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//===- ConstantFold.cpp - LLVM constant folder ----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements folding of constants for LLVM. This implements the
// (internal) ConstantFold.h interface, which is used by the
// ConstantExpr::get* methods to automatically fold constants when possible.
//
// The current constant folding implementation is implemented in two pieces: the
// pieces that don't need DataLayout, and the pieces that do. This is to avoid
// a dependence in IR on Target.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/ConstantFold.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;
using namespace llvm::PatternMatch;
//===----------------------------------------------------------------------===//
// ConstantFold*Instruction Implementations
//===----------------------------------------------------------------------===//
/// This function determines which opcode to use to fold two constant cast
/// expressions together. It uses CastInst::isEliminableCastPair to determine
/// the opcode. Consequently its just a wrapper around that function.
/// Determine if it is valid to fold a cast of a cast
static unsigned
foldConstantCastPair(
unsigned opc, ///< opcode of the second cast constant expression
ConstantExpr *Op, ///< the first cast constant expression
Type *DstTy ///< destination type of the first cast
) {
assert(Op && Op->isCast() && "Can't fold cast of cast without a cast!");
assert(DstTy && DstTy->isFirstClassType() && "Invalid cast destination type");
assert(CastInst::isCast(opc) && "Invalid cast opcode");
// The types and opcodes for the two Cast constant expressions
Type *SrcTy = Op->getOperand(0)->getType();
Type *MidTy = Op->getType();
Instruction::CastOps firstOp = Instruction::CastOps(Op->getOpcode());
Instruction::CastOps secondOp = Instruction::CastOps(opc);
// Assume that pointers are never more than 64 bits wide, and only use this
// for the middle type. Otherwise we could end up folding away illegal
// bitcasts between address spaces with different sizes.
IntegerType *FakeIntPtrTy = Type::getInt64Ty(DstTy->getContext());
// Let CastInst::isEliminableCastPair do the heavy lifting.
return CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, DstTy,
nullptr, FakeIntPtrTy, nullptr);
}
static Constant *FoldBitCast(Constant *V, Type *DestTy) {
Type *SrcTy = V->getType();
if (SrcTy == DestTy)
return V; // no-op cast
// Handle casts from one vector constant to another. We know that the src
// and dest type have the same size (otherwise its an illegal cast).
if (VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) {
if (V->isAllOnesValue())
return Constant::getAllOnesValue(DestTy);
// Canonicalize scalar-to-vector bitcasts into vector-to-vector bitcasts
// This allows for other simplifications (although some of them
// can only be handled by Analysis/ConstantFolding.cpp).
if (isa<ConstantInt>(V) || isa<ConstantFP>(V))
return ConstantExpr::getBitCast(ConstantVector::get(V), DestPTy);
return nullptr;
}
// Handle integral constant input.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
// See note below regarding the PPC_FP128 restriction.
if (DestTy->isFloatingPointTy() && !DestTy->isPPC_FP128Ty())
return ConstantFP::get(DestTy->getContext(),
APFloat(DestTy->getFltSemantics(),
CI->getValue()));
// Otherwise, can't fold this (vector?)
return nullptr;
}
// Handle ConstantFP input: FP -> Integral.
if (ConstantFP *FP = dyn_cast<ConstantFP>(V)) {
// PPC_FP128 is really the sum of two consecutive doubles, where the first
// double is always stored first in memory, regardless of the target
// endianness. The memory layout of i128, however, depends on the target
// endianness, and so we can't fold this without target endianness
// information. This should instead be handled by
// Analysis/ConstantFolding.cpp
if (FP->getType()->isPPC_FP128Ty())
return nullptr;
// Make sure dest type is compatible with the folded integer constant.
if (!DestTy->isIntegerTy())
return nullptr;
return ConstantInt::get(FP->getContext(),
FP->getValueAPF().bitcastToAPInt());
}
return nullptr;
}
/// V is an integer constant which only has a subset of its bytes used.
/// The bytes used are indicated by ByteStart (which is the first byte used,
/// counting from the least significant byte) and ByteSize, which is the number
/// of bytes used.
///
/// This function analyzes the specified constant to see if the specified byte
/// range can be returned as a simplified constant. If so, the constant is
/// returned, otherwise null is returned.
static Constant *ExtractConstantBytes(Constant *C, unsigned ByteStart,
unsigned ByteSize) {
assert(C->getType()->isIntegerTy() &&
(cast<IntegerType>(C->getType())->getBitWidth() & 7) == 0 &&
"Non-byte sized integer input");
[[maybe_unused]] unsigned CSize = cast<IntegerType>(C->getType())->getBitWidth()/8;
assert(ByteSize && "Must be accessing some piece");
assert(ByteStart+ByteSize <= CSize && "Extracting invalid piece from input");
assert(ByteSize != CSize && "Should not extract everything");
// Constant Integers are simple.
if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
APInt V = CI->getValue();
if (ByteStart)
V.lshrInPlace(ByteStart*8);
V = V.trunc(ByteSize*8);
return ConstantInt::get(CI->getContext(), V);
}
// In the input is a constant expr, we might be able to recursively simplify.
// If not, we definitely can't do anything.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE) return nullptr;
switch (CE->getOpcode()) {
default: return nullptr;
case Instruction::Shl: {
ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
if (!Amt)
return nullptr;
APInt ShAmt = Amt->getValue();
// Cannot analyze non-byte shifts.
if ((ShAmt & 7) != 0)
return nullptr;
ShAmt.lshrInPlace(3);
// If the extract is known to be all zeros, return zero.
if (ShAmt.uge(ByteStart + ByteSize))
return Constant::getNullValue(
IntegerType::get(CE->getContext(), ByteSize * 8));
// If the extract is known to be fully in the input, extract it.
if (ShAmt.ule(ByteStart))
return ExtractConstantBytes(CE->getOperand(0),
ByteStart - ShAmt.getZExtValue(), ByteSize);
// TODO: Handle the 'partially zero' case.
return nullptr;
}
}
}
static Constant *foldMaybeUndesirableCast(unsigned opc, Constant *V,
Type *DestTy) {
return ConstantExpr::isDesirableCastOp(opc)
? ConstantExpr::getCast(opc, V, DestTy)
: ConstantFoldCastInstruction(opc, V, DestTy);
}
Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
Type *DestTy) {
if (isa<PoisonValue>(V))
return PoisonValue::get(DestTy);
if (isa<UndefValue>(V)) {
// zext(undef) = 0, because the top bits will be zero.
// sext(undef) = 0, because the top bits will all be the same.
// [us]itofp(undef) = 0, because the result value is bounded.
if (opc == Instruction::ZExt || opc == Instruction::SExt ||
opc == Instruction::UIToFP || opc == Instruction::SIToFP)
return Constant::getNullValue(DestTy);
return UndefValue::get(DestTy);
}
if (V->isNullValue() && !DestTy->isX86_MMXTy() && !DestTy->isX86_AMXTy() &&
opc != Instruction::AddrSpaceCast)
return Constant::getNullValue(DestTy);
// If the cast operand is a constant expression, there's a few things we can
// do to try to simplify it.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (CE->isCast()) {
// Try hard to fold cast of cast because they are often eliminable.
if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy))
return foldMaybeUndesirableCast(newOpc, CE->getOperand(0), DestTy);
}
}
// If the cast operand is a constant vector, perform the cast by
// operating on each element. In the cast of bitcasts, the element
// count may be mismatched; don't attempt to handle that here.
if ((isa<ConstantVector>(V) || isa<ConstantDataVector>(V)) &&
DestTy->isVectorTy() &&
cast<FixedVectorType>(DestTy)->getNumElements() ==
cast<FixedVectorType>(V->getType())->getNumElements()) {
VectorType *DestVecTy = cast<VectorType>(DestTy);
Type *DstEltTy = DestVecTy->getElementType();
// Fast path for splatted constants.
