * -1));
return MergeResults(Op0, CI, true);
}
// Decompose or as an add if there are no common bits between the operands.
if (match(V, m_DisjointOr(m_Value(Op0), m_ConstantInt(CI))))
return MergeResults(Op0, CI, IsSigned);
if (match(V, m_NUWShl(m_Value(Op1), m_ConstantInt(CI))) && canUseSExt(CI)) {
if (CI->getSExtValue() < 0 || CI->getSExtValue() >= 64)
return {V, IsKnownNonNegative};
auto Result = decompose(Op1, Preconditions, IsSigned, DL);
Result.mul(int64_t{1} << CI->getSExtValue());
return Result;
}
if (match(V, m_NUWMul(m_Value(Op1), m_ConstantInt(CI))) && canUseSExt(CI) &&
(!CI->isNegative())) {
auto Result = decompose(Op1, Preconditions, IsSigned, DL);
Result.mul(CI->getSExtValue());
return Result;
}
if (match(V, m_NUWSub(m_Value(Op0), m_Value(Op1)))) {
auto ResA = decompose(Op0, Preconditions, IsSigned, DL);
auto ResB = decompose(Op1, Preconditions, IsSigned, DL);
ResA.sub(ResB);
return ResA;
}
return {V, IsKnownNonNegative};
}
ConstraintTy
ConstraintInfo::getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
SmallVectorImpl<Value *> &NewVariables) const {
assert(NewVariables.empty() && "NewVariables must be empty when passed in");
bool IsEq = false;
bool IsNe = false;
// Try to convert Pred to one of ULE/SLT/SLE/SLT.
switch (Pred) {
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_SGT:
case CmpInst::ICMP_SGE: {
Pred = CmpInst::getSwappedPredicate(Pred);
std::swap(Op0, Op1);
break;
}
case CmpInst::ICMP_EQ:
if (match(Op1, m_Zero())) {
Pred = CmpInst::ICMP_ULE;
} else {
IsEq = true;
Pred = CmpInst::ICMP_ULE;
}
break;
case CmpInst::ICMP_NE:
if (match(Op1, m_Zero())) {
Pred = CmpInst::getSwappedPredicate(CmpInst::ICMP_UGT);
std::swap(Op0, Op1);
} else {
IsNe = true;
Pred = CmpInst::ICMP_ULE;
}
break;
default:
break;
}
if (Pred != CmpInst::ICMP_ULE && Pred != CmpInst::ICMP_ULT &&
Pred != CmpInst::ICMP_SLE && Pred != CmpInst::ICMP_SLT)
return {};
SmallVector<ConditionTy, 4> Preconditions;
bool IsSigned = CmpInst::isSigned(Pred);
auto &Value2Index = getValue2Index(IsSigned);
auto ADec = decompose(Op0->stripPointerCastsSameRepresentation(),
Preconditions, IsSigned, DL);
auto BDec = decompose(Op1->stripPointerCastsSameRepresentation(),
Preconditions, IsSigned, DL);
int64_t Offset1 = ADec.Offset;
int64_t Offset2 = BDec.Offset;
Offset1 *= -1;
auto &VariablesA = ADec.Vars;
auto &VariablesB = BDec.Vars;
// First try to look up \p V in Value2Index and NewVariables. Otherwise add a
// new entry to NewVariables.
SmallDenseMap<Value *, unsigned> NewIndexMap;
auto GetOrAddIndex = [&Value2Index, &NewVariables,
&NewIndexMap](Value *V) -> unsigned {
auto V2I = Value2Index.find(V);
if (V2I != Value2Index.end())
return V2I->second;
auto Insert =
NewIndexMap.insert({V, Value2Index.size() + NewVariables.size() + 1});
if (Insert.second)
NewVariables.push_back(V);
return Insert.first->second;
};
// Make sure all variables have entries in Value2Index or NewVariables.
for (const auto &KV : concat<DecompEntry>(VariablesA, VariablesB))
GetOrAddIndex(KV.Variable);
// Build result constraint, by first adding all coefficients from A and then
// subtracting all coefficients from B.
ConstraintTy Res(
SmallVector<int64_t, 8>(Value2Index.size() + NewVariables.size() + 1, 0),
IsSigned, IsEq, IsNe);
// Collect variables that are known to be positive in all uses in the
// constraint.
SmallDenseMap<Value *, bool> KnownNonNegativeVariables;
auto &R = Res.Coefficients;
for (const auto &KV : VariablesA) {
R[GetOrAddIndex(KV.Variable)] += KV.Coefficient;
auto I =
KnownNonNegativeVariables.insert({KV.Variable, KV.IsKnownNonNegative});
I.first->second &= KV.IsKnownNonNegative;
}
for (const auto &KV : VariablesB) {
if (SubOverflow(R[GetOrAddIndex(KV.Variable)], KV.Coefficient,
R[GetOrAddIndex(KV.Variable)]))
return {};
auto I =
KnownNonNegativeVariables.insert({KV.Variable, KV.IsKnownNonNegative});
I.first->second &= KV.IsKnownNonNegative;
}
int64_t OffsetSum;
if (AddOverflow(Offset1, Offset2, OffsetSum))
return {};
if (Pred == (IsSigned ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT))
if (AddOverflow(OffsetSum, int64_t(-1), OffsetSum))
return {};
R[0] = OffsetSum;
Res.Preconditions = std::move(Preconditions);
// Remove any (Coefficient, Variable) entry where the Coefficient is 0 for new
// variables.
while (!NewVariables.empty()) {
int64_t Last = R.back();
if (Last != 0)
break;
R.pop_back();
Value *RemovedV = NewVariables.pop_back_val();
NewIndexMap.erase(RemovedV);
}
// Add extra constraints for variables that are known positive.
for (auto &KV : KnownNonNegativeVariables) {
if (!KV.second ||
(!Value2Index.contains(KV.first) && !NewIndexMap.contains(KV.first)))
continue;
SmallVector<int64_t, 8> C(Value2Index.size() + NewVariables.size() + 1, 0);
C[GetOrAddIndex(KV.first)] = -1;
Res.ExtraInfo.push_back(C);
}
return Res;
}
ConstraintTy ConstraintInfo::getConstraintForSolving(CmpInst::Predicate Pred,
Value *Op0,
Value *Op1) const {
Constant *NullC = Constant::getNullValue(Op0->getType());
// Handle trivially true compares directly to avoid adding V UGE 0 constraints
// for all variables in the unsigned system.
