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//===- InstructionCombining.cpp - Combine multiple instructions -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// InstructionCombining - Combine instructions to form fewer, simple
// instructions. This pass does not modify the CFG. This pass is where
// algebraic simplification happens.
//
// This pass combines things like:
// %Y = add i32 %X, 1
// %Z = add i32 %Y, 1
// into:
// %Z = add i32 %X, 2
//
// This is a simple worklist driven algorithm.
//
// This pass guarantees that the following canonicalizations are performed on
// the program:
// 1. If a binary operator has a constant operand, it is moved to the RHS
// 2. Bitwise operators with constant operands are always grouped so that
// shifts are performed first, then or's, then and's, then xor's.
// 3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible
// 4. All cmp instructions on boolean values are replaced with logical ops
// 5. add X, X is represented as (X*2) => (X << 1)
// 6. Multiplies with a power-of-two constant argument are transformed into
// shifts.
// ... etc.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm-c/Initialization.h"
#include "llvm-c/Transforms/InstCombine.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyBlockFrequencyInfo.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetFolder.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/Utils/Local.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/InstCombine/InstCombine.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <memory>
#include <string>
#include <utility>
#define DEBUG_TYPE "instcombine"
#include "llvm/Transforms/Utils/InstructionWorklist.h"
using namespace llvm;
using namespace llvm::PatternMatch;
STATISTIC(NumWorklistIterations,
"Number of instruction combining iterations performed");
STATISTIC(NumCombined , "Number of insts combined");
STATISTIC(NumConstProp, "Number of constant folds");
STATISTIC(NumDeadInst , "Number of dead inst eliminated");
STATISTIC(NumSunkInst , "Number of instructions sunk");
STATISTIC(NumExpand, "Number of expansions");
STATISTIC(NumFactor , "Number of factorizations");
STATISTIC(NumReassoc , "Number of reassociations");
DEBUG_COUNTER(VisitCounter, "instcombine-visit",
"Controls which instructions are visited");
// FIXME: these limits eventually should be as low as 2.
static constexpr unsigned InstCombineDefaultMaxIterations = 1000;
#ifndef NDEBUG
static constexpr unsigned InstCombineDefaultInfiniteLoopThreshold = 100;
#else
static constexpr unsigned InstCombineDefaultInfiniteLoopThreshold = 1000;
#endif
static cl::opt<bool>
EnableCodeSinking("instcombine-code-sinking", cl::desc("Enable code sinking"),
cl::init(true));
static cl::opt<unsigned> MaxSinkNumUsers(
"instcombine-max-sink-users", cl::init(32),
cl::desc("Maximum number of undroppable users for instruction sinking"));
static cl::opt<unsigned> LimitMaxIterations(
"instcombine-max-iterations",
cl::desc("Limit the maximum number of instruction combining iterations"),
cl::init(InstCombineDefaultMaxIterations));
static cl::opt<unsigned> InfiniteLoopDetectionThreshold(
"instcombine-infinite-loop-threshold",
cl::desc("Number of instruction combining iterations considered an "
"infinite loop"),
cl::init(InstCombineDefaultInfiniteLoopThreshold), cl::Hidden);
static cl::opt<unsigned>
MaxArraySize("instcombine-maxarray-size", cl::init(1024),
cl::desc("Maximum array size considered when doing a combine"));
// FIXME: Remove this flag when it is no longer necessary to convert
// llvm.dbg.declare to avoid inaccurate debug info. Setting this to false
// increases variable availability at the cost of accuracy. Variables that
// cannot be promoted by mem2reg or SROA will be described as living in memory
// for their entire lifetime. However, passes like DSE and instcombine can
// delete stores to the alloca, leading to misleading and inaccurate debug
// information. This flag can be removed when those passes are fixed.
static cl::opt<unsigned> ShouldLowerDbgDeclare("instcombine-lower-dbg-declare",
cl::Hidden, cl::init(true));
Optional<Instruction *>
InstCombiner::targetInstCombineIntrinsic(IntrinsicInst &II) {
// Handle target specific intrinsics
if (II.getCalledFunction()->isTargetIntrinsic()) {
return TTI.instCombineIntrinsic(*this, II);
}
return None;
}
Optional<Value *> InstCombiner::targetSimplifyDemandedUseBitsIntrinsic(
IntrinsicInst &II, APInt DemandedMask, KnownBits &Known,
bool &KnownBitsComputed) {
// Handle target specific intrinsics
if (II.getCalledFunction()->isTargetIntrinsic()) {
return TTI.simplifyDemandedUseBitsIntrinsic(*this, II, DemandedMask, Known,
KnownBitsComputed);
}
return None;
}
Optional<Value *> InstCombiner::targetSimplifyDemandedVectorEltsIntrinsic(
IntrinsicInst &II, APInt DemandedElts, APInt &UndefElts, APInt &UndefElts2,
APInt &UndefElts3,
std::function<void(Instruction *, unsigned, APInt, APInt &)>
SimplifyAndSetOp) {
// Handle target specific intrinsics
if (II.getCalledFunction()->isTargetIntrinsic()) {
return TTI.simplifyDemandedVectorEltsIntrinsic(
*this, II, DemandedElts, UndefElts, UndefElts2, UndefElts3,
SimplifyAndSetOp);
}
return None;
}
Value *InstCombinerImpl::EmitGEPOffset(User *GEP) {
return llvm::EmitGEPOffset(&Builder, DL, GEP);
}
/// Legal integers and common types are considered desirable. This is used to
/// avoid creating instructions with types that may not be supported well by the
/// the backend.
/// NOTE: This treats i8, i16 and i32 specially because they are common
/// types in frontend languages.
bool InstCombinerImpl::isDesirableIntType(unsigned BitWidth) const {
switch (BitWidth) {
case 8:
case 16:
case 32:
return true;
default:
return DL.isLegalInteger(BitWidth);
}
}
/// Return true if it is desirable to convert an integer computation from a
/// given bit width to a new bit width.
/// We don't want to convert from a legal to an illegal type or from a smaller
/// to a larger illegal type. A width of '1' is always treated as a desirable
/// type because i1 is a fundamental type in IR, and there are many specialized
/// optimizations for i1 types. Common/desirable widths are equally treated as
/// legal to convert to, in order to open up more combining opportunities.
bool InstCombinerImpl::shouldChangeType(unsigned FromWidth,
unsigned ToWidth) const {
bool FromLegal = FromWidth == 1 || DL.isLegalInteger(FromWidth);
bool ToLegal = ToWidth == 1 || DL.isLegalInteger(ToWidth);
// Convert to desirable widths even if they are not legal types.
// Only shrink types, to prevent infinite loops.
if (ToWidth < FromWidth && isDesirableIntType(ToWidth))
return true;
// If this is a legal integer from type, and the result would be an illegal
// type, don't do the transformation.
if (FromLegal && !ToLegal)
return false;
// Otherwise, if both are illegal, do not increase the size of the result. We
// do allow things like i160 -> i64, but not i64 -> i160.
if (!FromLegal && !ToLegal && ToWidth > FromWidth)
return false;
return true;
}
/// Return true if it is desirable to convert a computation from 'From' to 'To'.
/// We don't want to convert from a legal to an illegal type or from a smaller
/// to a larger illegal type. i1 is always treated as a legal type because it is
/// a fundamental type in IR, and there are many specialized optimizations for
/// i1 types.
bool InstCombinerImpl::shouldChangeType(Type *From, Type *To) const {
// TODO: This could be extended to allow vectors. Datalayout changes might be
// needed to properly support that.
if (!From->isIntegerTy() || !To->isIntegerTy())
return false;
unsigned FromWidth = From->getPrimitiveSizeInBits();
unsigned ToWidth = To->getPrimitiveSizeInBits();
return shouldChangeType(FromWidth, ToWidth);
}
// Return true, if No Signed Wrap should be maintained for I.
// The No Signed Wrap flag can be kept if the operation "B (I.getOpcode) C",
// where both B and C should be ConstantInts, results in a constant that does
// not overflow. This function only handles the Add and Sub opcodes. For
// all other opcodes, the function conservatively returns false.
static bool maintainNoSignedWrap(BinaryOperator &I, Value *B, Value *C) {
auto *OBO = dyn_cast<OverflowingBinaryOperator>(&I);
if (!OBO || !OBO->hasNoSignedWrap())
return false;
// We reason about Add and Sub Only.
Instruction::BinaryOps Opcode = I.getOpcode();
if (Opcode != Instruction::Add && Opcode != Instruction::Sub)
return false;
const APInt *BVal, *CVal;
if (!match(B, m_APInt(BVal)) || !match(C, m_APInt(CVal)))
return false;
bool Overflow = false;
if (Opcode == Instruction::Add)
(void)BVal->sadd_ov(*CVal, Overflow);
else
(void)BVal->ssub_ov(*CVal, Overflow);
return !Overflow;
}
static bool hasNoUnsignedWrap(BinaryOperator &I) {
auto *OBO = dyn_cast<OverflowingBinaryOperator>(&I);
return OBO && OBO->hasNoUnsignedWrap();
}
static bool hasNoSignedWrap(BinaryOperator &I) {
auto *OBO = dyn_cast<OverflowingBinaryOperator>(&I);
return OBO && OBO->hasNoSignedWrap();
}
/// Conservatively clears subclassOptionalData after a reassociation or
/// commutation. We preserve fast-math flags when applicable as they can be
/// preserved.
static void ClearSubclassDataAfterReassociation(BinaryOperator &I) {
FPMathOperator *FPMO = dyn_cast<FPMathOperator>(&I);
if (!FPMO) {
I.clearSubclassOptionalData();
return;
}
FastMathFlags FMF = I.getFastMathFlags();
I.clearSubclassOptionalData();
I.setFastMathFlags(FMF);
}
/// Combine constant operands of associative operations either before or after a
/// cast to eliminate one of the associative operations:
/// (op (cast (op X, C2)), C1) --> (cast (op X, op (C1, C2)))
/// (op (cast (op X, C2)), C1) --> (op (cast X), op (C1, C2))
static bool simplifyAssocCastAssoc(BinaryOperator *BinOp1,
InstCombinerImpl &IC) {
auto *Cast = dyn_cast<CastInst>(BinOp1->getOperand(0));
if (!Cast || !Cast->hasOneUse())
return false;
// TODO: Enhance logic for other casts and remove this check.
auto CastOpcode = Cast->getOpcode();
if (CastOpcode != Instruction::ZExt)
return false;
// TODO: Enhance logic for other BinOps and remove this check.
if (!BinOp1->isBitwiseLogicOp())
return false;
auto AssocOpcode = BinOp1->getOpcode();
auto *BinOp2 = dyn_cast<BinaryOperator>(Cast->getOperand(0));
if (!BinOp2 || !BinOp2->hasOneUse() || BinOp2->getOpcode() != AssocOpcode)
return false;
Constant *C1, *C2;
if (!match(BinOp1->getOperand(1), m_Constant(C1)) ||
!match(BinOp2->getOperand(1), m_Constant(C2)))
return false;
// TODO: This assumes a zext cast.
// Eg, if it was a trunc, we'd cast C1 to the source type because casting C2
// to the destination type might lose bits.
// Fold the constants together in the destination type:
// (op (cast (op X, C2)), C1) --> (op (cast X), FoldedC)
Type *DestTy = C1->getType();
Constant *CastC2 = ConstantExpr::getCast(CastOpcode, C2, DestTy);
Constant *FoldedC = ConstantExpr::get(AssocOpcode, C1, CastC2);
IC.replaceOperand(*Cast, 0, BinOp2->getOperand(0));
IC.replaceOperand(*BinOp1, 1, FoldedC);
return true;
}
// Simplifies IntToPtr/PtrToInt RoundTrip Cast To BitCast.
// inttoptr ( ptrtoint (x) ) --> x
Value *InstCombinerImpl::simplifyIntToPtrRoundTripCast(Value *Val) {
auto *IntToPtr = dyn_cast<IntToPtrInst>(Val);
if (IntToPtr && DL.getPointerTypeSizeInBits(IntToPtr->getDestTy()) ==
DL.getTypeSizeInBits(IntToPtr->getSrcTy())) {
auto *PtrToInt = dyn_cast<PtrToIntInst>(IntToPtr->getOperand(0));
Type *CastTy = IntToPtr->getDestTy();
if (PtrToInt &&
CastTy->getPointerAddressSpace() ==
PtrToInt->getSrcTy()->getPointerAddressSpace() &&
DL.getPointerTypeSizeInBits(PtrToInt->getSrcTy()) ==
DL.getTypeSizeInBits(PtrToInt->getDestTy())) {
return CastInst::CreateBitOrPointerCast(PtrToInt->getOperand(0), CastTy,
"", PtrToInt);
}
}
return nullptr;
}
/// This performs a few simplifications for operators that are associative or
/// commutative:
///
/// Commutative operators:
///
/// 1. Order operands such that they are listed from right (least complex) to
/// left (most complex). This puts constants before unary operators before
/// binary operators.
///
/// Associative operators:
///
/// 2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
/// 3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
///
/// Associative and commutative operators:
///
/// 4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
/// 5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
/// 6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
/// if C1 and C2 are constants.
bool InstCombinerImpl::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
Instruction::BinaryOps Opcode = I.getOpcode();
bool Changed = false;
do {
// Order operands such that they are listed from right (least complex) to
// left (most complex). This puts constants before unary operators before
// binary operators.
if (I.isCommutative() && getComplexity(I.getOperand(0)) <
getComplexity(I.getOperand(1)))
Changed = !I.swapOperands();
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
if (I.isAssociative()) {
// Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = I.getOperand(1);
// Does "B op C" simplify?
if (Value *V = simplifyBinOp(Opcode, B, C, SQ.getWithInstruction(&I))) {
// It simplifies to V. Form "A op V".
replaceOperand(I, 0, A);
replaceOperand(I, 1, V);
bool IsNUW = hasNoUnsignedWrap(I) && hasNoUnsignedWrap(*Op0);
bool IsNSW = maintainNoSignedWrap(I, B, C) && hasNoSignedWrap(*Op0);
// Conservatively clear all optional flags since they may not be
// preserved by the reassociation. Reset nsw/nuw based on the above
// analysis.
ClearSubclassDataAfterReassociation(I);
// Note: this is only valid because SimplifyBinOp doesn't look at
// the operands to Op0.
if (IsNUW)
I.setHasNoUnsignedWrap(true);
if (IsNSW)
I.setHasNoSignedWrap(true);
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = I.getOperand(0);
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "A op B" simplify?
if (Value *V = simplifyBinOp(Opcode, A, B, SQ.getWithInstruction(&I))) {
// It simplifies to V. Form "V op C".
replaceOperand(I, 0, V);
replaceOperand(I, 1, C);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
}
if (I.isAssociative() && I.isCommutative()) {
if (simplifyAssocCastAssoc(&I, *this)) {
Changed = true;
++NumReassoc;
continue;
}
// Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = I.getOperand(1);
// Does "C op A" simplify?
if (Value *V = simplifyBinOp(Opcode, C, A, SQ.getWithInstruction(&I))) {
// It simplifies to V. Form "V op B".
replaceOperand(I, 0, V);
replaceOperand(I, 1, B);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = I.getOperand(0);
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "C op A" simplify?
if (Value *V = simplifyBinOp(Opcode, C, A, SQ.getWithInstruction(&I))) {
// It simplifies to V. Form "B op V".
replaceOperand(I, 0, B);
replaceOperand(I, 1, V);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
Changed = true;
++NumReassoc;
continue;
}
}
// Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
// if C1 and C2 are constants.
Value *A, *B;
Constant *C1, *C2, *CRes;
if (Op0 && Op1 &&
Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
match(Op0, m_OneUse(m_BinOp(m_Value(A), m_Constant(C1)))) &&
match(Op1, m_OneUse(m_BinOp(m_Value(B), m_Constant(C2)))) &&
(CRes = ConstantFoldBinaryOpOperands(Opcode, C1, C2, DL))) {
bool IsNUW = hasNoUnsignedWrap(I) &&
hasNoUnsignedWrap(*Op0) &&
hasNoUnsignedWrap(*Op1);
BinaryOperator *NewBO = (IsNUW && Opcode == Instruction::Add) ?
BinaryOperator::CreateNUW(Opcode, A, B) :
BinaryOperator::Create(Opcode, A, B);
if (isa<FPMathOperator>(NewBO)) {
FastMathFlags Flags = I.getFastMathFlags();
Flags &= Op0->getFastMathFlags();
Flags &= Op1->getFastMathFlags();
NewBO->setFastMathFlags(Flags);
}
InsertNewInstWith(NewBO, I);
NewBO->takeName(Op1);
replaceOperand(I, 0, NewBO);
replaceOperand(I, 1, CRes);
// Conservatively clear the optional flags, since they may not be
// preserved by the reassociation.
ClearSubclassDataAfterReassociation(I);
if (IsNUW)
I.setHasNoUnsignedWrap(true);
Changed = true;
continue;
}
}
// No further simplifications.
return Changed;
} while (true);
}
/// Return whether "X LOp (Y ROp Z)" is always equal to
/// "(X LOp Y) ROp (X LOp Z)".
static bool leftDistributesOverRight(Instruction::BinaryOps LOp,
Instruction::BinaryOps ROp) {
// X & (Y | Z) <--> (X & Y) | (X & Z)
// X & (Y ^ Z) <--> (X & Y) ^ (X & Z)
if (LOp == Instruction::And)
return ROp == Instruction::Or || ROp == Instruction::Xor;
// X | (Y & Z) <--> (X | Y) & (X | Z)
if (LOp == Instruction::Or)
return ROp == Instruction::And;
// X * (Y + Z) <--> (X * Y) + (X * Z)
// X * (Y - Z) <--> (X * Y) - (X * Z)
if (LOp == Instruction::Mul)
return ROp == Instruction::Add || ROp == Instruction::Sub;
return false;
}
/// Return whether "(X LOp Y) ROp Z" is always equal to
/// "(X ROp Z) LOp (Y ROp Z)".
static bool rightDistributesOverLeft(Instruction::BinaryOps LOp,
Instruction::BinaryOps ROp) {
if (Instruction::isCommutative(ROp))
return leftDistributesOverRight(ROp, LOp);
// (X {&|^} Y) >> Z <--> (X >> Z) {&|^} (Y >> Z) for all shifts.
return Instruction::isBitwiseLogicOp(LOp) && Instruction::isShift(ROp);
// TODO: It would be nice to handle division, aka "(X + Y)/Z = X/Z + Y/Z",
// but this requires knowing that the addition does not overflow and other
// such subtleties.
}
/// This function returns identity value for given opcode, which can be used to
/// factor patterns like (X * 2) + X ==> (X * 2) + (X * 1) ==> X * (2 + 1).
static Value *getIdentityValue(Instruction::BinaryOps Opcode, Value *V) {
if (isa<Constant>(V))
return nullptr;
return ConstantExpr::getBinOpIdentity(Opcode, V->getType());
}
/// This function predicates factorization using distributive laws. By default,
/// it just returns the 'Op' inputs. But for special-cases like
/// 'add(shl(X, 5), ...)', this function will have TopOpcode == Instruction::Add
/// and Op = shl(X, 5). The 'shl' is treated as the more general 'mul X, 32' to
/// allow more factorization opportunities.
static Instruction::BinaryOps
getBinOpsForFactorization(Instruction::BinaryOps TopOpcode, BinaryOperator *Op,
Value *&LHS, Value *&RHS) {
assert(Op && "Expected a binary operator");
LHS = Op->getOperand(0);
RHS = Op->getOperand(1);
if (TopOpcode == Instruction::Add || TopOpcode == Instruction::Sub) {
Constant *C;
if (match(Op, m_Shl(m_Value(), m_Constant(C)))) {
// X << C --> X * (1 << C)
RHS = ConstantExpr::getShl(ConstantInt::get(Op->getType(), 1), C);
return Instruction::Mul;
}
// TODO: We can add other conversions e.g. shr => div etc.
}
return Op->getOpcode();
}
/// This tries to simplify binary operations by factorizing out common terms
/// (e. g. "(A*B)+(A*C)" -> "A*(B+C)").
Value *InstCombinerImpl::tryFactorization(BinaryOperator &I,
Instruction::BinaryOps InnerOpcode,
Value *A, Value *B, Value *C,
Value *D) {
assert(A && B && C && D && "All values must be provided");
Value *V = nullptr;
Value *SimplifiedInst = nullptr;
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
Instruction::BinaryOps TopLevelOpcode = I.getOpcode();
// Does "X op' Y" always equal "Y op' X"?
bool InnerCommutative = Instruction::isCommutative(InnerOpcode);
// Does "X op' (Y op Z)" always equal "(X op' Y) op (X op' Z)"?
if (leftDistributesOverRight(InnerOpcode, TopLevelOpcode))
// Does the instruction have the form "(A op' B) op (A op' D)" or, in the
// commutative case, "(A op' B) op (C op' A)"?
if (A == C || (InnerCommutative && A == D)) {
if (A != C)
std::swap(C, D);
// Consider forming "A op' (B op D)".
// If "B op D" simplifies then it can be formed with no cost.
V = simplifyBinOp(TopLevelOpcode, B, D, SQ.getWithInstruction(&I));
// If "B op D" doesn't simplify then only go on if both of the existing
// operations "A op' B" and "C op' D" will be zapped as no longer used.
if (!V && LHS->hasOneUse() && RHS->hasOneUse())
V = Builder.CreateBinOp(TopLevelOpcode, B, D, RHS->getName());
if (V) {
SimplifiedInst = Builder.CreateBinOp(InnerOpcode, A, V);
}
}
// Does "(X op Y) op' Z" always equal "(X op' Z) op (Y op' Z)"?
if (!SimplifiedInst && rightDistributesOverLeft(TopLevelOpcode, InnerOpcode))
// Does the instruction have the form "(A op' B) op (C op' B)" or, in the
// commutative case, "(A op' B) op (B op' D)"?
if (B == D || (InnerCommutative && B == C)) {
if (B != D)
std::swap(C, D);
// Consider forming "(A op C) op' B".