if (Constant *Splat = V->getSplatValue()) {
Constant *Res = foldMaybeUndesirableCast(opc, Splat, DstEltTy);
if (!Res)
return nullptr;
return ConstantVector::getSplat(
cast<VectorType>(DestTy)->getElementCount(), Res);
}
SmallVector<Constant *, 16> res;
Type *Ty = IntegerType::get(V->getContext(), 32);
for (unsigned i = 0,
e = cast<FixedVectorType>(V->getType())->getNumElements();
i != e; ++i) {
Constant *C = ConstantExpr::getExtractElement(V, ConstantInt::get(Ty, i));
Constant *Casted = foldMaybeUndesirableCast(opc, C, DstEltTy);
if (!Casted)
return nullptr;
res.push_back(Casted);
}
return ConstantVector::get(res);
}
// We actually have to do a cast now. Perform the cast according to the
// opcode specified.
switch (opc) {
default:
llvm_unreachable("Failed to cast constant expression");
case Instruction::FPTrunc:
case Instruction::FPExt:
if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
bool ignored;
APFloat Val = FPC->getValueAPF();
Val.convert(DestTy->getFltSemantics(), APFloat::rmNearestTiesToEven,
&ignored);
return ConstantFP::get(V->getContext(), Val);
}
return nullptr; // Can't fold.
case Instruction::FPToUI:
case Instruction::FPToSI:
if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
const APFloat &V = FPC->getValueAPF();
bool ignored;
uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
APSInt IntVal(DestBitWidth, opc == Instruction::FPToUI);
if (APFloat::opInvalidOp ==
V.convertToInteger(IntVal, APFloat::rmTowardZero, &ignored)) {
// Undefined behavior invoked - the destination type can't represent
// the input constant.
return PoisonValue::get(DestTy);
}
return ConstantInt::get(FPC->getContext(), IntVal);
}
return nullptr; // Can't fold.
case Instruction::UIToFP:
case Instruction::SIToFP:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
const APInt &api = CI->getValue();
APFloat apf(DestTy->getFltSemantics(),
APInt::getZero(DestTy->getPrimitiveSizeInBits()));
apf.convertFromAPInt(api, opc==Instruction::SIToFP,
APFloat::rmNearestTiesToEven);
return ConstantFP::get(V->getContext(), apf);
}
return nullptr;
case Instruction::ZExt:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth();
return ConstantInt::get(V->getContext(),
CI->getValue().zext(BitWidth));
}
return nullptr;
case Instruction::SExt:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth();
return ConstantInt::get(V->getContext(),
CI->getValue().sext(BitWidth));
}
return nullptr;
case Instruction::Trunc: {
if (V->getType()->isVectorTy())
return nullptr;
uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
return ConstantInt::get(V->getContext(),
CI->getValue().trunc(DestBitWidth));
}
// The input must be a constantexpr. See if we can simplify this based on
// the bytes we are demanding. Only do this if the source and dest are an
// even multiple of a byte.
if ((DestBitWidth & 7) == 0 &&
(cast<IntegerType>(V->getType())->getBitWidth() & 7) == 0)
if (Constant *Res = ExtractConstantBytes(V, 0, DestBitWidth / 8))
return Res;
return nullptr;
}
case Instruction::BitCast:
return FoldBitCast(V, DestTy);
case Instruction::AddrSpaceCast:
case Instruction::IntToPtr:
case Instruction::PtrToInt:
return nullptr;
}
}
Constant *llvm::ConstantFoldSelectInstruction(Constant *Cond,
Constant *V1, Constant *V2) {
// Check for i1 and vector true/false conditions.
if (Cond->isNullValue()) return V2;
if (Cond->isAllOnesValue()) return V1;
// If the condition is a vector constant, fold the result elementwise.
if (ConstantVector *CondV = dyn_cast<ConstantVector>(Cond)) {
auto *V1VTy = CondV->getType();
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(CondV->getContext(), 32);
for (unsigned i = 0, e = V1VTy->getNumElements(); i != e; ++i) {
Constant *V;
Constant *V1Element = ConstantExpr::getExtractElement(V1,
ConstantInt::get(Ty, i));
Constant *V2Element = ConstantExpr::getExtractElement(V2,
ConstantInt::get(Ty, i));
auto *Cond = cast<Constant>(CondV->getOperand(i));
if (isa<PoisonValue>(Cond)) {
V = PoisonValue::get(V1Element->getType());
} else if (V1Element == V2Element) {
V = V1Element;
} else if (isa<UndefValue>(Cond)) {
V = isa<UndefValue>(V1Element) ? V1Element : V2Element;
} else {
if (!isa<ConstantInt>(Cond)) break;
V = Cond->isNullValue() ? V2Element : V1Element;
}
Result.push_back(V);
}
// If we were able to build the vector, return it.
if (Result.size() == V1VTy->getNumElements())
return ConstantVector::get(Result);
}
if (isa<PoisonValue>(Cond))
return PoisonValue::get(V1->getType());
if (isa<UndefValue>(Cond)) {
if (isa<UndefValue>(V1)) return V1;
return V2;
}
if (V1 == V2) return V1;
if (isa<PoisonValue>(V1))
return V2;
if (isa<PoisonValue>(V2))
return V1;
// If the true or false value is undef, we can fold to the other value as
// long as the other value isn't poison.
auto NotPoison = [](Constant *C) {
if (isa<PoisonValue>(C))
return false;
// TODO: We can analyze ConstExpr by opcode to determine if there is any
// possibility of poison.
if (isa<ConstantExpr>(C))
return false;
if (isa<ConstantInt>(C) || isa<GlobalVariable>(C) || isa<ConstantFP>(C) ||
isa<ConstantPointerNull>(C) || isa<Function>(C))
return true;
if (C->getType()->isVectorTy())
return !C->containsPoisonElement() && !C->containsConstantExpression();
// TODO: Recursively analyze aggregates or other constants.
return false;
};
if (isa<UndefValue>(V1) && NotPoison(V2)) return V2;
if (isa<UndefValue>(V2) && NotPoison(V1)) return V1;
return nullptr;
}
Constant *llvm::ConstantFoldExtractElementInstruction(Constant *Val,
Constant *Idx) {
auto *ValVTy = cast<VectorType>(Val->getType());
// extractelt poison, C -> poison
// extractelt C, undef -> poison
if (isa<PoisonValue>(Val) || isa<UndefValue>(Idx))
return PoisonValue::get(ValVTy->getElementType());
// extractelt undef, C -> undef
if (isa<UndefValue>(Val))
return UndefValue::get(ValVTy->getElementType());
auto *CIdx = dyn_cast<ConstantInt>(Idx);
if (!CIdx)
return nullptr;
if (auto *ValFVTy = dyn_cast<FixedVectorType>(Val->getType())) {
// ee({w,x,y,z}, wrong_value) -> poison
if (CIdx->uge(ValFVTy->getNumElements()))
return PoisonValue::get(ValFVTy->getElementType());
}
// ee (gep (ptr, idx0, ...), idx) -> gep (ee (ptr, idx), ee (idx0, idx), ...)
