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ConstantFold.cpp
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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 "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"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/MathExtras.h"
using namespace llvm;
using namespace llvm::PatternMatch;
//===----------------------------------------------------------------------===//
// ConstantFold*Instruction Implementations
//===----------------------------------------------------------------------===//
/// Convert the specified vector Constant node to the specified vector type.
/// At this point, we know that the elements of the input vector constant are
/// all simple integer or FP values.
static Constant *BitCastConstantVector(Constant *CV, VectorType *DstTy) {
if (CV->isAllOnesValue()) return Constant::getAllOnesValue(DstTy);
if (CV->isNullValue()) return Constant::getNullValue(DstTy);
// Do not iterate on scalable vector. The num of elements is unknown at
// compile-time.
if (isa<ScalableVectorType>(DstTy))
return nullptr;
// If this cast changes element count then we can't handle it here:
// doing so requires endianness information. This should be handled by
// Analysis/ConstantFolding.cpp
unsigned NumElts = cast<FixedVectorType>(DstTy)->getNumElements();
if (NumElts != cast<FixedVectorType>(CV->getType())->getNumElements())
return nullptr;
Type *DstEltTy = DstTy->getElementType();
// Fast path for splatted constants.
if (Constant *Splat = CV->getSplatValue()) {
return ConstantVector::getSplat(DstTy->getElementCount(),
ConstantExpr::getBitCast(Splat, DstEltTy));
}
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(CV->getContext(), 32);
for (unsigned i = 0; i != NumElts; ++i) {
Constant *C =
ConstantExpr::getExtractElement(CV, ConstantInt::get(Ty, i));
C = ConstantExpr::getBitCast(C, DstEltTy);
Result.push_back(C);
}
return ConstantVector::get(Result);
}
/// 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
// Check to see if we are casting a pointer to an aggregate to a pointer to
// the first element. If so, return the appropriate GEP instruction.
if (PointerType *PTy = dyn_cast<PointerType>(V->getType()))
if (PointerType *DPTy = dyn_cast<PointerType>(DestTy))
if (PTy->getAddressSpace() == DPTy->getAddressSpace() &&
!PTy->isOpaque() && !DPTy->isOpaque() &&
PTy->getNonOpaquePointerElementType()->isSized()) {
SmallVector<Value*, 8> IdxList;
Value *Zero =
Constant::getNullValue(Type::getInt32Ty(DPTy->getContext()));
IdxList.push_back(Zero);
Type *ElTy = PTy->getNonOpaquePointerElementType();
while (ElTy && ElTy != DPTy->getNonOpaquePointerElementType()) {
ElTy = GetElementPtrInst::getTypeAtIndex(ElTy, (uint64_t)0);
IdxList.push_back(Zero);
}
if (ElTy == DPTy->getNonOpaquePointerElementType())
// This GEP is inbounds because all indices are zero.
return ConstantExpr::getInBoundsGetElementPtr(
PTy->getNonOpaquePointerElementType(), V, IdxList);
}
// 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 (VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) {
assert(DestPTy->getPrimitiveSizeInBits() ==
SrcTy->getPrimitiveSizeInBits() &&
"Not cast between same sized vectors!");
SrcTy = nullptr;
// First, check for null. Undef is already handled.
if (isa<ConstantAggregateZero>(V))
return Constant::getNullValue(DestTy);
// Handle ConstantVector and ConstantAggregateVector.
return BitCastConstantVector(V, DestPTy);
}
// 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);
}
// Finally, implement bitcast folding now. The code below doesn't handle
// bitcast right.
if (isa<ConstantPointerNull>(V)) // ptr->ptr cast.
return ConstantPointerNull::get(cast<PointerType>(DestTy));
// Handle integral constant input.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
if (DestTy->isIntegerTy())
// Integral -> Integral. This is a no-op because the bit widths must
// be the same. Consequently, we just fold to V.
return 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");
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::Or: {
Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
if (!RHS)
return nullptr;
// X | -1 -> -1.
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS))
if (RHSC->isMinusOne())
return RHSC;
Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
if (!LHS)
return nullptr;
return ConstantExpr::getOr(LHS, RHS);
}
case Instruction::And: {
Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
if (!RHS)
return nullptr;
// X & 0 -> 0.
if (RHS->isNullValue())
return RHS;
Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
if (!LHS)
return nullptr;
return ConstantExpr::getAnd(LHS, RHS);
}
case Instruction::LShr: {
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(CSize - ByteStart))
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(CSize - (ByteStart + ByteSize)))
return ExtractConstantBytes(CE->getOperand(0),
ByteStart + ShAmt.getZExtValue(), ByteSize);
// TODO: Handle the 'partially zero' case.
