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llvm-mirror/lib/Analysis/ConstantFolding.cpp
Chandler Carruth 49a7633378 [PM] Move TargetLibraryInfo into the Analysis library. 
While the term "Target" is in the name, it doesn't really have to do
with the LLVM Target library -- this isn't an abstraction which LLVM
targets generally need to implement or extend. It has much more to do
with modeling the various runtime libraries on different OSes and with
different runtime environments. The "target" in this sense is the more
general sense of a target of cross compilation.

This is in preparation for porting this analysis to the new pass
manager.

No functionality changed, and updates inbound for Clang and Polly.

llvm-svn: 226078
2015-01-15 02:16:27 +00:00

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//===-- ConstantFolding.cpp - Fold instructions into constants ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines routines for folding instructions into constants.
//
// Also, to supplement the basic IR ConstantExpr simplifications,
// this file defines some additional folding routines that can make use of
// DataLayout information. These functions cannot go in IR due to library
// dependency issues.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Config/config.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Operator.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include <cerrno>
#include <cmath>
#ifdef HAVE_FENV_H
#include <fenv.h>
#endif
using namespace llvm;
//===----------------------------------------------------------------------===//
// Constant Folding internal helper functions
//===----------------------------------------------------------------------===//
/// Constant fold bitcast, symbolically evaluating it with DataLayout.
/// This always returns a non-null constant, but it may be a
/// ConstantExpr if unfoldable.
static Constant *FoldBitCast(Constant *C, Type *DestTy,
const DataLayout &TD) {
// Catch the obvious splat cases.
if (C->isNullValue() && !DestTy->isX86_MMXTy())
return Constant::getNullValue(DestTy);
if (C->isAllOnesValue() && !DestTy->isX86_MMXTy() &&
!DestTy->isPtrOrPtrVectorTy()) // Don't get ones for ptr types!
return Constant::getAllOnesValue(DestTy);
// Handle a vector->integer cast.
if (IntegerType *IT = dyn_cast<IntegerType>(DestTy)) {
VectorType *VTy = dyn_cast<VectorType>(C->getType());
if (!VTy)
return ConstantExpr::getBitCast(C, DestTy);
unsigned NumSrcElts = VTy->getNumElements();
Type *SrcEltTy = VTy->getElementType();
// If the vector is a vector of floating point, convert it to vector of int
// to simplify things.
if (SrcEltTy->isFloatingPointTy()) {
unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits();
Type *SrcIVTy =
VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElts);
// Ask IR to do the conversion now that #elts line up.
C = ConstantExpr::getBitCast(C, SrcIVTy);
}
ConstantDataVector *CDV = dyn_cast<ConstantDataVector>(C);
if (!CDV)
return ConstantExpr::getBitCast(C, DestTy);
// Now that we know that the input value is a vector of integers, just shift
// and insert them into our result.
unsigned BitShift = TD.getTypeAllocSizeInBits(SrcEltTy);
APInt Result(IT->getBitWidth(), 0);
for (unsigned i = 0; i != NumSrcElts; ++i) {
Result <<= BitShift;
if (TD.isLittleEndian())
Result |= CDV->getElementAsInteger(NumSrcElts-i-1);
else
Result |= CDV->getElementAsInteger(i);
}
return ConstantInt::get(IT, Result);
}
// The code below only handles casts to vectors currently.
VectorType *DestVTy = dyn_cast<VectorType>(DestTy);
if (!DestVTy)
return ConstantExpr::getBitCast(C, DestTy);
// If this is a scalar -> vector cast, convert the input into a <1 x scalar>
// vector so the code below can handle it uniformly.
if (isa<ConstantFP>(C) || isa<ConstantInt>(C)) {
Constant *Ops = C; // don't take the address of C!
return FoldBitCast(ConstantVector::get(Ops), DestTy, TD);
}
// If this is a bitcast from constant vector -> vector, fold it.
if (!isa<ConstantDataVector>(C) && !isa<ConstantVector>(C))
return ConstantExpr::getBitCast(C, DestTy);
// If the element types match, IR can fold it.
unsigned NumDstElt = DestVTy->getNumElements();
unsigned NumSrcElt = C->getType()->getVectorNumElements();
if (NumDstElt == NumSrcElt)
return ConstantExpr::getBitCast(C, DestTy);
Type *SrcEltTy = C->getType()->getVectorElementType();
Type *DstEltTy = DestVTy->getElementType();
// Otherwise, we're changing the number of elements in a vector, which
// requires endianness information to do the right thing. For example,
// bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
// folds to (little endian):
// <4 x i32> <i32 0, i32 0, i32 1, i32 0>
// and to (big endian):
// <4 x i32> <i32 0, i32 0, i32 0, i32 1>
// First thing is first. We only want to think about integer here, so if
// we have something in FP form, recast it as integer.
if (DstEltTy->isFloatingPointTy()) {
// Fold to an vector of integers with same size as our FP type.
unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits();
Type *DestIVTy =
VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumDstElt);
// Recursively handle this integer conversion, if possible.
C = FoldBitCast(C, DestIVTy, TD);
// Finally, IR can handle this now that #elts line up.
return ConstantExpr::getBitCast(C, DestTy);
}
// Okay, we know the destination is integer, if the input is FP, convert
// it to integer first.
if (SrcEltTy->isFloatingPointTy()) {
unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits();
Type *SrcIVTy =
VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElt);
// Ask IR to do the conversion now that #elts line up.
C = ConstantExpr::getBitCast(C, SrcIVTy);
// If IR wasn't able to fold it, bail out.
if (!isa<ConstantVector>(C) && // FIXME: Remove ConstantVector.
!isa<ConstantDataVector>(C))
return C;
}
// Now we know that the input and output vectors are both integer vectors
// of the same size, and that their #elements is not the same. Do the
// conversion here, which depends on whether the input or output has
// more elements.
bool isLittleEndian = TD.isLittleEndian();
SmallVector<Constant*, 32> Result;
if (NumDstElt < NumSrcElt) {
// Handle: bitcast (<4 x i32> <i32 0, i32 1, i32 2, i32 3> to <2 x i64>)
Constant *Zero = Constant::getNullValue(DstEltTy);
unsigned Ratio = NumSrcElt/NumDstElt;
unsigned SrcBitSize = SrcEltTy->getPrimitiveSizeInBits();
unsigned SrcElt = 0;
for (unsigned i = 0; i != NumDstElt; ++i) {
// Build each element of the result.
Constant *Elt = Zero;
unsigned ShiftAmt = isLittleEndian ? 0 : SrcBitSize*(Ratio-1);
for (unsigned j = 0; j != Ratio; ++j) {
Constant *Src =dyn_cast<ConstantInt>(C->getAggregateElement(SrcElt++));
if (!Src) // Reject constantexpr elements.
return ConstantExpr::getBitCast(C, DestTy);
// Zero extend the element to the right size.
Src = ConstantExpr::getZExt(Src, Elt->getType());
// Shift it to the right place, depending on endianness.
Src = ConstantExpr::getShl(Src,
ConstantInt::get(Src->getType(), ShiftAmt));
ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize;
// Mix it in.
Elt = ConstantExpr::getOr(Elt, Src);
}
Result.push_back(Elt);
}
return ConstantVector::get(Result);
}
// Handle: bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
unsigned Ratio = NumDstElt/NumSrcElt;
unsigned DstBitSize = TD.getTypeSizeInBits(DstEltTy);
// Loop over each source value, expanding into multiple results.
for (unsigned i = 0; i != NumSrcElt; ++i) {
Constant *Src = dyn_cast<ConstantInt>(C->getAggregateElement(i));
if (!Src) // Reject constantexpr elements.
return ConstantExpr::getBitCast(C, DestTy);
unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1);
for (unsigned j = 0; j != Ratio; ++j) {
// Shift the piece of the value into the right place, depending on
// endianness.