if (auto *CE = dyn_cast<ConstantExpr>(Val)) {
if (auto *GEP = dyn_cast<GEPOperator>(CE)) {
SmallVector<Constant *, 8> Ops;
Ops.reserve(CE->getNumOperands());
for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) {
Constant *Op = CE->getOperand(i);
if (Op->getType()->isVectorTy()) {
Constant *ScalarOp = ConstantExpr::getExtractElement(Op, Idx);
if (!ScalarOp)
return nullptr;
Ops.push_back(ScalarOp);
} else
Ops.push_back(Op);
}
return CE->getWithOperands(Ops, ValVTy->getElementType(), false,
GEP->getSourceElementType());
} else if (CE->getOpcode() == Instruction::InsertElement) {
if (const auto *IEIdx = dyn_cast<ConstantInt>(CE->getOperand(2))) {
if (APSInt::isSameValue(APSInt(IEIdx->getValue()),
APSInt(CIdx->getValue()))) {
return CE->getOperand(1);
} else {
return ConstantExpr::getExtractElement(CE->getOperand(0), CIdx);
}
}
}
}
if (Constant *C = Val->getAggregateElement(CIdx))
return C;
// Lane < Splat minimum vector width => extractelt Splat(x), Lane -> x
if (CIdx->getValue().ult(ValVTy->getElementCount().getKnownMinValue())) {
if (Constant *SplatVal = Val->getSplatValue())
return SplatVal;
}
return nullptr;
}
Constant *llvm::ConstantFoldInsertElementInstruction(Constant *Val,
Constant *Elt,
Constant *Idx) {
if (isa<UndefValue>(Idx))
return PoisonValue::get(Val->getType());
// Inserting null into all zeros is still all zeros.
// TODO: This is true for undef and poison splats too.
if (isa<ConstantAggregateZero>(Val) && Elt->isNullValue())
return Val;
ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx);
if (!CIdx) return nullptr;
// Do not iterate on scalable vector. The num of elements is unknown at
// compile-time.
if (isa<ScalableVectorType>(Val->getType()))
return nullptr;
auto *ValTy = cast<FixedVectorType>(Val->getType());
unsigned NumElts = ValTy->getNumElements();
if (CIdx->uge(NumElts))
return PoisonValue::get(Val->getType());
SmallVector<Constant*, 16> Result;
Result.reserve(NumElts);
auto *Ty = Type::getInt32Ty(Val->getContext());
uint64_t IdxVal = CIdx->getZExtValue();
for (unsigned i = 0; i != NumElts; ++i) {
if (i == IdxVal) {
Result.push_back(Elt);
continue;
}
Constant *C = ConstantExpr::getExtractElement(Val, ConstantInt::get(Ty, i));
Result.push_back(C);
}
return ConstantVector::get(Result);
}
Constant *llvm::ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2,
ArrayRef<int> Mask) {
auto *V1VTy = cast<VectorType>(V1->getType());
unsigned MaskNumElts = Mask.size();
auto MaskEltCount =
ElementCount::get(MaskNumElts, isa<ScalableVectorType>(V1VTy));
Type *EltTy = V1VTy->getElementType();
// Poison shuffle mask -> poison value.
if (all_of(Mask, [](int Elt) { return Elt == PoisonMaskElem; })) {
return PoisonValue::get(VectorType::get(EltTy, MaskEltCount));
}
// If the mask is all zeros this is a splat, no need to go through all
// elements.
if (all_of(Mask, [](int Elt) { return Elt == 0; })) {
Type *Ty = IntegerType::get(V1->getContext(), 32);
Constant *Elt =
ConstantExpr::getExtractElement(V1, ConstantInt::get(Ty, 0));
if (Elt->isNullValue()) {
auto *VTy = VectorType::get(EltTy, MaskEltCount);
return ConstantAggregateZero::get(VTy);
} else if (!MaskEltCount.isScalable())
return ConstantVector::getSplat(MaskEltCount, Elt);
}
// Do not iterate on scalable vector. The num of elements is unknown at
// compile-time.
if (isa<ScalableVectorType>(V1VTy))
return nullptr;
unsigned SrcNumElts = V1VTy->getElementCount().getKnownMinValue();
// Loop over the shuffle mask, evaluating each element.
SmallVector<Constant*, 32> Result;
for (unsigned i = 0; i != MaskNumElts; ++i) {
int Elt = Mask[i];
if (Elt == -1) {
Result.push_back(UndefValue::get(EltTy));
continue;
}
Constant *InElt;
if (unsigned(Elt) >= SrcNumElts*2)
InElt = UndefValue::get(EltTy);
else if (unsigned(Elt) >= SrcNumElts) {
Type *Ty = IntegerType::get(V2->getContext(), 32);
InElt =
ConstantExpr::getExtractElement(V2,
ConstantInt::get(Ty, Elt - SrcNumElts));
} else {
Type *Ty = IntegerType::get(V1->getContext(), 32);
InElt = ConstantExpr::getExtractElement(V1, ConstantInt::get(Ty, Elt));
}
Result.push_back(InElt);
}
return ConstantVector::get(Result);
}
Constant *llvm::ConstantFoldExtractValueInstruction(Constant *Agg,
ArrayRef<unsigned> Idxs) {
// Base case: no indices, so return the entire value.
if (Idxs.empty())
return Agg;
if (Constant *C = Agg->getAggregateElement(Idxs[0]))
return ConstantFoldExtractValueInstruction(C, Idxs.slice(1));
return nullptr;
}
Constant *llvm::ConstantFoldInsertValueInstruction(Constant *Agg,
Constant *Val,
ArrayRef<unsigned> Idxs) {
// Base case: no indices, so replace the entire value.
if (Idxs.empty())
return Val;
unsigned NumElts;
if (StructType *ST = dyn_cast<StructType>(Agg->getType()))
NumElts = ST->getNumElements();
else
NumElts = cast<ArrayType>(Agg->getType())->getNumElements();
SmallVector<Constant*, 32> Result;
for (unsigned i = 0; i != NumElts; ++i) {
Constant *C = Agg->getAggregateElement(i);
if (!C) return nullptr;
if (Idxs[0] == i)
C = ConstantFoldInsertValueInstruction(C, Val, Idxs.slice(1));
Result.push_back(C);
}
if (StructType *ST = dyn_cast<StructType>(Agg->getType()))
return ConstantStruct::get(ST, Result);
return ConstantArray::get(cast<ArrayType>(Agg->getType()), Result);
}
Constant *llvm::ConstantFoldUnaryInstruction(unsigned Opcode, Constant *C) {
assert(Instruction::isUnaryOp(Opcode) && "Non-unary instruction detected");
// Handle scalar UndefValue and scalable vector UndefValue. Fixed-length
// vectors are always evaluated per element.
bool IsScalableVector = isa<ScalableVectorType>(C->getType());
bool HasScalarUndefOrScalableVectorUndef =
(!C->getType()->isVectorTy() || IsScalableVector) && isa<UndefValue>(C);
if (HasScalarUndefOrScalableVectorUndef) {
switch (static_cast<Instruction::UnaryOps>(Opcode)) {
case Instruction::FNeg:
return C; // -undef -> undef
case Instruction::UnaryOpsEnd:
llvm_unreachable("Invalid UnaryOp");
}
}
// Constant should not be UndefValue, unless these are vector constants.
assert(!HasScalarUndefOrScalableVectorUndef && "Unexpected UndefValue");
// We only have FP UnaryOps right now.
assert(!isa<ConstantInt>(C) && "Unexpected Integer UnaryOp");
if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
const APFloat &CV = CFP->getValueAPF();
switch (Opcode) {
default:
break;
case Instruction::FNeg:
return ConstantFP::get(C->getContext(), neg(CV));
}
} else if (auto *VTy = dyn_cast<FixedVectorType>(C->getType())) {
Type *Ty = IntegerType::get(VTy->getContext(), 32);
// Fast path for splatted constants.
if (Constant *Splat = C->getSplatValue())
if (Constant *Elt = ConstantFoldUnaryInstruction(Opcode, Splat))
return ConstantVector::getSplat(VTy->getElementCount(), Elt);
// Fold each element and create a vector constant from those constants.