// If "A op C" simplifies then it can be formed with no cost.
V = simplifyBinOp(TopLevelOpcode, A, C, SQ.getWithInstruction(&I));
// If "A op C" doesn't simplify then only go on if both of the existing
// operations "A op' B" and "C op' D" will be zapped as no longer used.
if (!V && LHS->hasOneUse() && RHS->hasOneUse())
V = Builder.CreateBinOp(TopLevelOpcode, A, C, LHS->getName());
if (V) {
SimplifiedInst = Builder.CreateBinOp(InnerOpcode, V, B);
}
}
if (SimplifiedInst) {
++NumFactor;
SimplifiedInst->takeName(&I);
// Check if we can add NSW/NUW flags to SimplifiedInst. If so, set them.
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(SimplifiedInst)) {
if (isa<OverflowingBinaryOperator>(SimplifiedInst)) {
bool HasNSW = false;
bool HasNUW = false;
if (isa<OverflowingBinaryOperator>(&I)) {
HasNSW = I.hasNoSignedWrap();
HasNUW = I.hasNoUnsignedWrap();
}
if (auto *LOBO = dyn_cast<OverflowingBinaryOperator>(LHS)) {
HasNSW &= LOBO->hasNoSignedWrap();
HasNUW &= LOBO->hasNoUnsignedWrap();
}
if (auto *ROBO = dyn_cast<OverflowingBinaryOperator>(RHS)) {
HasNSW &= ROBO->hasNoSignedWrap();
HasNUW &= ROBO->hasNoUnsignedWrap();
}
if (TopLevelOpcode == Instruction::Add &&
InnerOpcode == Instruction::Mul) {
// We can propagate 'nsw' if we know that
// %Y = mul nsw i16 %X, C
// %Z = add nsw i16 %Y, %X
// =>
// %Z = mul nsw i16 %X, C+1
//
// iff C+1 isn't INT_MIN
const APInt *CInt;
if (match(V, m_APInt(CInt))) {
if (!CInt->isMinSignedValue())
BO->setHasNoSignedWrap(HasNSW);
}
// nuw can be propagated with any constant or nuw value.
BO->setHasNoUnsignedWrap(HasNUW);
}
}
}
}
return SimplifiedInst;
}
/// This tries to simplify binary operations which some other binary operation
/// distributes over either by factorizing out common terms
/// (eg "(A*B)+(A*C)" -> "A*(B+C)") or expanding out if this results in
/// simplifications (eg: "A & (B | C) -> (A&B) | (A&C)" if this is a win).
/// Returns the simplified value, or null if it didn't simplify.
Value *InstCombinerImpl::SimplifyUsingDistributiveLaws(BinaryOperator &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS);
BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS);
Instruction::BinaryOps TopLevelOpcode = I.getOpcode();
{
// Factorization.
Value *A, *B, *C, *D;
Instruction::BinaryOps LHSOpcode, RHSOpcode;
if (Op0)
LHSOpcode = getBinOpsForFactorization(TopLevelOpcode, Op0, A, B);
if (Op1)
RHSOpcode = getBinOpsForFactorization(TopLevelOpcode, Op1, C, D);
// The instruction has the form "(A op' B) op (C op' D)". Try to factorize
// a common term.
if (Op0 && Op1 && LHSOpcode == RHSOpcode)
if (Value *V = tryFactorization(I, LHSOpcode, A, B, C, D))
return V;
// The instruction has the form "(A op' B) op (C)". Try to factorize common
// term.
if (Op0)
if (Value *Ident = getIdentityValue(LHSOpcode, RHS))
if (Value *V = tryFactorization(I, LHSOpcode, A, B, RHS, Ident))
return V;
// The instruction has the form "(B) op (C op' D)". Try to factorize common
// term.
if (Op1)
if (Value *Ident = getIdentityValue(RHSOpcode, LHS))
if (Value *V = tryFactorization(I, RHSOpcode, LHS, Ident, C, D))
return V;
}
// Expansion.
if (Op0 && rightDistributesOverLeft(Op0->getOpcode(), TopLevelOpcode)) {
// The instruction has the form "(A op' B) op C". See if expanding it out
// to "(A op C) op' (B op C)" results in simplifications.
Value *A = Op0->getOperand(0), *B = Op0->getOperand(1), *C = RHS;
Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op'
// Disable the use of undef because it's not safe to distribute undef.
auto SQDistributive = SQ.getWithInstruction(&I).getWithoutUndef();
Value *L = simplifyBinOp(TopLevelOpcode, A, C, SQDistributive);
Value *R = simplifyBinOp(TopLevelOpcode, B, C, SQDistributive);
// Do "A op C" and "B op C" both simplify?
if (L && R) {
// They do! Return "L op' R".
++NumExpand;
C = Builder.CreateBinOp(InnerOpcode, L, R);
C->takeName(&I);
return C;
}
// Does "A op C" simplify to the identity value for the inner opcode?
if (L && L == ConstantExpr::getBinOpIdentity(InnerOpcode, L->getType())) {
// They do! Return "B op C".
++NumExpand;
C = Builder.CreateBinOp(TopLevelOpcode, B, C);
C->takeName(&I);
return C;
}
// Does "B op C" simplify to the identity value for the inner opcode?
if (R && R == ConstantExpr::getBinOpIdentity(InnerOpcode, R->getType())) {
// They do! Return "A op C".
++NumExpand;
C = Builder.CreateBinOp(TopLevelOpcode, A, C);
C->takeName(&I);
return C;
}
}
if (Op1 && leftDistributesOverRight(TopLevelOpcode, Op1->getOpcode())) {
// The instruction has the form "A op (B op' C)". See if expanding it out
// to "(A op B) op' (A op C)" results in simplifications.
Value *A = LHS, *B = Op1->getOperand(0), *C = Op1->getOperand(1);
Instruction::BinaryOps InnerOpcode = Op1->getOpcode(); // op'
// Disable the use of undef because it's not safe to distribute undef.
auto SQDistributive = SQ.getWithInstruction(&I).getWithoutUndef();
Value *L = simplifyBinOp(TopLevelOpcode, A, B, SQDistributive);
Value *R = simplifyBinOp(TopLevelOpcode, A, C, SQDistributive);
// Do "A op B" and "A op C" both simplify?
if (L && R) {
// They do! Return "L op' R".
++NumExpand;
A = Builder.CreateBinOp(InnerOpcode, L, R);
A->takeName(&I);
return A;
}
// Does "A op B" simplify to the identity value for the inner opcode?
if (L && L == ConstantExpr::getBinOpIdentity(InnerOpcode, L->getType())) {
// They do! Return "A op C".
++NumExpand;
A = Builder.CreateBinOp(TopLevelOpcode, A, C);
A->takeName(&I);
return A;
}
// Does "A op C" simplify to the identity value for the inner opcode?
if (R && R == ConstantExpr::getBinOpIdentity(InnerOpcode, R->getType())) {
// They do! Return "A op B".
++NumExpand;
A = Builder.CreateBinOp(TopLevelOpcode, A, B);
A->takeName(&I);
return A;
}
}
return SimplifySelectsFeedingBinaryOp(I, LHS, RHS);
}
Value *InstCombinerImpl::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
Value *LHS,
Value *RHS) {
Value *A, *B, *C, *D, *E, *F;
bool LHSIsSelect = match(LHS, m_Select(m_Value(A), m_Value(B), m_Value(C)));
bool RHSIsSelect = match(RHS, m_Select(m_Value(D), m_Value(E), m_Value(F)));
if (!LHSIsSelect && !RHSIsSelect)
return nullptr;
FastMathFlags FMF;
BuilderTy::FastMathFlagGuard Guard(Builder);
if (isa<FPMathOperator>(&I)) {
FMF = I.getFastMathFlags();
Builder.setFastMathFlags(FMF);
}
Instruction::BinaryOps Opcode = I.getOpcode();
SimplifyQuery Q = SQ.getWithInstruction(&I);
Value *Cond, *True = nullptr, *False = nullptr;
if (LHSIsSelect && RHSIsSelect && A == D) {
// (A ? B : C) op (A ? E : F) -> A ? (B op E) : (C op F)
Cond = A;
True = simplifyBinOp(Opcode, B, E, FMF, Q);
False = simplifyBinOp(Opcode, C, F, FMF, Q);
if (LHS->hasOneUse() && RHS->hasOneUse()) {
if (False && !True)
True = Builder.CreateBinOp(Opcode, B, E);
else if (True && !False)
False = Builder.CreateBinOp(Opcode, C, F);
}
} else if (LHSIsSelect && LHS->hasOneUse()) {
// (A ? B : C) op Y -> A ? (B op Y) : (C op Y)
Cond = A;
True = simplifyBinOp(Opcode, B, RHS, FMF, Q);
False = simplifyBinOp(Opcode, C, RHS, FMF, Q);
} else if (RHSIsSelect && RHS->hasOneUse()) {
// X op (D ? E : F) -> D ? (X op E) : (X op F)
Cond = D;
True = simplifyBinOp(Opcode, LHS, E, FMF, Q);
False = simplifyBinOp(Opcode, LHS, F, FMF, Q);
}
if (!True || !False)
return nullptr;
Value *SI = Builder.CreateSelect(Cond, True, False);
SI->takeName(&I);
return SI;
}
/// Freely adapt every user of V as-if V was changed to !V.
/// WARNING: only if canFreelyInvertAllUsersOf() said this can be done.
void InstCombinerImpl::freelyInvertAllUsersOf(Value *I) {
for (User *U : I->users()) {
switch (cast<Instruction>(U)->getOpcode()) {
case Instruction::Select: {
auto *SI = cast<SelectInst>(U);
SI->swapValues();
SI->swapProfMetadata();
break;
}
case Instruction::Br:
cast<BranchInst>(U)->swapSuccessors(); // swaps prof metadata too
break;
case Instruction::Xor:
replaceInstUsesWith(cast<Instruction>(*U), I);
break;
default:
llvm_unreachable("Got unexpected user - out of sync with "
"canFreelyInvertAllUsersOf() ?");
}
}
}
/// Given a 'sub' instruction, return the RHS of the instruction if the LHS is a
/// constant zero (which is the 'negate' form).
Value *InstCombinerImpl::dyn_castNegVal(Value *V) const {
Value *NegV;
if (match(V, m_Neg(m_Value(NegV))))
return NegV;
// Constants can be considered to be negated values if they can be folded.
if (ConstantInt *C = dyn_cast<ConstantInt>(V))
return ConstantExpr::getNeg(C);
if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
if (C->getType()->getElementType()->isIntegerTy())
return ConstantExpr::getNeg(C);
if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) {
for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
Constant *Elt = CV->getAggregateElement(i);
if (!Elt)
return nullptr;
if (isa<UndefValue>(Elt))
continue;
if (!isa<ConstantInt>(Elt))
return nullptr;
}
return ConstantExpr::getNeg(CV);
}
// Negate integer vector splats.
if (auto *CV = dyn_cast<Constant>(V))
if (CV->getType()->isVectorTy() &&
CV->getType()->getScalarType()->isIntegerTy() && CV->getSplatValue())
return ConstantExpr::getNeg(CV);
return nullptr;
}
/// A binop with a constant operand and a sign-extended boolean operand may be
/// converted into a select of constants by applying the binary operation to
/// the constant with the two possible values of the extended boolean (0 or -1).
Instruction *InstCombinerImpl::foldBinopOfSextBoolToSelect(BinaryOperator &BO) {
// TODO: Handle non-commutative binop (constant is operand 0).
// TODO: Handle zext.
// TODO: Peek through 'not' of cast.
Value *BO0 = BO.getOperand(0);
Value *BO1 = BO.getOperand(1);
Value *X;
Constant *C;
if (!match(BO0, m_SExt(m_Value(X))) || !match(BO1, m_ImmConstant(C)) ||
!X->getType()->isIntOrIntVectorTy(1))
return nullptr;
// bo (sext i1 X), C --> select X, (bo -1, C), (bo 0, C)
Constant *Ones = ConstantInt::getAllOnesValue(BO.getType());
Constant *Zero = ConstantInt::getNullValue(BO.getType());
Value *TVal = Builder.CreateBinOp(BO.getOpcode(), Ones, C);
Value *FVal = Builder.CreateBinOp(BO.getOpcode(), Zero, C);
return SelectInst::Create(X, TVal, FVal);
}
static Constant *constantFoldOperationIntoSelectOperand(
Instruction &I, SelectInst *SI, Value *SO) {
auto *ConstSO = dyn_cast<Constant>(SO);
if (!ConstSO)
return nullptr;
SmallVector<Constant *> ConstOps;
for (Value *Op : I.operands()) {
if (Op == SI)
ConstOps.push_back(ConstSO);
else if (auto *C = dyn_cast<Constant>(Op))
ConstOps.push_back(C);
else
llvm_unreachable("Operands should be select or constant");
}
return ConstantFoldInstOperands(&I, ConstOps, I.getModule()->getDataLayout());
}
static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
InstCombiner::BuilderTy &Builder) {
if (auto *Cast = dyn_cast<CastInst>(&I))
return Builder.CreateCast(Cast->getOpcode(), SO, I.getType());
if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
assert(canConstantFoldCallTo(II, cast<Function>(II->getCalledOperand())) &&
"Expected constant-foldable intrinsic");
Intrinsic::ID IID = II->getIntrinsicID();
if (II->arg_size() == 1)
return Builder.CreateUnaryIntrinsic(IID, SO);
// This works for real binary ops like min/max (where we always expect the
// constant operand to be canonicalized as op1) and unary ops with a bonus
// constant argument like ctlz/cttz.
// TODO: Handle non-commutative binary intrinsics as below for binops.
assert(II->arg_size() == 2 && "Expected binary intrinsic");
assert(isa<Constant>(II->getArgOperand(1)) && "Expected constant operand");
return Builder.CreateBinaryIntrinsic(IID, SO, II->getArgOperand(1));
}
assert(I.isBinaryOp() && "Unexpected opcode for select folding");
// Figure out if the constant is the left or the right argument.
bool ConstIsRHS = isa<Constant>(I.getOperand(1));
Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
Value *Op0 = SO, *Op1 = ConstOperand;
if (!ConstIsRHS)
std::swap(Op0, Op1);
Value *NewBO = Builder.CreateBinOp(cast<BinaryOperator>(&I)->getOpcode(), Op0,
Op1, SO->getName() + ".op");
if (auto *NewBOI = dyn_cast<Instruction>(NewBO))
NewBOI->copyIRFlags(&I);
return NewBO;
}
Instruction *InstCombinerImpl::FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
bool FoldWithMultiUse) {
// Don't modify shared select instructions unless set FoldWithMultiUse
if (!SI->hasOneUse() && !FoldWithMultiUse)
return nullptr;
Value *TV = SI->getTrueValue();
Value *FV = SI->getFalseValue();
if (!(isa<Constant>(TV) || isa<Constant>(FV)))
return nullptr;
// Bool selects with constant operands can be folded to logical ops.
if (SI->getType()->isIntOrIntVectorTy(1))
return nullptr;
// If it's a bitcast involving vectors, make sure it has the same number of
// elements on both sides.
if (auto *BC = dyn_cast<BitCastInst>(&Op)) {
VectorType *DestTy = dyn_cast<VectorType>(BC->getDestTy());
VectorType *SrcTy = dyn_cast<VectorType>(BC->getSrcTy());
// Verify that either both or neither are vectors.
if ((SrcTy == nullptr) != (DestTy == nullptr))
return nullptr;
// If vectors, verify that they have the same number of elements.
if (SrcTy && SrcTy->getElementCount() != DestTy->getElementCount())
return nullptr;
}
// Test if a CmpInst instruction is used exclusively by a select as
// part of a minimum or maximum operation. If so, refrain from doing
// any other folding. This helps out other analyses which understand
// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
// and CodeGen. And in this case, at least one of the comparison
// operands has at least one user besides the compare (the select),
// which would often largely negate the benefit of folding anyway.
if (auto *CI = dyn_cast<CmpInst>(SI->getCondition())) {
if (CI->hasOneUse()) {
Value *Op0 = CI->getOperand(0), *Op1 = CI->getOperand(1);
// FIXME: This is a hack to avoid infinite looping with min/max patterns.
// We have to ensure that vector constants that only differ with
// undef elements are treated as equivalent.
auto areLooselyEqual = [](Value *A, Value *B) {
if (A == B)
return true;
// Test for vector constants.
Constant *ConstA, *ConstB;
if (!match(A, m_Constant(ConstA)) || !match(B, m_Constant(ConstB)))
return false;
// TODO: Deal with FP constants?
if (!A->getType()->isIntOrIntVectorTy() || A->getType() != B->getType())
return false;
// Compare for equality including undefs as equal.
auto *Cmp = ConstantExpr::getCompare(ICmpInst::ICMP_EQ, ConstA, ConstB);
const APInt *C;
return match(Cmp, m_APIntAllowUndef(C)) && C->isOne();
};
if ((areLooselyEqual(TV, Op0) && areLooselyEqual(FV, Op1)) ||
(areLooselyEqual(FV, Op0) && areLooselyEqual(TV, Op1)))
return nullptr;
}
}
// Make sure that one of the select arms constant folds successfully.
Value *NewTV = constantFoldOperationIntoSelectOperand(Op, SI, TV);
Value *NewFV = constantFoldOperationIntoSelectOperand(Op, SI, FV);
if (!NewTV && !NewFV)
return nullptr;
// Create an instruction for the arm that did not fold.
if (!NewTV)
NewTV = foldOperationIntoSelectOperand(Op, TV, Builder);
if (!NewFV)
NewFV = foldOperationIntoSelectOperand(Op, FV, Builder);
return SelectInst::Create(SI->getCondition(), NewTV, NewFV, "", nullptr, SI);
}
static Value *foldOperationIntoPhiValue(BinaryOperator *I, Value *InV,
InstCombiner::BuilderTy &Builder) {
bool ConstIsRHS = isa<Constant>(I->getOperand(1));
Constant *C = cast<Constant>(I->getOperand(ConstIsRHS));
Value *Op0 = InV, *Op1 = C;
if (!ConstIsRHS)
std::swap(Op0, Op1);
Value *RI = Builder.CreateBinOp(I->getOpcode(), Op0, Op1, "phi.bo");
auto *FPInst = dyn_cast<Instruction>(RI);
if (FPInst && isa<FPMathOperator>(FPInst))
FPInst->copyFastMathFlags(I);
return RI;
}
Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN) {
unsigned NumPHIValues = PN->getNumIncomingValues();
if (NumPHIValues == 0)
return nullptr;
// We normally only transform phis with a single use. However, if a PHI has
// multiple uses and they are all the same operation, we can fold *all* of the
// uses into the PHI.
if (!PN->hasOneUse()) {
// Walk the use list for the instruction, comparing them to I.
for (User *U : PN->users()) {
Instruction *UI = cast<Instruction>(U);
if (UI != &I && !I.isIdenticalTo(UI))
return nullptr;
}
// Otherwise, we can replace *all* users with the new PHI we form.
}
// Check to see if all of the operands of the PHI are simple constants
// (constantint/constantfp/undef). If there is one non-constant value,
// remember the BB it is in. If there is more than one or if *it* is a PHI,
// bail out. We don't do arbitrary constant expressions here because moving
// their computation can be expensive without a cost model.
BasicBlock *NonConstBB = nullptr;
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InVal = PN->getIncomingValue(i);
// For non-freeze, require constant operand
// For freeze, require non-undef, non-poison operand
if (!isa<FreezeInst>(I) && match(InVal, m_ImmConstant()))
continue;
if (isa<FreezeInst>(I) && isGuaranteedNotToBeUndefOrPoison(InVal))
continue;
if (isa<PHINode>(InVal)) return nullptr; // Itself a phi.
if (NonConstBB) return nullptr; // More than one non-const value.
NonConstBB = PN->getIncomingBlock(i);
// If the InVal is an invoke at the end of the pred block, then we can't
// insert a computation after it without breaking the edge.
if (isa<InvokeInst>(InVal))
if (cast<Instruction>(InVal)->getParent() == NonConstBB)
return nullptr;
// If the incoming non-constant value is reachable from the phis block,
// we'll push the operation across a loop backedge. This could result in
// an infinite combine loop, and is generally non-profitable (especially
// if the operation was originally outside the loop).
if (isPotentiallyReachable(PN->getParent(), NonConstBB, nullptr, &DT, LI))
return nullptr;
}
// If there is exactly one non-constant value, we can insert a copy of the
// operation in that block. However, if this is a critical edge, we would be
// inserting the computation on some other paths (e.g. inside a loop). Only
// do this if the pred block is unconditionally branching into the phi block.
// Also, make sure that the pred block is not dead code.
if (NonConstBB != nullptr) {
BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
if (!BI || !BI->isUnconditional() || !DT.isReachableFromEntry(NonConstBB))
return nullptr;
}
// Okay, we can do the transformation: create the new PHI node.
PHINode *NewPN = PHINode::Create(I.getType(), PN->getNumIncomingValues());
InsertNewInstBefore(NewPN, *PN);
NewPN->takeName(PN);
// If we are going to have to insert a new computation, do so right before the
// predecessor's terminator.
if (NonConstBB)
Builder.SetInsertPoint(NonConstBB->getTerminator());
// Next, add all of the operands to the PHI.
if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
// We only currently try to fold the condition of a select when it is a phi,
// not the true/false values.
Value *TrueV = SI->getTrueValue();
Value *FalseV = SI->getFalseValue();
BasicBlock *PhiTransBB = PN->getParent();
for (unsigned i = 0; i != NumPHIValues; ++i) {
BasicBlock *ThisBB = PN->getIncomingBlock(i);
Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
Value *InV = nullptr;
// Beware of ConstantExpr: it may eventually evaluate to getNullValue,
// even if currently isNullValue gives false.
Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i));
// For vector constants, we cannot use isNullValue to fold into
// FalseVInPred versus TrueVInPred. When we have individual nonzero
// elements in the vector, we will incorrectly fold InC to
// `TrueVInPred`.
if (InC && isa<ConstantInt>(InC))
InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
else {
// Generate the select in the same block as PN's current incoming block.