Constant *Elt = ConstantExpr::getLShr(Src,
ConstantInt::get(Src->getType(), ShiftAmt));
ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize;
// Truncate the element to an integer with the same pointer size and
// convert the element back to a pointer using a inttoptr.
if (DstEltTy->isPointerTy()) {
IntegerType *DstIntTy = Type::getIntNTy(C->getContext(), DstBitSize);
Constant *CE = ConstantExpr::getTrunc(Elt, DstIntTy);
Result.push_back(ConstantExpr::getIntToPtr(CE, DstEltTy));
continue;
}
// Truncate and remember this piece.
Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy));
}
}
return ConstantVector::get(Result);
}
/// If this constant is a constant offset from a global, return the global and
/// the constant. Because of constantexprs, this function is recursive.
static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
APInt &Offset, const DataLayout &TD) {
// Trivial case, constant is the global.
if ((GV = dyn_cast<GlobalValue>(C))) {
unsigned BitWidth = TD.getPointerTypeSizeInBits(GV->getType());
Offset = APInt(BitWidth, 0);
return true;
}
// Otherwise, if this isn't a constant expr, bail out.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE) return false;
// Look through ptr->int and ptr->ptr casts.
if (CE->getOpcode() == Instruction::PtrToInt ||
CE->getOpcode() == Instruction::BitCast ||
CE->getOpcode() == Instruction::AddrSpaceCast)
return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
// i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
GEPOperator *GEP = dyn_cast<GEPOperator>(CE);
if (!GEP)
return false;
unsigned BitWidth = TD.getPointerTypeSizeInBits(GEP->getType());
APInt TmpOffset(BitWidth, 0);
// If the base isn't a global+constant, we aren't either.
if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, TmpOffset, TD))
return false;
// Otherwise, add any offset that our operands provide.
if (!GEP->accumulateConstantOffset(TD, TmpOffset))
return false;
Offset = TmpOffset;
return true;
}
/// Recursive helper to read bits out of global. C is the constant being copied
/// out of. ByteOffset is an offset into C. CurPtr is the pointer to copy
/// results into and BytesLeft is the number of bytes left in
/// the CurPtr buffer. TD is the target data.
static bool ReadDataFromGlobal(Constant *C, uint64_t ByteOffset,
unsigned char *CurPtr, unsigned BytesLeft,
const DataLayout &TD) {
assert(ByteOffset <= TD.getTypeAllocSize(C->getType()) &&
"Out of range access");
// If this element is zero or undefined, we can just return since *CurPtr is
// zero initialized.
if (isa<ConstantAggregateZero>(C) || isa<UndefValue>(C))
return true;
if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
if (CI->getBitWidth() > 64 ||
(CI->getBitWidth() & 7) != 0)
return false;
uint64_t Val = CI->getZExtValue();
unsigned IntBytes = unsigned(CI->getBitWidth()/8);
for (unsigned i = 0; i != BytesLeft && ByteOffset != IntBytes; ++i) {
int n = ByteOffset;
if (!TD.isLittleEndian())
n = IntBytes - n - 1;
CurPtr[i] = (unsigned char)(Val >> (n * 8));
++ByteOffset;
}
return true;
}
if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
if (CFP->getType()->isDoubleTy()) {
C = FoldBitCast(C, Type::getInt64Ty(C->getContext()), TD);
return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD);
}
if (CFP->getType()->isFloatTy()){
C = FoldBitCast(C, Type::getInt32Ty(C->getContext()), TD);
return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD);
}
if (CFP->getType()->isHalfTy()){
C = FoldBitCast(C, Type::getInt16Ty(C->getContext()), TD);
return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD);
}
return false;
}
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
const StructLayout *SL = TD.getStructLayout(CS->getType());
unsigned Index = SL->getElementContainingOffset(ByteOffset);
uint64_t CurEltOffset = SL->getElementOffset(Index);
ByteOffset -= CurEltOffset;
while (1) {
// If the element access is to the element itself and not to tail padding,
// read the bytes from the element.
uint64_t EltSize = TD.getTypeAllocSize(CS->getOperand(Index)->getType());
if (ByteOffset < EltSize &&
!ReadDataFromGlobal(CS->getOperand(Index), ByteOffset, CurPtr,
BytesLeft, TD))
return false;
++Index;
// Check to see if we read from the last struct element, if so we're done.
if (Index == CS->getType()->getNumElements())
return true;
// If we read all of the bytes we needed from this element we're done.
uint64_t NextEltOffset = SL->getElementOffset(Index);
if (BytesLeft <= NextEltOffset - CurEltOffset - ByteOffset)
return true;
// Move to the next element of the struct.
CurPtr += NextEltOffset - CurEltOffset - ByteOffset;
BytesLeft -= NextEltOffset - CurEltOffset - ByteOffset;
ByteOffset = 0;
CurEltOffset = NextEltOffset;
}
// not reached.
}
if (isa<ConstantArray>(C) || isa<ConstantVector>(C) ||
isa<ConstantDataSequential>(C)) {
Type *EltTy = C->getType()->getSequentialElementType();
uint64_t EltSize = TD.getTypeAllocSize(EltTy);
uint64_t Index = ByteOffset / EltSize;
uint64_t Offset = ByteOffset - Index * EltSize;
uint64_t NumElts;
if (ArrayType *AT = dyn_cast<ArrayType>(C->getType()))
NumElts = AT->getNumElements();
else
NumElts = C->getType()->getVectorNumElements();
for (; Index != NumElts; ++Index) {
if (!ReadDataFromGlobal(C->getAggregateElement(Index), Offset, CurPtr,
BytesLeft, TD))
return false;
uint64_t BytesWritten = EltSize - Offset;
assert(BytesWritten <= EltSize && "Not indexing into this element?");
if (BytesWritten >= BytesLeft)
return true;
Offset = 0;
BytesLeft -= BytesWritten;
CurPtr += BytesWritten;
}
return true;
}
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
if (CE->getOpcode() == Instruction::IntToPtr &&
CE->getOperand(0)->getType() == TD.getIntPtrType(CE->getType())) {
return ReadDataFromGlobal(CE->getOperand(0), ByteOffset, CurPtr,
BytesLeft, TD);
}
}
// Otherwise, unknown initializer type.
return false;
}
static Constant *FoldReinterpretLoadFromConstPtr(Constant *C,
const DataLayout &TD) {
PointerType *PTy = cast<PointerType>(C->getType());
Type *LoadTy = PTy->getElementType();
IntegerType *IntType = dyn_cast<IntegerType>(LoadTy);
// If this isn't an integer load we can't fold it directly.
if (!IntType) {
unsigned AS = PTy->getAddressSpace();
// If this is a float/double load, we can try folding it as an int32/64 load
// and then bitcast the result. This can be useful for union cases. Note
// that address spaces don't matter here since we're not going to result in
// an actual new load.
Type *MapTy;
if (LoadTy->isHalfTy())
MapTy = Type::getInt16PtrTy(C->getContext(), AS);
else if (LoadTy->isFloatTy())
MapTy = Type::getInt32PtrTy(C->getContext(), AS);
else if (LoadTy->isDoubleTy())
MapTy = Type::getInt64PtrTy(C->getContext(), AS);
else if (LoadTy->isVectorTy()) {
MapTy = PointerType::getIntNPtrTy(C->getContext(),
TD.getTypeAllocSizeInBits(LoadTy),
AS);
} else
return nullptr;
C = FoldBitCast(C, MapTy, TD);
if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, TD))
return FoldBitCast(Res, LoadTy, TD);
return nullptr;
}
unsigned BytesLoaded = (IntType->getBitWidth() + 7) / 8;
if (BytesLoaded > 32 || BytesLoaded == 0)
return nullptr;
GlobalValue *GVal;
APInt Offset;
if (!IsConstantOffsetFromGlobal(C, GVal, Offset, TD))
return nullptr;
GlobalVariable *GV = dyn_cast<GlobalVariable>(GVal);
if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer() ||
!GV->getInitializer()->getType()->isSized())
return nullptr;
// If we're loading off the beginning of the global, some bytes may be valid,
// but we don't try to handle this.
if (Offset.isNegative())
return nullptr;
// If we're not accessing anything in this constant, the result is undefined.