SmallVector<Constant *, 16> Result;
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *Elt = ConstantExpr::getExtractElement(C, ExtractIdx);
Constant *Res = ConstantFoldUnaryInstruction(Opcode, Elt);
if (!Res)
return nullptr;
Result.push_back(Res);
}
return ConstantVector::get(Result);
}
// We don't know how to fold this.
return nullptr;
}
Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
Constant *C2) {
assert(Instruction::isBinaryOp(Opcode) && "Non-binary instruction detected");
// Simplify BinOps with their identity values first. They are no-ops and we
// can always return the other value, including undef or poison values.
if (Constant *Identity = ConstantExpr::getBinOpIdentity(
Opcode, C1->getType(), /*AllowRHSIdentity*/ false)) {
if (C1 == Identity)
return C2;
if (C2 == Identity)
return C1;
} else if (Constant *Identity = ConstantExpr::getBinOpIdentity(
Opcode, C1->getType(), /*AllowRHSIdentity*/ true)) {
if (C2 == Identity)
return C1;
}
// Binary operations propagate poison.
if (isa<PoisonValue>(C1) || isa<PoisonValue>(C2))
return PoisonValue::get(C1->getType());
// Handle scalar UndefValue and scalable vector UndefValue. Fixed-length
// vectors are always evaluated per element.
bool IsScalableVector = isa<ScalableVectorType>(C1->getType());
bool HasScalarUndefOrScalableVectorUndef =
(!C1->getType()->isVectorTy() || IsScalableVector) &&
(isa<UndefValue>(C1) || isa<UndefValue>(C2));
if (HasScalarUndefOrScalableVectorUndef) {
switch (static_cast<Instruction::BinaryOps>(Opcode)) {
case Instruction::Xor:
if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
// Handle undef ^ undef -> 0 special case. This is a common
// idiom (misuse).
return Constant::getNullValue(C1->getType());
[[fallthrough]];
case Instruction::Add:
case Instruction::Sub:
return UndefValue::get(C1->getType());
case Instruction::And:
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef & undef -> undef
return C1;
return Constant::getNullValue(C1->getType()); // undef & X -> 0
case Instruction::Mul: {
// undef * undef -> undef
if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
return C1;
const APInt *CV;
// X * undef -> undef if X is odd
if (match(C1, m_APInt(CV)) || match(C2, m_APInt(CV)))
if ((*CV)[0])
return UndefValue::get(C1->getType());
// X * undef -> 0 otherwise
return Constant::getNullValue(C1->getType());
}
case Instruction::SDiv:
case Instruction::UDiv:
// X / undef -> poison
// X / 0 -> poison
if (match(C2, m_CombineOr(m_Undef(), m_Zero())))
return PoisonValue::get(C2->getType());
// undef / X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::URem:
case Instruction::SRem:
// X % undef -> poison
// X % 0 -> poison
if (match(C2, m_CombineOr(m_Undef(), m_Zero())))
return PoisonValue::get(C2->getType());
// undef % X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::Or: // X | undef -> -1
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef | undef -> undef
return C1;
return Constant::getAllOnesValue(C1->getType()); // undef | X -> ~0
case Instruction::LShr:
// X >>l undef -> poison
if (isa<UndefValue>(C2))
return PoisonValue::get(C2->getType());
// undef >>l X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::AShr:
// X >>a undef -> poison
if (isa<UndefValue>(C2))
return PoisonValue::get(C2->getType());
// TODO: undef >>a X -> poison if the shift is exact
// undef >>a X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::Shl:
// X << undef -> undef
if (isa<UndefValue>(C2))
return PoisonValue::get(C2->getType());
// undef << X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::FSub:
// -0.0 - undef --> undef (consistent with "fneg undef")
if (match(C1, m_NegZeroFP()) && isa<UndefValue>(C2))
return C2;
[[fallthrough]];
case Instruction::FAdd:
case Instruction::FMul:
case Instruction::FDiv:
case Instruction::FRem:
// [any flop] undef, undef -> undef
if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
return C1;
// [any flop] C, undef -> NaN
// [any flop] undef, C -> NaN
// We could potentially specialize NaN/Inf constants vs. 'normal'
// constants (possibly differently depending on opcode and operand). This
// would allow returning undef sometimes. But it is always safe to fold to
// NaN because we can choose the undef operand as NaN, and any FP opcode
// with a NaN operand will propagate NaN.
return ConstantFP::getNaN(C1->getType());
case Instruction::BinaryOpsEnd:
llvm_unreachable("Invalid BinaryOp");
}
}
// Neither constant should be UndefValue, unless these are vector constants.
assert((!HasScalarUndefOrScalableVectorUndef) && "Unexpected UndefValue");
// Handle simplifications when the RHS is a constant int.
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
switch (Opcode) {
case Instruction::Mul:
if (CI2->isZero())
return C2; // X * 0 == 0
break;
case Instruction::UDiv:
case Instruction::SDiv:
if (CI2->isZero())
return PoisonValue::get(CI2->getType()); // X / 0 == poison
break;
case Instruction::URem:
case Instruction::SRem:
if (CI2->isOne())
return Constant::getNullValue(CI2->getType()); // X % 1 == 0
if (CI2->isZero())
return PoisonValue::get(CI2->getType()); // X % 0 == poison
break;
case Instruction::And:
if (CI2->isZero())
return C2; // X & 0 == 0
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
// If and'ing the address of a global with a constant, fold it.
if (CE1->getOpcode() == Instruction::PtrToInt &&
isa<GlobalValue>(CE1->getOperand(0))) {
GlobalValue *GV = cast<GlobalValue>(CE1->getOperand(0));
Align GVAlign; // defaults to 1
if (Module *TheModule = GV->getParent()) {
const DataLayout &DL = TheModule->getDataLayout();
GVAlign = GV->getPointerAlignment(DL);
// If the function alignment is not specified then assume that it
// is 4.
// This is dangerous; on x86, the alignment of the pointer
// corresponds to the alignment of the function, but might be less
// than 4 if it isn't explicitly specified.
// However, a fix for this behaviour was reverted because it
// increased code size (see https://reviews.llvm.org/D55115)
// FIXME: This code should be deleted once existing targets have
// appropriate defaults
if (isa<Function>(GV) && !DL.getFunctionPtrAlign())
GVAlign = Align(4);
} else if (isa<GlobalVariable>(GV)) {
GVAlign = cast<GlobalVariable>(GV)->getAlign().valueOrOne();
}
if (GVAlign > 1) {
unsigned DstWidth = CI2->getBitWidth();
unsigned SrcWidth = std::min(DstWidth, Log2(GVAlign));
APInt BitsNotSet(APInt::getLowBitsSet(DstWidth, SrcWidth));
// If checking bits we know are clear, return zero.
if ((CI2->getValue() & BitsNotSet) == CI2->getValue())
return Constant::getNullValue(CI2->getType());
}
}
}
break;
case Instruction::Or:
if (CI2->isMinusOne())
return C2; // X | -1 == -1
break;
case Instruction::Xor:
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
switch (CE1->getOpcode()) {
default:
break;
case Instruction::ICmp:
case Instruction::FCmp:
// cmp pred ^ true -> cmp !pred
assert(CI2->isOne());
CmpInst::Predicate pred = (CmpInst::Predicate)CE1->getPredicate();
pred = CmpInst::getInversePredicate(pred);
return ConstantExpr::getCompare(pred, CE1->getOperand(0),
CE1->getOperand(1));
}
}
break;
}
} else if (isa<ConstantInt>(C1)) {
// If C1 is a ConstantInt and C2 is not, swap the operands.