if ((Pred == CmpInst::ICMP_ULE && Op0 == NullC) ||
(Pred == CmpInst::ICMP_UGE && Op1 == NullC)) {
auto &Value2Index = getValue2Index(false);
// Return constraint that's trivially true.
return ConstraintTy(SmallVector<int64_t, 8>(Value2Index.size(), 0), false,
false, false);
}
// If both operands are known to be non-negative, change signed predicates to
// unsigned ones. This increases the reasoning effectiveness in combination
// with the signed <-> unsigned transfer logic.
if (CmpInst::isSigned(Pred) &&
isKnownNonNegative(Op0, DL, /*Depth=*/MaxAnalysisRecursionDepth - 1) &&
isKnownNonNegative(Op1, DL, /*Depth=*/MaxAnalysisRecursionDepth - 1))
Pred = CmpInst::getUnsignedPredicate(Pred);
SmallVector<Value *> NewVariables;
ConstraintTy R = getConstraint(Pred, Op0, Op1, NewVariables);
if (!NewVariables.empty())
return {};
return R;
}
bool ConstraintTy::isValid(const ConstraintInfo &Info) const {
return Coefficients.size() > 0 &&
all_of(Preconditions, [&Info](const ConditionTy &C) {
return Info.doesHold(C.Pred, C.Op0, C.Op1);
});
}
std::optional<bool>
ConstraintTy::isImpliedBy(const ConstraintSystem &CS) const {
bool IsConditionImplied = CS.isConditionImplied(Coefficients);
if (IsEq || IsNe) {
auto NegatedOrEqual = ConstraintSystem::negateOrEqual(Coefficients);
bool IsNegatedOrEqualImplied =
!NegatedOrEqual.empty() && CS.isConditionImplied(NegatedOrEqual);
// In order to check that `%a == %b` is true (equality), both conditions `%a
// >= %b` and `%a <= %b` must hold true. When checking for equality (`IsEq`
// is true), we return true if they both hold, false in the other cases.
if (IsConditionImplied && IsNegatedOrEqualImplied)
return IsEq;
auto Negated = ConstraintSystem::negate(Coefficients);
bool IsNegatedImplied = !Negated.empty() && CS.isConditionImplied(Negated);
auto StrictLessThan = ConstraintSystem::toStrictLessThan(Coefficients);
bool IsStrictLessThanImplied =
!StrictLessThan.empty() && CS.isConditionImplied(StrictLessThan);
// In order to check that `%a != %b` is true (non-equality), either
// condition `%a > %b` or `%a < %b` must hold true. When checking for
// non-equality (`IsNe` is true), we return true if one of the two holds,
// false in the other cases.
if (IsNegatedImplied || IsStrictLessThanImplied)
return IsNe;
return std::nullopt;
}
if (IsConditionImplied)
return true;
auto Negated = ConstraintSystem::negate(Coefficients);
auto IsNegatedImplied = !Negated.empty() && CS.isConditionImplied(Negated);
if (IsNegatedImplied)
return false;
// Neither the condition nor its negated holds, did not prove anything.
return std::nullopt;
}
bool ConstraintInfo::doesHold(CmpInst::Predicate Pred, Value *A,
Value *B) const {
auto R = getConstraintForSolving(Pred, A, B);
return R.isValid(*this) &&
getCS(R.IsSigned).isConditionImplied(R.Coefficients);
}
void ConstraintInfo::transferToOtherSystem(
CmpInst::Predicate Pred, Value *A, Value *B, unsigned NumIn,
unsigned NumOut, SmallVectorImpl<StackEntry> &DFSInStack) {
auto IsKnownNonNegative = [this](Value *V) {
return doesHold(CmpInst::ICMP_SGE, V, ConstantInt::get(V->getType(), 0)) ||
isKnownNonNegative(V, DL, /*Depth=*/MaxAnalysisRecursionDepth - 1);
};
// Check if we can combine facts from the signed and unsigned systems to
// derive additional facts.
if (!A->getType()->isIntegerTy())
return;
// FIXME: This currently depends on the order we add facts. Ideally we
// would first add all known facts and only then try to add additional
// facts.
switch (Pred) {
default:
break;
case CmpInst::ICMP_ULT:
case CmpInst::ICMP_ULE:
// If B is a signed positive constant, then A >=s 0 and A <s (or <=s) B.
if (IsKnownNonNegative(B)) {
addFact(CmpInst::ICMP_SGE, A, ConstantInt::get(B->getType(), 0), NumIn,
NumOut, DFSInStack);
addFact(CmpInst::getSignedPredicate(Pred), A, B, NumIn, NumOut,
DFSInStack);
}
break;
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_UGT:
// If A is a signed positive constant, then B >=s 0 and A >s (or >=s) B.