if (Offset.getZExtValue() >=
TD.getTypeAllocSize(GV->getInitializer()->getType()))
return UndefValue::get(IntType);
unsigned char RawBytes[32] = {0};
if (!ReadDataFromGlobal(GV->getInitializer(), Offset.getZExtValue(), RawBytes,
BytesLoaded, TD))
return nullptr;
APInt ResultVal = APInt(IntType->getBitWidth(), 0);
if (TD.isLittleEndian()) {
ResultVal = RawBytes[BytesLoaded - 1];
for (unsigned i = 1; i != BytesLoaded; ++i) {
ResultVal <<= 8;
ResultVal |= RawBytes[BytesLoaded - 1 - i];
}
} else {
ResultVal = RawBytes[0];
for (unsigned i = 1; i != BytesLoaded; ++i) {
ResultVal <<= 8;
ResultVal |= RawBytes[i];
}
}
return ConstantInt::get(IntType->getContext(), ResultVal);
}
static Constant *ConstantFoldLoadThroughBitcast(ConstantExpr *CE,
const DataLayout *DL) {
if (!DL)
return nullptr;
auto *DestPtrTy = dyn_cast<PointerType>(CE->getType());
if (!DestPtrTy)
return nullptr;
Type *DestTy = DestPtrTy->getElementType();
Constant *C = ConstantFoldLoadFromConstPtr(CE->getOperand(0), DL);
if (!C)
return nullptr;
do {
Type *SrcTy = C->getType();
// If the type sizes are the same and a cast is legal, just directly
// cast the constant.
if (DL->getTypeSizeInBits(DestTy) == DL->getTypeSizeInBits(SrcTy)) {
Instruction::CastOps Cast = Instruction::BitCast;
// If we are going from a pointer to int or vice versa, we spell the cast
// differently.
if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
Cast = Instruction::IntToPtr;
else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
Cast = Instruction::PtrToInt;
if (CastInst::castIsValid(Cast, C, DestTy))
return ConstantExpr::getCast(Cast, C, DestTy);
}
// If this isn't an aggregate type, there is nothing we can do to drill down
// and find a bitcastable constant.
if (!SrcTy->isAggregateType())
return nullptr;
// We're simulating a load through a pointer that was bitcast to point to
// a different type, so we can try to walk down through the initial
// elements of an aggregate to see if some part of th e aggregate is
// castable to implement the "load" semantic model.
C = C->getAggregateElement(0u);
} while (C);
return nullptr;
}
/// Return the value that a load from C would produce if it is constant and
/// determinable. If this is not determinable, return null.
Constant *llvm::ConstantFoldLoadFromConstPtr(Constant *C,
const DataLayout *TD) {
// First, try the easy cases:
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
if (GV->isConstant() && GV->hasDefinitiveInitializer())
return GV->getInitializer();
// If the loaded value isn't a constant expr, we can't handle it.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE)
return nullptr;
if (CE->getOpcode() == Instruction::GetElementPtr) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0))) {
if (GV->isConstant() && GV->hasDefinitiveInitializer()) {
if (Constant *V =
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE))
return V;
}
}
}
if (CE->getOpcode() == Instruction::BitCast)
if (Constant *LoadedC = ConstantFoldLoadThroughBitcast(CE, TD))
return LoadedC;
// Instead of loading constant c string, use corresponding integer value
// directly if string length is small enough.
StringRef Str;
if (TD && getConstantStringInfo(CE, Str) && !Str.empty()) {
unsigned StrLen = Str.size();
Type *Ty = cast<PointerType>(CE->getType())->getElementType();
unsigned NumBits = Ty->getPrimitiveSizeInBits();
// Replace load with immediate integer if the result is an integer or fp
// value.
if ((NumBits >> 3) == StrLen + 1 && (NumBits & 7) == 0 &&
(isa<IntegerType>(Ty) || Ty->isFloatingPointTy())) {
APInt StrVal(NumBits, 0);
APInt SingleChar(NumBits, 0);
if (TD->isLittleEndian()) {
for (signed i = StrLen-1; i >= 0; i--) {
SingleChar = (uint64_t) Str[i] & UCHAR_MAX;
StrVal = (StrVal << 8) | SingleChar;
}
} else {
for (unsigned i = 0; i < StrLen; i++) {
SingleChar = (uint64_t) Str[i] & UCHAR_MAX;
StrVal = (StrVal << 8) | SingleChar;
}
// Append NULL at the end.
SingleChar = 0;
StrVal = (StrVal << 8) | SingleChar;
}
Constant *Res = ConstantInt::get(CE->getContext(), StrVal);
if (Ty->isFloatingPointTy())
Res = ConstantExpr::getBitCast(Res, Ty);
return Res;
}
}
// If this load comes from anywhere in a constant global, and if the global
// is all undef or zero, we know what it loads.
if (GlobalVariable *GV =
dyn_cast<GlobalVariable>(GetUnderlyingObject(CE, TD))) {
if (GV->isConstant() && GV->hasDefinitiveInitializer()) {
Type *ResTy = cast<PointerType>(C->getType())->getElementType();
if (GV->getInitializer()->isNullValue())
return Constant::getNullValue(ResTy);
if (isa<UndefValue>(GV->getInitializer()))
return UndefValue::get(ResTy);
}
}
// Try hard to fold loads from bitcasted strange and non-type-safe things.
if (TD)
return FoldReinterpretLoadFromConstPtr(CE, *TD);
return nullptr;
}
static Constant *ConstantFoldLoadInst(const LoadInst *LI, const DataLayout *TD){
if (LI->isVolatile()) return nullptr;
if (Constant *C = dyn_cast<Constant>(LI->getOperand(0)))
return ConstantFoldLoadFromConstPtr(C, TD);
return nullptr;
}
/// One of Op0/Op1 is a constant expression.
/// Attempt to symbolically evaluate the result of a binary operator merging
/// these together. If target data info is available, it is provided as DL,
/// otherwise DL is null.
static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
Constant *Op1, const DataLayout *DL){
// SROA
// Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
// Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
// bits.
if (Opc == Instruction::And && DL) {
unsigned BitWidth = DL->getTypeSizeInBits(Op0->getType()->getScalarType());
APInt KnownZero0(BitWidth, 0), KnownOne0(BitWidth, 0);
APInt KnownZero1(BitWidth, 0), KnownOne1(BitWidth, 0);
computeKnownBits(Op0, KnownZero0, KnownOne0, DL);
computeKnownBits(Op1, KnownZero1, KnownOne1, DL);
if ((KnownOne1 | KnownZero0).isAllOnesValue()) {
// All the bits of Op0 that the 'and' could be masking are already zero.
return Op0;
}
if ((KnownOne0 | KnownZero1).isAllOnesValue()) {
// All the bits of Op1 that the 'and' could be masking are already zero.
return Op1;
}
APInt KnownZero = KnownZero0 | KnownZero1;
APInt KnownOne = KnownOne0 & KnownOne1;
if ((KnownZero | KnownOne).isAllOnesValue()) {
return ConstantInt::get(Op0->getType(), KnownOne);
}
}
// If the constant expr is something like &A[123] - &A[4].f, fold this into a
// constant. This happens frequently when iterating over a global array.
if (Opc == Instruction::Sub && DL) {
GlobalValue *GV1, *GV2;
APInt Offs1, Offs2;
if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *DL))
if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *DL) &&
GV1 == GV2) {
unsigned OpSize = DL->getTypeSizeInBits(Op0->getType());
// (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
// PtrToInt may change the bitwidth so we have convert to the right size
// first.
return ConstantInt::get(Op0->getType(), Offs1.zextOrTrunc(OpSize) -
Offs2.zextOrTrunc(OpSize));
}
}
return nullptr;
}
/// If array indices are not pointer-sized integers, explicitly cast them so
/// that they aren't implicitly casted by the getelementptr.