if (Instruction::isCommutative(Opcode))
return ConstantExpr::isDesirableBinOp(Opcode)
? ConstantExpr::get(Opcode, C2, C1)
: ConstantFoldBinaryInstruction(Opcode, C2, C1);
}
if (ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) {
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
const APInt &C1V = CI1->getValue();
const APInt &C2V = CI2->getValue();
switch (Opcode) {
default:
break;
case Instruction::Add:
return ConstantInt::get(CI1->getContext(), C1V + C2V);
case Instruction::Sub:
return ConstantInt::get(CI1->getContext(), C1V - C2V);
case Instruction::Mul:
return ConstantInt::get(CI1->getContext(), C1V * C2V);
case Instruction::UDiv:
assert(!CI2->isZero() && "Div by zero handled above");
return ConstantInt::get(CI1->getContext(), C1V.udiv(C2V));
case Instruction::SDiv:
assert(!CI2->isZero() && "Div by zero handled above");
if (C2V.isAllOnes() && C1V.isMinSignedValue())
return PoisonValue::get(CI1->getType()); // MIN_INT / -1 -> poison
return ConstantInt::get(CI1->getContext(), C1V.sdiv(C2V));
case Instruction::URem:
assert(!CI2->isZero() && "Div by zero handled above");
return ConstantInt::get(CI1->getContext(), C1V.urem(C2V));
case Instruction::SRem:
assert(!CI2->isZero() && "Div by zero handled above");
if (C2V.isAllOnes() && C1V.isMinSignedValue())
return PoisonValue::get(CI1->getType()); // MIN_INT % -1 -> poison
return ConstantInt::get(CI1->getContext(), C1V.srem(C2V));
case Instruction::And:
return ConstantInt::get(CI1->getContext(), C1V & C2V);
case Instruction::Or:
return ConstantInt::get(CI1->getContext(), C1V | C2V);
case Instruction::Xor:
return ConstantInt::get(CI1->getContext(), C1V ^ C2V);
case Instruction::Shl:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.shl(C2V));
return PoisonValue::get(C1->getType()); // too big shift is poison
case Instruction::LShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.lshr(C2V));
return PoisonValue::get(C1->getType()); // too big shift is poison
case Instruction::AShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.ashr(C2V));
return PoisonValue::get(C1->getType()); // too big shift is poison
}
}
switch (Opcode) {
case Instruction::SDiv:
case Instruction::UDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::Shl:
if (CI1->isZero()) return C1;
break;
default:
break;
}
} else if (ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) {
if (ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) {
const APFloat &C1V = CFP1->getValueAPF();
const APFloat &C2V = CFP2->getValueAPF();
APFloat C3V = C1V; // copy for modification
switch (Opcode) {
default:
break;
case Instruction::FAdd:
(void)C3V.add(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FSub:
(void)C3V.subtract(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FMul:
(void)C3V.multiply(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FDiv:
(void)C3V.divide(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FRem:
(void)C3V.mod(C2V);
return ConstantFP::get(C1->getContext(), C3V);
}
}
} else if (auto *VTy = dyn_cast<VectorType>(C1->getType())) {
// Fast path for splatted constants.
if (Constant *C2Splat = C2->getSplatValue()) {
if (Instruction::isIntDivRem(Opcode) && C2Splat->isNullValue())
return PoisonValue::get(VTy);
if (Constant *C1Splat = C1->getSplatValue()) {
Constant *Res =
ConstantExpr::isDesirableBinOp(Opcode)
? ConstantExpr::get(Opcode, C1Splat, C2Splat)
: ConstantFoldBinaryInstruction(Opcode, C1Splat, C2Splat);
if (!Res)
return nullptr;
return ConstantVector::getSplat(VTy->getElementCount(), Res);
}
}
if (auto *FVTy = dyn_cast<FixedVectorType>(VTy)) {
// Fold each element and create a vector constant from those constants.
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(FVTy->getContext(), 32);
for (unsigned i = 0, e = FVTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);
// If any element of a divisor vector is zero, the whole op is poison.
if (Instruction::isIntDivRem(Opcode) && RHS->isNullValue())
return PoisonValue::get(VTy);
Constant *Res = ConstantExpr::isDesirableBinOp(Opcode)
? ConstantExpr::get(Opcode, LHS, RHS)
: ConstantFoldBinaryInstruction(Opcode, LHS, RHS);
if (!Res)
return nullptr;
Result.push_back(Res);
}
return ConstantVector::get(Result);
}
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
// Given ((a + b) + c), if (b + c) folds to something interesting, return
// (a + (b + c)).
if (Instruction::isAssociative(Opcode) && CE1->getOpcode() == Opcode) {
Constant *T = ConstantExpr::get(Opcode, CE1->getOperand(1), C2);
if (!isa<ConstantExpr>(T) || cast<ConstantExpr>(T)->getOpcode() != Opcode)
return ConstantExpr::get(Opcode, CE1->getOperand(0), T);
}
} else if (isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flop them around and fold the
// other way if possible.
if (Instruction::isCommutative(Opcode))
return ConstantFoldBinaryInstruction(Opcode, C2, C1);
}
// i1 can be simplified in many cases.
if (C1->getType()->isIntegerTy(1)) {
switch (Opcode) {
case Instruction::Add:
case Instruction::Sub:
return ConstantExpr::getXor(C1, C2);
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
// We can assume that C2 == 0. If it were one the result would be
// undefined because the shift value is as large as the bitwidth.
return C1;
case Instruction::SDiv:
case Instruction::UDiv:
// We can assume that C2 == 1. If it were zero the result would be
// undefined through division by zero.
return C1;
case Instruction::URem:
case Instruction::SRem:
// We can assume that C2 == 1. If it were zero the result would be
// undefined through division by zero.
return ConstantInt::getFalse(C1->getContext());
default:
break;
}
}
// We don't know how to fold this.
return nullptr;
}
static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
auto isGlobalUnsafeForEquality = [](const GlobalValue *GV) {
if (GV->isInterposable() || GV->hasGlobalUnnamedAddr())
return true;
if (const auto *GVar = dyn_cast<GlobalVariable>(GV)) {
Type *Ty = GVar->getValueType();
// A global with opaque type might end up being zero sized.
if (!Ty->isSized())
return true;
// A global with an empty type might lie at the address of any other
// global.
if (Ty->isEmptyTy())
return true;
}
return false;
};
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!isGlobalUnsafeForEquality(GV1) && !isGlobalUnsafeForEquality(GV2))
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}
/// This function determines if there is anything we can decide about the two
/// constants provided. This doesn't need to handle simple things like integer
/// comparisons, but should instead handle ConstantExprs and GlobalValues.
/// If we can determine that the two constants have a particular relation to
/// each other, we should return the corresponding ICmp predicate, otherwise
/// return ICmpInst::BAD_ICMP_PREDICATE.
static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2) {
assert(V1->getType() == V2->getType() &&
"Cannot compare different types of values!");
if (V1 == V2) return ICmpInst::ICMP_EQ;
// The following folds only apply to pointers.
if (!V1->getType()->isPointerTy())
return ICmpInst::BAD_ICMP_PREDICATE;
// To simplify this code we canonicalize the relation so that the first
// operand is always the most "complex" of the two. We consider simple
// constants (like ConstantPointerNull) to be the simplest, followed by
// BlockAddress, GlobalValues, and ConstantExpr's (the most complex).
auto GetComplexity = [](Constant *V) {
if (isa<ConstantExpr>(V))
return 3;
if (isa<GlobalValue>(V))
return 2;
if (isa<BlockAddress>(V))
return 1;
return 0;
};
if (GetComplexity(V1) < GetComplexity(V2)) {
ICmpInst::Predicate SwappedRelation = evaluateICmpRelation(V2, V1);
if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE)
return ICmpInst::getSwappedPredicate(SwappedRelation);
return ICmpInst::BAD_ICMP_PREDICATE;
}
if (const BlockAddress *BA = dyn_cast<BlockAddress>(V1)) {
// Now we know that the RHS is a BlockAddress or simple constant.
if (const BlockAddress *BA2 = dyn_cast<BlockAddress>(V2)) {
// Block address in another function can't equal this one, but block
// addresses in the current function might be the same if blocks are
// empty.
if (BA2->getFunction() != BA->getFunction())
return ICmpInst::ICMP_NE;
} else if (isa<ConstantPointerNull>(V2)) {
return ICmpInst::ICMP_NE;
}
} else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V1)) {
// Now we know that the RHS is a GlobalValue, BlockAddress or simple
// constant.
if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
return areGlobalsPotentiallyEqual(GV, GV2);
} else if (isa<BlockAddress>(V2)) {
return ICmpInst::ICMP_NE; // Globals never equal labels.