if (IsKnownNonNegative(A)) {
addFact(CmpInst::ICMP_SGE, B, ConstantInt::get(B->getType(), 0), NumIn,
NumOut, DFSInStack);
addFact(CmpInst::getSignedPredicate(Pred), A, B, NumIn, NumOut,
DFSInStack);
}
break;
case CmpInst::ICMP_SLT:
if (IsKnownNonNegative(A))
addFact(CmpInst::ICMP_ULT, A, B, NumIn, NumOut, DFSInStack);
break;
case CmpInst::ICMP_SGT: {
if (doesHold(CmpInst::ICMP_SGE, B, ConstantInt::get(B->getType(), -1)))
addFact(CmpInst::ICMP_UGE, A, ConstantInt::get(B->getType(), 0), NumIn,
NumOut, DFSInStack);
if (IsKnownNonNegative(B))
addFact(CmpInst::ICMP_UGT, A, B, NumIn, NumOut, DFSInStack);
break;
}
case CmpInst::ICMP_SGE:
if (IsKnownNonNegative(B))
addFact(CmpInst::ICMP_UGE, A, B, NumIn, NumOut, DFSInStack);
break;
}
}
#ifndef NDEBUG
static void dumpConstraint(ArrayRef<int64_t> C,
const DenseMap<Value *, unsigned> &Value2Index) {
ConstraintSystem CS(Value2Index);
CS.addVariableRowFill(C);
CS.dump();
}
#endif
void State::addInfoForInductions(BasicBlock &BB) {
auto *L = LI.getLoopFor(&BB);
if (!L || L->getHeader() != &BB)
return;
Value *A;
Value *B;
CmpInst::Predicate Pred;
if (!match(BB.getTerminator(),
m_Br(m_ICmp(Pred, m_Value(A), m_Value(B)), m_Value(), m_Value())))
return;
PHINode *PN = dyn_cast<PHINode>(A);
if (!PN) {
Pred = CmpInst::getSwappedPredicate(Pred);
std::swap(A, B);
PN = dyn_cast<PHINode>(A);
}
if (!PN || PN->getParent() != &BB || PN->getNumIncomingValues() != 2 ||
!SE.isSCEVable(PN->getType()))
return;
BasicBlock *InLoopSucc = nullptr;
if (Pred == CmpInst::ICMP_NE)
InLoopSucc = cast<BranchInst>(BB.getTerminator())->getSuccessor(0);
else if (Pred == CmpInst::ICMP_EQ)
InLoopSucc = cast<BranchInst>(BB.getTerminator())->getSuccessor(1);
else
return;
if (!L->contains(InLoopSucc) || !L->isLoopExiting(&BB) || InLoopSucc == &BB)
return;
auto *AR = dyn_cast_or_null<SCEVAddRecExpr>(SE.getSCEV(PN));
BasicBlock *LoopPred = L->getLoopPredecessor();
if (!AR || AR->getLoop() != L || !LoopPred)
return;
const SCEV *StartSCEV = AR->getStart();
Value *StartValue = nullptr;
if (auto *C = dyn_cast<SCEVConstant>(StartSCEV)) {
StartValue = C->getValue();
} else {
StartValue = PN->getIncomingValueForBlock(LoopPred);
assert(SE.getSCEV(StartValue) == StartSCEV && "inconsistent start value");
}
DomTreeNode *DTN = DT.getNode(InLoopSucc);
auto IncUnsigned = SE.getMonotonicPredicateType(AR, CmpInst::ICMP_UGT);
auto IncSigned = SE.getMonotonicPredicateType(AR, CmpInst::ICMP_SGT);
bool MonotonicallyIncreasingUnsigned =
IncUnsigned && *IncUnsigned == ScalarEvolution::MonotonicallyIncreasing;
bool MonotonicallyIncreasingSigned =
IncSigned && *IncSigned == ScalarEvolution::MonotonicallyIncreasing;
// If SCEV guarantees that AR does not wrap, PN >= StartValue can be added
// unconditionally.
if (MonotonicallyIncreasingUnsigned)
WorkList.push_back(
FactOrCheck::getConditionFact(DTN, CmpInst::ICMP_UGE, PN, StartValue));
if (MonotonicallyIncreasingSigned)
WorkList.push_back(
FactOrCheck::getConditionFact(DTN, CmpInst::ICMP_SGE, PN, StartValue));
APInt StepOffset;
if (auto *C = dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
StepOffset = C->getAPInt();
else
return;
// Make sure the bound B is loop-invariant.
if (!L->isLoopInvariant(B))
return;
// Handle negative steps.
if (StepOffset.isNegative()) {
// TODO: Extend to allow steps > -1.
if (!(-StepOffset).isOne())
return;
// AR may wrap.
// Add StartValue >= PN conditional on B <= StartValue which guarantees that
// the loop exits before wrapping with a step of -1.
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_UGE, StartValue, PN,
ConditionTy(CmpInst::ICMP_ULE, B, StartValue)));
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_SGE, StartValue, PN,
ConditionTy(CmpInst::ICMP_SLE, B, StartValue)));
// Add PN > B conditional on B <= StartValue which guarantees that the loop
// exits when reaching B with a step of -1.
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_UGT, PN, B,
ConditionTy(CmpInst::ICMP_ULE, B, StartValue)));
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_SGT, PN, B,
ConditionTy(CmpInst::ICMP_SLE, B, StartValue)));
return;
}
// Make sure AR either steps by 1 or that the value we compare against is a
// GEP based on the same start value and all offsets are a multiple of the
// step size, to guarantee that the induction will reach the value.
if (StepOffset.isZero() || StepOffset.isNegative())
return;
if (!StepOffset.isOne()) {
// Check whether B-Start is known to be a multiple of StepOffset.
const SCEV *BMinusStart = SE.getMinusSCEV(SE.getSCEV(B), StartSCEV);
if (isa<SCEVCouldNotCompute>(BMinusStart) ||
!SE.getConstantMultiple(BMinusStart).urem(StepOffset).isZero())
return;
}
// AR may wrap. Add PN >= StartValue conditional on StartValue <= B which
// guarantees that the loop exits before wrapping in combination with the
// restrictions on B and the step above.
if (!MonotonicallyIncreasingUnsigned)
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_UGE, PN, StartValue,
ConditionTy(CmpInst::ICMP_ULE, StartValue, B)));
if (!MonotonicallyIncreasingSigned)
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_SGE, PN, StartValue,
ConditionTy(CmpInst::ICMP_SLE, StartValue, B)));
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_ULT, PN, B,
ConditionTy(CmpInst::ICMP_ULE, StartValue, B)));
WorkList.push_back(FactOrCheck::getConditionFact(
DTN, CmpInst::ICMP_SLT, PN, B,
ConditionTy(CmpInst::ICMP_SLE, StartValue, B)));
}
void State::addInfoFor(BasicBlock &BB) {
addInfoForInductions(BB);
// True as long as long as the current instruction is guaranteed to execute.
bool GuaranteedToExecute = true;
// Queue conditions and assumes.
for (Instruction &I : BB) {
if (auto Cmp = dyn_cast<ICmpInst>(&I)) {
for (Use &U : Cmp->uses()) {
auto *UserI = getContextInstForUse(U);
auto *DTN = DT.getNode(UserI->getParent());
if (!DTN)
continue;
WorkList.push_back(FactOrCheck::getCheck(DTN, &U));
}
continue;
}
auto *II = dyn_cast<IntrinsicInst>(&I);
Intrinsic::ID ID = II ? II->getIntrinsicID() : Intrinsic::not_intrinsic;
switch (ID) {
case Intrinsic::assume: {
Value *A, *B;
CmpInst::Predicate Pred;
if (!match(I.getOperand(0), m_ICmp(Pred, m_Value(A), m_Value(B))))
break;
if (GuaranteedToExecute) {
// The assume is guaranteed to execute when BB is entered, hence Cond
// holds on entry to BB.