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;
}
case Instruction::ZExt: {
unsigned SrcBitSize =
cast<IntegerType>(CE->getOperand(0)->getType())->getBitWidth();
// If extracting something that is completely zero, return 0.
if (ByteStart*8 >= SrcBitSize)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If exactly extracting the input, return it.
if (ByteStart == 0 && ByteSize*8 == SrcBitSize)
return CE->getOperand(0);
// If extracting something completely in the input, if the input is a
// multiple of 8 bits, recurse.
if ((SrcBitSize&7) == 0 && (ByteStart+ByteSize)*8 <= SrcBitSize)
return ExtractConstantBytes(CE->getOperand(0), ByteStart, ByteSize);
// Otherwise, if extracting a subset of the input, which is not multiple of
// 8 bits, do a shift and trunc to get the bits.
if ((ByteStart+ByteSize)*8 < SrcBitSize) {
assert((SrcBitSize&7) && "Shouldn't get byte sized case here");
Constant *Res = CE->getOperand(0);
if (ByteStart)
Res = ConstantExpr::getLShr(Res,
ConstantInt::get(Res->getType(), ByteStart*8));
return ConstantExpr::getTrunc(Res, IntegerType::get(C->getContext(),
ByteSize*8));
}
// TODO: Handle the 'partially zero' case.
return nullptr;
}
}
}
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 ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy);
} else if (CE->getOpcode() == Instruction::GetElementPtr &&
// Do not fold addrspacecast (gep 0, .., 0). It might make the
// addrspacecast uncanonicalized.
opc != Instruction::AddrSpaceCast &&
// Do not fold bitcast (gep) with inrange index, as this loses
// information.
!cast<GEPOperator>(CE)->getInRangeIndex().hasValue() &&
// Do not fold if the gep type is a vector, as bitcasting
// operand 0 of a vector gep will result in a bitcast between
// different sizes.
!CE->getType()->isVectorTy()) {
// If all of the indexes in the GEP are null values, there is no pointer
// adjustment going on. We might as well cast the source pointer.
bool isAllNull = true;
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
if (!CE->getOperand(i)->isNullValue()) {
isAllNull = false;
break;
}
if (isAllNull)
// This is casting one pointer type to another, always BitCast
return ConstantExpr::getPointerCast(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()) {
return ConstantVector::getSplat(
cast<VectorType>(DestTy)->getElementCount(),
ConstantExpr::getCast(opc, Splat, DstEltTy));
}
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));
res.push_back(ConstantExpr::getCast(opc, C, DstEltTy));
}
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->isHalfTy() ? APFloat::IEEEhalf() :
DestTy->isFloatTy() ? APFloat::IEEEsingle() :
DestTy->isDoubleTy() ? APFloat::IEEEdouble() :
DestTy->isX86_FP80Ty() ? APFloat::x87DoubleExtended() :
DestTy->isFP128Ty() ? APFloat::IEEEquad() :
DestTy->isPPC_FP128Ty() ? APFloat::PPCDoubleDouble() :
APFloat::Bogus(),
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::IntToPtr: //always treated as unsigned
if (V->isNullValue()) // Is it an integral null value?
return ConstantPointerNull::get(cast<PointerType>(DestTy));
return nullptr; // Other pointer types cannot be casted
case Instruction::PtrToInt: // always treated as unsigned
// Is it a null pointer value?
if (V->isNullValue())
return ConstantInt::get(DestTy, 0);
// Other pointer types cannot be casted
return nullptr;
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:
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;
if (ConstantExpr *TrueVal = dyn_cast<ConstantExpr>(V1)) {
if (TrueVal->getOpcode() == Instruction::Select)
if (TrueVal->getOperand(0) == Cond)
return ConstantExpr::getSelect(Cond, TrueVal->getOperand(1), V2);
}
if (ConstantExpr *FalseVal = dyn_cast<ConstantExpr>(V2)) {
if (FalseVal->getOpcode() == Instruction::Select)
if (FalseVal->getOperand(0) == Cond)
return ConstantExpr::getSelect(Cond, V1, FalseVal->getOperand(2));
}
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());
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();
// Undefined shuffle mask -> undefined value.
if (all_of(Mask, [](int Elt) { return Elt == UndefMaskElem; })) {
return UndefValue::get(FixedVectorType::get(EltTy, MaskNumElts));
}
// 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()) {
Constant *Elt = ConstantExpr::get(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);
Result.push_back(ConstantExpr::get(Opcode, Elt));
}
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.
// FIXME: remove unnecessary duplicated identity patterns below.
// FIXME: Use AllowRHSConstant with getBinOpIdentity to handle additional ops,
// like X << 0 = X.
Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, C1->getType());
if (Identity) {
if (C1 == Identity)
return C2;
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());
LLVM_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 / 1 -> undef
if (match(C2, m_One()))
return C1;
// 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 0 -> undef
if (match(C2, m_Zero()))
return C1;
// 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());
// undef >>a 0 -> undef
if (match(C2, m_Zero()))
return C1;
// 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 << 0 -> undef
if (match(C2, m_Zero()))
return C1;
// 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;
LLVM_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());