// Note: ThisBB need not be the NonConstBB because vector constants
// which are constants by definition are handled here.
// FIXME: This can lead to an increase in IR generation because we might
// generate selects for vector constant phi operand, that could not be
// folded to TrueVInPred or FalseVInPred as done for ConstantInt. For
// non-vector phis, this transformation was always profitable because
// the select would be generated exactly once in the NonConstBB.
Builder.SetInsertPoint(ThisBB->getTerminator());
InV = Builder.CreateSelect(PN->getIncomingValue(i), TrueVInPred,
FalseVInPred, "phi.sel");
}
NewPN->addIncoming(InV, ThisBB);
}
} else if (CmpInst *CI = dyn_cast<CmpInst>(&I)) {
Constant *C = cast<Constant>(I.getOperand(1));
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV = nullptr;
if (auto *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
else
InV = Builder.CreateCmp(CI->getPredicate(), PN->getIncomingValue(i),
C, "phi.cmp");
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
} else if (auto *BO = dyn_cast<BinaryOperator>(&I)) {
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV = foldOperationIntoPhiValue(BO, PN->getIncomingValue(i),
Builder);
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
} else if (isa<FreezeInst>(&I)) {
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV;
if (NonConstBB == PN->getIncomingBlock(i))
InV = Builder.CreateFreeze(PN->getIncomingValue(i), "phi.fr");
else
InV = PN->getIncomingValue(i);
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
} else {
CastInst *CI = cast<CastInst>(&I);
Type *RetTy = CI->getType();
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InV;
if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
else
InV = Builder.CreateCast(CI->getOpcode(), PN->getIncomingValue(i),
I.getType(), "phi.cast");
NewPN->addIncoming(InV, PN->getIncomingBlock(i));
}
}
for (User *U : make_early_inc_range(PN->users())) {
Instruction *User = cast<Instruction>(U);
if (User == &I) continue;
replaceInstUsesWith(*User, NewPN);
eraseInstFromFunction(*User);
}
return replaceInstUsesWith(I, NewPN);
}
Instruction *InstCombinerImpl::foldBinopWithPhiOperands(BinaryOperator &BO) {
// TODO: This should be similar to the incoming values check in foldOpIntoPhi:
// we are guarding against replicating the binop in >1 predecessor.
// This could miss matching a phi with 2 constant incoming values.
auto *Phi0 = dyn_cast<PHINode>(BO.getOperand(0));
auto *Phi1 = dyn_cast<PHINode>(BO.getOperand(1));
if (!Phi0 || !Phi1 || !Phi0->hasOneUse() || !Phi1->hasOneUse() ||
Phi0->getNumOperands() != 2 || Phi1->getNumOperands() != 2)
return nullptr;
// TODO: Remove the restriction for binop being in the same block as the phis.
if (BO.getParent() != Phi0->getParent() ||
BO.getParent() != Phi1->getParent())
return nullptr;
// Match a pair of incoming constants for one of the predecessor blocks.
BasicBlock *ConstBB, *OtherBB;
Constant *C0, *C1;
if (match(Phi0->getIncomingValue(0), m_ImmConstant(C0))) {
ConstBB = Phi0->getIncomingBlock(0);
OtherBB = Phi0->getIncomingBlock(1);
} else if (match(Phi0->getIncomingValue(1), m_ImmConstant(C0))) {
ConstBB = Phi0->getIncomingBlock(1);
OtherBB = Phi0->getIncomingBlock(0);
} else {
return nullptr;
}
if (!match(Phi1->getIncomingValueForBlock(ConstBB), m_ImmConstant(C1)))
return nullptr;
// The block that we are hoisting to must reach here unconditionally.
// Otherwise, we could be speculatively executing an expensive or
// non-speculative op.
auto *PredBlockBranch = dyn_cast<BranchInst>(OtherBB->getTerminator());
if (!PredBlockBranch || PredBlockBranch->isConditional() ||
!DT.isReachableFromEntry(OtherBB))
return nullptr;
// TODO: This check could be tightened to only apply to binops (div/rem) that
// are not safe to speculatively execute. But that could allow hoisting
// potentially expensive instructions (fdiv for example).
for (auto BBIter = BO.getParent()->begin(); &*BBIter != &BO; ++BBIter)
if (!isGuaranteedToTransferExecutionToSuccessor(&*BBIter))
return nullptr;
// Fold constants for the predecessor block with constant incoming values.
Constant *NewC = ConstantFoldBinaryOpOperands(BO.getOpcode(), C0, C1, DL);
if (!NewC)
return nullptr;
// Make a new binop in the predecessor block with the non-constant incoming
// values.
Builder.SetInsertPoint(PredBlockBranch);
Value *NewBO = Builder.CreateBinOp(BO.getOpcode(),
Phi0->getIncomingValueForBlock(OtherBB),
Phi1->getIncomingValueForBlock(OtherBB));
if (auto *NotFoldedNewBO = dyn_cast<BinaryOperator>(NewBO))
NotFoldedNewBO->copyIRFlags(&BO);
// Replace the binop with a phi of the new values. The old phis are dead.
PHINode *NewPhi = PHINode::Create(BO.getType(), 2);
NewPhi->addIncoming(NewBO, OtherBB);
NewPhi->addIncoming(NewC, ConstBB);
return NewPhi;
}
Instruction *InstCombinerImpl::foldBinOpIntoSelectOrPhi(BinaryOperator &I) {
if (!isa<Constant>(I.getOperand(1)))
return nullptr;
if (auto *Sel = dyn_cast<SelectInst>(I.getOperand(0))) {
if (Instruction *NewSel = FoldOpIntoSelect(I, Sel))
return NewSel;
} else if (auto *PN = dyn_cast<PHINode>(I.getOperand(0))) {
if (Instruction *NewPhi = foldOpIntoPhi(I, PN))
return NewPhi;
}
return nullptr;
}
/// Given a pointer type and a constant offset, determine whether or not there
/// is a sequence of GEP indices into the pointed type that will land us at the
/// specified offset. If so, fill them into NewIndices and return the resultant
/// element type, otherwise return null.
static Type *findElementAtOffset(PointerType *PtrTy, int64_t IntOffset,
SmallVectorImpl<Value *> &NewIndices,
const DataLayout &DL) {
// Only used by visitGEPOfBitcast(), which is skipped for opaque pointers.
Type *Ty = PtrTy->getNonOpaquePointerElementType();
if (!Ty->isSized())
return nullptr;
APInt Offset(DL.getIndexTypeSizeInBits(PtrTy), IntOffset);
SmallVector<APInt> Indices = DL.getGEPIndicesForOffset(Ty, Offset);
if (!Offset.isZero())
return nullptr;
for (const APInt &Index : Indices)
NewIndices.push_back(ConstantInt::get(PtrTy->getContext(), Index));
return Ty;
}
static bool shouldMergeGEPs(GEPOperator &GEP, GEPOperator &Src) {
// If this GEP has only 0 indices, it is the same pointer as
// Src. If Src is not a trivial GEP too, don't combine
// the indices.
if (GEP.hasAllZeroIndices() && !Src.hasAllZeroIndices() &&
!Src.hasOneUse())
return false;
return true;
}
/// Return a value X such that Val = X * Scale, or null if none.
/// If the multiplication is known not to overflow, then NoSignedWrap is set.
Value *InstCombinerImpl::Descale(Value *Val, APInt Scale, bool &NoSignedWrap) {
assert(isa<IntegerType>(Val->getType()) && "Can only descale integers!");
assert(cast<IntegerType>(Val->getType())->getBitWidth() ==
Scale.getBitWidth() && "Scale not compatible with value!");
// If Val is zero or Scale is one then Val = Val * Scale.
if (match(Val, m_Zero()) || Scale == 1) {
NoSignedWrap = true;
return Val;
}
// If Scale is zero then it does not divide Val.
if (Scale.isMinValue())
return nullptr;
// Look through chains of multiplications, searching for a constant that is
// divisible by Scale. For example, descaling X*(Y*(Z*4)) by a factor of 4
// will find the constant factor 4 and produce X*(Y*Z). Descaling X*(Y*8) by
// a factor of 4 will produce X*(Y*2). The principle of operation is to bore
// down from Val:
//
// Val = M1 * X || Analysis starts here and works down
// M1 = M2 * Y || Doesn't descend into terms with more
// M2 = Z * 4 \/ than one use
//
// Then to modify a term at the bottom:
//
// Val = M1 * X
// M1 = Z * Y || Replaced M2 with Z
//
// Then to work back up correcting nsw flags.
// Op - the term we are currently analyzing. Starts at Val then drills down.
// Replaced with its descaled value before exiting from the drill down loop.
Value *Op = Val;
// Parent - initially null, but after drilling down notes where Op came from.
// In the example above, Parent is (Val, 0) when Op is M1, because M1 is the
// 0'th operand of Val.
std::pair<Instruction *, unsigned> Parent;
// Set if the transform requires a descaling at deeper levels that doesn't
// overflow.
bool RequireNoSignedWrap = false;
// Log base 2 of the scale. Negative if not a power of 2.
int32_t logScale = Scale.exactLogBase2();
for (;; Op = Parent.first->getOperand(Parent.second)) { // Drill down
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op)) {
// If Op is a constant divisible by Scale then descale to the quotient.
APInt Quotient(Scale), Remainder(Scale); // Init ensures right bitwidth.
APInt::sdivrem(CI->getValue(), Scale, Quotient, Remainder);
if (!Remainder.isMinValue())
// Not divisible by Scale.
return nullptr;
// Replace with the quotient in the parent.
Op = ConstantInt::get(CI->getType(), Quotient);
NoSignedWrap = true;
break;
}
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op)) {
if (BO->getOpcode() == Instruction::Mul) {
// Multiplication.
NoSignedWrap = BO->hasNoSignedWrap();
if (RequireNoSignedWrap && !NoSignedWrap)
return nullptr;
// There are three cases for multiplication: multiplication by exactly
// the scale, multiplication by a constant different to the scale, and
// multiplication by something else.
Value *LHS = BO->getOperand(0);
Value *RHS = BO->getOperand(1);
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
// Multiplication by a constant.
if (CI->getValue() == Scale) {
// Multiplication by exactly the scale, replace the multiplication
// by its left-hand side in the parent.
Op = LHS;
break;
}
// Otherwise drill down into the constant.
if (!Op->hasOneUse())
return nullptr;
Parent = std::make_pair(BO, 1);
continue;
}
// Multiplication by something else. Drill down into the left-hand side
// since that's where the reassociate pass puts the good stuff.
if (!Op->hasOneUse())
return nullptr;
Parent = std::make_pair(BO, 0);
continue;
}
if (logScale > 0 && BO->getOpcode() == Instruction::Shl &&
isa<ConstantInt>(BO->getOperand(1))) {
// Multiplication by a power of 2.
NoSignedWrap = BO->hasNoSignedWrap();
if (RequireNoSignedWrap && !NoSignedWrap)
return nullptr;
Value *LHS = BO->getOperand(0);
int32_t Amt = cast<ConstantInt>(BO->getOperand(1))->
getLimitedValue(Scale.getBitWidth());
// Op = LHS << Amt.
if (Amt == logScale) {
// Multiplication by exactly the scale, replace the multiplication
// by its left-hand side in the parent.
Op = LHS;
break;
}
if (Amt < logScale || !Op->hasOneUse())
return nullptr;
// Multiplication by more than the scale. Reduce the multiplying amount
// by the scale in the parent.
Parent = std::make_pair(BO, 1);
Op = ConstantInt::get(BO->getType(), Amt - logScale);
break;
}
}
if (!Op->hasOneUse())
return nullptr;
if (CastInst *Cast = dyn_cast<CastInst>(Op)) {
if (Cast->getOpcode() == Instruction::SExt) {
// Op is sign-extended from a smaller type, descale in the smaller type.
unsigned SmallSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
APInt SmallScale = Scale.trunc(SmallSize);
// Suppose Op = sext X, and we descale X as Y * SmallScale. We want to
// descale Op as (sext Y) * Scale. In order to have
// sext (Y * SmallScale) = (sext Y) * Scale
// some conditions need to hold however: SmallScale must sign-extend to
// Scale and the multiplication Y * SmallScale should not overflow.
if (SmallScale.sext(Scale.getBitWidth()) != Scale)
// SmallScale does not sign-extend to Scale.
return nullptr;
assert(SmallScale.exactLogBase2() == logScale);
// Require that Y * SmallScale must not overflow.
RequireNoSignedWrap = true;
// Drill down through the cast.
Parent = std::make_pair(Cast, 0);
Scale = SmallScale;
continue;
}
if (Cast->getOpcode() == Instruction::Trunc) {
// Op is truncated from a larger type, descale in the larger type.
// Suppose Op = trunc X, and we descale X as Y * sext Scale. Then
// trunc (Y * sext Scale) = (trunc Y) * Scale
// always holds. However (trunc Y) * Scale may overflow even if
// trunc (Y * sext Scale) does not, so nsw flags need to be cleared
// from this point up in the expression (see later).
if (RequireNoSignedWrap)
return nullptr;
// Drill down through the cast.
unsigned LargeSize = Cast->getSrcTy()->getPrimitiveSizeInBits();
Parent = std::make_pair(Cast, 0);
Scale = Scale.sext(LargeSize);
if (logScale + 1 == (int32_t)Cast->getType()->getPrimitiveSizeInBits())
logScale = -1;
assert(Scale.exactLogBase2() == logScale);
continue;
}
}
// Unsupported expression, bail out.
return nullptr;
}
// If Op is zero then Val = Op * Scale.
if (match(Op, m_Zero())) {
NoSignedWrap = true;
return Op;
}
// We know that we can successfully descale, so from here on we can safely
// modify the IR. Op holds the descaled version of the deepest term in the
// expression. NoSignedWrap is 'true' if multiplying Op by Scale is known
// not to overflow.
if (!Parent.first)
// The expression only had one term.
return Op;
// Rewrite the parent using the descaled version of its operand.
assert(Parent.first->hasOneUse() && "Drilled down when more than one use!");
assert(Op != Parent.first->getOperand(Parent.second) &&
"Descaling was a no-op?");
replaceOperand(*Parent.first, Parent.second, Op);
Worklist.push(Parent.first);
// Now work back up the expression correcting nsw flags. The logic is based
// on the following observation: if X * Y is known not to overflow as a signed
// multiplication, and Y is replaced by a value Z with smaller absolute value,
// then X * Z will not overflow as a signed multiplication either. As we work
// our way up, having NoSignedWrap 'true' means that the descaled value at the
// current level has strictly smaller absolute value than the original.
Instruction *Ancestor = Parent.first;
do {
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Ancestor)) {
// If the multiplication wasn't nsw then we can't say anything about the
// value of the descaled multiplication, and we have to clear nsw flags
// from this point on up.
bool OpNoSignedWrap = BO->hasNoSignedWrap();
NoSignedWrap &= OpNoSignedWrap;
if (NoSignedWrap != OpNoSignedWrap) {
BO->setHasNoSignedWrap(NoSignedWrap);
Worklist.push(Ancestor);
}
} else if (Ancestor->getOpcode() == Instruction::Trunc) {
// The fact that the descaled input to the trunc has smaller absolute
// value than the original input doesn't tell us anything useful about
// the absolute values of the truncations.
NoSignedWrap = false;
}
assert((Ancestor->getOpcode() != Instruction::SExt || NoSignedWrap) &&
"Failed to keep proper track of nsw flags while drilling down?");
if (Ancestor == Val)
// Got to the top, all done!
return Val;
// Move up one level in the expression.
assert(Ancestor->hasOneUse() && "Drilled down when more than one use!");
Ancestor = Ancestor->user_back();
} while (true);
}
Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
if (!isa<VectorType>(Inst.getType()))
return nullptr;
BinaryOperator::BinaryOps Opcode = Inst.getOpcode();
Value *LHS = Inst.getOperand(0), *RHS = Inst.getOperand(1);
assert(cast<VectorType>(LHS->getType())->getElementCount() ==
cast<VectorType>(Inst.getType())->getElementCount());
assert(cast<VectorType>(RHS->getType())->getElementCount() ==
cast<VectorType>(Inst.getType())->getElementCount());
// If both operands of the binop are vector concatenations, then perform the
// narrow binop on each pair of the source operands followed by concatenation
// of the results.
Value *L0, *L1, *R0, *R1;
ArrayRef<int> Mask;
if (match(LHS, m_Shuffle(m_Value(L0), m_Value(L1), m_Mask(Mask))) &&
match(RHS, m_Shuffle(m_Value(R0), m_Value(R1), m_SpecificMask(Mask))) &&
LHS->hasOneUse() && RHS->hasOneUse() &&
cast<ShuffleVectorInst>(LHS)->isConcat() &&
cast<ShuffleVectorInst>(RHS)->isConcat()) {
// This transform does not have the speculative execution constraint as
// below because the shuffle is a concatenation. The new binops are
// operating on exactly the same elements as the existing binop.
// TODO: We could ease the mask requirement to allow different undef lanes,
// but that requires an analysis of the binop-with-undef output value.
Value *NewBO0 = Builder.CreateBinOp(Opcode, L0, R0);
if (auto *BO = dyn_cast<BinaryOperator>(NewBO0))
BO->copyIRFlags(&Inst);
Value *NewBO1 = Builder.CreateBinOp(Opcode, L1, R1);
if (auto *BO = dyn_cast<BinaryOperator>(NewBO1))
BO->copyIRFlags(&Inst);
return new ShuffleVectorInst(NewBO0, NewBO1, Mask);
}
// It may not be safe to reorder shuffles and things like div, urem, etc.
// because we may trap when executing those ops on unknown vector elements.
// See PR20059.
if (!isSafeToSpeculativelyExecute(&Inst))
return nullptr;
auto createBinOpShuffle = [&](Value *X, Value *Y, ArrayRef<int> M) {
Value *XY = Builder.CreateBinOp(Opcode, X, Y);
if (auto *BO = dyn_cast<BinaryOperator>(XY))
BO->copyIRFlags(&Inst);
return new ShuffleVectorInst(XY, M);
};
// If both arguments of the binary operation are shuffles that use the same
// mask and shuffle within a single vector, move the shuffle after the binop.
Value *V1, *V2;
if (match(LHS, m_Shuffle(m_Value(V1), m_Undef(), m_Mask(Mask))) &&
match(RHS, m_Shuffle(m_Value(V2), m_Undef(), m_SpecificMask(Mask))) &&
V1->getType() == V2->getType() &&
(LHS->hasOneUse() || RHS->hasOneUse() || LHS == RHS)) {
// Op(shuffle(V1, Mask), shuffle(V2, Mask)) -> shuffle(Op(V1, V2), Mask)
return createBinOpShuffle(V1, V2, Mask);
}
// If both arguments of a commutative binop are select-shuffles that use the
// same mask with commuted operands, the shuffles are unnecessary.
if (Inst.isCommutative() &&
match(LHS, m_Shuffle(m_Value(V1), m_Value(V2), m_Mask(Mask))) &&
match(RHS,
m_Shuffle(m_Specific(V2), m_Specific(V1), m_SpecificMask(Mask)))) {
auto *LShuf = cast<ShuffleVectorInst>(LHS);
auto *RShuf = cast<ShuffleVectorInst>(RHS);
// TODO: Allow shuffles that contain undefs in the mask?
// That is legal, but it reduces undef knowledge.
// TODO: Allow arbitrary shuffles by shuffling after binop?
// That might be legal, but we have to deal with poison.
if (LShuf->isSelect() &&
!is_contained(LShuf->getShuffleMask(), UndefMaskElem) &&
RShuf->isSelect() &&
!is_contained(RShuf->getShuffleMask(), UndefMaskElem)) {
// Example:
// LHS = shuffle V1, V2, <0, 5, 6, 3>
// RHS = shuffle V2, V1, <0, 5, 6, 3>
// LHS + RHS --> (V10+V20, V21+V11, V22+V12, V13+V23) --> V1 + V2
Instruction *NewBO = BinaryOperator::Create(Opcode, V1, V2);
NewBO->copyIRFlags(&Inst);
return NewBO;
}
}
// If one argument is a shuffle within one vector and the other is a constant,
// try moving the shuffle after the binary operation. This canonicalization
// intends to move shuffles closer to other shuffles and binops closer to
// other binops, so they can be folded. It may also enable demanded elements
// transforms.
Constant *C;
auto *InstVTy = dyn_cast<FixedVectorType>(Inst.getType());
if (InstVTy &&
match(&Inst,
m_c_BinOp(m_OneUse(m_Shuffle(m_Value(V1), m_Undef(), m_Mask(Mask))),
m_ImmConstant(C))) &&
cast<FixedVectorType>(V1->getType())->getNumElements() <=
InstVTy->getNumElements()) {
assert(InstVTy->getScalarType() == V1->getType()->getScalarType() &&
"Shuffle should not change scalar type");
// Find constant NewC that has property:
// shuffle(NewC, ShMask) = C
// If such constant does not exist (example: ShMask=<0,0> and C=<1,2>)
// reorder is not possible. A 1-to-1 mapping is not required. Example:
// ShMask = <1,1,2,2> and C = <5,5,6,6> --> NewC = <undef,5,6,undef>
bool ConstOp1 = isa<Constant>(RHS);
ArrayRef<int> ShMask = Mask;
unsigned SrcVecNumElts =
cast<FixedVectorType>(V1->getType())->getNumElements();
UndefValue *UndefScalar = UndefValue::get(C->getType()->getScalarType());
SmallVector<Constant *, 16> NewVecC(SrcVecNumElts, UndefScalar);
bool MayChange = true;
unsigned NumElts = InstVTy->getNumElements();
for (unsigned I = 0; I < NumElts; ++I) {
Constant *CElt = C->getAggregateElement(I);
if (ShMask[I] >= 0) {
assert(ShMask[I] < (int)NumElts && "Not expecting narrowing shuffle");
Constant *NewCElt = NewVecC[ShMask[I]];
// Bail out if:
// 1. The constant vector contains a constant expression.