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(I.getParent()), Pred, A, B));
} else {
WorkList.emplace_back(
FactOrCheck::getInstFact(DT.getNode(I.getParent()), &I));
}
break;
}
// Enqueue ssub_with_overflow for simplification.
case Intrinsic::ssub_with_overflow:
WorkList.push_back(
FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
break;
// Enqueue the intrinsics to add extra info.
case Intrinsic::umin:
case Intrinsic::umax:
case Intrinsic::smin:
case Intrinsic::smax:
// TODO: handle llvm.abs as well
WorkList.push_back(
FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
// TODO: Check if it is possible to instead only added the min/max facts
// when simplifying uses of the min/max intrinsics.
if (!isGuaranteedNotToBePoison(&I))
break;
[[fallthrough]];
case Intrinsic::abs:
WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
break;
}
GuaranteedToExecute &= isGuaranteedToTransferExecutionToSuccessor(&I);
}
if (auto *Switch = dyn_cast<SwitchInst>(BB.getTerminator())) {
for (auto &Case : Switch->cases()) {
BasicBlock *Succ = Case.getCaseSuccessor();
Value *V = Case.getCaseValue();
if (!canAddSuccessor(BB, Succ))
continue;
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(Succ), CmpInst::ICMP_EQ, Switch->getCondition(), V));
}
return;
}
auto *Br = dyn_cast<BranchInst>(BB.getTerminator());
if (!Br || !Br->isConditional())
return;
Value *Cond = Br->getCondition();
// If the condition is a chain of ORs/AND and the successor only has the
// current block as predecessor, queue conditions for the successor.
Value *Op0, *Op1;
if (match(Cond, m_LogicalOr(m_Value(Op0), m_Value(Op1))) ||
match(Cond, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
bool IsOr = match(Cond, m_LogicalOr());
bool IsAnd = match(Cond, m_LogicalAnd());
// If there's a select that matches both AND and OR, we need to commit to
// one of the options. Arbitrarily pick OR.
if (IsOr && IsAnd)
IsAnd = false;
BasicBlock *Successor = Br->getSuccessor(IsOr ? 1 : 0);
if (canAddSuccessor(BB, Successor)) {
SmallVector<Value *> CondWorkList;
SmallPtrSet<Value *, 8> SeenCond;
auto QueueValue = [&CondWorkList, &SeenCond](Value *V) {
if (SeenCond.insert(V).second)
CondWorkList.push_back(V);
};
QueueValue(Op1);
QueueValue(Op0);
while (!CondWorkList.empty()) {
Value *Cur = CondWorkList.pop_back_val();
if (auto *Cmp = dyn_cast<ICmpInst>(Cur)) {
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(Successor),
IsOr ? CmpInst::getInversePredicate(Cmp->getPredicate())
: Cmp->getPredicate(),
Cmp->getOperand(0), Cmp->getOperand(1)));
continue;
}
if (IsOr && match(Cur, m_LogicalOr(m_Value(Op0), m_Value(Op1)))) {
QueueValue(Op1);
QueueValue(Op0);
continue;
}
if (IsAnd && match(Cur, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
QueueValue(Op1);
QueueValue(Op0);
continue;
}
}
}
return;
}
auto *CmpI = dyn_cast<ICmpInst>(Br->getCondition());
if (!CmpI)
return;
if (canAddSuccessor(BB, Br->getSuccessor(0)))
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(Br->getSuccessor(0)), CmpI->getPredicate(),
CmpI->getOperand(0), CmpI->getOperand(1)));
if (canAddSuccessor(BB, Br->getSuccessor(1)))
WorkList.emplace_back(FactOrCheck::getConditionFact(
DT.getNode(Br->getSuccessor(1)),
CmpInst::getInversePredicate(CmpI->getPredicate()), CmpI->getOperand(0),
CmpI->getOperand(1)));
}
#ifndef NDEBUG
static void dumpUnpackedICmp(raw_ostream &OS, ICmpInst::Predicate Pred,
Value *LHS, Value *RHS) {
OS << "icmp " << Pred << ' ';
LHS->printAsOperand(OS, /*PrintType=*/true);
OS << ", ";
RHS->printAsOperand(OS, /*PrintType=*/false);
}
#endif
namespace {
/// Helper to keep track of a condition and if it should be treated as negated
/// for reproducer construction.
/// Pred == Predicate::BAD_ICMP_PREDICATE indicates that this entry is a
/// placeholder to keep the ReproducerCondStack in sync with DFSInStack.
struct ReproducerEntry {
ICmpInst::Predicate Pred;
Value *LHS;
Value *RHS;
ReproducerEntry(ICmpInst::Predicate Pred, Value *LHS, Value *RHS)
: Pred(Pred), LHS(LHS), RHS(RHS) {}
};
} // namespace
/// Helper function to generate a reproducer function for simplifying \p Cond.
/// The reproducer function contains a series of @llvm.assume calls, one for
/// each condition in \p Stack. For each condition, the operand instruction are
/// cloned until we reach operands that have an entry in \p Value2Index. Those
/// will then be added as function arguments. \p DT is used to order cloned
/// instructions. The reproducer function will get added to \p M, if it is
/// non-null. Otherwise no reproducer function is generated.
static void generateReproducer(CmpInst *Cond, Module *M,
ArrayRef<ReproducerEntry> Stack,
ConstraintInfo &Info, DominatorTree &DT) {
if (!M)
return;
LLVMContext &Ctx = Cond->getContext();
LLVM_DEBUG(dbgs() << "Creating reproducer for " << *Cond << "\n");
ValueToValueMapTy Old2New;
SmallVector<Value *> Args;
SmallPtrSet<Value *, 8> Seen;
// Traverse Cond and its operands recursively until we reach a value that's in
// Value2Index or not an instruction, or not a operation that
// ConstraintElimination can decompose. Such values will be considered as
// external inputs to the reproducer, they are collected and added as function
// arguments later.