static Constant *CastGEPIndices(ArrayRef<Constant *> Ops,
Type *ResultTy, const DataLayout *TD,
const TargetLibraryInfo *TLI) {
if (!TD)
return nullptr;
Type *IntPtrTy = TD->getIntPtrType(ResultTy);
bool Any = false;
SmallVector<Constant*, 32> NewIdxs;
for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
if ((i == 1 ||
!isa<StructType>(GetElementPtrInst::getIndexedType(
Ops[0]->getType(),
Ops.slice(1, i - 1)))) &&
Ops[i]->getType() != IntPtrTy) {
Any = true;
NewIdxs.push_back(ConstantExpr::getCast(CastInst::getCastOpcode(Ops[i],
true,
IntPtrTy,
true),
Ops[i], IntPtrTy));
} else
NewIdxs.push_back(Ops[i]);
}
if (!Any)
return nullptr;
Constant *C = ConstantExpr::getGetElementPtr(Ops[0], NewIdxs);
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
if (Constant *Folded = ConstantFoldConstantExpression(CE, TD, TLI))
C = Folded;
}
return C;
}
/// Strip the pointer casts, but preserve the address space information.
static Constant* StripPtrCastKeepAS(Constant* Ptr) {
assert(Ptr->getType()->isPointerTy() && "Not a pointer type");
PointerType *OldPtrTy = cast<PointerType>(Ptr->getType());
Ptr = Ptr->stripPointerCasts();
PointerType *NewPtrTy = cast<PointerType>(Ptr->getType());
// Preserve the address space number of the pointer.
if (NewPtrTy->getAddressSpace() != OldPtrTy->getAddressSpace()) {
NewPtrTy = NewPtrTy->getElementType()->getPointerTo(
OldPtrTy->getAddressSpace());
Ptr = ConstantExpr::getPointerCast(Ptr, NewPtrTy);
}
return Ptr;
}
/// If we can symbolically evaluate the GEP constant expression, do so.
static Constant *SymbolicallyEvaluateGEP(ArrayRef<Constant *> Ops,
Type *ResultTy, const DataLayout *TD,
const TargetLibraryInfo *TLI) {
Constant *Ptr = Ops[0];
if (!TD || !Ptr->getType()->getPointerElementType()->isSized() ||
!Ptr->getType()->isPointerTy())
return nullptr;
Type *IntPtrTy = TD->getIntPtrType(Ptr->getType());
Type *ResultElementTy = ResultTy->getPointerElementType();
// If this is a constant expr gep that is effectively computing an
// "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
for (unsigned i = 1, e = Ops.size(); i != e; ++i)
if (!isa<ConstantInt>(Ops[i])) {
// If this is "gep i8* Ptr, (sub 0, V)", fold this as:
// "inttoptr (sub (ptrtoint Ptr), V)"
if (Ops.size() == 2 && ResultElementTy->isIntegerTy(8)) {
ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[1]);
assert((!CE || CE->getType() == IntPtrTy) &&
"CastGEPIndices didn't canonicalize index types!");
if (CE && CE->getOpcode() == Instruction::Sub &&
CE->getOperand(0)->isNullValue()) {
Constant *Res = ConstantExpr::getPtrToInt(Ptr, CE->getType());
Res = ConstantExpr::getSub(Res, CE->getOperand(1));
Res = ConstantExpr::getIntToPtr(Res, ResultTy);
if (ConstantExpr *ResCE = dyn_cast<ConstantExpr>(Res))
Res = ConstantFoldConstantExpression(ResCE, TD, TLI);
return Res;
}
}
return nullptr;
}
unsigned BitWidth = TD->getTypeSizeInBits(IntPtrTy);
APInt Offset =
APInt(BitWidth, TD->getIndexedOffset(Ptr->getType(),
makeArrayRef((Value *const*)
Ops.data() + 1,
Ops.size() - 1)));
Ptr = StripPtrCastKeepAS(Ptr);
// If this is a GEP of a GEP, fold it all into a single GEP.
while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
SmallVector<Value *, 4> NestedOps(GEP->op_begin() + 1, GEP->op_end());
// Do not try the incorporate the sub-GEP if some index is not a number.
bool AllConstantInt = true;
for (unsigned i = 0, e = NestedOps.size(); i != e; ++i)
if (!isa<ConstantInt>(NestedOps[i])) {
AllConstantInt = false;
break;
}
if (!AllConstantInt)
break;
Ptr = cast<Constant>(GEP->getOperand(0));
Offset += APInt(BitWidth,
TD->getIndexedOffset(Ptr->getType(), NestedOps));
Ptr = StripPtrCastKeepAS(Ptr);
}
// If the base value for this address is a literal integer value, fold the
// getelementptr to the resulting integer value casted to the pointer type.
APInt BasePtr(BitWidth, 0);
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
if (CE->getOpcode() == Instruction::IntToPtr) {
if (ConstantInt *Base = dyn_cast<ConstantInt>(CE->getOperand(0)))
BasePtr = Base->getValue().zextOrTrunc(BitWidth);
}
}
if (Ptr->isNullValue() || BasePtr != 0) {
Constant *C = ConstantInt::get(Ptr->getContext(), Offset + BasePtr);
return ConstantExpr::getIntToPtr(C, ResultTy);
}
// Otherwise form a regular getelementptr. Recompute the indices so that
// we eliminate over-indexing of the notional static type array bounds.
// This makes it easy to determine if the getelementptr is "inbounds".
// Also, this helps GlobalOpt do SROA on GlobalVariables.
Type *Ty = Ptr->getType();
assert(Ty->isPointerTy() && "Forming regular GEP of non-pointer type");
SmallVector<Constant *, 32> NewIdxs;
do {
if (SequentialType *ATy = dyn_cast<SequentialType>(Ty)) {
if (ATy->isPointerTy()) {
// The only pointer indexing we'll do is on the first index of the GEP.
if (!NewIdxs.empty())
break;
// Only handle pointers to sized types, not pointers to functions.
if (!ATy->getElementType()->isSized())
return nullptr;
}
// Determine which element of the array the offset points into.
APInt ElemSize(BitWidth, TD->getTypeAllocSize(ATy->getElementType()));
if (ElemSize == 0)
// The element size is 0. This may be [0 x Ty]*, so just use a zero
// index for this level and proceed to the next level to see if it can
// accommodate the offset.
NewIdxs.push_back(ConstantInt::get(IntPtrTy, 0));
else {
// The element size is non-zero divide the offset by the element
// size (rounding down), to compute the index at this level.
APInt NewIdx = Offset.udiv(ElemSize);
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(IntPtrTy, NewIdx));
}
Ty = ATy->getElementType();
} else if (StructType *STy = dyn_cast<StructType>(Ty)) {
// If we end up with an offset that isn't valid for this struct type, we
// can't re-form this GEP in a regular form, so bail out. The pointer
// operand likely went through casts that are necessary to make the GEP
// sensible.
const StructLayout &SL = *TD->getStructLayout(STy);
if (Offset.uge(SL.getSizeInBytes()))
break;
// Determine which field of the struct the offset points into. The
// getZExtValue is fine as we've already ensured that the offset is
// within the range representable by the StructLayout API.
unsigned ElIdx = SL.getElementContainingOffset(Offset.getZExtValue());
NewIdxs.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
ElIdx));
Offset -= APInt(BitWidth, SL.getElementOffset(ElIdx));
Ty = STy->getTypeAtIndex(ElIdx);
} else {
// We've reached some non-indexable type.
break;
}
} while (Ty != ResultElementTy);
// If we haven't used up the entire offset by descending the static
// type, then the offset is pointing into the middle of an indivisible
// member, so we can't simplify it.
if (Offset != 0)
return nullptr;
// Create a GEP.
Constant *C = ConstantExpr::getGetElementPtr(Ptr, NewIdxs);
assert(C->getType()->getPointerElementType() == Ty &&
"Computed GetElementPtr has unexpected type!");
// If we ended up indexing a member with a type that doesn't match
// the type of what the original indices indexed, add a cast.
if (Ty != ResultElementTy)
C = FoldBitCast(C, ResultTy, *TD);
return C;
}
//===----------------------------------------------------------------------===//
// Constant Folding public APIs
//===----------------------------------------------------------------------===//
/// Try to constant fold the specified instruction.
/// If successful, the constant result is returned, if not, null is returned.
/// Note that this fails if not all of the operands are constant. Otherwise,
/// this function can only fail when attempting to fold instructions like loads
/// and stores, which have no constant expression form.