// 2. The shuffle needs an element of the constant vector that can't
// be mapped to a new constant vector.
// 3. This is a widening shuffle that copies elements of V1 into the
// extended elements (extending with undef is allowed).
if (!CElt || (!isa<UndefValue>(NewCElt) && NewCElt != CElt) ||
I >= SrcVecNumElts) {
MayChange = false;
break;
}
NewVecC[ShMask[I]] = CElt;
}
// If this is a widening shuffle, we must be able to extend with undef
// elements. If the original binop does not produce an undef in the high
// lanes, then this transform is not safe.
// Similarly for undef lanes due to the shuffle mask, we can only
// transform binops that preserve undef.
// TODO: We could shuffle those non-undef constant values into the
// result by using a constant vector (rather than an undef vector)
// as operand 1 of the new binop, but that might be too aggressive
// for target-independent shuffle creation.
if (I >= SrcVecNumElts || ShMask[I] < 0) {
Constant *MaybeUndef =
ConstOp1
? ConstantFoldBinaryOpOperands(Opcode, UndefScalar, CElt, DL)
: ConstantFoldBinaryOpOperands(Opcode, CElt, UndefScalar, DL);
if (!MaybeUndef || !match(MaybeUndef, m_Undef())) {
MayChange = false;
break;
}
}
}
if (MayChange) {
Constant *NewC = ConstantVector::get(NewVecC);
// It may not be safe to execute a binop on a vector with undef elements
// because the entire instruction can be folded to undef or create poison
// that did not exist in the original code.
if (Inst.isIntDivRem() || (Inst.isShift() && ConstOp1))
NewC = getSafeVectorConstantForBinop(Opcode, NewC, ConstOp1);
// Op(shuffle(V1, Mask), C) -> shuffle(Op(V1, NewC), Mask)
// Op(C, shuffle(V1, Mask)) -> shuffle(Op(NewC, V1), Mask)
Value *NewLHS = ConstOp1 ? V1 : NewC;
Value *NewRHS = ConstOp1 ? NewC : V1;
return createBinOpShuffle(NewLHS, NewRHS, Mask);
}
}
// Try to reassociate to sink a splat shuffle after a binary operation.
if (Inst.isAssociative() && Inst.isCommutative()) {
// Canonicalize shuffle operand as LHS.
if (isa<ShuffleVectorInst>(RHS))
std::swap(LHS, RHS);
Value *X;
ArrayRef<int> MaskC;
int SplatIndex;
Value *Y, *OtherOp;
if (!match(LHS,
m_OneUse(m_Shuffle(m_Value(X), m_Undef(), m_Mask(MaskC)))) ||
!match(MaskC, m_SplatOrUndefMask(SplatIndex)) ||
X->getType() != Inst.getType() ||
!match(RHS, m_OneUse(m_BinOp(Opcode, m_Value(Y), m_Value(OtherOp)))))
return nullptr;
// FIXME: This may not be safe if the analysis allows undef elements. By
// moving 'Y' before the splat shuffle, we are implicitly assuming
// that it is not undef/poison at the splat index.
if (isSplatValue(OtherOp, SplatIndex)) {
std::swap(Y, OtherOp);
} else if (!isSplatValue(Y, SplatIndex)) {
return nullptr;
}
// X and Y are splatted values, so perform the binary operation on those
// values followed by a splat followed by the 2nd binary operation:
// bo (splat X), (bo Y, OtherOp) --> bo (splat (bo X, Y)), OtherOp
Value *NewBO = Builder.CreateBinOp(Opcode, X, Y);
SmallVector<int, 8> NewMask(MaskC.size(), SplatIndex);
Value *NewSplat = Builder.CreateShuffleVector(NewBO, NewMask);
Instruction *R = BinaryOperator::Create(Opcode, NewSplat, OtherOp);
// Intersect FMF on both new binops. Other (poison-generating) flags are
// dropped to be safe.
if (isa<FPMathOperator>(R)) {
R->copyFastMathFlags(&Inst);
R->andIRFlags(RHS);
}
if (auto *NewInstBO = dyn_cast<BinaryOperator>(NewBO))
NewInstBO->copyIRFlags(R);
return R;
}
return nullptr;
}
/// Try to narrow the width of a binop if at least 1 operand is an extend of
/// of a value. This requires a potentially expensive known bits check to make
/// sure the narrow op does not overflow.
Instruction *InstCombinerImpl::narrowMathIfNoOverflow(BinaryOperator &BO) {
// We need at least one extended operand.
Value *Op0 = BO.getOperand(0), *Op1 = BO.getOperand(1);
// If this is a sub, we swap the operands since we always want an extension
// on the RHS. The LHS can be an extension or a constant.
if (BO.getOpcode() == Instruction::Sub)
std::swap(Op0, Op1);
Value *X;
bool IsSext = match(Op0, m_SExt(m_Value(X)));
if (!IsSext && !match(Op0, m_ZExt(m_Value(X))))
return nullptr;
// If both operands are the same extension from the same source type and we
// can eliminate at least one (hasOneUse), this might work.
CastInst::CastOps CastOpc = IsSext ? Instruction::SExt : Instruction::ZExt;
Value *Y;
if (!(match(Op1, m_ZExtOrSExt(m_Value(Y))) && X->getType() == Y->getType() &&
cast<Operator>(Op1)->getOpcode() == CastOpc &&
(Op0->hasOneUse() || Op1->hasOneUse()))) {
// If that did not match, see if we have a suitable constant operand.
// Truncating and extending must produce the same constant.
Constant *WideC;
if (!Op0->hasOneUse() || !match(Op1, m_Constant(WideC)))
return nullptr;
Constant *NarrowC = ConstantExpr::getTrunc(WideC, X->getType());
if (ConstantExpr::getCast(CastOpc, NarrowC, BO.getType()) != WideC)
return nullptr;
Y = NarrowC;
}
// Swap back now that we found our operands.
if (BO.getOpcode() == Instruction::Sub)
std::swap(X, Y);
// Both operands have narrow versions. Last step: the math must not overflow
// in the narrow width.
if (!willNotOverflow(BO.getOpcode(), X, Y, BO, IsSext))
return nullptr;
// bo (ext X), (ext Y) --> ext (bo X, Y)
// bo (ext X), C --> ext (bo X, C')
Value *NarrowBO = Builder.CreateBinOp(BO.getOpcode(), X, Y, "narrow");
if (auto *NewBinOp = dyn_cast<BinaryOperator>(NarrowBO)) {
if (IsSext)
NewBinOp->setHasNoSignedWrap();
else
NewBinOp->setHasNoUnsignedWrap();
}
return CastInst::Create(CastOpc, NarrowBO, BO.getType());
}
static bool isMergedGEPInBounds(GEPOperator &GEP1, GEPOperator &GEP2) {
// At least one GEP must be inbounds.
if (!GEP1.isInBounds() && !GEP2.isInBounds())
return false;
return (GEP1.isInBounds() || GEP1.hasAllZeroIndices()) &&
(GEP2.isInBounds() || GEP2.hasAllZeroIndices());
}
/// Thread a GEP operation with constant indices through the constant true/false
/// arms of a select.
static Instruction *foldSelectGEP(GetElementPtrInst &GEP,
InstCombiner::BuilderTy &Builder) {
if (!GEP.hasAllConstantIndices())
return nullptr;
Instruction *Sel;
Value *Cond;
Constant *TrueC, *FalseC;
if (!match(GEP.getPointerOperand(), m_Instruction(Sel)) ||
!match(Sel,
m_Select(m_Value(Cond), m_Constant(TrueC), m_Constant(FalseC))))
return nullptr;
// gep (select Cond, TrueC, FalseC), IndexC --> select Cond, TrueC', FalseC'
// Propagate 'inbounds' and metadata from existing instructions.
// Note: using IRBuilder to create the constants for efficiency.
SmallVector<Value *, 4> IndexC(GEP.indices());
bool IsInBounds = GEP.isInBounds();
Type *Ty = GEP.getSourceElementType();
Value *NewTrueC = Builder.CreateGEP(Ty, TrueC, IndexC, "", IsInBounds);
Value *NewFalseC = Builder.CreateGEP(Ty, FalseC, IndexC, "", IsInBounds);
return SelectInst::Create(Cond, NewTrueC, NewFalseC, "", nullptr, Sel);
}
Instruction *InstCombinerImpl::visitGEPOfGEP(GetElementPtrInst &GEP,
GEPOperator *Src) {
// Combine Indices - If the source pointer to this getelementptr instruction
// is a getelementptr instruction with matching element type, combine the
// indices of the two getelementptr instructions into a single instruction.
if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
return nullptr;
if (Src->getResultElementType() == GEP.getSourceElementType() &&
Src->getNumOperands() == 2 && GEP.getNumOperands() == 2 &&
Src->hasOneUse()) {
Value *GO1 = GEP.getOperand(1);
Value *SO1 = Src->getOperand(1);
if (LI) {
// Try to reassociate loop invariant GEP chains to enable LICM.
if (Loop *L = LI->getLoopFor(GEP.getParent())) {
// Reassociate the two GEPs if SO1 is variant in the loop and GO1 is
// invariant: this breaks the dependence between GEPs and allows LICM
// to hoist the invariant part out of the loop.
if (L->isLoopInvariant(GO1) && !L->isLoopInvariant(SO1)) {
// The swapped GEPs are inbounds if both original GEPs are inbounds
// and the sign of the offsets is the same. For simplicity, only
// handle both offsets being non-negative.
bool IsInBounds = Src->isInBounds() && GEP.isInBounds() &&
isKnownNonNegative(SO1, DL, 0, &AC, &GEP, &DT) &&
isKnownNonNegative(GO1, DL, 0, &AC, &GEP, &DT);
// Put NewSrc at same location as %src.
Builder.SetInsertPoint(cast<Instruction>(Src));
Value *NewSrc = Builder.CreateGEP(GEP.getSourceElementType(),
Src->getPointerOperand(), GO1,
Src->getName(), IsInBounds);
GetElementPtrInst *NewGEP = GetElementPtrInst::Create(
GEP.getSourceElementType(), NewSrc, {SO1});
NewGEP->setIsInBounds(IsInBounds);
return NewGEP;
}
}
}
}
// Note that if our source is a gep chain itself then we wait for that
// chain to be resolved before we perform this transformation. This
// avoids us creating a TON of code in some cases.
if (auto *SrcGEP = dyn_cast<GEPOperator>(Src->getOperand(0)))
if (SrcGEP->getNumOperands() == 2 && shouldMergeGEPs(*Src, *SrcGEP))
return nullptr; // Wait until our source is folded to completion.
// For constant GEPs, use a more general offset-based folding approach.
// Only do this for opaque pointers, as the result element type may change.
Type *PtrTy = Src->getType()->getScalarType();
if (PtrTy->isOpaquePointerTy() && GEP.hasAllConstantIndices() &&
(Src->hasOneUse() || Src->hasAllConstantIndices())) {
// Split Src into a variable part and a constant suffix.
gep_type_iterator GTI = gep_type_begin(*Src);
Type *BaseType = GTI.getIndexedType();
bool IsFirstType = true;
unsigned NumVarIndices = 0;
for (auto Pair : enumerate(Src->indices())) {
if (!isa<ConstantInt>(Pair.value())) {
BaseType = GTI.getIndexedType();
IsFirstType = false;
NumVarIndices = Pair.index() + 1;
}
++GTI;
}
// Determine the offset for the constant suffix of Src.
APInt Offset(DL.getIndexTypeSizeInBits(PtrTy), 0);
if (NumVarIndices != Src->getNumIndices()) {
// FIXME: getIndexedOffsetInType() does not handled scalable vectors.
if (isa<ScalableVectorType>(BaseType))
return nullptr;
SmallVector<Value *> ConstantIndices;
if (!IsFirstType)
ConstantIndices.push_back(
Constant::getNullValue(Type::getInt32Ty(GEP.getContext())));
append_range(ConstantIndices, drop_begin(Src->indices(), NumVarIndices));
Offset += DL.getIndexedOffsetInType(BaseType, ConstantIndices);
}
// Add the offset for GEP (which is fully constant).
if (!GEP.accumulateConstantOffset(DL, Offset))
return nullptr;
APInt OffsetOld = Offset;
// Convert the total offset back into indices.
SmallVector<APInt> ConstIndices =
DL.getGEPIndicesForOffset(BaseType, Offset);
if (!Offset.isZero() || (!IsFirstType && !ConstIndices[0].isZero())) {
// If both GEP are constant-indexed, and cannot be merged in either way,
// convert them to a GEP of i8.
if (Src->hasAllConstantIndices())
return isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP))
? GetElementPtrInst::CreateInBounds(
Builder.getInt8Ty(), Src->getOperand(0),
Builder.getInt(OffsetOld), GEP.getName())
: GetElementPtrInst::Create(
Builder.getInt8Ty(), Src->getOperand(0),
Builder.getInt(OffsetOld), GEP.getName());
return nullptr;
}
bool IsInBounds = isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP));
SmallVector<Value *> Indices;
append_range(Indices, drop_end(Src->indices(),
Src->getNumIndices() - NumVarIndices));
for (const APInt &Idx : drop_begin(ConstIndices, !IsFirstType)) {
Indices.push_back(ConstantInt::get(GEP.getContext(), Idx));
// Even if the total offset is inbounds, we may end up representing it
// by first performing a larger negative offset, and then a smaller
// positive one. The large negative offset might go out of bounds. Only
// preserve inbounds if all signs are the same.
IsInBounds &= Idx.isNonNegative() == ConstIndices[0].isNonNegative();
}
return IsInBounds
? GetElementPtrInst::CreateInBounds(Src->getSourceElementType(),
Src->getOperand(0), Indices,
GEP.getName())
: GetElementPtrInst::Create(Src->getSourceElementType(),
Src->getOperand(0), Indices,
GEP.getName());
}
if (Src->getResultElementType() != GEP.getSourceElementType())
return nullptr;
SmallVector<Value*, 8> Indices;
// Find out whether the last index in the source GEP is a sequential idx.
bool EndsWithSequential = false;
for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
I != E; ++I)
EndsWithSequential = I.isSequential();
// Can we combine the two pointer arithmetics offsets?
if (EndsWithSequential) {
// Replace: gep (gep %P, long B), long A, ...
// With: T = long A+B; gep %P, T, ...
Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
Value *GO1 = GEP.getOperand(1);
// If they aren't the same type, then the input hasn't been processed
// by the loop above yet (which canonicalizes sequential index types to
// intptr_t). Just avoid transforming this until the input has been
// normalized.
if (SO1->getType() != GO1->getType())
return nullptr;
Value *Sum =
simplifyAddInst(GO1, SO1, false, false, SQ.getWithInstruction(&GEP));
// Only do the combine when we are sure the cost after the
// merge is never more than that before the merge.
if (Sum == nullptr)
return nullptr;
// Update the GEP in place if possible.
if (Src->getNumOperands() == 2) {
GEP.setIsInBounds(isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP)));
replaceOperand(GEP, 0, Src->getOperand(0));
replaceOperand(GEP, 1, Sum);
return &GEP;
}
Indices.append(Src->op_begin()+1, Src->op_end()-1);
Indices.push_back(Sum);
Indices.append(GEP.op_begin()+2, GEP.op_end());
} else if (isa<Constant>(*GEP.idx_begin()) &&
cast<Constant>(*GEP.idx_begin())->isNullValue() &&
Src->getNumOperands() != 1) {
// Otherwise we can do the fold if the first index of the GEP is a zero
Indices.append(Src->op_begin()+1, Src->op_end());
Indices.append(GEP.idx_begin()+1, GEP.idx_end());
}
if (!Indices.empty())
return isMergedGEPInBounds(*Src, *cast<GEPOperator>(&GEP))
? GetElementPtrInst::CreateInBounds(
Src->getSourceElementType(), Src->getOperand(0), Indices,
GEP.getName())
: GetElementPtrInst::Create(Src->getSourceElementType(),
Src->getOperand(0), Indices,
GEP.getName());
return nullptr;
}
// Note that we may have also stripped an address space cast in between.
Instruction *InstCombinerImpl::visitGEPOfBitcast(BitCastInst *BCI,
GetElementPtrInst &GEP) {
// With opaque pointers, there is no pointer element type we can use to
// adjust the GEP type.
PointerType *SrcType = cast<PointerType>(BCI->getSrcTy());
if (SrcType->isOpaque())
return nullptr;
Type *GEPEltType = GEP.getSourceElementType();
Type *SrcEltType = SrcType->getNonOpaquePointerElementType();
Value *SrcOp = BCI->getOperand(0);
// GEP directly using the source operand if this GEP is accessing an element
// of a bitcasted pointer to vector or array of the same dimensions:
// gep (bitcast <c x ty>* X to [c x ty]*), Y, Z --> gep X, Y, Z
// gep (bitcast [c x ty]* X to <c x ty>*), Y, Z --> gep X, Y, Z
auto areMatchingArrayAndVecTypes = [](Type *ArrTy, Type *VecTy,
const DataLayout &DL) {
auto *VecVTy = cast<FixedVectorType>(VecTy);
return ArrTy->getArrayElementType() == VecVTy->getElementType() &&
ArrTy->getArrayNumElements() == VecVTy->getNumElements() &&
DL.getTypeAllocSize(ArrTy) == DL.getTypeAllocSize(VecTy);
};
if (GEP.getNumOperands() == 3 &&
((GEPEltType->isArrayTy() && isa<FixedVectorType>(SrcEltType) &&
areMatchingArrayAndVecTypes(GEPEltType, SrcEltType, DL)) ||
(isa<FixedVectorType>(GEPEltType) && SrcEltType->isArrayTy() &&
areMatchingArrayAndVecTypes(SrcEltType, GEPEltType, DL)))) {
// Create a new GEP here, as using `setOperand()` followed by
// `setSourceElementType()` won't actually update the type of the
// existing GEP Value. Causing issues if this Value is accessed when
// constructing an AddrSpaceCastInst
SmallVector<Value *, 8> Indices(GEP.indices());
Value *NGEP =
Builder.CreateGEP(SrcEltType, SrcOp, Indices, "", GEP.isInBounds());
NGEP->takeName(&GEP);
// Preserve GEP address space to satisfy users
if (NGEP->getType()->getPointerAddressSpace() != GEP.getAddressSpace())
return new AddrSpaceCastInst(NGEP, GEP.getType());
return replaceInstUsesWith(GEP, NGEP);
}
// See if we can simplify:
// X = bitcast A* to B*
// Y = gep X, <...constant indices...>
// into a gep of the original struct. This is important for SROA and alias
// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
unsigned OffsetBits = DL.getIndexTypeSizeInBits(GEP.getType());
APInt Offset(OffsetBits, 0);
// If the bitcast argument is an allocation, The bitcast is for convertion
// to actual type of allocation. Removing such bitcasts, results in having
// GEPs with i8* base and pure byte offsets. That means GEP is not aware of
// struct or array hierarchy.
// By avoiding such GEPs, phi translation and MemoryDependencyAnalysis have
// a better chance to succeed.
if (!isa<BitCastInst>(SrcOp) && GEP.accumulateConstantOffset(DL, Offset) &&
!isAllocationFn(SrcOp, &TLI)) {
// If this GEP instruction doesn't move the pointer, just replace the GEP
// with a bitcast of the real input to the dest type.
if (!Offset) {
// If the bitcast is of an allocation, and the allocation will be
// converted to match the type of the cast, don't touch this.
if (isa<AllocaInst>(SrcOp)) {
// See if the bitcast simplifies, if so, don't nuke this GEP yet.
if (Instruction *I = visitBitCast(*BCI)) {
if (I != BCI) {
I->takeName(BCI);
BCI->getParent()->getInstList().insert(BCI->getIterator(), I);
replaceInstUsesWith(*BCI, I);
}
return &GEP;
}
}
if (SrcType->getPointerAddressSpace() != GEP.getAddressSpace())
return new AddrSpaceCastInst(SrcOp, GEP.getType());
return new BitCastInst(SrcOp, GEP.getType());
}
// Otherwise, if the offset is non-zero, we need to find out if there is a
// field at Offset in 'A's type. If so, we can pull the cast through the
// GEP.
SmallVector<Value *, 8> NewIndices;
if (findElementAtOffset(SrcType, Offset.getSExtValue(), NewIndices, DL)) {
Value *NGEP = Builder.CreateGEP(SrcEltType, SrcOp, NewIndices, "",
GEP.isInBounds());
if (NGEP->getType() == GEP.getType())
return replaceInstUsesWith(GEP, NGEP);
NGEP->takeName(&GEP);
if (NGEP->getType()->getPointerAddressSpace() != GEP.getAddressSpace())
return new AddrSpaceCastInst(NGEP, GEP.getType());
return new BitCastInst(NGEP, GEP.getType());
}
}
return nullptr;
}
Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
Value *PtrOp = GEP.getOperand(0);
SmallVector<Value *, 8> Indices(GEP.indices());
Type *GEPType = GEP.getType();
Type *GEPEltType = GEP.getSourceElementType();
bool IsGEPSrcEleScalable = isa<ScalableVectorType>(GEPEltType);
if (Value *V = simplifyGEPInst(GEPEltType, PtrOp, Indices, GEP.isInBounds(),
SQ.getWithInstruction(&GEP)))
return replaceInstUsesWith(GEP, V);
// For vector geps, use the generic demanded vector support.
// Skip if GEP return type is scalable. The number of elements is unknown at
// compile-time.
if (auto *GEPFVTy = dyn_cast<FixedVectorType>(GEPType)) {
auto VWidth = GEPFVTy->getNumElements();
APInt UndefElts(VWidth, 0);
APInt AllOnesEltMask(APInt::getAllOnes(VWidth));
if (Value *V = SimplifyDemandedVectorElts(&GEP, AllOnesEltMask,
UndefElts)) {
if (V != &GEP)
return replaceInstUsesWith(GEP, V);
return &GEP;
}
// TODO: 1) Scalarize splat operands, 2) scalarize entire instruction if
// possible (decide on canonical form for pointer broadcast), 3) exploit
// undef elements to decrease demanded bits
}
// Eliminate unneeded casts for indices, and replace indices which displace
// by multiples of a zero size type with zero.
bool MadeChange = false;
// Index width may not be the same width as pointer width.