auto CollectArguments = [&](ArrayRef<Value *> Ops, bool IsSigned) {
auto &Value2Index = Info.getValue2Index(IsSigned);
SmallVector<Value *, 4> WorkList(Ops);
while (!WorkList.empty()) {
Value *V = WorkList.pop_back_val();
if (!Seen.insert(V).second)
continue;
if (Old2New.find(V) != Old2New.end())
continue;
if (isa<Constant>(V))
continue;
auto *I = dyn_cast<Instruction>(V);
if (Value2Index.contains(V) || !I ||
!isa<CmpInst, BinaryOperator, GEPOperator, CastInst>(V)) {
Old2New[V] = V;
Args.push_back(V);
LLVM_DEBUG(dbgs() << " found external input " << *V << "\n");
} else {
append_range(WorkList, I->operands());
}
}
};
for (auto &Entry : Stack)
if (Entry.Pred != ICmpInst::BAD_ICMP_PREDICATE)
CollectArguments({Entry.LHS, Entry.RHS}, ICmpInst::isSigned(Entry.Pred));
CollectArguments(Cond, ICmpInst::isSigned(Cond->getPredicate()));
SmallVector<Type *> ParamTys;
for (auto *P : Args)
ParamTys.push_back(P->getType());
FunctionType *FTy = FunctionType::get(Cond->getType(), ParamTys,
/*isVarArg=*/false);
Function *F = Function::Create(FTy, Function::ExternalLinkage,
Cond->getModule()->getName() +
Cond->getFunction()->getName() + "repro",
M);
// Add arguments to the reproducer function for each external value collected.
for (unsigned I = 0; I < Args.size(); ++I) {
F->getArg(I)->setName(Args[I]->getName());
Old2New[Args[I]] = F->getArg(I);
}
BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
IRBuilder<> Builder(Entry);
Builder.CreateRet(Builder.getTrue());
Builder.SetInsertPoint(Entry->getTerminator());
// Clone instructions in \p Ops and their operands recursively until reaching
// an value in Value2Index (external input to the reproducer). Update Old2New
// mapping for the original and cloned instructions. Sort instructions to
// clone by dominance, then insert the cloned instructions in the function.
auto CloneInstructions = [&](ArrayRef<Value *> Ops, bool IsSigned) {
SmallVector<Value *, 4> WorkList(Ops);
SmallVector<Instruction *> ToClone;
auto &Value2Index = Info.getValue2Index(IsSigned);
while (!WorkList.empty()) {
Value *V = WorkList.pop_back_val();
if (Old2New.find(V) != Old2New.end())
continue;
auto *I = dyn_cast<Instruction>(V);
if (!Value2Index.contains(V) && I) {
Old2New[V] = nullptr;
ToClone.push_back(I);
append_range(WorkList, I->operands());
}
}
sort(ToClone,
[&DT](Instruction *A, Instruction *B) { return DT.dominates(A, B); });
for (Instruction *I : ToClone) {
Instruction *Cloned = I->clone();
Old2New[I] = Cloned;
Old2New[I]->setName(I->getName());
Cloned->insertBefore(&*Builder.GetInsertPoint());
Cloned->dropUnknownNonDebugMetadata();
Cloned->setDebugLoc({});
}
};
// Materialize the assumptions for the reproducer using the entries in Stack.
// That is, first clone the operands of the condition recursively until we
// reach an external input to the reproducer and add them to the reproducer
// function. Then add an ICmp for the condition (with the inverse predicate if
// the entry is negated) and an assert using the ICmp.
for (auto &Entry : Stack) {
if (Entry.Pred == ICmpInst::BAD_ICMP_PREDICATE)
continue;
LLVM_DEBUG(dbgs() << " Materializing assumption ";
dumpUnpackedICmp(dbgs(), Entry.Pred, Entry.LHS, Entry.RHS);
dbgs() << "\n");
CloneInstructions({Entry.LHS, Entry.RHS}, CmpInst::isSigned(Entry.Pred));
auto *Cmp = Builder.CreateICmp(Entry.Pred, Entry.LHS, Entry.RHS);
Builder.CreateAssumption(Cmp);
}
// Finally, clone the condition to reproduce and remap instruction operands in
// the reproducer using Old2New.
CloneInstructions(Cond, CmpInst::isSigned(Cond->getPredicate()));
Entry->getTerminator()->setOperand(0, Cond);
remapInstructionsInBlocks({Entry}, Old2New);
assert(!verifyFunction(*F, &dbgs()));
}
static std::optional<bool> checkCondition(CmpInst::Predicate Pred, Value *A,
Value *B, Instruction *CheckInst,
ConstraintInfo &Info) {
LLVM_DEBUG(dbgs() << "Checking " << *CheckInst << "\n");
auto R = Info.getConstraintForSolving(Pred, A, B);
if (R.empty() || !R.isValid(Info)){
LLVM_DEBUG(dbgs() << " failed to decompose condition\n");
return std::nullopt;
}
auto &CSToUse = Info.getCS(R.IsSigned);
// If there was extra information collected during decomposition, apply
// it now and remove it immediately once we are done with reasoning
// about the constraint.
for (auto &Row : R.ExtraInfo)
CSToUse.addVariableRow(Row);
auto InfoRestorer = make_scope_exit([&]() {
for (unsigned I = 0; I < R.ExtraInfo.size(); ++I)
CSToUse.popLastConstraint();
});
if (auto ImpliedCondition = R.isImpliedBy(CSToUse)) {
if (!DebugCounter::shouldExecute(EliminatedCounter))
return std::nullopt;
LLVM_DEBUG({
dbgs() << "Condition ";
dumpUnpackedICmp(
dbgs(), *ImpliedCondition ? Pred : CmpInst::getInversePredicate(Pred),
A, B);
dbgs() << " implied by dominating constraints\n";
CSToUse.dump();
});
return ImpliedCondition;
}
return std::nullopt;
}
static bool checkAndReplaceCondition(
CmpInst *Cmp, ConstraintInfo &Info, unsigned NumIn, unsigned NumOut,
Instruction *ContextInst, Module *ReproducerModule,
ArrayRef<ReproducerEntry> ReproducerCondStack, DominatorTree &DT,
SmallVectorImpl<Instruction *> &ToRemove) {
auto ReplaceCmpWithConstant = [&](CmpInst *Cmp, bool IsTrue) {
generateReproducer(Cmp, ReproducerModule, ReproducerCondStack, Info, DT);
Constant *ConstantC = ConstantInt::getBool(
CmpInst::makeCmpResultType(Cmp->getType()), IsTrue);
Cmp->replaceUsesWithIf(ConstantC, [&DT, NumIn, NumOut,
ContextInst](Use &U) {
auto *UserI = getContextInstForUse(U);
auto *DTN = DT.getNode(UserI->getParent());
if (!DTN || DTN->getDFSNumIn() < NumIn || DTN->getDFSNumOut() > NumOut)
return false;
if (UserI->getParent() == ContextInst->getParent() &&
UserI->comesBefore(ContextInst))
return false;
// Conditions in an assume trivially simplify to true. Skip uses
// in assume calls to not destroy the available information.