Constant *llvm::ConstantFoldInstruction(Instruction *I,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
// Handle PHI nodes quickly here...
if (PHINode *PN = dyn_cast<PHINode>(I)) {
Constant *CommonValue = nullptr;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PN->getIncomingValue(i);
// If the incoming value is undef then skip it. Note that while we could
// skip the value if it is equal to the phi node itself we choose not to
// because that would break the rule that constant folding only applies if
// all operands are constants.
if (isa<UndefValue>(Incoming))
continue;
// If the incoming value is not a constant, then give up.
Constant *C = dyn_cast<Constant>(Incoming);
if (!C)
return nullptr;
// Fold the PHI's operands.
if (ConstantExpr *NewC = dyn_cast<ConstantExpr>(C))
C = ConstantFoldConstantExpression(NewC, TD, TLI);
// If the incoming value is a different constant to
// the one we saw previously, then give up.
if (CommonValue && C != CommonValue)
return nullptr;
CommonValue = C;
}
// If we reach here, all incoming values are the same constant or undef.
return CommonValue ? CommonValue : UndefValue::get(PN->getType());
}
// Scan the operand list, checking to see if they are all constants, if so,
// hand off to ConstantFoldInstOperands.
SmallVector<Constant*, 8> Ops;
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
Constant *Op = dyn_cast<Constant>(*i);
if (!Op)
return nullptr; // All operands not constant!
// Fold the Instruction's operands.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(Op))
Op = ConstantFoldConstantExpression(NewCE, TD, TLI);
Ops.push_back(Op);
}
if (const CmpInst *CI = dyn_cast<CmpInst>(I))
return ConstantFoldCompareInstOperands(CI->getPredicate(), Ops[0], Ops[1],
TD, TLI);
if (const LoadInst *LI = dyn_cast<LoadInst>(I))
return ConstantFoldLoadInst(LI, TD);
if (InsertValueInst *IVI = dyn_cast<InsertValueInst>(I)) {
return ConstantExpr::getInsertValue(
cast<Constant>(IVI->getAggregateOperand()),
cast<Constant>(IVI->getInsertedValueOperand()),
IVI->getIndices());
}
if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I)) {
return ConstantExpr::getExtractValue(
cast<Constant>(EVI->getAggregateOperand()),
EVI->getIndices());
}
return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops, TD, TLI);
}
static Constant *
ConstantFoldConstantExpressionImpl(const ConstantExpr *CE, const DataLayout *TD,
const TargetLibraryInfo *TLI,
SmallPtrSetImpl<ConstantExpr *> &FoldedOps) {
SmallVector<Constant *, 8> Ops;
for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end(); i != e;
++i) {
Constant *NewC = cast<Constant>(*i);
// Recursively fold the ConstantExpr's operands. If we have already folded
// a ConstantExpr, we don't have to process it again.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(NewC)) {
if (FoldedOps.insert(NewCE).second)
NewC = ConstantFoldConstantExpressionImpl(NewCE, TD, TLI, FoldedOps);
}
Ops.push_back(NewC);
}
if (CE->isCompare())
return ConstantFoldCompareInstOperands(CE->getPredicate(), Ops[0], Ops[1],
TD, TLI);
return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(), Ops, TD, TLI);
}
/// Attempt to fold the constant expression
/// using the specified DataLayout. If successful, the constant result is
/// result is returned, if not, null is returned.
Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
SmallPtrSet<ConstantExpr *, 4> FoldedOps;
return ConstantFoldConstantExpressionImpl(CE, TD, TLI, FoldedOps);
}
/// Attempt to constant fold an instruction with the
/// specified opcode and operands. If successful, the constant result is
/// returned, if not, null is returned. Note that this function can fail when
/// attempting to fold instructions like loads and stores, which have no
/// constant expression form.
///
/// TODO: This function neither utilizes nor preserves nsw/nuw/inbounds/etc
/// information, due to only being passed an opcode and operands. Constant
/// folding using this function strips this information.
///
Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, Type *DestTy,
ArrayRef<Constant *> Ops,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
// Handle easy binops first.
if (Instruction::isBinaryOp(Opcode)) {
if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1])) {
if (Constant *C = SymbolicallyEvaluateBinop(Opcode, Ops[0], Ops[1], TD))
return C;
}
return ConstantExpr::get(Opcode, Ops[0], Ops[1]);
}
switch (Opcode) {
default: return nullptr;
case Instruction::ICmp:
case Instruction::FCmp: llvm_unreachable("Invalid for compares");
case Instruction::Call:
if (Function *F = dyn_cast<Function>(Ops.back()))
if (canConstantFoldCallTo(F))
return ConstantFoldCall(F, Ops.slice(0, Ops.size() - 1), TLI);
return nullptr;
case Instruction::PtrToInt:
// If the input is a inttoptr, eliminate the pair. This requires knowing
// the width of a pointer, so it can't be done in ConstantExpr::getCast.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) {
if (TD && CE->getOpcode() == Instruction::IntToPtr) {
Constant *Input = CE->getOperand(0);
unsigned InWidth = Input->getType()->getScalarSizeInBits();
unsigned PtrWidth = TD->getPointerTypeSizeInBits(CE->getType());
if (PtrWidth < InWidth) {
Constant *Mask =
ConstantInt::get(CE->getContext(),
APInt::getLowBitsSet(InWidth, PtrWidth));
Input = ConstantExpr::getAnd(Input, Mask);
}
// Do a zext or trunc to get to the dest size.
return ConstantExpr::getIntegerCast(Input, DestTy, false);
}
}
return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
case Instruction::IntToPtr:
// If the input is a ptrtoint, turn the pair into a ptr to ptr bitcast if
// the int size is >= the ptr size and the address spaces are the same.
// This requires knowing the width of a pointer, so it can't be done in
// ConstantExpr::getCast.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) {
if (TD && CE->getOpcode() == Instruction::PtrToInt) {
Constant *SrcPtr = CE->getOperand(0);
unsigned SrcPtrSize = TD->getPointerTypeSizeInBits(SrcPtr->getType());
unsigned MidIntSize = CE->getType()->getScalarSizeInBits();
if (MidIntSize >= SrcPtrSize) {
unsigned SrcAS = SrcPtr->getType()->getPointerAddressSpace();
if (SrcAS == DestTy->getPointerAddressSpace())
return FoldBitCast(CE->getOperand(0), DestTy, *TD);
}
}
}
return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::AddrSpaceCast:
return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
case Instruction::BitCast:
if (TD)
return FoldBitCast(Ops[0], DestTy, *TD);
return ConstantExpr::getBitCast(Ops[0], DestTy);
case Instruction::Select:
return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
case Instruction::ExtractElement:
return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
case Instruction::InsertElement:
return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
case Instruction::ShuffleVector:
return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
case Instruction::GetElementPtr:
if (Constant *C = CastGEPIndices(Ops, DestTy, TD, TLI))
return C;
if (Constant *C = SymbolicallyEvaluateGEP(Ops, DestTy, TD, TLI))
return C;
return ConstantExpr::getGetElementPtr(Ops[0], Ops.slice(1));
}
}
/// Attempt to constant fold a compare
/// instruction (icmp/fcmp) with the specified operands. If it fails, it
/// returns a constant expression of the specified operands.
Constant *llvm::ConstantFoldCompareInstOperands(unsigned Predicate,
Constant *Ops0, Constant *Ops1,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
// fold: icmp (inttoptr x), null -> icmp x, 0
// fold: icmp (ptrtoint x), 0 -> icmp x, null
// fold: icmp (inttoptr x), (inttoptr y) -> icmp trunc/zext x, trunc/zext y
// fold: icmp (ptrtoint x), (ptrtoint y) -> icmp x, y
//
// ConstantExpr::getCompare cannot do this, because it doesn't have TD
// around to know if bit truncation is happening.
if (ConstantExpr *CE0 = dyn_cast<ConstantExpr>(Ops0)) {
if (TD && Ops1->isNullValue()) {
if (CE0->getOpcode() == Instruction::IntToPtr) {
Type *IntPtrTy = TD->getIntPtrType(CE0->getType());
// Convert the integer value to the right size to ensure we get the
// proper extension or truncation.