// Data layout chooses the right type based on supported integer types.
Type *NewScalarIndexTy =
DL.getIndexType(GEP.getPointerOperandType()->getScalarType());
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end(); I != E;
++I, ++GTI) {
// Skip indices into struct types.
if (GTI.isStruct())
continue;
Type *IndexTy = (*I)->getType();
Type *NewIndexType =
IndexTy->isVectorTy()
? VectorType::get(NewScalarIndexTy,
cast<VectorType>(IndexTy)->getElementCount())
: NewScalarIndexTy;
// If the element type has zero size then any index over it is equivalent
// to an index of zero, so replace it with zero if it is not zero already.
Type *EltTy = GTI.getIndexedType();
if (EltTy->isSized() && DL.getTypeAllocSize(EltTy).isZero())
if (!isa<Constant>(*I) || !match(I->get(), m_Zero())) {
*I = Constant::getNullValue(NewIndexType);
MadeChange = true;
}
if (IndexTy != NewIndexType) {
// If we are using a wider index than needed for this platform, shrink
// it to what we need. If narrower, sign-extend it to what we need.
// This explicit cast can make subsequent optimizations more obvious.
*I = Builder.CreateIntCast(*I, NewIndexType, true);
MadeChange = true;
}
}
if (MadeChange)
return &GEP;
// Check to see if the inputs to the PHI node are getelementptr instructions.
if (auto *PN = dyn_cast<PHINode>(PtrOp)) {
auto *Op1 = dyn_cast<GetElementPtrInst>(PN->getOperand(0));
if (!Op1)
return nullptr;
// Don't fold a GEP into itself through a PHI node. This can only happen
// through the back-edge of a loop. Folding a GEP into itself means that
// the value of the previous iteration needs to be stored in the meantime,
// thus requiring an additional register variable to be live, but not
// actually achieving anything (the GEP still needs to be executed once per
// loop iteration).
if (Op1 == &GEP)
return nullptr;
int DI = -1;
for (auto I = PN->op_begin()+1, E = PN->op_end(); I !=E; ++I) {
auto *Op2 = dyn_cast<GetElementPtrInst>(*I);
if (!Op2 || Op1->getNumOperands() != Op2->getNumOperands() ||
Op1->getSourceElementType() != Op2->getSourceElementType())
return nullptr;
// As for Op1 above, don't try to fold a GEP into itself.
if (Op2 == &GEP)
return nullptr;
// Keep track of the type as we walk the GEP.
Type *CurTy = nullptr;
for (unsigned J = 0, F = Op1->getNumOperands(); J != F; ++J) {
if (Op1->getOperand(J)->getType() != Op2->getOperand(J)->getType())
return nullptr;
if (Op1->getOperand(J) != Op2->getOperand(J)) {
if (DI == -1) {
// We have not seen any differences yet in the GEPs feeding the
// PHI yet, so we record this one if it is allowed to be a
// variable.
// The first two arguments can vary for any GEP, the rest have to be
// static for struct slots
if (J > 1) {
assert(CurTy && "No current type?");
if (CurTy->isStructTy())
return nullptr;
}
DI = J;
} else {
// The GEP is different by more than one input. While this could be
// extended to support GEPs that vary by more than one variable it
// doesn't make sense since it greatly increases the complexity and
// would result in an R+R+R addressing mode which no backend
// directly supports and would need to be broken into several
// simpler instructions anyway.
return nullptr;
}
}
// Sink down a layer of the type for the next iteration.
if (J > 0) {
if (J == 1) {
CurTy = Op1->getSourceElementType();
} else {
CurTy =
GetElementPtrInst::getTypeAtIndex(CurTy, Op1->getOperand(J));
}
}
}
}
// If not all GEPs are identical we'll have to create a new PHI node.
// Check that the old PHI node has only one use so that it will get
// removed.
if (DI != -1 && !PN->hasOneUse())
return nullptr;
auto *NewGEP = cast<GetElementPtrInst>(Op1->clone());
if (DI == -1) {
// All the GEPs feeding the PHI are identical. Clone one down into our
// BB so that it can be merged with the current GEP.
} else {
// All the GEPs feeding the PHI differ at a single offset. Clone a GEP
// into the current block so it can be merged, and create a new PHI to
// set that index.
PHINode *NewPN;
{
IRBuilderBase::InsertPointGuard Guard(Builder);
Builder.SetInsertPoint(PN);
NewPN = Builder.CreatePHI(Op1->getOperand(DI)->getType(),
PN->getNumOperands());
}
for (auto &I : PN->operands())
NewPN->addIncoming(cast<GEPOperator>(I)->getOperand(DI),
PN->getIncomingBlock(I));
NewGEP->setOperand(DI, NewPN);
}
GEP.getParent()->getInstList().insert(
GEP.getParent()->getFirstInsertionPt(), NewGEP);
replaceOperand(GEP, 0, NewGEP);
PtrOp = NewGEP;
}
if (auto *Src = dyn_cast<GEPOperator>(PtrOp))
if (Instruction *I = visitGEPOfGEP(GEP, Src))
return I;
// Skip if GEP source element type is scalable. The type alloc size is unknown
// at compile-time.
if (GEP.getNumIndices() == 1 && !IsGEPSrcEleScalable) {
unsigned AS = GEP.getPointerAddressSpace();
if (GEP.getOperand(1)->getType()->getScalarSizeInBits() ==
DL.getIndexSizeInBits(AS)) {
uint64_t TyAllocSize = DL.getTypeAllocSize(GEPEltType).getFixedSize();
bool Matched = false;
uint64_t C;
Value *V = nullptr;
if (TyAllocSize == 1) {
V = GEP.getOperand(1);
Matched = true;
} else if (match(GEP.getOperand(1),
m_AShr(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize == 1ULL << C)
Matched = true;
} else if (match(GEP.getOperand(1),
m_SDiv(m_Value(V), m_ConstantInt(C)))) {
if (TyAllocSize == C)
Matched = true;
}
// Canonicalize (gep i8* X, (ptrtoint Y)-(ptrtoint X)) to (bitcast Y), but
// only if both point to the same underlying object (otherwise provenance
// is not necessarily retained).
Value *Y;
Value *X = GEP.getOperand(0);
if (Matched &&
match(V, m_Sub(m_PtrToInt(m_Value(Y)), m_PtrToInt(m_Specific(X)))) &&
getUnderlyingObject(X) == getUnderlyingObject(Y))
return CastInst::CreatePointerBitCastOrAddrSpaceCast(Y, GEPType);
}
}
// We do not handle pointer-vector geps here.
if (GEPType->isVectorTy())
return nullptr;
// Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
Value *StrippedPtr = PtrOp->stripPointerCasts();
PointerType *StrippedPtrTy = cast<PointerType>(StrippedPtr->getType());
// TODO: The basic approach of these folds is not compatible with opaque
// pointers, because we can't use bitcasts as a hint for a desirable GEP
// type. Instead, we should perform canonicalization directly on the GEP
// type. For now, skip these.
if (StrippedPtr != PtrOp && !StrippedPtrTy->isOpaque()) {
bool HasZeroPointerIndex = false;
Type *StrippedPtrEltTy = StrippedPtrTy->getNonOpaquePointerElementType();
if (auto *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
HasZeroPointerIndex = C->isZero();
// Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
// into : GEP [10 x i8]* X, i32 0, ...
//
// Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
// into : GEP i8* X, ...
//
// This occurs when the program declares an array extern like "int X[];"
if (HasZeroPointerIndex) {
if (auto *CATy = dyn_cast<ArrayType>(GEPEltType)) {
// GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
if (CATy->getElementType() == StrippedPtrEltTy) {
// -> GEP i8* X, ...
SmallVector<Value *, 8> Idx(drop_begin(GEP.indices()));
GetElementPtrInst *Res = GetElementPtrInst::Create(
StrippedPtrEltTy, StrippedPtr, Idx, GEP.getName());
Res->setIsInBounds(GEP.isInBounds());
if (StrippedPtrTy->getAddressSpace() == GEP.getAddressSpace())
return Res;
// Insert Res, and create an addrspacecast.
// e.g.,
// GEP (addrspacecast i8 addrspace(1)* X to [0 x i8]*), i32 0, ...
// ->
// %0 = GEP i8 addrspace(1)* X, ...
// addrspacecast i8 addrspace(1)* %0 to i8*
return new AddrSpaceCastInst(Builder.Insert(Res), GEPType);
}
if (auto *XATy = dyn_cast<ArrayType>(StrippedPtrEltTy)) {
// GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
if (CATy->getElementType() == XATy->getElementType()) {
// -> GEP [10 x i8]* X, i32 0, ...
// At this point, we know that the cast source type is a pointer
// to an array of the same type as the destination pointer
// array. Because the array type is never stepped over (there
// is a leading zero) we can fold the cast into this GEP.
if (StrippedPtrTy->getAddressSpace() == GEP.getAddressSpace()) {
GEP.setSourceElementType(XATy);
return replaceOperand(GEP, 0, StrippedPtr);
}
// Cannot replace the base pointer directly because StrippedPtr's
// address space is different. Instead, create a new GEP followed by
// an addrspacecast.
// e.g.,
// GEP (addrspacecast [10 x i8] addrspace(1)* X to [0 x i8]*),
// i32 0, ...
// ->
// %0 = GEP [10 x i8] addrspace(1)* X, ...
// addrspacecast i8 addrspace(1)* %0 to i8*
SmallVector<Value *, 8> Idx(GEP.indices());
Value *NewGEP =
Builder.CreateGEP(StrippedPtrEltTy, StrippedPtr, Idx,
GEP.getName(), GEP.isInBounds());
return new AddrSpaceCastInst(NewGEP, GEPType);
}
}
}
} else if (GEP.getNumOperands() == 2 && !IsGEPSrcEleScalable) {
// Skip if GEP source element type is scalable. The type alloc size is
// unknown at compile-time.
// Transform things like: %t = getelementptr i32*
// bitcast ([2 x i32]* %str to i32*), i32 %V into: %t1 = getelementptr [2
// x i32]* %str, i32 0, i32 %V; bitcast
if (StrippedPtrEltTy->isArrayTy() &&
DL.getTypeAllocSize(StrippedPtrEltTy->getArrayElementType()) ==
DL.getTypeAllocSize(GEPEltType)) {
Type *IdxType = DL.getIndexType(GEPType);
Value *Idx[2] = {Constant::getNullValue(IdxType), GEP.getOperand(1)};
Value *NewGEP = Builder.CreateGEP(StrippedPtrEltTy, StrippedPtr, Idx,
GEP.getName(), GEP.isInBounds());
// V and GEP are both pointer types --> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP, GEPType);
}
// Transform things like:
// %V = mul i64 %N, 4
// %t = getelementptr i8* bitcast (i32* %arr to i8*), i32 %V
// into: %t1 = getelementptr i32* %arr, i32 %N; bitcast
if (GEPEltType->isSized() && StrippedPtrEltTy->isSized()) {
// Check that changing the type amounts to dividing the index by a scale
// factor.
uint64_t ResSize = DL.getTypeAllocSize(GEPEltType).getFixedSize();
uint64_t SrcSize = DL.getTypeAllocSize(StrippedPtrEltTy).getFixedSize();
if (ResSize && SrcSize % ResSize == 0) {
Value *Idx = GEP.getOperand(1);
unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
uint64_t Scale = SrcSize / ResSize;
// Earlier transforms ensure that the index has the right type
// according to Data Layout, which considerably simplifies the
// logic by eliminating implicit casts.
assert(Idx->getType() == DL.getIndexType(GEPType) &&
"Index type does not match the Data Layout preferences");
bool NSW;
if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
// Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
// If the multiplication NewIdx * Scale may overflow then the new
// GEP may not be "inbounds".
Value *NewGEP =
Builder.CreateGEP(StrippedPtrEltTy, StrippedPtr, NewIdx,
GEP.getName(), GEP.isInBounds() && NSW);
// The NewGEP must be pointer typed, so must the old one -> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP,
GEPType);
}
}
}
// Similarly, transform things like:
// getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
// (where tmp = 8*tmp2) into:
// getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
if (GEPEltType->isSized() && StrippedPtrEltTy->isSized() &&
StrippedPtrEltTy->isArrayTy()) {
// Check that changing to the array element type amounts to dividing the
// index by a scale factor.
uint64_t ResSize = DL.getTypeAllocSize(GEPEltType).getFixedSize();
uint64_t ArrayEltSize =
DL.getTypeAllocSize(StrippedPtrEltTy->getArrayElementType())
.getFixedSize();
if (ResSize && ArrayEltSize % ResSize == 0) {
Value *Idx = GEP.getOperand(1);
unsigned BitWidth = Idx->getType()->getPrimitiveSizeInBits();
uint64_t Scale = ArrayEltSize / ResSize;
// Earlier transforms ensure that the index has the right type
// according to the Data Layout, which considerably simplifies
// the logic by eliminating implicit casts.
assert(Idx->getType() == DL.getIndexType(GEPType) &&
"Index type does not match the Data Layout preferences");
bool NSW;
if (Value *NewIdx = Descale(Idx, APInt(BitWidth, Scale), NSW)) {
// Successfully decomposed Idx as NewIdx * Scale, form a new GEP.
// If the multiplication NewIdx * Scale may overflow then the new
// GEP may not be "inbounds".
Type *IndTy = DL.getIndexType(GEPType);
Value *Off[2] = {Constant::getNullValue(IndTy), NewIdx};
Value *NewGEP =
Builder.CreateGEP(StrippedPtrEltTy, StrippedPtr, Off,
GEP.getName(), GEP.isInBounds() && NSW);
// The NewGEP must be pointer typed, so must the old one -> BitCast
return CastInst::CreatePointerBitCastOrAddrSpaceCast(NewGEP,
GEPType);
}
}
}
}
}
// addrspacecast between types is canonicalized as a bitcast, then an
// addrspacecast. To take advantage of the below bitcast + struct GEP, look
// through the addrspacecast.
Value *ASCStrippedPtrOp = PtrOp;
if (auto *ASC = dyn_cast<AddrSpaceCastInst>(PtrOp)) {
// X = bitcast A addrspace(1)* to B addrspace(1)*
// Y = addrspacecast A addrspace(1)* to B addrspace(2)*
// Z = gep Y, <...constant indices...>
// Into an addrspacecasted GEP of the struct.
if (auto *BC = dyn_cast<BitCastInst>(ASC->getOperand(0)))
ASCStrippedPtrOp = BC;
}
if (auto *BCI = dyn_cast<BitCastInst>(ASCStrippedPtrOp))
if (Instruction *I = visitGEPOfBitcast(BCI, GEP))
return I;
if (!GEP.isInBounds()) {
unsigned IdxWidth =
DL.getIndexSizeInBits(PtrOp->getType()->getPointerAddressSpace());
APInt BasePtrOffset(IdxWidth, 0);
Value *UnderlyingPtrOp =
PtrOp->stripAndAccumulateInBoundsConstantOffsets(DL,
BasePtrOffset);
if (auto *AI = dyn_cast<AllocaInst>(UnderlyingPtrOp)) {
if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
BasePtrOffset.isNonNegative()) {
APInt AllocSize(
IdxWidth,
DL.getTypeAllocSize(AI->getAllocatedType()).getKnownMinSize());
if (BasePtrOffset.ule(AllocSize)) {
return GetElementPtrInst::CreateInBounds(
GEP.getSourceElementType(), PtrOp, Indices, GEP.getName());
}
}
}
}
if (Instruction *R = foldSelectGEP(GEP, Builder))
return R;
return nullptr;
}
static bool isNeverEqualToUnescapedAlloc(Value *V, const TargetLibraryInfo &TLI,
Instruction *AI) {
if (isa<ConstantPointerNull>(V))
return true;
if (auto *LI = dyn_cast<LoadInst>(V))
return isa<GlobalVariable>(LI->getPointerOperand());
// Two distinct allocations will never be equal.
return isAllocLikeFn(V, &TLI) && V != AI;
}
/// Given a call CB which uses an address UsedV, return true if we can prove the
/// call's only possible effect is storing to V.
static bool isRemovableWrite(CallBase &CB, Value *UsedV,
const TargetLibraryInfo &TLI) {
if (!CB.use_empty())
// TODO: add recursion if returned attribute is present
return false;
if (CB.isTerminator())
// TODO: remove implementation restriction
return false;
if (!CB.willReturn() || !CB.doesNotThrow())
return false;
// If the only possible side effect of the call is writing to the alloca,
// and the result isn't used, we can safely remove any reads implied by the
// call including those which might read the alloca itself.
Optional<MemoryLocation> Dest = MemoryLocation::getForDest(&CB, TLI);
return Dest && Dest->Ptr == UsedV;
}
static bool isAllocSiteRemovable(Instruction *AI,
SmallVectorImpl<WeakTrackingVH> &Users,
const TargetLibraryInfo &TLI) {
SmallVector<Instruction*, 4> Worklist;
const Optional<StringRef> Family = getAllocationFamily(AI, &TLI);
Worklist.push_back(AI);
do {
Instruction *PI = Worklist.pop_back_val();
for (User *U : PI->users()) {
Instruction *I = cast<Instruction>(U);
switch (I->getOpcode()) {
default:
// Give up the moment we see something we can't handle.
return false;
case Instruction::AddrSpaceCast:
case Instruction::BitCast:
case Instruction::GetElementPtr:
Users.emplace_back(I);
Worklist.push_back(I);
continue;
case Instruction::ICmp: {
ICmpInst *ICI = cast<ICmpInst>(I);
// We can fold eq/ne comparisons with null to false/true, respectively.
// We also fold comparisons in some conditions provided the alloc has
// not escaped (see isNeverEqualToUnescapedAlloc).
if (!ICI->isEquality())
return false;
unsigned OtherIndex = (ICI->getOperand(0) == PI) ? 1 : 0;
if (!isNeverEqualToUnescapedAlloc(ICI->getOperand(OtherIndex), TLI, AI))
return false;
Users.emplace_back(I);
continue;
}
case Instruction::Call:
// Ignore no-op and store intrinsics.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
return false;
case Intrinsic::memmove:
case Intrinsic::memcpy:
case Intrinsic::memset: {
MemIntrinsic *MI = cast<MemIntrinsic>(II);
if (MI->isVolatile() || MI->getRawDest() != PI)
return false;
LLVM_FALLTHROUGH;
}
case Intrinsic::assume:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::objectsize:
Users.emplace_back(I);
continue;
case Intrinsic::launder_invariant_group:
case Intrinsic::strip_invariant_group:
Users.emplace_back(I);
Worklist.push_back(I);
continue;
}
}
if (isRemovableWrite(*cast<CallBase>(I), PI, TLI)) {
Users.emplace_back(I);
continue;
}
if (getFreedOperand(cast<CallBase>(I), &TLI) == PI &&
getAllocationFamily(I, &TLI) == Family) {
assert(Family);
Users.emplace_back(I);
continue;
}
if (getReallocatedOperand(cast<CallBase>(I), &TLI) == PI &&
getAllocationFamily(I, &TLI) == Family) {
assert(Family);
Users.emplace_back(I);
Worklist.push_back(I);
continue;
}
return false;
case Instruction::Store: {
StoreInst *SI = cast<StoreInst>(I);
if (SI->isVolatile() || SI->getPointerOperand() != PI)
return false;
Users.emplace_back(I);
continue;
}
}
llvm_unreachable("missing a return?");
}
} while (!Worklist.empty());
return true;
}
Instruction *InstCombinerImpl::visitAllocSite(Instruction &MI) {
assert(isa<AllocaInst>(MI) || isRemovableAlloc(&cast<CallBase>(MI), &TLI));
// If we have a malloc call which is only used in any amount of comparisons to
// null and free calls, delete the calls and replace the comparisons with true
// or false as appropriate.
// This is based on the principle that we can substitute our own allocation
// function (which will never return null) rather than knowledge of the
// specific function being called. In some sense this can change the permitted
// outputs of a program (when we convert a malloc to an alloca, the fact that
// the allocation is now on the stack is potentially visible, for example),
// but we believe in a permissible manner.
SmallVector<WeakTrackingVH, 64> Users;
// If we are removing an alloca with a dbg.declare, insert dbg.value calls
// before each store.
SmallVector<DbgVariableIntrinsic *, 8> DVIs;
std::unique_ptr<DIBuilder> DIB;
if (isa<AllocaInst>(MI)) {
findDbgUsers(DVIs, &MI);
DIB.reset(new DIBuilder(*MI.getModule(), /*AllowUnresolved=*/false));
}
if (isAllocSiteRemovable(&MI, Users, TLI)) {
for (unsigned i = 0, e = Users.size(); i != e; ++i) {
// Lowering all @llvm.objectsize calls first because they may
// use a bitcast/GEP of the alloca we are removing.
if (!Users[i])
continue;
Instruction *I = cast<Instruction>(&*Users[i]);
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
if (II->getIntrinsicID() == Intrinsic::objectsize) {
Value *Result =
lowerObjectSizeCall(II, DL, &TLI, AA, /*MustSucceed=*/true);
replaceInstUsesWith(*I, Result);
eraseInstFromFunction(*I);
Users[i] = nullptr; // Skip examining in the next loop.