auto *II = dyn_cast<IntrinsicInst>(U.getUser());
return !II || II->getIntrinsicID() != Intrinsic::assume;
});
NumCondsRemoved++;
if (Cmp->use_empty())
ToRemove.push_back(Cmp);
return true;
};
if (auto ImpliedCondition =
checkCondition(Cmp->getPredicate(), Cmp->getOperand(0),
Cmp->getOperand(1), Cmp, Info))
return ReplaceCmpWithConstant(Cmp, *ImpliedCondition);
return false;
}
static bool checkAndReplaceMinMax(MinMaxIntrinsic *MinMax, ConstraintInfo &Info,
SmallVectorImpl<Instruction *> &ToRemove) {
auto ReplaceMinMaxWithOperand = [&](MinMaxIntrinsic *MinMax, bool UseLHS) {
// TODO: generate reproducer for min/max.
MinMax->replaceAllUsesWith(MinMax->getOperand(UseLHS ? 0 : 1));
ToRemove.push_back(MinMax);
return true;
};
ICmpInst::Predicate Pred =
ICmpInst::getNonStrictPredicate(MinMax->getPredicate());
if (auto ImpliedCondition = checkCondition(
Pred, MinMax->getOperand(0), MinMax->getOperand(1), MinMax, Info))
return ReplaceMinMaxWithOperand(MinMax, *ImpliedCondition);
if (auto ImpliedCondition = checkCondition(
Pred, MinMax->getOperand(1), MinMax->getOperand(0), MinMax, Info))
return ReplaceMinMaxWithOperand(MinMax, !*ImpliedCondition);
return false;
}
static void
removeEntryFromStack(const StackEntry &E, ConstraintInfo &Info,
Module *ReproducerModule,
SmallVectorImpl<ReproducerEntry> &ReproducerCondStack,
SmallVectorImpl<StackEntry> &DFSInStack) {
Info.popLastConstraint(E.IsSigned);
// Remove variables in the system that went out of scope.
auto &Mapping = Info.getValue2Index(E.IsSigned);
for (Value *V : E.ValuesToRelease)
Mapping.erase(V);
Info.popLastNVariables(E.IsSigned, E.ValuesToRelease.size());
DFSInStack.pop_back();
if (ReproducerModule)
ReproducerCondStack.pop_back();
}
/// Check if either the first condition of an AND or OR is implied by the
/// (negated in case of OR) second condition or vice versa.
static bool checkOrAndOpImpliedByOther(
FactOrCheck &CB, ConstraintInfo &Info, Module *ReproducerModule,
SmallVectorImpl<ReproducerEntry> &ReproducerCondStack,
SmallVectorImpl<StackEntry> &DFSInStack) {
CmpInst::Predicate Pred;
Value *A, *B;
Instruction *JoinOp = CB.getContextInst();
CmpInst *CmpToCheck = cast<CmpInst>(CB.getInstructionToSimplify());
unsigned OtherOpIdx = JoinOp->getOperand(0) == CmpToCheck ? 1 : 0;
// Don't try to simplify the first condition of a select by the second, as
// this may make the select more poisonous than the original one.
// TODO: check if the first operand may be poison.
if (OtherOpIdx != 0 && isa<SelectInst>(JoinOp))
return false;
if (!match(JoinOp->getOperand(OtherOpIdx),
m_ICmp(Pred, m_Value(A), m_Value(B))))
return false;
// For OR, check if the negated condition implies CmpToCheck.
bool IsOr = match(JoinOp, m_LogicalOr());
if (IsOr)
Pred = CmpInst::getInversePredicate(Pred);
// Optimistically add fact from first condition.
unsigned OldSize = DFSInStack.size();
Info.addFact(Pred, A, B, CB.NumIn, CB.NumOut, DFSInStack);
if (OldSize == DFSInStack.size())
return false;
bool Changed = false;
// Check if the second condition can be simplified now.
if (auto ImpliedCondition =
checkCondition(CmpToCheck->getPredicate(), CmpToCheck->getOperand(0),
CmpToCheck->getOperand(1), CmpToCheck, Info)) {
if (IsOr && isa<SelectInst>(JoinOp)) {
JoinOp->setOperand(
OtherOpIdx == 0 ? 2 : 0,
ConstantInt::getBool(JoinOp->getType(), *ImpliedCondition));
} else
JoinOp->setOperand(
1 - OtherOpIdx,
ConstantInt::getBool(JoinOp->getType(), *ImpliedCondition));
Changed = true;
}
// Remove entries again.
while (OldSize < DFSInStack.size()) {
StackEntry E = DFSInStack.back();
removeEntryFromStack(E, Info, ReproducerModule, ReproducerCondStack,
DFSInStack);
}
return Changed;
}
void ConstraintInfo::addFact(CmpInst::Predicate Pred, Value *A, Value *B,
unsigned NumIn, unsigned NumOut,
SmallVectorImpl<StackEntry> &DFSInStack) {
// If the constraint has a pre-condition, skip the constraint if it does not
// hold.