} else if (isa<ConstantPointerNull>(V2)) {
// GlobalVals can never be null unless they have external weak linkage.
// We don't try to evaluate aliases here.
// NOTE: We should not be doing this constant folding if null pointer
// is considered valid for the function. But currently there is no way to
// query it from the Constant type.
if (!GV->hasExternalWeakLinkage() && !isa<GlobalAlias>(GV) &&
!NullPointerIsDefined(nullptr /* F */,
GV->getType()->getAddressSpace()))
return ICmpInst::ICMP_UGT;
}
} else if (auto *CE1 = dyn_cast<ConstantExpr>(V1)) {
// Ok, the LHS is known to be a constantexpr. The RHS can be any of a
// constantexpr, a global, block address, or a simple constant.
Constant *CE1Op0 = CE1->getOperand(0);
switch (CE1->getOpcode()) {
case Instruction::GetElementPtr: {
GEPOperator *CE1GEP = cast<GEPOperator>(CE1);
// Ok, since this is a getelementptr, we know that the constant has a
// pointer type. Check the various cases.
if (isa<ConstantPointerNull>(V2)) {
// If we are comparing a GEP to a null pointer, check to see if the base
// of the GEP equals the null pointer.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) {
// If its not weak linkage, the GVal must have a non-zero address
// so the result is greater-than
if (!GV->hasExternalWeakLinkage() && CE1GEP->isInBounds())
return ICmpInst::ICMP_UGT;
}
} else if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) {
if (GV != GV2) {
if (CE1GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(GV, GV2);
return ICmpInst::BAD_ICMP_PREDICATE;
}
}
} else if (const auto *CE2GEP = dyn_cast<GEPOperator>(V2)) {
// By far the most common case to handle is when the base pointers are
// obviously to the same global.
const Constant *CE2Op0 = cast<Constant>(CE2GEP->getPointerOperand());
if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) {
// Don't know relative ordering, but check for inequality.
if (CE1Op0 != CE2Op0) {
if (CE1GEP->hasAllZeroIndices() && CE2GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(cast<GlobalValue>(CE1Op0),
cast<GlobalValue>(CE2Op0));
return ICmpInst::BAD_ICMP_PREDICATE;
}
}
}
break;
}
default:
break;
}
}
return ICmpInst::BAD_ICMP_PREDICATE;
}
Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
Constant *C1, Constant *C2) {
Type *ResultTy;
if (VectorType *VT = dyn_cast<VectorType>(C1->getType()))
ResultTy = VectorType::get(Type::getInt1Ty(C1->getContext()),
VT->getElementCount());
else
ResultTy = Type::getInt1Ty(C1->getContext());
// Fold FCMP_FALSE/FCMP_TRUE unconditionally.
if (Predicate == FCmpInst::FCMP_FALSE)
return Constant::getNullValue(ResultTy);
if (Predicate == FCmpInst::FCMP_TRUE)
return Constant::getAllOnesValue(ResultTy);
// Handle some degenerate cases first
if (isa<PoisonValue>(C1) || isa<PoisonValue>(C2))
return PoisonValue::get(ResultTy);
if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
bool isIntegerPredicate = ICmpInst::isIntPredicate(Predicate);
// For EQ and NE, we can always pick a value for the undef to make the
// predicate pass or fail, so we can return undef.
// Also, if both operands are undef, we can return undef for int comparison.
if (ICmpInst::isEquality(Predicate) || (isIntegerPredicate && C1 == C2))
return UndefValue::get(ResultTy);
// Otherwise, for integer compare, pick the same value as the non-undef
// operand, and fold it to true or false.
if (isIntegerPredicate)
return ConstantInt::get(ResultTy, CmpInst::isTrueWhenEqual(Predicate));
// Choosing NaN for the undef will always make unordered comparison succeed
// and ordered comparison fails.
return ConstantInt::get(ResultTy, CmpInst::isUnordered(Predicate));
}
if (C2->isNullValue()) {
// The caller is expected to commute the operands if the constant expression
// is C2.
// C1 >= 0 --> true
if (Predicate == ICmpInst::ICMP_UGE)
return Constant::getAllOnesValue(ResultTy);
// C1 < 0 --> false
if (Predicate == ICmpInst::ICMP_ULT)
return Constant::getNullValue(ResultTy);
}
// If the comparison is a comparison between two i1's, simplify it.
if (C1->getType()->isIntegerTy(1)) {
switch (Predicate) {
case ICmpInst::ICMP_EQ:
if (isa<ConstantInt>(C2))
return ConstantExpr::getXor(C1, ConstantExpr::getNot(C2));
return ConstantExpr::getXor(ConstantExpr::getNot(C1), C2);
case ICmpInst::ICMP_NE:
return ConstantExpr::getXor(C1, C2);
default:
break;
}
}
if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) {
const APInt &V1 = cast<ConstantInt>(C1)->getValue();
const APInt &V2 = cast<ConstantInt>(C2)->getValue();
return ConstantInt::get(ResultTy, ICmpInst::compare(V1, V2, Predicate));
} else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) {
const APFloat &C1V = cast<ConstantFP>(C1)->getValueAPF();
const APFloat &C2V = cast<ConstantFP>(C2)->getValueAPF();
return ConstantInt::get(ResultTy, FCmpInst::compare(C1V, C2V, Predicate));
} else if (auto *C1VTy = dyn_cast<VectorType>(C1->getType())) {
// Fast path for splatted constants.
if (Constant *C1Splat = C1->getSplatValue())
if (Constant *C2Splat = C2->getSplatValue())
return ConstantVector::getSplat(
C1VTy->getElementCount(),
ConstantExpr::getCompare(Predicate, C1Splat, C2Splat));
// Do not iterate on scalable vector. The number of elements is unknown at
// compile-time.
if (isa<ScalableVectorType>(C1VTy))
return nullptr;
// If we can constant fold the comparison of each element, constant fold
// the whole vector comparison.
SmallVector<Constant*, 4> ResElts;
Type *Ty = IntegerType::get(C1->getContext(), 32);
// Compare the elements, producing an i1 result or constant expr.
for (unsigned I = 0, E = C1VTy->getElementCount().getKnownMinValue();
I != E; ++I) {
Constant *C1E =
ConstantExpr::getExtractElement(C1, ConstantInt::get(Ty, I));
Constant *C2E =
ConstantExpr::getExtractElement(C2, ConstantInt::get(Ty, I));
ResElts.push_back(ConstantExpr::getCompare(Predicate, C1E, C2E));
}
return ConstantVector::get(ResElts);
}
if (C1->getType()->isFPOrFPVectorTy()) {
if (C1 == C2) {
// We know that C1 == C2 || isUnordered(C1, C2).
if (Predicate == FCmpInst::FCMP_ONE)
return ConstantInt::getFalse(ResultTy);
else if (Predicate == FCmpInst::FCMP_UEQ)
return ConstantInt::getTrue(ResultTy);
}
} else {
// Evaluate the relation between the two constants, per the predicate.
int Result = -1; // -1 = unknown, 0 = known false, 1 = known true.
switch (evaluateICmpRelation(C1, C2)) {
default: llvm_unreachable("Unknown relational!");
case ICmpInst::BAD_ICMP_PREDICATE:
break; // Couldn't determine anything about these constants.
case ICmpInst::ICMP_EQ: // We know the constants are equal!