}
}
}
for (unsigned i = 0, e = Users.size(); i != e; ++i) {
if (!Users[i])
continue;
Instruction *I = cast<Instruction>(&*Users[i]);
if (ICmpInst *C = dyn_cast<ICmpInst>(I)) {
replaceInstUsesWith(*C,
ConstantInt::get(Type::getInt1Ty(C->getContext()),
C->isFalseWhenEqual()));
} else if (auto *SI = dyn_cast<StoreInst>(I)) {
for (auto *DVI : DVIs)
if (DVI->isAddressOfVariable())
ConvertDebugDeclareToDebugValue(DVI, SI, *DIB);
} else {
// Casts, GEP, or anything else: we're about to delete this instruction,
// so it can not have any valid uses.
replaceInstUsesWith(*I, PoisonValue::get(I->getType()));
}
eraseInstFromFunction(*I);
}
if (InvokeInst *II = dyn_cast<InvokeInst>(&MI)) {
// Replace invoke with a NOP intrinsic to maintain the original CFG
Module *M = II->getModule();
Function *F = Intrinsic::getDeclaration(M, Intrinsic::donothing);
InvokeInst::Create(F, II->getNormalDest(), II->getUnwindDest(),
None, "", II->getParent());
}
// Remove debug intrinsics which describe the value contained within the
// alloca. In addition to removing dbg.{declare,addr} which simply point to
// the alloca, remove dbg.value(<alloca>, ..., DW_OP_deref)'s as well, e.g.:
//
// ```
// define void @foo(i32 %0) {
// %a = alloca i32 ; Deleted.
// store i32 %0, i32* %a
// dbg.value(i32 %0, "arg0") ; Not deleted.
// dbg.value(i32* %a, "arg0", DW_OP_deref) ; Deleted.
// call void @trivially_inlinable_no_op(i32* %a)
// ret void
// }
// ```
//
// This may not be required if we stop describing the contents of allocas
// using dbg.value(<alloca>, ..., DW_OP_deref), but we currently do this in
// the LowerDbgDeclare utility.
//
// If there is a dead store to `%a` in @trivially_inlinable_no_op, the
// "arg0" dbg.value may be stale after the call. However, failing to remove
// the DW_OP_deref dbg.value causes large gaps in location coverage.
for (auto *DVI : DVIs)
if (DVI->isAddressOfVariable() || DVI->getExpression()->startsWithDeref())
DVI->eraseFromParent();
return eraseInstFromFunction(MI);
}
return nullptr;
}
/// Move the call to free before a NULL test.
///
/// Check if this free is accessed after its argument has been test
/// against NULL (property 0).
/// If yes, it is legal to move this call in its predecessor block.
///
/// The move is performed only if the block containing the call to free
/// will be removed, i.e.:
/// 1. it has only one predecessor P, and P has two successors
/// 2. it contains the call, noops, and an unconditional branch
/// 3. its successor is the same as its predecessor's successor
///
/// The profitability is out-of concern here and this function should
/// be called only if the caller knows this transformation would be
/// profitable (e.g., for code size).
static Instruction *tryToMoveFreeBeforeNullTest(CallInst &FI,
const DataLayout &DL) {
Value *Op = FI.getArgOperand(0);
BasicBlock *FreeInstrBB = FI.getParent();
BasicBlock *PredBB = FreeInstrBB->getSinglePredecessor();
// Validate part of constraint #1: Only one predecessor
// FIXME: We can extend the number of predecessor, but in that case, we
// would duplicate the call to free in each predecessor and it may
// not be profitable even for code size.
if (!PredBB)
return nullptr;
// Validate constraint #2: Does this block contains only the call to
// free, noops, and an unconditional branch?
BasicBlock *SuccBB;
Instruction *FreeInstrBBTerminator = FreeInstrBB->getTerminator();
if (!match(FreeInstrBBTerminator, m_UnconditionalBr(SuccBB)))
return nullptr;
// If there are only 2 instructions in the block, at this point,
// this is the call to free and unconditional.
// If there are more than 2 instructions, check that they are noops
// i.e., they won't hurt the performance of the generated code.
if (FreeInstrBB->size() != 2) {
for (const Instruction &Inst : FreeInstrBB->instructionsWithoutDebug()) {
if (&Inst == &FI || &Inst == FreeInstrBBTerminator)
continue;
auto *Cast = dyn_cast<CastInst>(&Inst);
if (!Cast || !Cast->isNoopCast(DL))
return nullptr;
}
}
// Validate the rest of constraint #1 by matching on the pred branch.
Instruction *TI = PredBB->getTerminator();
BasicBlock *TrueBB, *FalseBB;
ICmpInst::Predicate Pred;
if (!match(TI, m_Br(m_ICmp(Pred,
m_CombineOr(m_Specific(Op),
m_Specific(Op->stripPointerCasts())),
m_Zero()),
TrueBB, FalseBB)))
return nullptr;
if (Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)
return nullptr;
// Validate constraint #3: Ensure the null case just falls through.
if (SuccBB != (Pred == ICmpInst::ICMP_EQ ? TrueBB : FalseBB))
return nullptr;
assert(FreeInstrBB == (Pred == ICmpInst::ICMP_EQ ? FalseBB : TrueBB) &&
"Broken CFG: missing edge from predecessor to successor");
// At this point, we know that everything in FreeInstrBB can be moved
// before TI.
for (Instruction &Instr : llvm::make_early_inc_range(*FreeInstrBB)) {
if (&Instr == FreeInstrBBTerminator)
break;
Instr.moveBefore(TI);
}
assert(FreeInstrBB->size() == 1 &&
"Only the branch instruction should remain");
// Now that we've moved the call to free before the NULL check, we have to
// remove any attributes on its parameter that imply it's non-null, because
// those attributes might have only been valid because of the NULL check, and
// we can get miscompiles if we keep them. This is conservative if non-null is
// also implied by something other than the NULL check, but it's guaranteed to
// be correct, and the conservativeness won't matter in practice, since the
// attributes are irrelevant for the call to free itself and the pointer
// shouldn't be used after the call.
AttributeList Attrs = FI.getAttributes();
Attrs = Attrs.removeParamAttribute(FI.getContext(), 0, Attribute::NonNull);
Attribute Dereferenceable = Attrs.getParamAttr(0, Attribute::Dereferenceable);
if (Dereferenceable.isValid()) {
uint64_t Bytes = Dereferenceable.getDereferenceableBytes();
Attrs = Attrs.removeParamAttribute(FI.getContext(), 0,
Attribute::Dereferenceable);
Attrs = Attrs.addDereferenceableOrNullParamAttr(FI.getContext(), 0, Bytes);
}
FI.setAttributes(Attrs);
return &FI;
}
Instruction *InstCombinerImpl::visitFree(CallInst &FI, Value *Op) {
// free undef -> unreachable.
if (isa<UndefValue>(Op)) {
// Leave a marker since we can't modify the CFG here.
CreateNonTerminatorUnreachable(&FI);
return eraseInstFromFunction(FI);
}
// If we have 'free null' delete the instruction. This can happen in stl code
// when lots of inlining happens.
if (isa<ConstantPointerNull>(Op))
return eraseInstFromFunction(FI);
// If we had free(realloc(...)) with no intervening uses, then eliminate the
// realloc() entirely.
CallInst *CI = dyn_cast<CallInst>(Op);
if (CI && CI->hasOneUse())
if (Value *ReallocatedOp = getReallocatedOperand(CI, &TLI))
return eraseInstFromFunction(*replaceInstUsesWith(*CI, ReallocatedOp));
// If we optimize for code size, try to move the call to free before the null
// test so that simplify cfg can remove the empty block and dead code
// elimination the branch. I.e., helps to turn something like:
// if (foo) free(foo);
// into
// free(foo);
//
// Note that we can only do this for 'free' and not for any flavor of
// 'operator delete'; there is no 'operator delete' symbol for which we are
// permitted to invent a call, even if we're passing in a null pointer.
if (MinimizeSize) {
LibFunc Func;
if (TLI.getLibFunc(FI, Func) && TLI.has(Func) && Func == LibFunc_free)
if (Instruction *I = tryToMoveFreeBeforeNullTest(FI, DL))
return I;
}
return nullptr;
}
static bool isMustTailCall(Value *V) {
if (auto *CI = dyn_cast<CallInst>(V))
return CI->isMustTailCall();
return false;
}
Instruction *InstCombinerImpl::visitReturnInst(ReturnInst &RI) {
if (RI.getNumOperands() == 0) // ret void
return nullptr;
Value *ResultOp = RI.getOperand(0);
Type *VTy = ResultOp->getType();
if (!VTy->isIntegerTy() || isa<Constant>(ResultOp))
return nullptr;
// Don't replace result of musttail calls.
if (isMustTailCall(ResultOp))
return nullptr;
// There might be assume intrinsics dominating this return that completely
// determine the value. If so, constant fold it.
KnownBits Known = computeKnownBits(ResultOp, 0, &RI);
if (Known.isConstant())
return replaceOperand(RI, 0,
Constant::getIntegerValue(VTy, Known.getConstant()));
return nullptr;
}
// WARNING: keep in sync with SimplifyCFGOpt::simplifyUnreachable()!
Instruction *InstCombinerImpl::visitUnreachableInst(UnreachableInst &I) {
// Try to remove the previous instruction if it must lead to unreachable.
// This includes instructions like stores and "llvm.assume" that may not get
// removed by simple dead code elimination.
while (Instruction *Prev = I.getPrevNonDebugInstruction()) {
// While we theoretically can erase EH, that would result in a block that
// used to start with an EH no longer starting with EH, which is invalid.
// To make it valid, we'd need to fixup predecessors to no longer refer to
// this block, but that changes CFG, which is not allowed in InstCombine.
if (Prev->isEHPad())
return nullptr; // Can not drop any more instructions. We're done here.
if (!isGuaranteedToTransferExecutionToSuccessor(Prev))
return nullptr; // Can not drop any more instructions. We're done here.
// Otherwise, this instruction can be freely erased,
// even if it is not side-effect free.
// A value may still have uses before we process it here (for example, in
// another unreachable block), so convert those to poison.
replaceInstUsesWith(*Prev, PoisonValue::get(Prev->getType()));
eraseInstFromFunction(*Prev);
}
assert(I.getParent()->sizeWithoutDebug() == 1 && "The block is now empty.");
// FIXME: recurse into unconditional predecessors?
return nullptr;
}
Instruction *InstCombinerImpl::visitUnconditionalBranchInst(BranchInst &BI) {
assert(BI.isUnconditional() && "Only for unconditional branches.");
// If this store is the second-to-last instruction in the basic block
// (excluding debug info and bitcasts of pointers) and if the block ends with
// an unconditional branch, try to move the store to the successor block.
auto GetLastSinkableStore = [](BasicBlock::iterator BBI) {
auto IsNoopInstrForStoreMerging = [](BasicBlock::iterator BBI) {
return BBI->isDebugOrPseudoInst() ||
(isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy());
};
BasicBlock::iterator FirstInstr = BBI->getParent()->begin();
do {
if (BBI != FirstInstr)
--BBI;
} while (BBI != FirstInstr && IsNoopInstrForStoreMerging(BBI));
return dyn_cast<StoreInst>(BBI);
};
if (StoreInst *SI = GetLastSinkableStore(BasicBlock::iterator(BI)))
if (mergeStoreIntoSuccessor(*SI))
return &BI;
return nullptr;
}
Instruction *InstCombinerImpl::visitBranchInst(BranchInst &BI) {
if (BI.isUnconditional())
return visitUnconditionalBranchInst(BI);
// Change br (not X), label True, label False to: br X, label False, True
Value *X = nullptr;
if (match(&BI, m_Br(m_Not(m_Value(X)), m_BasicBlock(), m_BasicBlock())) &&
!isa<Constant>(X)) {
// Swap Destinations and condition...
BI.swapSuccessors();
return replaceOperand(BI, 0, X);
}
// If the condition is irrelevant, remove the use so that other
// transforms on the condition become more effective.
if (!isa<ConstantInt>(BI.getCondition()) &&
BI.getSuccessor(0) == BI.getSuccessor(1))
return replaceOperand(
BI, 0, ConstantInt::getFalse(BI.getCondition()->getType()));
// Canonicalize, for example, fcmp_one -> fcmp_oeq.
CmpInst::Predicate Pred;
if (match(&BI, m_Br(m_OneUse(m_FCmp(Pred, m_Value(), m_Value())),
m_BasicBlock(), m_BasicBlock())) &&
!isCanonicalPredicate(Pred)) {
// Swap destinations and condition.
CmpInst *Cond = cast<CmpInst>(BI.getCondition());
Cond->setPredicate(CmpInst::getInversePredicate(Pred));
BI.swapSuccessors();
Worklist.push(Cond);
return &BI;
}
return nullptr;
}
Instruction *InstCombinerImpl::visitSwitchInst(SwitchInst &SI) {
Value *Cond = SI.getCondition();
Value *Op0;
ConstantInt *AddRHS;
if (match(Cond, m_Add(m_Value(Op0), m_ConstantInt(AddRHS)))) {
// Change 'switch (X+4) case 1:' into 'switch (X) case -3'.
for (auto Case : SI.cases()) {
Constant *NewCase = ConstantExpr::getSub(Case.getCaseValue(), AddRHS);
assert(isa<ConstantInt>(NewCase) &&
"Result of expression should be constant");
Case.setValue(cast<ConstantInt>(NewCase));
}
return replaceOperand(SI, 0, Op0);
}
KnownBits Known = computeKnownBits(Cond, 0, &SI);
unsigned LeadingKnownZeros = Known.countMinLeadingZeros();
unsigned LeadingKnownOnes = Known.countMinLeadingOnes();
// Compute the number of leading bits we can ignore.
// TODO: A better way to determine this would use ComputeNumSignBits().
for (auto &C : SI.cases()) {
LeadingKnownZeros = std::min(
LeadingKnownZeros, C.getCaseValue()->getValue().countLeadingZeros());
LeadingKnownOnes = std::min(
LeadingKnownOnes, C.getCaseValue()->getValue().countLeadingOnes());
}
unsigned NewWidth = Known.getBitWidth() - std::max(LeadingKnownZeros, LeadingKnownOnes);
// Shrink the condition operand if the new type is smaller than the old type.
// But do not shrink to a non-standard type, because backend can't generate
// good code for that yet.
// TODO: We can make it aggressive again after fixing PR39569.
if (NewWidth > 0 && NewWidth < Known.getBitWidth() &&
shouldChangeType(Known.getBitWidth(), NewWidth)) {
IntegerType *Ty = IntegerType::get(SI.getContext(), NewWidth);
Builder.SetInsertPoint(&SI);
Value *NewCond = Builder.CreateTrunc(Cond, Ty, "trunc");
for (auto Case : SI.cases()) {
APInt TruncatedCase = Case.getCaseValue()->getValue().trunc(NewWidth);
Case.setValue(ConstantInt::get(SI.getContext(), TruncatedCase));
}
return replaceOperand(SI, 0, NewCond);
}
return nullptr;
}
Instruction *InstCombinerImpl::visitExtractValueInst(ExtractValueInst &EV) {
Value *Agg = EV.getAggregateOperand();
if (!EV.hasIndices())
return replaceInstUsesWith(EV, Agg);
if (Value *V = simplifyExtractValueInst(Agg, EV.getIndices(),
SQ.getWithInstruction(&EV)))
return replaceInstUsesWith(EV, V);
if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
// We're extracting from an insertvalue instruction, compare the indices
const unsigned *exti, *exte, *insi, *inse;
for (exti = EV.idx_begin(), insi = IV->idx_begin(),
exte = EV.idx_end(), inse = IV->idx_end();
exti != exte && insi != inse;
++exti, ++insi) {
if (*insi != *exti)
// The insert and extract both reference distinctly different elements.
// This means the extract is not influenced by the insert, and we can
// replace the aggregate operand of the extract with the aggregate
// operand of the insert. i.e., replace
// %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
// %E = extractvalue { i32, { i32 } } %I, 0
// with
// %E = extractvalue { i32, { i32 } } %A, 0
return ExtractValueInst::Create(IV->getAggregateOperand(),
EV.getIndices());
}
if (exti == exte && insi == inse)
// Both iterators are at the end: Index lists are identical. Replace
// %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
// %C = extractvalue { i32, { i32 } } %B, 1, 0
// with "i32 42"
return replaceInstUsesWith(EV, IV->getInsertedValueOperand());
if (exti == exte) {
// The extract list is a prefix of the insert list. i.e. replace
// %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
// %E = extractvalue { i32, { i32 } } %I, 1
// with
// %X = extractvalue { i32, { i32 } } %A, 1
// %E = insertvalue { i32 } %X, i32 42, 0
// by switching the order of the insert and extract (though the
// insertvalue should be left in, since it may have other uses).
Value *NewEV = Builder.CreateExtractValue(IV->getAggregateOperand(),
EV.getIndices());
return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
makeArrayRef(insi, inse));
}
if (insi == inse)
// The insert list is a prefix of the extract list
// We can simply remove the common indices from the extract and make it
// operate on the inserted value instead of the insertvalue result.
// i.e., replace
// %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
// %E = extractvalue { i32, { i32 } } %I, 1, 0
// with
// %E extractvalue { i32 } { i32 42 }, 0
return ExtractValueInst::Create(IV->getInsertedValueOperand(),
makeArrayRef(exti, exte));
}
if (WithOverflowInst *WO = dyn_cast<WithOverflowInst>(Agg)) {
// extractvalue (any_mul_with_overflow X, -1), 0 --> -X
Intrinsic::ID OvID = WO->getIntrinsicID();
if (*EV.idx_begin() == 0 &&
(OvID == Intrinsic::smul_with_overflow ||
OvID == Intrinsic::umul_with_overflow) &&
match(WO->getArgOperand(1), m_AllOnes())) {
return BinaryOperator::CreateNeg(WO->getArgOperand(0));
}
// We're extracting from an overflow intrinsic, see if we're the only user,
// which allows us to simplify multiple result intrinsics to simpler
// things that just get one value.
if (WO->hasOneUse()) {
// Check if we're grabbing only the result of a 'with overflow' intrinsic
// and replace it with a traditional binary instruction.
if (*EV.idx_begin() == 0) {
Instruction::BinaryOps BinOp = WO->getBinaryOp();
Value *LHS = WO->getLHS(), *RHS = WO->getRHS();
// Replace the old instruction's uses with poison.
replaceInstUsesWith(*WO, PoisonValue::get(WO->getType()));
eraseInstFromFunction(*WO);
return BinaryOperator::Create(BinOp, LHS, RHS);
}
assert(*EV.idx_begin() == 1 &&
"unexpected extract index for overflow inst");
// If only the overflow result is used, and the right hand side is a
// constant (or constant splat), we can remove the intrinsic by directly
// checking for overflow.
const APInt *C;
if (match(WO->getRHS(), m_APInt(C))) {
// Compute the no-wrap range for LHS given RHS=C, then construct an
// equivalent icmp, potentially using an offset.
ConstantRange NWR =
ConstantRange::makeExactNoWrapRegion(WO->getBinaryOp(), *C,
WO->getNoWrapKind());
CmpInst::Predicate Pred;
APInt NewRHSC, Offset;
NWR.getEquivalentICmp(Pred, NewRHSC, Offset);
auto *OpTy = WO->getRHS()->getType();
auto *NewLHS = WO->getLHS();
if (Offset != 0)
NewLHS = Builder.CreateAdd(NewLHS, ConstantInt::get(OpTy, Offset));
return new ICmpInst(ICmpInst::getInversePredicate(Pred), NewLHS,
ConstantInt::get(OpTy, NewRHSC));
}
}
}
if (LoadInst *L = dyn_cast<LoadInst>(Agg))
// If the (non-volatile) load only has one use, we can rewrite this to a
// load from a GEP. This reduces the size of the load. If a load is used
// only by extractvalue instructions then this either must have been
// optimized before, or it is a struct with padding, in which case we
// don't want to do the transformation as it loses padding knowledge.
if (L->isSimple() && L->hasOneUse()) {
// extractvalue has integer indices, getelementptr has Value*s. Convert.
SmallVector<Value*, 4> Indices;
// Prefix an i32 0 since we need the first element.
Indices.push_back(Builder.getInt32(0));
for (unsigned Idx : EV.indices())
Indices.push_back(Builder.getInt32(Idx));
// We need to insert these at the location of the old load, not at that of
// the extractvalue.
Builder.SetInsertPoint(L);
Value *GEP = Builder.CreateInBoundsGEP(L->getType(),
L->getPointerOperand(), Indices);
Instruction *NL = Builder.CreateLoad(EV.getType(), GEP);
// Whatever aliasing information we had for the orignal load must also
// hold for the smaller load, so propagate the annotations.
NL->setAAMetadata(L->getAAMetadata());
// Returning the load directly will cause the main loop to insert it in
// the wrong spot, so use replaceInstUsesWith().
return replaceInstUsesWith(EV, NL);
}
// We could simplify extracts from other values. Note that nested extracts may
// already be simplified implicitly by the above: extract (extract (insert) )
// will be translated into extract ( insert ( extract ) ) first and then just
// the value inserted, if appropriate. Similarly for extracts from single-use
// loads: extract (extract (load)) will be translated to extract (load (gep))
// and if again single-use then via load (gep (gep)) to load (gep).
// However, double extracts from e.g. function arguments or return values
// aren't handled yet.
return nullptr;
}
/// Return 'true' if the given typeinfo will match anything.
static bool isCatchAll(EHPersonality Personality, Constant *TypeInfo) {
switch (Personality) {
case EHPersonality::GNU_C:
case EHPersonality::GNU_C_SjLj:
case EHPersonality::Rust:
// The GCC C EH and Rust personality only exists to support cleanups, so
// it's not clear what the semantics of catch clauses are.
return false;
case EHPersonality::Unknown:
return false;
case EHPersonality::GNU_Ada:
// While __gnat_all_others_value will match any Ada exception, it doesn't
// match foreign exceptions (or didn't, before gcc-4.7).
return false;
case EHPersonality::GNU_CXX:
case EHPersonality::GNU_CXX_SjLj:
case EHPersonality::GNU_ObjC:
case EHPersonality::MSVC_X86SEH:
case EHPersonality::MSVC_TableSEH:
case EHPersonality::MSVC_CXX:
case EHPersonality::CoreCLR:
case EHPersonality::Wasm_CXX:
case EHPersonality::XL_CXX:
return TypeInfo->isNullValue();
}
llvm_unreachable("invalid enum");
}
static bool shorter_filter(const Value *LHS, const Value *RHS) {
return
cast<ArrayType>(LHS->getType())->getNumElements()
<
cast<ArrayType>(RHS->getType())->getNumElements();
}
Instruction *InstCombinerImpl::visitLandingPadInst(LandingPadInst &LI) {
// The logic here should be correct for any real-world personality function.