SmallVector<Value *> NewVariables;
auto R = getConstraint(Pred, A, B, NewVariables);
// TODO: Support non-equality for facts as well.
if (!R.isValid(*this) || R.isNe())
return;
LLVM_DEBUG(dbgs() << "Adding '"; dumpUnpackedICmp(dbgs(), Pred, A, B);
dbgs() << "'\n");
bool Added = false;
auto &CSToUse = getCS(R.IsSigned);
if (R.Coefficients.empty())
return;
Added |= CSToUse.addVariableRowFill(R.Coefficients);
// If R has been added to the system, add the new variables and queue it for
// removal once it goes out-of-scope.
if (Added) {
SmallVector<Value *, 2> ValuesToRelease;
auto &Value2Index = getValue2Index(R.IsSigned);
for (Value *V : NewVariables) {
Value2Index.insert({V, Value2Index.size() + 1});
ValuesToRelease.push_back(V);
}
LLVM_DEBUG({
dbgs() << " constraint: ";
dumpConstraint(R.Coefficients, getValue2Index(R.IsSigned));
dbgs() << "\n";
});
DFSInStack.emplace_back(NumIn, NumOut, R.IsSigned,
std::move(ValuesToRelease));
if (!R.IsSigned) {
for (Value *V : NewVariables) {
ConstraintTy VarPos(SmallVector<int64_t, 8>(Value2Index.size() + 1, 0),
false, false, false);
VarPos.Coefficients[Value2Index[V]] = -1;
CSToUse.addVariableRow(VarPos.Coefficients);
DFSInStack.emplace_back(NumIn, NumOut, R.IsSigned,
SmallVector<Value *, 2>());
}
}
if (R.isEq()) {
// Also add the inverted constraint for equality constraints.
for (auto &Coeff : R.Coefficients)
Coeff *= -1;
CSToUse.addVariableRowFill(R.Coefficients);
DFSInStack.emplace_back(NumIn, NumOut, R.IsSigned,
SmallVector<Value *, 2>());
}
}
}
static bool replaceSubOverflowUses(IntrinsicInst *II, Value *A, Value *B,
SmallVectorImpl<Instruction *> &ToRemove) {
bool Changed = false;
IRBuilder<> Builder(II->getParent(), II->getIterator());
Value *Sub = nullptr;
for (User *U : make_early_inc_range(II->users())) {
if (match(U, m_ExtractValue<0>(m_Value()))) {
if (!Sub)
Sub = Builder.CreateSub(A, B);
U->replaceAllUsesWith(Sub);
Changed = true;
} else if (match(U, m_ExtractValue<1>(m_Value()))) {
U->replaceAllUsesWith(Builder.getFalse());
Changed = true;
} else
continue;
if (U->use_empty()) {
auto *I = cast<Instruction>(U);
ToRemove.push_back(I);
I->setOperand(0, PoisonValue::get(II->getType()));
Changed = true;
}
}
if (II->use_empty()) {
II->eraseFromParent();
Changed = true;
}
return Changed;
}
static bool
tryToSimplifyOverflowMath(IntrinsicInst *II, ConstraintInfo &Info,
SmallVectorImpl<Instruction *> &ToRemove) {
auto DoesConditionHold = [](CmpInst::Predicate Pred, Value *A, Value *B,
ConstraintInfo &Info) {
auto R = Info.getConstraintForSolving(Pred, A, B);
if (R.size() < 2 || !R.isValid(Info))
return false;
auto &CSToUse = Info.getCS(R.IsSigned);
return CSToUse.isConditionImplied(R.Coefficients);
};
bool Changed = false;
if (II->getIntrinsicID() == Intrinsic::ssub_with_overflow) {
// If A s>= B && B s>= 0, ssub.with.overflow(a, b) should not overflow and
// can be simplified to a regular sub.
Value *A = II->getArgOperand(0);
Value *B = II->getArgOperand(1);
if (!DoesConditionHold(CmpInst::ICMP_SGE, A, B, Info) ||
!DoesConditionHold(CmpInst::ICMP_SGE, B,
ConstantInt::get(A->getType(), 0), Info))
return false;
Changed = replaceSubOverflowUses(II, A, B, ToRemove);
}
return Changed;
}
static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
ScalarEvolution &SE,
OptimizationRemarkEmitter &ORE) {
bool Changed = false;
DT.updateDFSNumbers();
SmallVector<Value *> FunctionArgs;
for (Value &Arg : F.args())
FunctionArgs.push_back(&Arg);
ConstraintInfo Info(F.getParent()->getDataLayout(), FunctionArgs);
State S(DT, LI, SE);
std::unique_ptr<Module> ReproducerModule(
DumpReproducers ? new Module(F.getName(), F.getContext()) : nullptr);
// First, collect conditions implied by branches and blocks with their
// Dominator DFS in and out numbers.
for (BasicBlock &BB : F) {
if (!DT.getNode(&BB))
continue;
S.addInfoFor(BB);
}
// Next, sort worklist by dominance, so that dominating conditions to check
// and facts come before conditions and facts dominated by them. If a
// condition to check and a fact have the same numbers, conditional facts come
// first. Assume facts and checks are ordered according to their relative
// order in the containing basic block. Also make sure conditions with
// constant operands come before conditions without constant operands. This
// increases the effectiveness of the current signed <-> unsigned fact
// transfer logic.
stable_sort(S.WorkList, [](const FactOrCheck &A, const FactOrCheck &B) {
auto HasNoConstOp = [](const FactOrCheck &B) {
Value *V0 = B.isConditionFact() ? B.Cond.Op0 : B.Inst->getOperand(0);
Value *V1 = B.isConditionFact() ? B.Cond.Op1 : B.Inst->getOperand(1);
return !isa<ConstantInt>(V0) && !isa<ConstantInt>(V1);
};
// If both entries have the same In numbers, conditional facts come first.
// Otherwise use the relative order in the basic block.
if (A.NumIn == B.NumIn) {
if (A.isConditionFact() && B.isConditionFact()) {
bool NoConstOpA = HasNoConstOp(A);
bool NoConstOpB = HasNoConstOp(B);
return NoConstOpA < NoConstOpB;
}
if (A.isConditionFact())
return true;
if (B.isConditionFact())
return false;
auto *InstA = A.getContextInst();
auto *InstB = B.getContextInst();
return InstA->comesBefore(InstB);
}
return A.NumIn < B.NumIn;
});
SmallVector<Instruction *> ToRemove;
// Finally, process ordered worklist and eliminate implied conditions.