Constant *C = ConstantExpr::getIntegerCast(CE0->getOperand(0),
IntPtrTy, false);
Constant *Null = Constant::getNullValue(C->getType());
return ConstantFoldCompareInstOperands(Predicate, C, Null, TD, TLI);
}
// Only do this transformation if the int is intptrty in size, otherwise
// there is a truncation or extension that we aren't modeling.
if (CE0->getOpcode() == Instruction::PtrToInt) {
Type *IntPtrTy = TD->getIntPtrType(CE0->getOperand(0)->getType());
if (CE0->getType() == IntPtrTy) {
Constant *C = CE0->getOperand(0);
Constant *Null = Constant::getNullValue(C->getType());
return ConstantFoldCompareInstOperands(Predicate, C, Null, TD, TLI);
}
}
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops1)) {
if (TD && CE0->getOpcode() == CE1->getOpcode()) {
if (CE0->getOpcode() == Instruction::IntToPtr) {
Type *IntPtrTy = TD->getIntPtrType(CE0->getType());
// Convert the integer value to the right size to ensure we get the
// proper extension or truncation.
Constant *C0 = ConstantExpr::getIntegerCast(CE0->getOperand(0),
IntPtrTy, false);
Constant *C1 = ConstantExpr::getIntegerCast(CE1->getOperand(0),
IntPtrTy, false);
return ConstantFoldCompareInstOperands(Predicate, C0, C1, TD, TLI);
}
// Only do this transformation if the int is intptrty in size, otherwise
// there is a truncation or extension that we aren't modeling.
if (CE0->getOpcode() == Instruction::PtrToInt) {
Type *IntPtrTy = TD->getIntPtrType(CE0->getOperand(0)->getType());
if (CE0->getType() == IntPtrTy &&
CE0->getOperand(0)->getType() == CE1->getOperand(0)->getType()) {
return ConstantFoldCompareInstOperands(Predicate,
CE0->getOperand(0),
CE1->getOperand(0),
TD,
TLI);
}
}
}
}
// icmp eq (or x, y), 0 -> (icmp eq x, 0) & (icmp eq y, 0)
// icmp ne (or x, y), 0 -> (icmp ne x, 0) | (icmp ne y, 0)
if ((Predicate == ICmpInst::ICMP_EQ || Predicate == ICmpInst::ICMP_NE) &&
CE0->getOpcode() == Instruction::Or && Ops1->isNullValue()) {
Constant *LHS =
ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(0), Ops1,
TD, TLI);
Constant *RHS =
ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(1), Ops1,
TD, TLI);
unsigned OpC =
Predicate == ICmpInst::ICMP_EQ ? Instruction::And : Instruction::Or;
Constant *Ops[] = { LHS, RHS };
return ConstantFoldInstOperands(OpC, LHS->getType(), Ops, TD, TLI);
}
}
return ConstantExpr::getCompare(Predicate, Ops0, Ops1);
}
/// Given a constant and a getelementptr constantexpr, return the constant value
/// being addressed by the constant expression, or null if something is funny
/// and we can't decide.
Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
ConstantExpr *CE) {
if (!CE->getOperand(1)->isNullValue())
return nullptr; // Do not allow stepping over the value!
// Loop over all of the operands, tracking down which value we are
// addressing.
for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i) {
C = C->getAggregateElement(CE->getOperand(i));
if (!C)
return nullptr;
}
return C;
}
/// Given a constant and getelementptr indices (with an *implied* zero pointer
/// index that is not in the list), return the constant value being addressed by
/// a virtual load, or null if something is funny and we can't decide.
Constant *llvm::ConstantFoldLoadThroughGEPIndices(Constant *C,
ArrayRef<Constant*> Indices) {
// Loop over all of the operands, tracking down which value we are
// addressing.
for (unsigned i = 0, e = Indices.size(); i != e; ++i) {
C = C->getAggregateElement(Indices[i]);
if (!C)
return nullptr;
}
return C;
}
//===----------------------------------------------------------------------===//
// Constant Folding for Calls
//
/// Return true if it's even possible to fold a call to the specified function.
bool llvm::canConstantFoldCallTo(const Function *F) {
switch (F->getIntrinsicID()) {
case Intrinsic::fabs:
case Intrinsic::minnum:
case Intrinsic::maxnum:
case Intrinsic::log:
case Intrinsic::log2:
case Intrinsic::log10:
case Intrinsic::exp:
case Intrinsic::exp2:
case Intrinsic::floor:
case Intrinsic::ceil:
case Intrinsic::sqrt:
case Intrinsic::pow:
case Intrinsic::powi:
case Intrinsic::bswap:
case Intrinsic::ctpop:
case Intrinsic::ctlz:
case Intrinsic::cttz:
case Intrinsic::fma:
case Intrinsic::fmuladd:
case Intrinsic::copysign:
case Intrinsic::round:
case Intrinsic::sadd_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::umul_with_overflow:
case Intrinsic::convert_from_fp16:
case Intrinsic::convert_to_fp16:
case Intrinsic::x86_sse_cvtss2si:
case Intrinsic::x86_sse_cvtss2si64:
case Intrinsic::x86_sse_cvttss2si:
case Intrinsic::x86_sse_cvttss2si64:
case Intrinsic::x86_sse2_cvtsd2si:
case Intrinsic::x86_sse2_cvtsd2si64:
case Intrinsic::x86_sse2_cvttsd2si:
case Intrinsic::x86_sse2_cvttsd2si64:
return true;
default:
return false;
case 0: break;
}
if (!F->hasName())
return false;
StringRef Name = F->getName();
// In these cases, the check of the length is required. We don't want to
// return true for a name like "cos\0blah" which strcmp would return equal to
// "cos", but has length 8.
switch (Name[0]) {
default: return false;
case 'a':
return Name == "acos" || Name == "asin" || Name == "atan" || Name =="atan2";
case 'c':
return Name == "cos" || Name == "ceil" || Name == "cosf" || Name == "cosh";
case 'e':
return Name == "exp" || Name == "exp2";
case 'f':
return Name == "fabs" || Name == "fmod" || Name == "floor";
case 'l':
return Name == "log" || Name == "log10";
case 'p':
return Name == "pow";
case 's':
return Name == "sin" || Name == "sinh" || Name == "sqrt" ||
Name == "sinf" || Name == "sqrtf";
case 't':
return Name == "tan" || Name == "tanh";
}
}
static Constant *GetConstantFoldFPValue(double V, Type *Ty) {
if (Ty->isHalfTy()) {
APFloat APF(V);
bool unused;
APF.convert(APFloat::IEEEhalf, APFloat::rmNearestTiesToEven, &unused);
return ConstantFP::get(Ty->getContext(), APF);
}
if (Ty->isFloatTy())
return ConstantFP::get(Ty->getContext(), APFloat((float)V));
if (Ty->isDoubleTy())
return ConstantFP::get(Ty->getContext(), APFloat(V));
llvm_unreachable("Can only constant fold half/float/double");
}
namespace {
/// Clear the floating-point exception state.
static inline void llvm_fenv_clearexcept() {
#if defined(HAVE_FENV_H) && HAVE_DECL_FE_ALL_EXCEPT
feclearexcept(FE_ALL_EXCEPT);
#endif
errno = 0;
}
/// Test if a floating-point exception was raised.