// If we know the constants are equal, we can decide the result of this
// computation precisely.
Result = ICmpInst::isTrueWhenEqual(Predicate);
break;
case ICmpInst::ICMP_ULT:
switch (Predicate) {
case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_ULE:
Result = 1; break;
case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_UGE:
Result = 0; break;
default:
break;
}
break;
case ICmpInst::ICMP_SLT:
switch (Predicate) {
case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_SLE:
Result = 1; break;
case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_SGE:
Result = 0; break;
default:
break;
}
break;
case ICmpInst::ICMP_UGT:
switch (Predicate) {
case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_UGE:
Result = 1; break;
case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_ULE:
Result = 0; break;
default:
break;
}
break;
case ICmpInst::ICMP_SGT:
switch (Predicate) {
case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_SGE:
Result = 1; break;
case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_SLE:
Result = 0; break;
default:
break;
}
break;
case ICmpInst::ICMP_ULE:
if (Predicate == ICmpInst::ICMP_UGT)
Result = 0;
if (Predicate == ICmpInst::ICMP_ULT || Predicate == ICmpInst::ICMP_ULE)
Result = 1;
break;
case ICmpInst::ICMP_SLE:
if (Predicate == ICmpInst::ICMP_SGT)
Result = 0;
if (Predicate == ICmpInst::ICMP_SLT || Predicate == ICmpInst::ICMP_SLE)
Result = 1;
break;
case ICmpInst::ICMP_UGE:
if (Predicate == ICmpInst::ICMP_ULT)
Result = 0;
if (Predicate == ICmpInst::ICMP_UGT || Predicate == ICmpInst::ICMP_UGE)
Result = 1;
break;
case ICmpInst::ICMP_SGE:
if (Predicate == ICmpInst::ICMP_SLT)
Result = 0;
if (Predicate == ICmpInst::ICMP_SGT || Predicate == ICmpInst::ICMP_SGE)
Result = 1;
break;
case ICmpInst::ICMP_NE:
if (Predicate == ICmpInst::ICMP_EQ)
Result = 0;
if (Predicate == ICmpInst::ICMP_NE)
Result = 1;
break;
}
// If we evaluated the result, return it now.
if (Result != -1)
return ConstantInt::get(ResultTy, Result);
if ((!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) ||
(C1->isNullValue() && !C2->isNullValue())) {
// If C2 is a constant expr and C1 isn't, flip them around and fold the
// other way if possible.
// Also, if C1 is null and C2 isn't, flip them around.
Predicate = ICmpInst::getSwappedPredicate(Predicate);
return ConstantExpr::getICmp(Predicate, C2, C1);
}
}
return nullptr;
}
/// Test whether the given sequence of *normalized* indices is "inbounds".
template<typename IndexTy>
static bool isInBoundsIndices(ArrayRef<IndexTy> Idxs) {
// No indices means nothing that could be out of bounds.
if (Idxs.empty()) return true;
// If the first index is zero, it's in bounds.
if (cast<Constant>(Idxs[0])->isNullValue()) return true;
// If the first index is one and all the rest are zero, it's in bounds,
// by the one-past-the-end rule.
if (auto *CI = dyn_cast<ConstantInt>(Idxs[0])) {
if (!CI->isOne())
return false;
} else {
auto *CV = cast<ConstantDataVector>(Idxs[0]);
CI = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());
if (!CI || !CI->isOne())
return false;
}
for (unsigned i = 1, e = Idxs.size(); i != e; ++i)
if (!cast<Constant>(Idxs[i])->isNullValue())
return false;
return true;
}
/// Test whether a given ConstantInt is in-range for a SequentialType.
static bool isIndexInRangeOfArrayType(uint64_t NumElements,
const ConstantInt *CI) {
// We cannot bounds check the index if it doesn't fit in an int64_t.
if (CI->getValue().getSignificantBits() > 64)
return false;
// A negative index or an index past the end of our sequential type is
// considered out-of-range.
int64_t IndexVal = CI->getSExtValue();
if (IndexVal < 0 || (IndexVal != 0 && (uint64_t)IndexVal >= NumElements))
return false;
// Otherwise, it is in-range.
return true;
}
// Combine Indices - If the source pointer to this getelementptr instruction
// is a getelementptr instruction, combine the indices of the two
// getelementptr instructions into a single instruction.
static Constant *foldGEPOfGEP(GEPOperator *GEP, Type *PointeeTy, bool InBounds,
ArrayRef<Value *> Idxs) {
if (PointeeTy != GEP->getResultElementType())
return nullptr;
// Leave inrange handling to DL-aware constant folding.
if (GEP->getInRange())
return nullptr;
Constant *Idx0 = cast<Constant>(Idxs[0]);
if (Idx0->isNullValue()) {
// Handle the simple case of a zero index.
SmallVector<Value*, 16> NewIndices;
NewIndices.reserve(Idxs.size() + GEP->getNumIndices());
NewIndices.append(GEP->idx_begin(), GEP->idx_end());
NewIndices.append(Idxs.begin() + 1, Idxs.end());
return ConstantExpr::getGetElementPtr(
GEP->getSourceElementType(), cast<Constant>(GEP->getPointerOperand()),
NewIndices, InBounds && GEP->isInBounds());
}
gep_type_iterator LastI = gep_type_end(GEP);
for (gep_type_iterator I = gep_type_begin(GEP), E = gep_type_end(GEP);
I != E; ++I)
LastI = I;
// We can't combine GEPs if the last index is a struct type.
if (!LastI.isSequential())
return nullptr;
// We could perform the transform with non-constant index, but prefer leaving
// it as GEP of GEP rather than GEP of add for now.
ConstantInt *CI = dyn_cast<ConstantInt>(Idx0);
if (!CI)
return nullptr;
// TODO: This code may be extended to handle vectors as well.
auto *LastIdx = cast<Constant>(GEP->getOperand(GEP->getNumOperands()-1));
Type *LastIdxTy = LastIdx->getType();
if (LastIdxTy->isVectorTy())
return nullptr;
SmallVector<Value*, 16> NewIndices;
NewIndices.reserve(Idxs.size() + GEP->getNumIndices());
NewIndices.append(GEP->idx_begin(), GEP->idx_end() - 1);
// Add the last index of the source with the first index of the new GEP.