// However if that turns out not to be true, the offending logic can always
// be conditioned on the personality function, like the catch-all logic is.
EHPersonality Personality =
classifyEHPersonality(LI.getParent()->getParent()->getPersonalityFn());
// Simplify the list of clauses, eg by removing repeated catch clauses
// (these are often created by inlining).
bool MakeNewInstruction = false; // If true, recreate using the following:
SmallVector<Constant *, 16> NewClauses; // - Clauses for the new instruction;
bool CleanupFlag = LI.isCleanup(); // - The new instruction is a cleanup.
SmallPtrSet<Value *, 16> AlreadyCaught; // Typeinfos known caught already.
for (unsigned i = 0, e = LI.getNumClauses(); i != e; ++i) {
bool isLastClause = i + 1 == e;
if (LI.isCatch(i)) {
// A catch clause.
Constant *CatchClause = LI.getClause(i);
Constant *TypeInfo = CatchClause->stripPointerCasts();
// If we already saw this clause, there is no point in having a second
// copy of it.
if (AlreadyCaught.insert(TypeInfo).second) {
// This catch clause was not already seen.
NewClauses.push_back(CatchClause);
} else {
// Repeated catch clause - drop the redundant copy.
MakeNewInstruction = true;
}
// If this is a catch-all then there is no point in keeping any following
// clauses or marking the landingpad as having a cleanup.
if (isCatchAll(Personality, TypeInfo)) {
if (!isLastClause)
MakeNewInstruction = true;
CleanupFlag = false;
break;
}
} else {
// A filter clause. If any of the filter elements were already caught
// then they can be dropped from the filter. It is tempting to try to
// exploit the filter further by saying that any typeinfo that does not
// occur in the filter can't be caught later (and thus can be dropped).
// However this would be wrong, since typeinfos can match without being
// equal (for example if one represents a C++ class, and the other some
// class derived from it).
assert(LI.isFilter(i) && "Unsupported landingpad clause!");
Constant *FilterClause = LI.getClause(i);
ArrayType *FilterType = cast<ArrayType>(FilterClause->getType());
unsigned NumTypeInfos = FilterType->getNumElements();
// An empty filter catches everything, so there is no point in keeping any
// following clauses or marking the landingpad as having a cleanup. By
// dealing with this case here the following code is made a bit simpler.
if (!NumTypeInfos) {
NewClauses.push_back(FilterClause);
if (!isLastClause)
MakeNewInstruction = true;
CleanupFlag = false;
break;
}
bool MakeNewFilter = false; // If true, make a new filter.
SmallVector<Constant *, 16> NewFilterElts; // New elements.
if (isa<ConstantAggregateZero>(FilterClause)) {
// Not an empty filter - it contains at least one null typeinfo.
assert(NumTypeInfos > 0 && "Should have handled empty filter already!");
Constant *TypeInfo =
Constant::getNullValue(FilterType->getElementType());
// If this typeinfo is a catch-all then the filter can never match.
if (isCatchAll(Personality, TypeInfo)) {
// Throw the filter away.
MakeNewInstruction = true;
continue;
}
// There is no point in having multiple copies of this typeinfo, so
// discard all but the first copy if there is more than one.
NewFilterElts.push_back(TypeInfo);
if (NumTypeInfos > 1)
MakeNewFilter = true;
} else {
ConstantArray *Filter = cast<ConstantArray>(FilterClause);
SmallPtrSet<Value *, 16> SeenInFilter; // For uniquing the elements.
NewFilterElts.reserve(NumTypeInfos);
// Remove any filter elements that were already caught or that already
// occurred in the filter. While there, see if any of the elements are
// catch-alls. If so, the filter can be discarded.
bool SawCatchAll = false;
for (unsigned j = 0; j != NumTypeInfos; ++j) {
Constant *Elt = Filter->getOperand(j);
Constant *TypeInfo = Elt->stripPointerCasts();
if (isCatchAll(Personality, TypeInfo)) {
// This element is a catch-all. Bail out, noting this fact.
SawCatchAll = true;
break;
}
// Even if we've seen a type in a catch clause, we don't want to
// remove it from the filter. An unexpected type handler may be
// set up for a call site which throws an exception of the same
// type caught. In order for the exception thrown by the unexpected
// handler to propagate correctly, the filter must be correctly
// described for the call site.
//
// Example:
//
// void unexpected() { throw 1;}
// void foo() throw (int) {
// std::set_unexpected(unexpected);
// try {
// throw 2.0;
// } catch (int i) {}
// }
// There is no point in having multiple copies of the same typeinfo in
// a filter, so only add it if we didn't already.
if (SeenInFilter.insert(TypeInfo).second)
NewFilterElts.push_back(cast<Constant>(Elt));
}
// A filter containing a catch-all cannot match anything by definition.
if (SawCatchAll) {
// Throw the filter away.
MakeNewInstruction = true;
continue;
}
// If we dropped something from the filter, make a new one.
if (NewFilterElts.size() < NumTypeInfos)
MakeNewFilter = true;
}
if (MakeNewFilter) {
FilterType = ArrayType::get(FilterType->getElementType(),
NewFilterElts.size());
FilterClause = ConstantArray::get(FilterType, NewFilterElts);
MakeNewInstruction = true;
}
NewClauses.push_back(FilterClause);
// If the new filter is empty then it will catch everything so there is
// no point in keeping any following clauses or marking the landingpad
// as having a cleanup. The case of the original filter being empty was
// already handled above.
if (MakeNewFilter && !NewFilterElts.size()) {
assert(MakeNewInstruction && "New filter but not a new instruction!");
CleanupFlag = false;
break;
}
}
}
// If several filters occur in a row then reorder them so that the shortest
// filters come first (those with the smallest number of elements). This is
// advantageous because shorter filters are more likely to match, speeding up
// unwinding, but mostly because it increases the effectiveness of the other
// filter optimizations below.
for (unsigned i = 0, e = NewClauses.size(); i + 1 < e; ) {
unsigned j;
// Find the maximal 'j' s.t. the range [i, j) consists entirely of filters.
for (j = i; j != e; ++j)
if (!isa<ArrayType>(NewClauses[j]->getType()))
break;
// Check whether the filters are already sorted by length. We need to know
// if sorting them is actually going to do anything so that we only make a
// new landingpad instruction if it does.
for (unsigned k = i; k + 1 < j; ++k)
if (shorter_filter(NewClauses[k+1], NewClauses[k])) {
// Not sorted, so sort the filters now. Doing an unstable sort would be
// correct too but reordering filters pointlessly might confuse users.
std::stable_sort(NewClauses.begin() + i, NewClauses.begin() + j,
shorter_filter);
MakeNewInstruction = true;
break;
}
// Look for the next batch of filters.
i = j + 1;
}
// If typeinfos matched if and only if equal, then the elements of a filter L
// that occurs later than a filter F could be replaced by the intersection of
// the elements of F and L. In reality two typeinfos can match without being
// equal (for example if one represents a C++ class, and the other some class
// derived from it) so it would be wrong to perform this transform in general.
// However the transform is correct and useful if F is a subset of L. In that
// case L can be replaced by F, and thus removed altogether since repeating a
// filter is pointless. So here we look at all pairs of filters F and L where
// L follows F in the list of clauses, and remove L if every element of F is
// an element of L. This can occur when inlining C++ functions with exception
// specifications.
for (unsigned i = 0; i + 1 < NewClauses.size(); ++i) {
// Examine each filter in turn.
Value *Filter = NewClauses[i];
ArrayType *FTy = dyn_cast<ArrayType>(Filter->getType());
if (!FTy)
// Not a filter - skip it.
continue;
unsigned FElts = FTy->getNumElements();
// Examine each filter following this one. Doing this backwards means that
// we don't have to worry about filters disappearing under us when removed.
for (unsigned j = NewClauses.size() - 1; j != i; --j) {
Value *LFilter = NewClauses[j];
ArrayType *LTy = dyn_cast<ArrayType>(LFilter->getType());
if (!LTy)
// Not a filter - skip it.
continue;
// If Filter is a subset of LFilter, i.e. every element of Filter is also
// an element of LFilter, then discard LFilter.
SmallVectorImpl<Constant *>::iterator J = NewClauses.begin() + j;
// If Filter is empty then it is a subset of LFilter.
if (!FElts) {
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
// Move on to the next filter.
continue;
}
unsigned LElts = LTy->getNumElements();
// If Filter is longer than LFilter then it cannot be a subset of it.
if (FElts > LElts)
// Move on to the next filter.
continue;
// At this point we know that LFilter has at least one element.
if (isa<ConstantAggregateZero>(LFilter)) { // LFilter only contains zeros.
// Filter is a subset of LFilter iff Filter contains only zeros (as we
// already know that Filter is not longer than LFilter).
if (isa<ConstantAggregateZero>(Filter)) {
assert(FElts <= LElts && "Should have handled this case earlier!");
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
}
// Move on to the next filter.
continue;
}
ConstantArray *LArray = cast<ConstantArray>(LFilter);
if (isa<ConstantAggregateZero>(Filter)) { // Filter only contains zeros.
// Since Filter is non-empty and contains only zeros, it is a subset of
// LFilter iff LFilter contains a zero.
assert(FElts > 0 && "Should have eliminated the empty filter earlier!");
for (unsigned l = 0; l != LElts; ++l)
if (LArray->getOperand(l)->isNullValue()) {
// LFilter contains a zero - discard it.
NewClauses.erase(J);
MakeNewInstruction = true;
break;
}
// Move on to the next filter.
continue;
}
// At this point we know that both filters are ConstantArrays. Loop over
// operands to see whether every element of Filter is also an element of
// LFilter. Since filters tend to be short this is probably faster than
// using a method that scales nicely.
ConstantArray *FArray = cast<ConstantArray>(Filter);
bool AllFound = true;
for (unsigned f = 0; f != FElts; ++f) {
Value *FTypeInfo = FArray->getOperand(f)->stripPointerCasts();
AllFound = false;
for (unsigned l = 0; l != LElts; ++l) {
Value *LTypeInfo = LArray->getOperand(l)->stripPointerCasts();
if (LTypeInfo == FTypeInfo) {
AllFound = true;
break;
}
}
if (!AllFound)
break;
}
if (AllFound) {
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
}
// Move on to the next filter.
}
}
// If we changed any of the clauses, replace the old landingpad instruction
// with a new one.
if (MakeNewInstruction) {
LandingPadInst *NLI = LandingPadInst::Create(LI.getType(),
NewClauses.size());
for (unsigned i = 0, e = NewClauses.size(); i != e; ++i)
NLI->addClause(NewClauses[i]);
// A landing pad with no clauses must have the cleanup flag set. It is
// theoretically possible, though highly unlikely, that we eliminated all
// clauses. If so, force the cleanup flag to true.
if (NewClauses.empty())
CleanupFlag = true;
NLI->setCleanup(CleanupFlag);
return NLI;
}
// Even if none of the clauses changed, we may nonetheless have understood
// that the cleanup flag is pointless. Clear it if so.
if (LI.isCleanup() != CleanupFlag) {
assert(!CleanupFlag && "Adding a cleanup, not removing one?!");
LI.setCleanup(CleanupFlag);
return &LI;
}
return nullptr;
}
Value *
InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
// Try to push freeze through instructions that propagate but don't produce
// poison as far as possible. If an operand of freeze follows three
// conditions 1) one-use, 2) does not produce poison, and 3) has all but one
// guaranteed-non-poison operands then push the freeze through to the one
// operand that is not guaranteed non-poison. The actual transform is as
// follows.
// Op1 = ... ; Op1 can be posion
// Op0 = Inst(Op1, NonPoisonOps...) ; Op0 has only one use and only have
// ; single guaranteed-non-poison operands
// ... = Freeze(Op0)
// =>
// Op1 = ...
// Op1.fr = Freeze(Op1)
// ... = Inst(Op1.fr, NonPoisonOps...)
auto *OrigOp = OrigFI.getOperand(0);
auto *OrigOpInst = dyn_cast<Instruction>(OrigOp);
// While we could change the other users of OrigOp to use freeze(OrigOp), that
// potentially reduces their optimization potential, so let's only do this iff
// the OrigOp is only used by the freeze.
if (!OrigOpInst || !OrigOpInst->hasOneUse() || isa<PHINode>(OrigOp))
return nullptr;
// We can't push the freeze through an instruction which can itself create
// poison. If the only source of new poison is flags, we can simply
// strip them (since we know the only use is the freeze and nothing can
// benefit from them.)
if (canCreateUndefOrPoison(cast<Operator>(OrigOp), /*ConsiderFlags*/ false))
return nullptr;
// If operand is guaranteed not to be poison, there is no need to add freeze
// to the operand. So we first find the operand that is not guaranteed to be
// poison.
Use *MaybePoisonOperand = nullptr;
for (Use &U : OrigOpInst->operands()) {
if (isGuaranteedNotToBeUndefOrPoison(U.get()))
continue;
if (!MaybePoisonOperand)
MaybePoisonOperand = &U;
else
return nullptr;
}
OrigOpInst->dropPoisonGeneratingFlags();
// If all operands are guaranteed to be non-poison, we can drop freeze.
if (!MaybePoisonOperand)
return OrigOp;
Builder.SetInsertPoint(OrigOpInst);
auto *FrozenMaybePoisonOperand = Builder.CreateFreeze(
MaybePoisonOperand->get(), MaybePoisonOperand->get()->getName() + ".fr");
replaceUse(*MaybePoisonOperand, FrozenMaybePoisonOperand);
return OrigOp;
}
Instruction *InstCombinerImpl::foldFreezeIntoRecurrence(FreezeInst &FI,
PHINode *PN) {
// Detect whether this is a recurrence with a start value and some number of
// backedge values. We'll check whether we can push the freeze through the
// backedge values (possibly dropping poison flags along the way) until we
// reach the phi again. In that case, we can move the freeze to the start
// value.
Use *StartU = nullptr;
SmallVector<Value *> Worklist;
for (Use &U : PN->incoming_values()) {
if (DT.dominates(PN->getParent(), PN->getIncomingBlock(U))) {
// Add backedge value to worklist.
Worklist.push_back(U.get());
continue;
}
// Don't bother handling multiple start values.
if (StartU)
return nullptr;
StartU = &U;
}
if (!StartU || Worklist.empty())
return nullptr; // Not a recurrence.
Value *StartV = StartU->get();
BasicBlock *StartBB = PN->getIncomingBlock(*StartU);
bool StartNeedsFreeze = !isGuaranteedNotToBeUndefOrPoison(StartV);
// We can't insert freeze if the the start value is the result of the
// terminator (e.g. an invoke).
if (StartNeedsFreeze && StartBB->getTerminator() == StartV)
return nullptr;
SmallPtrSet<Value *, 32> Visited;
SmallVector<Instruction *> DropFlags;
while (!Worklist.empty()) {
Value *V = Worklist.pop_back_val();
if (!Visited.insert(V).second)
continue;
if (Visited.size() > 32)
return nullptr; // Limit the total number of values we inspect.
// Assume that PN is non-poison, because it will be after the transform.
if (V == PN || isGuaranteedNotToBeUndefOrPoison(V))
continue;
Instruction *I = dyn_cast<Instruction>(V);
if (!I || canCreateUndefOrPoison(cast<Operator>(I),
/*ConsiderFlags*/ false))
return nullptr;
DropFlags.push_back(I);
append_range(Worklist, I->operands());
}
for (Instruction *I : DropFlags)
I->dropPoisonGeneratingFlags();
if (StartNeedsFreeze) {
Builder.SetInsertPoint(StartBB->getTerminator());
Value *FrozenStartV = Builder.CreateFreeze(StartV,
StartV->getName() + ".fr");
replaceUse(*StartU, FrozenStartV);
}
return replaceInstUsesWith(FI, PN);
}
bool InstCombinerImpl::freezeOtherUses(FreezeInst &FI) {
Value *Op = FI.getOperand(0);
if (isa<Constant>(Op) || Op->hasOneUse())
return false;
// Move the freeze directly after the definition of its operand, so that
// it dominates the maximum number of uses. Note that it may not dominate
// *all* uses if the operand is an invoke/callbr and the use is in a phi on
// the normal/default destination. This is why the domination check in the
// replacement below is still necessary.
Instruction *MoveBefore = nullptr;
if (isa<Argument>(Op)) {
MoveBefore = &FI.getFunction()->getEntryBlock().front();
while (isa<AllocaInst>(MoveBefore))
MoveBefore = MoveBefore->getNextNode();
} else if (auto *PN = dyn_cast<PHINode>(Op)) {
MoveBefore = PN->getParent()->getFirstNonPHI();
} else if (auto *II = dyn_cast<InvokeInst>(Op)) {
MoveBefore = II->getNormalDest()->getFirstNonPHI();
} else if (auto *CB = dyn_cast<CallBrInst>(Op)) {
MoveBefore = CB->getDefaultDest()->getFirstNonPHI();
} else {
auto *I = cast<Instruction>(Op);
assert(!I->isTerminator() && "Cannot be a terminator");
MoveBefore = I->getNextNode();
}
bool Changed = false;
if (&FI != MoveBefore) {
FI.moveBefore(MoveBefore);
Changed = true;
}
Op->replaceUsesWithIf(&FI, [&](Use &U) -> bool {
bool Dominates = DT.dominates(&FI, U);
Changed |= Dominates;
return Dominates;
});
return Changed;
}
Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
Value *Op0 = I.getOperand(0);
if (Value *V = simplifyFreezeInst(Op0, SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
// freeze (phi const, x) --> phi const, (freeze x)
if (auto *PN = dyn_cast<PHINode>(Op0)) {
if (Instruction *NV = foldOpIntoPhi(I, PN))
return NV;
if (Instruction *NV = foldFreezeIntoRecurrence(I, PN))
return NV;
}
if (Value *NI = pushFreezeToPreventPoisonFromPropagating(I))
return replaceInstUsesWith(I, NI);
// If I is freeze(undef), check its uses and fold it to a fixed constant.
// - or: pick -1
// - select's condition: if the true value is constant, choose it by making
// the condition true.
// - default: pick 0
//
// Note that this transform is intentionally done here rather than
// via an analysis in InstSimplify or at individual user sites. That is
// because we must produce the same value for all uses of the freeze -
// it's the reason "freeze" exists!
//
// TODO: This could use getBinopAbsorber() / getBinopIdentity() to avoid
// duplicating logic for binops at least.
auto getUndefReplacement = [&I](Type *Ty) {
Constant *BestValue = nullptr;
Constant *NullValue = Constant::getNullValue(Ty);
for (const auto *U : I.users()) {
Constant *C = NullValue;
if (match(U, m_Or(m_Value(), m_Value())))
C = ConstantInt::getAllOnesValue(Ty);
else if (match(U, m_Select(m_Specific(&I), m_Constant(), m_Value())))
C = ConstantInt::getTrue(Ty);
if (!BestValue)
BestValue = C;
else if (BestValue != C)
BestValue = NullValue;
}
assert(BestValue && "Must have at least one use");
return BestValue;
};
if (match(Op0, m_Undef()))
return replaceInstUsesWith(I, getUndefReplacement(I.getType()));
Constant *C;
if (match(Op0, m_Constant(C)) && C->containsUndefOrPoisonElement()) {
Constant *ReplaceC = getUndefReplacement(I.getType()->getScalarType());
return replaceInstUsesWith(I, Constant::replaceUndefsWith(C, ReplaceC));
}
// Replace uses of Op with freeze(Op).
if (freezeOtherUses(I))
return &I;
return nullptr;
}
/// Check for case where the call writes to an otherwise dead alloca. This
/// shows up for unused out-params in idiomatic C/C++ code. Note that this
/// helper *only* analyzes the write; doesn't check any other legality aspect.
static bool SoleWriteToDeadLocal(Instruction *I, TargetLibraryInfo &TLI) {
auto *CB = dyn_cast<CallBase>(I);
if (!CB)
// TODO: handle e.g. store to alloca here - only worth doing if we extend
// to allow reload along used path as described below. Otherwise, this
// is simply a store to a dead allocation which will be removed.
return false;
Optional<MemoryLocation> Dest = MemoryLocation::getForDest(CB, TLI);
if (!Dest)
return false;
auto *AI = dyn_cast<AllocaInst>(getUnderlyingObject(Dest->Ptr));
if (!AI)
// TODO: allow malloc?
return false;
// TODO: allow memory access dominated by move point? Note that since AI
// could have a reference to itself captured by the call, we would need to
// account for cycles in doing so.
SmallVector<const User *> AllocaUsers;
SmallPtrSet<const User *, 4> Visited;
auto pushUsers = [&](const Instruction &I) {
for (const User *U : I.users()) {
if (Visited.insert(U).second)
AllocaUsers.push_back(U);
}
};
pushUsers(*AI);
while (!AllocaUsers.empty()) {
auto *UserI = cast<Instruction>(AllocaUsers.pop_back_val());
if (isa<BitCastInst>(UserI) || isa<GetElementPtrInst>(UserI) ||
isa<AddrSpaceCastInst>(UserI)) {
pushUsers(*UserI);
continue;
}
if (UserI == CB)
continue;
// TODO: support lifetime.start/end here
return false;
}
return true;
}
/// Try to move the specified instruction from its current block into the
/// beginning of DestBlock, which can only happen if it's safe to move the
/// instruction past all of the instructions between it and the end of its
/// block.
static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock,
TargetLibraryInfo &TLI) {
BasicBlock *SrcBlock = I->getParent();
// Cannot move control-flow-involving, volatile loads, vaarg, etc.
if (isa<PHINode>(I) || I->isEHPad() || I->mayThrow() || !I->willReturn() ||
I->isTerminator())
return false;
// Do not sink static or dynamic alloca instructions. Static allocas must
// remain in the entry block, and dynamic allocas must not be sunk in between
// a stacksave / stackrestore pair, which would incorrectly shorten its
// lifetime.
if (isa<AllocaInst>(I))
return false;
// Do not sink into catchswitch blocks.
if (isa<CatchSwitchInst>(DestBlock->getTerminator()))
return false;
// Do not sink convergent call instructions.
if (auto *CI = dyn_cast<CallInst>(I)) {
if (CI->isConvergent())
return false;
}
// Unless we can prove that the memory write isn't visibile except on the
// path we're sinking to, we must bail.
if (I->mayWriteToMemory()) {
if (!SoleWriteToDeadLocal(I, TLI))
return false;
}
// We can only sink load instructions if there is nothing between the load and
// the end of block that could change the value.
if (I->mayReadFromMemory()) {
// We don't want to do any sophisticated alias analysis, so we only check
// the instructions after I in I's parent block if we try to sink to its
// successor block.
if (DestBlock->getUniquePredecessor() != I->getParent())
return false;
for (BasicBlock::iterator Scan = std::next(I->getIterator()),
E = I->getParent()->end();
Scan != E; ++Scan)
if (Scan->mayWriteToMemory())
return false;
}
I->dropDroppableUses([DestBlock](const Use *U) {
if (auto *I = dyn_cast<Instruction>(U->getUser()))
return I->getParent() != DestBlock;
return true;
});
/// FIXME: We could remove droppable uses that are not dominated by
/// the new position.