static inline bool llvm_fenv_testexcept() {
int errno_val = errno;
if (errno_val == ERANGE || errno_val == EDOM)
return true;
#if defined(HAVE_FENV_H) && HAVE_DECL_FE_ALL_EXCEPT && HAVE_DECL_FE_INEXACT
if (fetestexcept(FE_ALL_EXCEPT & ~FE_INEXACT))
return true;
#endif
return false;
}
} // End namespace
static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
Type *Ty) {
llvm_fenv_clearexcept();
V = NativeFP(V);
if (llvm_fenv_testexcept()) {
llvm_fenv_clearexcept();
return nullptr;
}
return GetConstantFoldFPValue(V, Ty);
}
static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
double V, double W, Type *Ty) {
llvm_fenv_clearexcept();
V = NativeFP(V, W);
if (llvm_fenv_testexcept()) {
llvm_fenv_clearexcept();
return nullptr;
}
return GetConstantFoldFPValue(V, Ty);
}
/// Attempt to fold an SSE floating point to integer conversion of a constant
/// floating point. If roundTowardZero is false, the default IEEE rounding is
/// used (toward nearest, ties to even). This matches the behavior of the
/// non-truncating SSE instructions in the default rounding mode. The desired
/// integer type Ty is used to select how many bits are available for the
/// result. Returns null if the conversion cannot be performed, otherwise
/// returns the Constant value resulting from the conversion.
static Constant *ConstantFoldConvertToInt(const APFloat &Val,
bool roundTowardZero, Type *Ty) {
// All of these conversion intrinsics form an integer of at most 64bits.
unsigned ResultWidth = Ty->getIntegerBitWidth();
assert(ResultWidth <= 64 &&
"Can only constant fold conversions to 64 and 32 bit ints");
uint64_t UIntVal;
bool isExact = false;
APFloat::roundingMode mode = roundTowardZero? APFloat::rmTowardZero
: APFloat::rmNearestTiesToEven;
APFloat::opStatus status = Val.convertToInteger(&UIntVal, ResultWidth,
/*isSigned=*/true, mode,
&isExact);
if (status != APFloat::opOK && status != APFloat::opInexact)
return nullptr;
return ConstantInt::get(Ty, UIntVal, /*isSigned=*/true);
}
static double getValueAsDouble(ConstantFP *Op) {
Type *Ty = Op->getType();
if (Ty->isFloatTy())
return Op->getValueAPF().convertToFloat();
if (Ty->isDoubleTy())
return Op->getValueAPF().convertToDouble();
bool unused;
APFloat APF = Op->getValueAPF();
APF.convert(APFloat::IEEEdouble, APFloat::rmNearestTiesToEven, &unused);
return APF.convertToDouble();
}
static Constant *ConstantFoldScalarCall(StringRef Name, unsigned IntrinsicID,
Type *Ty, ArrayRef<Constant *> Operands,
const TargetLibraryInfo *TLI) {
if (Operands.size() == 1) {
if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
if (IntrinsicID == Intrinsic::convert_to_fp16) {
APFloat Val(Op->getValueAPF());
bool lost = false;
Val.convert(APFloat::IEEEhalf, APFloat::rmNearestTiesToEven, &lost);
return ConstantInt::get(Ty->getContext(), Val.bitcastToAPInt());
}
if (!Ty->isHalfTy() && !Ty->isFloatTy() && !Ty->isDoubleTy())
return nullptr;
if (IntrinsicID == Intrinsic::round) {
APFloat V = Op->getValueAPF();
V.roundToIntegral(APFloat::rmNearestTiesToAway);
return ConstantFP::get(Ty->getContext(), V);
}
/// We only fold functions with finite arguments. Folding NaN and inf is
/// likely to be aborted with an exception anyway, and some host libms
/// have known errors raising exceptions.
if (Op->getValueAPF().isNaN() || Op->getValueAPF().isInfinity())
return nullptr;
/// Currently APFloat versions of these functions do not exist, so we use
/// the host native double versions. Float versions are not called
/// directly but for all these it is true (float)(f((double)arg)) ==
/// f(arg). Long double not supported yet.
double V = getValueAsDouble(Op);
switch (IntrinsicID) {
default: break;
case Intrinsic::fabs:
return ConstantFoldFP(fabs, V, Ty);
#if HAVE_LOG2
case Intrinsic::log2:
return ConstantFoldFP(log2, V, Ty);
#endif
#if HAVE_LOG
case Intrinsic::log:
return ConstantFoldFP(log, V, Ty);
#endif
#if HAVE_LOG10
case Intrinsic::log10:
return ConstantFoldFP(log10, V, Ty);
#endif
#if HAVE_EXP
case Intrinsic::exp:
return ConstantFoldFP(exp, V, Ty);
#endif
#if HAVE_EXP2
case Intrinsic::exp2:
return ConstantFoldFP(exp2, V, Ty);
#endif
case Intrinsic::floor:
return ConstantFoldFP(floor, V, Ty);
case Intrinsic::ceil:
return ConstantFoldFP(ceil, V, Ty);
}
if (!TLI)
return nullptr;
switch (Name[0]) {
case 'a':
if (Name == "acos" && TLI->has(LibFunc::acos))
return ConstantFoldFP(acos, V, Ty);
else if (Name == "asin" && TLI->has(LibFunc::asin))
return ConstantFoldFP(asin, V, Ty);
else if (Name == "atan" && TLI->has(LibFunc::atan))
return ConstantFoldFP(atan, V, Ty);
break;
case 'c':
if (Name == "ceil" && TLI->has(LibFunc::ceil))
return ConstantFoldFP(ceil, V, Ty);
else if (Name == "cos" && TLI->has(LibFunc::cos))
return ConstantFoldFP(cos, V, Ty);
else if (Name == "cosh" && TLI->has(LibFunc::cosh))
return ConstantFoldFP(cosh, V, Ty);
else if (Name == "cosf" && TLI->has(LibFunc::cosf))
return ConstantFoldFP(cos, V, Ty);
break;
case 'e':
if (Name == "exp" && TLI->has(LibFunc::exp))
return ConstantFoldFP(exp, V, Ty);
if (Name == "exp2" && TLI->has(LibFunc::exp2)) {
// Constant fold exp2(x) as pow(2,x) in case the host doesn't have a
// C99 library.
return ConstantFoldBinaryFP(pow, 2.0, V, Ty);
}
break;
case 'f':
if (Name == "fabs" && TLI->has(LibFunc::fabs))
return ConstantFoldFP(fabs, V, Ty);
else if (Name == "floor" && TLI->has(LibFunc::floor))
return ConstantFoldFP(floor, V, Ty);
break;
case 'l':
if (Name == "log" && V > 0 && TLI->has(LibFunc::log))
return ConstantFoldFP(log, V, Ty);
else if (Name == "log10" && V > 0 && TLI->has(LibFunc::log10))
return ConstantFoldFP(log10, V, Ty);
else if (IntrinsicID == Intrinsic::sqrt &&
(Ty->isHalfTy() || Ty->isFloatTy() || Ty->isDoubleTy())) {
if (V >= -0.0)
return ConstantFoldFP(sqrt, V, Ty);
else {
// Unlike the sqrt definitions in C/C++, POSIX, and IEEE-754 - which
// all guarantee or favor returning NaN - the square root of a
// negative number is not defined for the LLVM sqrt intrinsic.
// This is because the intrinsic should only be emitted in place of
// libm's sqrt function when using "no-nans-fp-math".
return UndefValue::get(Ty);
}
}
break;
case 's':
if (Name == "sin" && TLI->has(LibFunc::sin))
return ConstantFoldFP(sin, V, Ty);
else if (Name == "sinh" && TLI->has(LibFunc::sinh))
return ConstantFoldFP(sinh, V, Ty);
else if (Name == "sqrt" && V >= 0 && TLI->has(LibFunc::sqrt))
return ConstantFoldFP(sqrt, V, Ty);
else if (Name == "sqrtf" && V >= 0 && TLI->has(LibFunc::sqrtf))
return ConstantFoldFP(sqrt, V, Ty);
else if (Name == "sinf" && TLI->has(LibFunc::sinf))
return ConstantFoldFP(sin, V, Ty);
break;
case 't':
if (Name == "tan" && TLI->has(LibFunc::tan))
return ConstantFoldFP(tan, V, Ty);
else if (Name == "tanh" && TLI->has(LibFunc::tanh))
return ConstantFoldFP(tanh, V, Ty);
break;
default:
break;
}
return nullptr;
}
if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
switch (IntrinsicID) {
case Intrinsic::bswap:
return ConstantInt::get(Ty->getContext(), Op->getValue().byteSwap());
case Intrinsic::ctpop:
return ConstantInt::get(Ty, Op->getValue().countPopulation());
case Intrinsic::convert_from_fp16: {
APFloat Val(APFloat::IEEEhalf, Op->getValue());
bool lost = false;
APFloat::opStatus status =
Val.convert(APFloat::IEEEsingle, APFloat::rmNearestTiesToEven, &lost);
// Conversion is always precise.