// Make sure to handle the case when they are actually different types.
if (LastIdxTy != Idx0->getType()) {
unsigned CommonExtendedWidth =
std::max(LastIdxTy->getIntegerBitWidth(),
Idx0->getType()->getIntegerBitWidth());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
Type *CommonTy =
Type::getIntNTy(LastIdxTy->getContext(), CommonExtendedWidth);
if (Idx0->getType() != CommonTy)
Idx0 = ConstantFoldCastInstruction(Instruction::SExt, Idx0, CommonTy);
if (LastIdx->getType() != CommonTy)
LastIdx =
ConstantFoldCastInstruction(Instruction::SExt, LastIdx, CommonTy);
if (!Idx0 || !LastIdx)
return nullptr;
}
NewIndices.push_back(ConstantExpr::get(Instruction::Add, Idx0, LastIdx));
NewIndices.append(Idxs.begin() + 1, Idxs.end());
return ConstantExpr::getGetElementPtr(
GEP->getSourceElementType(), cast<Constant>(GEP->getPointerOperand()),
NewIndices, InBounds && GEP->isInBounds());
}
Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
bool InBounds,
std::optional<ConstantRange> InRange,
ArrayRef<Value *> Idxs) {
if (Idxs.empty()) return C;
Type *GEPTy = GetElementPtrInst::getGEPReturnType(
C, ArrayRef((Value *const *)Idxs.data(), Idxs.size()));
if (isa<PoisonValue>(C))
return PoisonValue::get(GEPTy);
if (isa<UndefValue>(C))
// If inbounds, we can choose an out-of-bounds pointer as a base pointer.
return InBounds ? PoisonValue::get(GEPTy) : UndefValue::get(GEPTy);
auto IsNoOp = [&]() {
// Avoid losing inrange information.
if (InRange)
return false;
return all_of(Idxs, [](Value *Idx) {
Constant *IdxC = cast<Constant>(Idx);
return IdxC->isNullValue() || isa<UndefValue>(IdxC);
});
};
if (IsNoOp())
return GEPTy->isVectorTy() && !C->getType()->isVectorTy()
? ConstantVector::getSplat(
cast<VectorType>(GEPTy)->getElementCount(), C)
: C;
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
if (auto *GEP = dyn_cast<GEPOperator>(CE))
if (Constant *C = foldGEPOfGEP(GEP, PointeeTy, InBounds, Idxs))
return C;
// Check to see if any array indices are not within the corresponding
// notional array or vector bounds. If so, try to determine if they can be
// factored out into preceding dimensions.
SmallVector<Constant *, 8> NewIdxs;
Type *Ty = PointeeTy;
Type *Prev = C->getType();
auto GEPIter = gep_type_begin(PointeeTy, Idxs);
bool Unknown =
!isa<ConstantInt>(Idxs[0]) && !isa<ConstantDataVector>(Idxs[0]);
for (unsigned i = 1, e = Idxs.size(); i != e;
Prev = Ty, Ty = (++GEPIter).getIndexedType(), ++i) {
if (!isa<ConstantInt>(Idxs[i]) && !isa<ConstantDataVector>(Idxs[i])) {
// We don't know if it's in range or not.
Unknown = true;
continue;
}
if (!isa<ConstantInt>(Idxs[i - 1]) && !isa<ConstantDataVector>(Idxs[i - 1]))
// Skip if the type of the previous index is not supported.
continue;
if (isa<StructType>(Ty)) {
// The verify makes sure that GEPs into a struct are in range.
continue;
}
if (isa<VectorType>(Ty)) {
// There can be awkward padding in after a non-power of two vector.
Unknown = true;
continue;
}
auto *STy = cast<ArrayType>(Ty);
if (ConstantInt *CI = dyn_cast<ConstantInt>(Idxs[i])) {
if (isIndexInRangeOfArrayType(STy->getNumElements(), CI))
// It's in range, skip to the next index.
continue;
if (CI->isNegative()) {
// It's out of range and negative, don't try to factor it.
Unknown = true;
continue;
}
} else {
auto *CV = cast<ConstantDataVector>(Idxs[i]);
bool IsInRange = true;
for (unsigned I = 0, E = CV->getNumElements(); I != E; ++I) {
auto *CI = cast<ConstantInt>(CV->getElementAsConstant(I));
IsInRange &= isIndexInRangeOfArrayType(STy->getNumElements(), CI);
if (CI->isNegative()) {
Unknown = true;
break;
}
}
if (IsInRange || Unknown)
// It's in range, skip to the next index.
// It's out of range and negative, don't try to factor it.
continue;
}
if (isa<StructType>(Prev)) {
// It's out of range, but the prior dimension is a struct
// so we can't do anything about it.
Unknown = true;
continue;
}
// Determine the number of elements in our sequential type.
uint64_t NumElements = STy->getArrayNumElements();
if (!NumElements) {
Unknown = true;
continue;
}
// It's out of range, but we can factor it into the prior
// dimension.
NewIdxs.resize(Idxs.size());
// Expand the current index or the previous index to a vector from a scalar
// if necessary.
Constant *CurrIdx = cast<Constant>(Idxs[i]);
auto *PrevIdx =
NewIdxs[i - 1] ? NewIdxs[i - 1] : cast<Constant>(Idxs[i - 1]);
bool IsCurrIdxVector = CurrIdx->getType()->isVectorTy();
bool IsPrevIdxVector = PrevIdx->getType()->isVectorTy();
bool UseVector = IsCurrIdxVector || IsPrevIdxVector;
if (!IsCurrIdxVector && IsPrevIdxVector)
CurrIdx = ConstantDataVector::getSplat(
cast<FixedVectorType>(PrevIdx->getType())->getNumElements(), CurrIdx);
if (!IsPrevIdxVector && IsCurrIdxVector)
PrevIdx = ConstantDataVector::getSplat(
cast<FixedVectorType>(CurrIdx->getType())->getNumElements(), PrevIdx);
Constant *Factor =
ConstantInt::get(CurrIdx->getType()->getScalarType(), NumElements);
if (UseVector)
Factor = ConstantDataVector::getSplat(
IsPrevIdxVector
? cast<FixedVectorType>(PrevIdx->getType())->getNumElements()
: cast<FixedVectorType>(CurrIdx->getType())->getNumElements(),
Factor);
NewIdxs[i] =
ConstantFoldBinaryInstruction(Instruction::SRem, CurrIdx, Factor);
Constant *Div =
ConstantFoldBinaryInstruction(Instruction::SDiv, CurrIdx, Factor);
// We're working on either ConstantInt or vectors of ConstantInt,
// so these should always fold.
assert(NewIdxs[i] != nullptr && Div != nullptr && "Should have folded");
unsigned CommonExtendedWidth =
std::max(PrevIdx->getType()->getScalarSizeInBits(),
Div->getType()->getScalarSizeInBits());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
// Before adding, extend both operands to i64 to avoid
// overflow trouble.
Type *ExtendedTy = Type::getIntNTy(Div->getContext(), CommonExtendedWidth);
if (UseVector)
ExtendedTy = FixedVectorType::get(
ExtendedTy,
IsPrevIdxVector
? cast<FixedVectorType>(PrevIdx->getType())->getNumElements()
: cast<FixedVectorType>(CurrIdx->getType())->getNumElements());
if (!PrevIdx->getType()->isIntOrIntVectorTy(CommonExtendedWidth))
PrevIdx =
ConstantFoldCastInstruction(Instruction::SExt, PrevIdx, ExtendedTy);
if (!Div->getType()->isIntOrIntVectorTy(CommonExtendedWidth))
Div = ConstantFoldCastInstruction(Instruction::SExt, Div, ExtendedTy);
assert(PrevIdx && Div && "Should have folded");
NewIdxs[i - 1] = ConstantExpr::getAdd(PrevIdx, Div);
}
// If we did any factoring, start over with the adjusted indices.
if (!NewIdxs.empty()) {
for (unsigned i = 0, e = Idxs.size(); i != e; ++i)
if (!NewIdxs[i]) NewIdxs[i] = cast<Constant>(Idxs[i]);
return ConstantExpr::getGetElementPtr(PointeeTy, C, NewIdxs, InBounds,
InRange);
}
// If all indices are known integers and normalized, we can do a simple
// check for the "inbounds" property.
if (!Unknown && !InBounds)
if (auto *GV = dyn_cast<GlobalVariable>(C))
if (!GV->hasExternalWeakLinkage() && GV->getValueType() == PointeeTy &&
isInBoundsIndices(Idxs))
return ConstantExpr::getGetElementPtr(PointeeTy, C, Idxs,
/*InBounds=*/true, InRange);
return nullptr;
}