BasicBlock::iterator InsertPos = DestBlock->getFirstInsertionPt();
I->moveBefore(&*InsertPos);
++NumSunkInst;
// Also sink all related debug uses from the source basic block. Otherwise we
// get debug use before the def. Attempt to salvage debug uses first, to
// maximise the range variables have location for. If we cannot salvage, then
// mark the location undef: we know it was supposed to receive a new location
// here, but that computation has been sunk.
SmallVector<DbgVariableIntrinsic *, 2> DbgUsers;
findDbgUsers(DbgUsers, I);
// Process the sinking DbgUsers in reverse order, as we only want to clone the
// last appearing debug intrinsic for each given variable.
SmallVector<DbgVariableIntrinsic *, 2> DbgUsersToSink;
for (DbgVariableIntrinsic *DVI : DbgUsers)
if (DVI->getParent() == SrcBlock)
DbgUsersToSink.push_back(DVI);
llvm::sort(DbgUsersToSink,
[](auto *A, auto *B) { return B->comesBefore(A); });
SmallVector<DbgVariableIntrinsic *, 2> DIIClones;
SmallSet<DebugVariable, 4> SunkVariables;
for (auto User : DbgUsersToSink) {
// A dbg.declare instruction should not be cloned, since there can only be
// one per variable fragment. It should be left in the original place
// because the sunk instruction is not an alloca (otherwise we could not be
// here).
if (isa<DbgDeclareInst>(User))
continue;
DebugVariable DbgUserVariable =
DebugVariable(User->getVariable(), User->getExpression(),
User->getDebugLoc()->getInlinedAt());
if (!SunkVariables.insert(DbgUserVariable).second)
continue;
DIIClones.emplace_back(cast<DbgVariableIntrinsic>(User->clone()));
if (isa<DbgDeclareInst>(User) && isa<CastInst>(I))
DIIClones.back()->replaceVariableLocationOp(I, I->getOperand(0));
LLVM_DEBUG(dbgs() << "CLONE: " << *DIIClones.back() << '\n');
}
// Perform salvaging without the clones, then sink the clones.
if (!DIIClones.empty()) {
salvageDebugInfoForDbgValues(*I, DbgUsers);
// The clones are in reverse order of original appearance, reverse again to
// maintain the original order.
for (auto &DIIClone : llvm::reverse(DIIClones)) {
DIIClone->insertBefore(&*InsertPos);
LLVM_DEBUG(dbgs() << "SINK: " << *DIIClone << '\n');
}
}
return true;
}
bool InstCombinerImpl::run() {
while (!Worklist.isEmpty()) {
// Walk deferred instructions in reverse order, and push them to the
// worklist, which means they'll end up popped from the worklist in-order.
while (Instruction *I = Worklist.popDeferred()) {
// Check to see if we can DCE the instruction. We do this already here to
// reduce the number of uses and thus allow other folds to trigger.
// Note that eraseInstFromFunction() may push additional instructions on
// the deferred worklist, so this will DCE whole instruction chains.
if (isInstructionTriviallyDead(I, &TLI)) {
eraseInstFromFunction(*I);
++NumDeadInst;
continue;
}
Worklist.push(I);
}
Instruction *I = Worklist.removeOne();
if (I == nullptr) continue; // skip null values.
// Check to see if we can DCE the instruction.
if (isInstructionTriviallyDead(I, &TLI)) {
eraseInstFromFunction(*I);
++NumDeadInst;
continue;
}
if (!DebugCounter::shouldExecute(VisitCounter))
continue;
// Instruction isn't dead, see if we can constant propagate it.
if (!I->use_empty() &&
(I->getNumOperands() == 0 || isa<Constant>(I->getOperand(0)))) {
if (Constant *C = ConstantFoldInstruction(I, DL, &TLI)) {
LLVM_DEBUG(dbgs() << "IC: ConstFold to: " << *C << " from: " << *I
<< '\n');
// Add operands to the worklist.
replaceInstUsesWith(*I, C);
++NumConstProp;
if (isInstructionTriviallyDead(I, &TLI))
eraseInstFromFunction(*I);
MadeIRChange = true;
continue;
}
}
// See if we can trivially sink this instruction to its user if we can
// prove that the successor is not executed more frequently than our block.
// Return the UserBlock if successful.
auto getOptionalSinkBlockForInst =
[this](Instruction *I) -> Optional<BasicBlock *> {
if (!EnableCodeSinking)
return None;
BasicBlock *BB = I->getParent();
BasicBlock *UserParent = nullptr;
unsigned NumUsers = 0;
for (auto *U : I->users()) {
if (U->isDroppable())
continue;
if (NumUsers > MaxSinkNumUsers)
return None;
Instruction *UserInst = cast<Instruction>(U);
// Special handling for Phi nodes - get the block the use occurs in.
if (PHINode *PN = dyn_cast<PHINode>(UserInst)) {
for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) {
if (PN->getIncomingValue(i) == I) {
// Bail out if we have uses in different blocks. We don't do any
// sophisticated analysis (i.e finding NearestCommonDominator of
// these use blocks).
if (UserParent && UserParent != PN->getIncomingBlock(i))
return None;
UserParent = PN->getIncomingBlock(i);
}
}
assert(UserParent && "expected to find user block!");
} else {
if (UserParent && UserParent != UserInst->getParent())
return None;
UserParent = UserInst->getParent();
}
// Make sure these checks are done only once, naturally we do the checks
// the first time we get the userparent, this will save compile time.
if (NumUsers == 0) {
// Try sinking to another block. If that block is unreachable, then do
// not bother. SimplifyCFG should handle it.
if (UserParent == BB || !DT.isReachableFromEntry(UserParent))
return None;
auto *Term = UserParent->getTerminator();
// See if the user is one of our successors that has only one
// predecessor, so that we don't have to split the critical edge.
// Another option where we can sink is a block that ends with a
// terminator that does not pass control to other block (such as
// return or unreachable or resume). In this case:
// - I dominates the User (by SSA form);
// - the User will be executed at most once.
// So sinking I down to User is always profitable or neutral.
if (UserParent->getUniquePredecessor() != BB && !succ_empty(Term))
return None;
assert(DT.dominates(BB, UserParent) && "Dominance relation broken?");
}
NumUsers++;
}
// No user or only has droppable users.
if (!UserParent)
return None;
return UserParent;
};
auto OptBB = getOptionalSinkBlockForInst(I);
if (OptBB) {
auto *UserParent = *OptBB;
// Okay, the CFG is simple enough, try to sink this instruction.
if (TryToSinkInstruction(I, UserParent, TLI)) {
LLVM_DEBUG(dbgs() << "IC: Sink: " << *I << '\n');
MadeIRChange = true;
// We'll add uses of the sunk instruction below, but since
// sinking can expose opportunities for it's *operands* add
// them to the worklist
for (Use &U : I->operands())
if (Instruction *OpI = dyn_cast<Instruction>(U.get()))
Worklist.push(OpI);
}
}
// Now that we have an instruction, try combining it to simplify it.
Builder.SetInsertPoint(I);
Builder.CollectMetadataToCopy(
I, {LLVMContext::MD_dbg, LLVMContext::MD_annotation});
#ifndef NDEBUG
std::string OrigI;
#endif
LLVM_DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
LLVM_DEBUG(dbgs() << "IC: Visiting: " << OrigI << '\n');
if (Instruction *Result = visit(*I)) {
++NumCombined;
// Should we replace the old instruction with a new one?
if (Result != I) {
LLVM_DEBUG(dbgs() << "IC: Old = " << *I << '\n'
<< " New = " << *Result << '\n');
Result->copyMetadata(*I,
{LLVMContext::MD_dbg, LLVMContext::MD_annotation});
// Everything uses the new instruction now.
I->replaceAllUsesWith(Result);
// Move the name to the new instruction first.
Result->takeName(I);
// Insert the new instruction into the basic block...
BasicBlock *InstParent = I->getParent();
BasicBlock::iterator InsertPos = I->getIterator();
// Are we replace a PHI with something that isn't a PHI, or vice versa?
if (isa<PHINode>(Result) != isa<PHINode>(I)) {
// We need to fix up the insertion point.
if (isa<PHINode>(I)) // PHI -> Non-PHI
InsertPos = InstParent->getFirstInsertionPt();
else // Non-PHI -> PHI
InsertPos = InstParent->getFirstNonPHI()->getIterator();
}
InstParent->getInstList().insert(InsertPos, Result);
// Push the new instruction and any users onto the worklist.
Worklist.pushUsersToWorkList(*Result);
Worklist.push(Result);
eraseInstFromFunction(*I);
} else {
LLVM_DEBUG(dbgs() << "IC: Mod = " << OrigI << '\n'
<< " New = " << *I << '\n');
// If the instruction was modified, it's possible that it is now dead.
// if so, remove it.
if (isInstructionTriviallyDead(I, &TLI)) {
eraseInstFromFunction(*I);
} else {
Worklist.pushUsersToWorkList(*I);
Worklist.push(I);
}
}
MadeIRChange = true;
}
}
Worklist.zap();
return MadeIRChange;
}
// Track the scopes used by !alias.scope and !noalias. In a function, a
// @llvm.experimental.noalias.scope.decl is only useful if that scope is used
// by both sets. If not, the declaration of the scope can be safely omitted.
// The MDNode of the scope can be omitted as well for the instructions that are
// part of this function. We do not do that at this point, as this might become
// too time consuming to do.
class AliasScopeTracker {
SmallPtrSet<const MDNode *, 8> UsedAliasScopesAndLists;
SmallPtrSet<const MDNode *, 8> UsedNoAliasScopesAndLists;
public:
void analyse(Instruction *I) {
// This seems to be faster than checking 'mayReadOrWriteMemory()'.
if (!I->hasMetadataOtherThanDebugLoc())
return;
auto Track = [](Metadata *ScopeList, auto &Container) {
const auto *MDScopeList = dyn_cast_or_null<MDNode>(ScopeList);
if (!MDScopeList || !Container.insert(MDScopeList).second)
return;
for (auto &MDOperand : MDScopeList->operands())
if (auto *MDScope = dyn_cast<MDNode>(MDOperand))
Container.insert(MDScope);
};
Track(I->getMetadata(LLVMContext::MD_alias_scope), UsedAliasScopesAndLists);
Track(I->getMetadata(LLVMContext::MD_noalias), UsedNoAliasScopesAndLists);
}
bool isNoAliasScopeDeclDead(Instruction *Inst) {
NoAliasScopeDeclInst *Decl = dyn_cast<NoAliasScopeDeclInst>(Inst);
if (!Decl)
return false;
assert(Decl->use_empty() &&
"llvm.experimental.noalias.scope.decl in use ?");
const MDNode *MDSL = Decl->getScopeList();
assert(MDSL->getNumOperands() == 1 &&
"llvm.experimental.noalias.scope should refer to a single scope");
auto &MDOperand = MDSL->getOperand(0);
if (auto *MD = dyn_cast<MDNode>(MDOperand))
return !UsedAliasScopesAndLists.contains(MD) ||
!UsedNoAliasScopesAndLists.contains(MD);
// Not an MDNode ? throw away.
return true;
}
};
/// Populate the IC worklist from a function, by walking it in depth-first
/// order and adding all reachable code to the worklist.
///
/// This has a couple of tricks to make the code faster and more powerful. In
/// particular, we constant fold and DCE instructions as we go, to avoid adding
/// them to the worklist (this significantly speeds up instcombine on code where
/// many instructions are dead or constant). Additionally, if we find a branch
/// whose condition is a known constant, we only visit the reachable successors.
static bool prepareICWorklistFromFunction(Function &F, const DataLayout &DL,
const TargetLibraryInfo *TLI,
InstructionWorklist &ICWorklist) {
bool MadeIRChange = false;
SmallPtrSet<BasicBlock *, 32> Visited;
SmallVector<BasicBlock*, 256> Worklist;
Worklist.push_back(&F.front());
SmallVector<Instruction *, 128> InstrsForInstructionWorklist;
DenseMap<Constant *, Constant *> FoldedConstants;
AliasScopeTracker SeenAliasScopes;
do {
BasicBlock *BB = Worklist.pop_back_val();
// We have now visited this block! If we've already been here, ignore it.
if (!Visited.insert(BB).second)
continue;
for (Instruction &Inst : llvm::make_early_inc_range(*BB)) {
// ConstantProp instruction if trivially constant.
if (!Inst.use_empty() &&
(Inst.getNumOperands() == 0 || isa<Constant>(Inst.getOperand(0))))
if (Constant *C = ConstantFoldInstruction(&Inst, DL, TLI)) {
LLVM_DEBUG(dbgs() << "IC: ConstFold to: " << *C << " from: " << Inst
<< '\n');
Inst.replaceAllUsesWith(C);
++NumConstProp;
if (isInstructionTriviallyDead(&Inst, TLI))
Inst.eraseFromParent();
MadeIRChange = true;
continue;
}
// See if we can constant fold its operands.
for (Use &U : Inst.operands()) {
if (!isa<ConstantVector>(U) && !isa<ConstantExpr>(U))
continue;
auto *C = cast<Constant>(U);
Constant *&FoldRes = FoldedConstants[C];
if (!FoldRes)
FoldRes = ConstantFoldConstant(C, DL, TLI);
if (FoldRes != C) {
LLVM_DEBUG(dbgs() << "IC: ConstFold operand of: " << Inst
<< "\n Old = " << *C
<< "\n New = " << *FoldRes << '\n');
U = FoldRes;
MadeIRChange = true;
}
}
// Skip processing debug and pseudo intrinsics in InstCombine. Processing
// these call instructions consumes non-trivial amount of time and
// provides no value for the optimization.
if (!Inst.isDebugOrPseudoInst()) {
InstrsForInstructionWorklist.push_back(&Inst);
SeenAliasScopes.analyse(&Inst);
}
}
// Recursively visit successors. If this is a branch or switch on a
// constant, only visit the reachable successor.
Instruction *TI = BB->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
Worklist.push_back(ReachableBB);
continue;
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
Worklist.push_back(SI->findCaseValue(Cond)->getCaseSuccessor());
continue;
}
}
append_range(Worklist, successors(TI));
} while (!Worklist.empty());
// Remove instructions inside unreachable blocks. This prevents the
// instcombine code from having to deal with some bad special cases, and
// reduces use counts of instructions.
for (BasicBlock &BB : F) {
if (Visited.count(&BB))
continue;
unsigned NumDeadInstInBB;
unsigned NumDeadDbgInstInBB;
std::tie(NumDeadInstInBB, NumDeadDbgInstInBB) =
removeAllNonTerminatorAndEHPadInstructions(&BB);
MadeIRChange |= NumDeadInstInBB + NumDeadDbgInstInBB > 0;
NumDeadInst += NumDeadInstInBB;
}
// Once we've found all of the instructions to add to instcombine's worklist,
// add them in reverse order. This way instcombine will visit from the top
// of the function down. This jives well with the way that it adds all uses
// of instructions to the worklist after doing a transformation, thus avoiding
// some N^2 behavior in pathological cases.
ICWorklist.reserve(InstrsForInstructionWorklist.size());
for (Instruction *Inst : reverse(InstrsForInstructionWorklist)) {
// DCE instruction if trivially dead. As we iterate in reverse program
// order here, we will clean up whole chains of dead instructions.
if (isInstructionTriviallyDead(Inst, TLI) ||
SeenAliasScopes.isNoAliasScopeDeclDead(Inst)) {
++NumDeadInst;
LLVM_DEBUG(dbgs() << "IC: DCE: " << *Inst << '\n');
salvageDebugInfo(*Inst);
Inst->eraseFromParent();
MadeIRChange = true;
continue;
}
ICWorklist.push(Inst);
}
return MadeIRChange;
}
static bool combineInstructionsOverFunction(
Function &F, InstructionWorklist &Worklist, AliasAnalysis *AA,
AssumptionCache &AC, TargetLibraryInfo &TLI, TargetTransformInfo &TTI,
DominatorTree &DT, OptimizationRemarkEmitter &ORE, BlockFrequencyInfo *BFI,
ProfileSummaryInfo *PSI, unsigned MaxIterations, LoopInfo *LI) {
auto &DL = F.getParent()->getDataLayout();
MaxIterations = std::min(MaxIterations, LimitMaxIterations.getValue());
/// Builder - This is an IRBuilder that automatically inserts new
/// instructions into the worklist when they are created.
IRBuilder<TargetFolder, IRBuilderCallbackInserter> Builder(
F.getContext(), TargetFolder(DL),
IRBuilderCallbackInserter([&Worklist, &AC](Instruction *I) {
Worklist.add(I);
if (auto *Assume = dyn_cast<AssumeInst>(I))
AC.registerAssumption(Assume);
}));
// Lower dbg.declare intrinsics otherwise their value may be clobbered
// by instcombiner.
bool MadeIRChange = false;
if (ShouldLowerDbgDeclare)
MadeIRChange = LowerDbgDeclare(F);
// Iterate while there is work to do.
unsigned Iteration = 0;
while (true) {
++NumWorklistIterations;
++Iteration;
if (Iteration > InfiniteLoopDetectionThreshold) {
report_fatal_error(
"Instruction Combining seems stuck in an infinite loop after " +
Twine(InfiniteLoopDetectionThreshold) + " iterations.");
}
if (Iteration > MaxIterations) {
LLVM_DEBUG(dbgs() << "\n\n[IC] Iteration limit #" << MaxIterations
<< " on " << F.getName()
<< " reached; stopping before reaching a fixpoint\n");
break;
}
LLVM_DEBUG(dbgs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on "
<< F.getName() << "\n");
MadeIRChange |= prepareICWorklistFromFunction(F, DL, &TLI, Worklist);
InstCombinerImpl IC(Worklist, Builder, F.hasMinSize(), AA, AC, TLI, TTI, DT,
ORE, BFI, PSI, DL, LI);
IC.MaxArraySizeForCombine = MaxArraySize;
if (!IC.run())
break;
MadeIRChange = true;
}
return MadeIRChange;
}
InstCombinePass::InstCombinePass() : MaxIterations(LimitMaxIterations) {}
InstCombinePass::InstCombinePass(unsigned MaxIterations)
: MaxIterations(MaxIterations) {}
PreservedAnalyses InstCombinePass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
auto *LI = AM.getCachedResult<LoopAnalysis>(F);
auto *AA = &AM.getResult<AAManager>(F);
auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
ProfileSummaryInfo *PSI =
MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
auto *BFI = (PSI && PSI->hasProfileSummary()) ?
&AM.getResult<BlockFrequencyAnalysis>(F) : nullptr;
if (!combineInstructionsOverFunction(F, Worklist, AA, AC, TLI, TTI, DT, ORE,
BFI, PSI, MaxIterations, LI))
// No changes, all analyses are preserved.
return PreservedAnalyses::all();
// Mark all the analyses that instcombine updates as preserved.
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
void InstructionCombiningPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<BasicAAWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addRequired<ProfileSummaryInfoWrapperPass>();
LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
}
bool InstructionCombiningPass::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
// Required analyses.
auto AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &ORE = getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
// Optional analyses.
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
ProfileSummaryInfo *PSI =
&getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
BlockFrequencyInfo *BFI =
(PSI && PSI->hasProfileSummary()) ?
&getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() :
nullptr;
return combineInstructionsOverFunction(F, Worklist, AA, AC, TLI, TTI, DT, ORE,
BFI, PSI, MaxIterations, LI);
}
char InstructionCombiningPass::ID = 0;
InstructionCombiningPass::InstructionCombiningPass()
: FunctionPass(ID), MaxIterations(InstCombineDefaultMaxIterations) {
initializeInstructionCombiningPassPass(*PassRegistry::getPassRegistry());
}
InstructionCombiningPass::InstructionCombiningPass(unsigned MaxIterations)
: FunctionPass(ID), MaxIterations(MaxIterations) {
initializeInstructionCombiningPassPass(*PassRegistry::getPassRegistry());
}
INITIALIZE_PASS_BEGIN(InstructionCombiningPass, "instcombine",
"Combine redundant instructions", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LazyBlockFrequencyInfoPass)
INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
INITIALIZE_PASS_END(InstructionCombiningPass, "instcombine",
"Combine redundant instructions", false, false)
// Initialization Routines
void llvm::initializeInstCombine(PassRegistry &Registry) {
initializeInstructionCombiningPassPass(Registry);
}
void LLVMInitializeInstCombine(LLVMPassRegistryRef R) {
initializeInstructionCombiningPassPass(*unwrap(R));
}
FunctionPass *llvm::createInstructionCombiningPass() {
return new InstructionCombiningPass();
}
FunctionPass *llvm::createInstructionCombiningPass(unsigned MaxIterations) {
return new InstructionCombiningPass(MaxIterations);
}
void LLVMAddInstructionCombiningPass(LLVMPassManagerRef PM) {
unwrap(PM)->add(createInstructionCombiningPass());
}