(void)status;
assert(status == APFloat::opOK && !lost &&
"Precision lost during fp16 constfolding");
return ConstantFP::get(Ty->getContext(), Val);
}
default:
return nullptr;
}
}
// Support ConstantVector in case we have an Undef in the top.
if (isa<ConstantVector>(Operands[0]) ||
isa<ConstantDataVector>(Operands[0])) {
Constant *Op = cast<Constant>(Operands[0]);
switch (IntrinsicID) {
default: break;
case Intrinsic::x86_sse_cvtss2si:
case Intrinsic::x86_sse_cvtss2si64:
case Intrinsic::x86_sse2_cvtsd2si:
case Intrinsic::x86_sse2_cvtsd2si64:
if (ConstantFP *FPOp =
dyn_cast_or_null<ConstantFP>(Op->getAggregateElement(0U)))
return ConstantFoldConvertToInt(FPOp->getValueAPF(),
/*roundTowardZero=*/false, Ty);
case Intrinsic::x86_sse_cvttss2si:
case Intrinsic::x86_sse_cvttss2si64:
case Intrinsic::x86_sse2_cvttsd2si:
case Intrinsic::x86_sse2_cvttsd2si64:
if (ConstantFP *FPOp =
dyn_cast_or_null<ConstantFP>(Op->getAggregateElement(0U)))
return ConstantFoldConvertToInt(FPOp->getValueAPF(),
/*roundTowardZero=*/true, Ty);
}
}
if (isa<UndefValue>(Operands[0])) {
if (IntrinsicID == Intrinsic::bswap)
return Operands[0];
return nullptr;
}
return nullptr;
}
if (Operands.size() == 2) {
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
if (!Ty->isHalfTy() && !Ty->isFloatTy() && !Ty->isDoubleTy())
return nullptr;
double Op1V = getValueAsDouble(Op1);
if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
if (Op2->getType() != Op1->getType())
return nullptr;
double Op2V = getValueAsDouble(Op2);
if (IntrinsicID == Intrinsic::pow) {
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty);
}
if (IntrinsicID == Intrinsic::copysign) {
APFloat V1 = Op1->getValueAPF();
APFloat V2 = Op2->getValueAPF();
V1.copySign(V2);
return ConstantFP::get(Ty->getContext(), V1);
}
if (IntrinsicID == Intrinsic::minnum) {
const APFloat &C1 = Op1->getValueAPF();
const APFloat &C2 = Op2->getValueAPF();
return ConstantFP::get(Ty->getContext(), minnum(C1, C2));
}
if (IntrinsicID == Intrinsic::maxnum) {
const APFloat &C1 = Op1->getValueAPF();
const APFloat &C2 = Op2->getValueAPF();
return ConstantFP::get(Ty->getContext(), maxnum(C1, C2));
}
if (!TLI)
return nullptr;
if (Name == "pow" && TLI->has(LibFunc::pow))
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty);
if (Name == "fmod" && TLI->has(LibFunc::fmod))
return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty);
if (Name == "atan2" && TLI->has(LibFunc::atan2))
return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty);
} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
if (IntrinsicID == Intrinsic::powi && Ty->isHalfTy())
return ConstantFP::get(Ty->getContext(),
APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
if (IntrinsicID == Intrinsic::powi && Ty->isFloatTy())
return ConstantFP::get(Ty->getContext(),
APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
if (IntrinsicID == Intrinsic::powi && Ty->isDoubleTy())
return ConstantFP::get(Ty->getContext(),
APFloat((double)std::pow((double)Op1V,
(int)Op2C->getZExtValue())));
}
return nullptr;
}
if (ConstantInt *Op1 = dyn_cast<ConstantInt>(Operands[0])) {
if (ConstantInt *Op2 = dyn_cast<ConstantInt>(Operands[1])) {
switch (IntrinsicID) {
default: break;
case Intrinsic::sadd_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::umul_with_overflow: {
APInt Res;
bool Overflow;
switch (IntrinsicID) {
default: llvm_unreachable("Invalid case");
case Intrinsic::sadd_with_overflow:
Res = Op1->getValue().sadd_ov(Op2->getValue(), Overflow);
break;
case Intrinsic::uadd_with_overflow:
Res = Op1->getValue().uadd_ov(Op2->getValue(), Overflow);
break;
case Intrinsic::ssub_with_overflow:
Res = Op1->getValue().ssub_ov(Op2->getValue(), Overflow);
break;
case Intrinsic::usub_with_overflow:
Res = Op1->getValue().usub_ov(Op2->getValue(), Overflow);
break;
case Intrinsic::smul_with_overflow:
Res = Op1->getValue().smul_ov(Op2->getValue(), Overflow);
break;
case Intrinsic::umul_with_overflow:
Res = Op1->getValue().umul_ov(Op2->getValue(), Overflow);
break;
}
Constant *Ops[] = {
ConstantInt::get(Ty->getContext(), Res),
ConstantInt::get(Type::getInt1Ty(Ty->getContext()), Overflow)
};
return ConstantStruct::get(cast<StructType>(Ty), Ops);
}
case Intrinsic::cttz:
if (Op2->isOne() && Op1->isZero()) // cttz(0, 1) is undef.
return UndefValue::get(Ty);
return ConstantInt::get(Ty, Op1->getValue().countTrailingZeros());
case Intrinsic::ctlz:
if (Op2->isOne() && Op1->isZero()) // ctlz(0, 1) is undef.
return UndefValue::get(Ty);
return ConstantInt::get(Ty, Op1->getValue().countLeadingZeros());
}
}
return nullptr;
}
return nullptr;
}
if (Operands.size() != 3)
return nullptr;
if (const ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
if (const ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
if (const ConstantFP *Op3 = dyn_cast<ConstantFP>(Operands[2])) {
switch (IntrinsicID) {
default: break;
case Intrinsic::fma:
case Intrinsic::fmuladd: {
APFloat V = Op1->getValueAPF();
APFloat::opStatus s = V.fusedMultiplyAdd(Op2->getValueAPF(),
Op3->getValueAPF(),
APFloat::rmNearestTiesToEven);
if (s != APFloat::opInvalidOp)
return ConstantFP::get(Ty->getContext(), V);
return nullptr;
}
}
}
}
}
return nullptr;
}
static Constant *ConstantFoldVectorCall(StringRef Name, unsigned IntrinsicID,
VectorType *VTy,
ArrayRef<Constant *> Operands,
const TargetLibraryInfo *TLI) {
SmallVector<Constant *, 4> Result(VTy->getNumElements());
SmallVector<Constant *, 4> Lane(Operands.size());
Type *Ty = VTy->getElementType();
for (unsigned I = 0, E = VTy->getNumElements(); I != E; ++I) {
// Gather a column of constants.
for (unsigned J = 0, JE = Operands.size(); J != JE; ++J) {
Constant *Agg = Operands[J]->getAggregateElement(I);
if (!Agg)
return nullptr;
Lane[J] = Agg;
}
// Use the regular scalar folding to simplify this column.
Constant *Folded = ConstantFoldScalarCall(Name, IntrinsicID, Ty, Lane, TLI);
if (!Folded)
return nullptr;
Result[I] = Folded;
}
return ConstantVector::get(Result);
}
/// Attempt to constant fold a call to the specified function
/// with the specified arguments, returning null if unsuccessful.
Constant *
llvm::ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
const TargetLibraryInfo *TLI) {
if (!F->hasName())
return nullptr;
StringRef Name = F->getName();
Type *Ty = F->getReturnType();
if (VectorType *VTy = dyn_cast<VectorType>(Ty))
return ConstantFoldVectorCall(Name, F->getIntrinsicID(), VTy, Operands, TLI);
return ConstantFoldScalarCall(Name, F->getIntrinsicID(), Ty, Operands, TLI);
}
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