SmallVector<StackEntry, 16> DFSInStack;
SmallVector<ReproducerEntry> ReproducerCondStack;
for (FactOrCheck &CB : S.WorkList) {
// First, pop entries from the stack that are out-of-scope for CB. Remove
// the corresponding entry from the constraint system.
while (!DFSInStack.empty()) {
auto &E = DFSInStack.back();
LLVM_DEBUG(dbgs() << "Top of stack : " << E.NumIn << " " << E.NumOut
<< "\n");
LLVM_DEBUG(dbgs() << "CB: " << CB.NumIn << " " << CB.NumOut << "\n");
assert(E.NumIn <= CB.NumIn);
if (CB.NumOut <= E.NumOut)
break;
LLVM_DEBUG({
dbgs() << "Removing ";
dumpConstraint(Info.getCS(E.IsSigned).getLastConstraint(),
Info.getValue2Index(E.IsSigned));
dbgs() << "\n";
});
removeEntryFromStack(E, Info, ReproducerModule.get(), ReproducerCondStack,
DFSInStack);
}
// For a block, check if any CmpInsts become known based on the current set
// of constraints.
if (CB.isCheck()) {
Instruction *Inst = CB.getInstructionToSimplify();
if (!Inst)
continue;
LLVM_DEBUG(dbgs() << "Processing condition to simplify: " << *Inst
<< "\n");
if (auto *II = dyn_cast<WithOverflowInst>(Inst)) {
Changed |= tryToSimplifyOverflowMath(II, Info, ToRemove);
} else if (auto *Cmp = dyn_cast<ICmpInst>(Inst)) {
bool Simplified = checkAndReplaceCondition(
Cmp, Info, CB.NumIn, CB.NumOut, CB.getContextInst(),
ReproducerModule.get(), ReproducerCondStack, S.DT, ToRemove);
if (!Simplified &&
match(CB.getContextInst(), m_LogicalOp(m_Value(), m_Value()))) {
Simplified =
checkOrAndOpImpliedByOther(CB, Info, ReproducerModule.get(),
ReproducerCondStack, DFSInStack);
}
Changed |= Simplified;
} else if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(Inst)) {
Changed |= checkAndReplaceMinMax(MinMax, Info, ToRemove);
}
continue;
}
auto AddFact = [&](CmpInst::Predicate Pred, Value *A, Value *B) {
LLVM_DEBUG(dbgs() << "Processing fact to add to the system: ";
dumpUnpackedICmp(dbgs(), Pred, A, B); dbgs() << "\n");
if (Info.getCS(CmpInst::isSigned(Pred)).size() > MaxRows) {
LLVM_DEBUG(
dbgs()
<< "Skip adding constraint because system has too many rows.\n");
return;
}
Info.addFact(Pred, A, B, CB.NumIn, CB.NumOut, DFSInStack);
if (ReproducerModule && DFSInStack.size() > ReproducerCondStack.size())
ReproducerCondStack.emplace_back(Pred, A, B);
Info.transferToOtherSystem(Pred, A, B, CB.NumIn, CB.NumOut, DFSInStack);
if (ReproducerModule && DFSInStack.size() > ReproducerCondStack.size()) {
// Add dummy entries to ReproducerCondStack to keep it in sync with
// DFSInStack.
for (unsigned I = 0,
E = (DFSInStack.size() - ReproducerCondStack.size());
I < E; ++I) {
ReproducerCondStack.emplace_back(ICmpInst::BAD_ICMP_PREDICATE,
nullptr, nullptr);
}
}
};
ICmpInst::Predicate Pred;
if (!CB.isConditionFact()) {
Value *X;
if (match(CB.Inst, m_Intrinsic<Intrinsic::abs>(m_Value(X)))) {
// If is_int_min_poison is true then we may assume llvm.abs >= 0.
if (cast<ConstantInt>(CB.Inst->getOperand(1))->isOne())
AddFact(CmpInst::ICMP_SGE, CB.Inst,
ConstantInt::get(CB.Inst->getType(), 0));
AddFact(CmpInst::ICMP_SGE, CB.Inst, X);
continue;
}
if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(CB.Inst)) {
Pred = ICmpInst::getNonStrictPredicate(MinMax->getPredicate());
AddFact(Pred, MinMax, MinMax->getLHS());
AddFact(Pred, MinMax, MinMax->getRHS());
continue;
}
}
Value *A = nullptr, *B = nullptr;
if (CB.isConditionFact()) {
Pred = CB.Cond.Pred;
A = CB.Cond.Op0;
B = CB.Cond.Op1;
if (CB.DoesHold.Pred != CmpInst::BAD_ICMP_PREDICATE &&
!Info.doesHold(CB.DoesHold.Pred, CB.DoesHold.Op0, CB.DoesHold.Op1)) {
LLVM_DEBUG({
dbgs() << "Not adding fact ";
dumpUnpackedICmp(dbgs(), Pred, A, B);
dbgs() << " because precondition ";
dumpUnpackedICmp(dbgs(), CB.DoesHold.Pred, CB.DoesHold.Op0,
CB.DoesHold.Op1);
dbgs() << " does not hold.\n";
});
continue;
}
} else {
bool Matched = match(CB.Inst, m_Intrinsic<Intrinsic::assume>(
m_ICmp(Pred, m_Value(A), m_Value(B))));
(void)Matched;
assert(Matched && "Must have an assume intrinsic with a icmp operand");
}
AddFact(Pred, A, B);
}
if (ReproducerModule && !ReproducerModule->functions().empty()) {
std::string S;
raw_string_ostream StringS(S);
ReproducerModule->print(StringS, nullptr);
StringS.flush();
OptimizationRemark Rem(DEBUG_TYPE, "Reproducer", &F);
Rem << ore::NV("module") << S;
ORE.emit(Rem);
}
#ifndef NDEBUG
unsigned SignedEntries =
count_if(DFSInStack, [](const StackEntry &E) { return E.IsSigned; });
assert(Info.getCS(false).size() - FunctionArgs.size() ==
DFSInStack.size() - SignedEntries &&
"updates to CS and DFSInStack are out of sync");
assert(Info.getCS(true).size() == SignedEntries &&
"updates to CS and DFSInStack are out of sync");
#endif
for (Instruction *I : ToRemove)
I->eraseFromParent();
return Changed;
}
PreservedAnalyses ConstraintEliminationPass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &LI = AM.getResult<LoopAnalysis>(F);
auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
if (!eliminateConstraints(F, DT, LI, SE, ORE))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<LoopAnalysis>();
PA.preserve<ScalarEvolutionAnalysis>();
PA.preserveSet<CFGAnalyses>();
return PA;
}