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llvm-project/llvm/lib/Analysis/ConstantFolding.cpp

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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 VMCore ConstantExpr simplifications,
// this file defines some additional folding routines that can make use of
// TargetData information. These functions cannot go in VMCore due to library
// dependency issues.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include <cerrno>
#include <cmath>
using namespace llvm;
//===----------------------------------------------------------------------===//
// Constant Folding internal helper functions
//===----------------------------------------------------------------------===//
/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with
/// TargetData. This always returns a non-null constant, but it may be a
/// ConstantExpr if unfoldable.
static Constant *FoldBitCast(Constant *C, const Type *DestTy,
const TargetData &TD) {
// This only handles casts to vectors currently.
const VectorType *DestVTy = dyn_cast<VectorType>(DestTy);
if (DestVTy == 0)
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, 1), DestTy, TD);
}
// If this is a bitcast from constant vector -> vector, fold it.
ConstantVector *CV = dyn_cast<ConstantVector>(C);
if (CV == 0)
return ConstantExpr::getBitCast(C, DestTy);
// If the element types match, VMCore can fold it.
unsigned NumDstElt = DestVTy->getNumElements();
unsigned NumSrcElt = CV->getNumOperands();
if (NumDstElt == NumSrcElt)
return ConstantExpr::getBitCast(C, DestTy);
const Type *SrcEltTy = CV->getType()->getElementType();
const 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->isFloatingPoint()) {
// Fold to an vector of integers with same size as our FP type.
unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits();
const Type *DestIVTy =
VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumDstElt);
// Recursively handle this integer conversion, if possible.
C = FoldBitCast(C, DestIVTy, TD);
if (!C) return ConstantExpr::getBitCast(C, DestTy);
// Finally, VMCore 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->isFloatingPoint()) {
unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits();
const Type *SrcIVTy =
VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElt);
// Ask VMCore to do the conversion now that #elts line up.
C = ConstantExpr::getBitCast(C, SrcIVTy);
CV = dyn_cast<ConstantVector>(C);
if (!CV) // If VMCore wasn't able to fold it, bail out.
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>(CV->getOperand(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);
}
} else {
// Handle: bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
unsigned Ratio = NumDstElt/NumSrcElt;
unsigned DstBitSize = DstEltTy->getPrimitiveSizeInBits();
// Loop over each source value, expanding into multiple results.
for (unsigned i = 0; i != NumSrcElt; ++i) {
Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(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 and remember this piece.
Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy));
}
}
}
return ConstantVector::get(Result.data(), Result.size());
}
/// IsConstantOffsetFromGlobal - If this constant is actually 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,
int64_t &Offset, const TargetData &TD) {
// Trivial case, constant is the global.
if ((GV = dyn_cast<GlobalValue>(C))) {
Offset = 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)
return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
// i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
if (CE->getOpcode() == Instruction::GetElementPtr) {
// Cannot compute this if the element type of the pointer is missing size
// info.
if (!cast<PointerType>(CE->getOperand(0)->getType())
->getElementType()->isSized())
return false;
// If the base isn't a global+constant, we aren't either.
if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
return false;
// Otherwise, add any offset that our operands provide.
gep_type_iterator GTI = gep_type_begin(CE);
for (User::const_op_iterator i = CE->op_begin() + 1, e = CE->op_end();
i != e; ++i, ++GTI) {
ConstantInt *CI = dyn_cast<ConstantInt>(*i);
if (!CI) return false; // Index isn't a simple constant?
if (CI->getZExtValue() == 0) continue; // Not adding anything.
if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
// N = N + Offset
Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue());
} else {
const SequentialType *SQT = cast<SequentialType>(*GTI);
Offset += TD.getTypeAllocSize(SQT->getElementType())*CI->getSExtValue();
}
}
return true;
}
return false;
}
/// ReadDataFromGlobal - 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 TargetData &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) {
CurPtr[i] = (unsigned char)(Val >> (ByteOffset * 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);
}
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 (ConstantArray *CA = dyn_cast<ConstantArray>(C)) {
uint64_t EltSize = TD.getTypeAllocSize(CA->getType()->getElementType());
uint64_t Index = ByteOffset / EltSize;
uint64_t Offset = ByteOffset - Index * EltSize;
for (; Index != CA->getType()->getNumElements(); ++Index) {
if (!ReadDataFromGlobal(CA->getOperand(Index), Offset, CurPtr,
BytesLeft, TD))
return false;
if (EltSize >= BytesLeft)
return true;
Offset = 0;
BytesLeft -= EltSize;
CurPtr += EltSize;
}
return true;
}
if (ConstantVector *CV = dyn_cast<ConstantVector>(C)) {
uint64_t EltSize = TD.getTypeAllocSize(CV->getType()->getElementType());
uint64_t Index = ByteOffset / EltSize;
uint64_t Offset = ByteOffset - Index * EltSize;
for (; Index != CV->getType()->getNumElements(); ++Index) {
if (!ReadDataFromGlobal(CV->getOperand(Index), Offset, CurPtr,
BytesLeft, TD))
return false;
if (EltSize >= BytesLeft)
return true;
Offset = 0;
BytesLeft -= EltSize;
CurPtr += EltSize;
}
return true;
}
// Otherwise, unknown initializer type.
return false;
}
static Constant *FoldReinterpretLoadFromConstPtr(Constant *C,
const TargetData &TD) {
const Type *LoadTy = cast<PointerType>(C->getType())->getElementType();
const IntegerType *IntType = dyn_cast<IntegerType>(LoadTy);
// If this isn't an integer load we can't fold it directly.
if (!IntType) {
// 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.
const Type *MapTy;
if (LoadTy->isFloatTy())
MapTy = Type::getInt32PtrTy(C->getContext());
else if (LoadTy->isDoubleTy())
MapTy = Type::getInt64PtrTy(C->getContext());
else if (isa<VectorType>(LoadTy)) {
MapTy = IntegerType::get(C->getContext(),
TD.getTypeAllocSizeInBits(LoadTy));
MapTy = PointerType::getUnqual(MapTy);
} else
return 0;
C = FoldBitCast(C, MapTy, TD);
if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, TD))
return FoldBitCast(Res, LoadTy, TD);
return 0;
}
unsigned BytesLoaded = (IntType->getBitWidth() + 7) / 8;
if (BytesLoaded > 32 || BytesLoaded == 0) return 0;
GlobalValue *GVal;
int64_t Offset;
if (!IsConstantOffsetFromGlobal(C, GVal, Offset, TD))
return 0;
GlobalVariable *GV = dyn_cast<GlobalVariable>(GVal);
if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer() ||
!GV->getInitializer()->getType()->isSized())
return 0;
// 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 < 0) return 0;
// If we're not accessing anything in this constant, the result is undefined.
if (uint64_t(Offset) >= TD.getTypeAllocSize(GV->getInitializer()->getType()))
return UndefValue::get(IntType);
unsigned char RawBytes[32] = {0};
if (!ReadDataFromGlobal(GV->getInitializer(), Offset, RawBytes,
BytesLoaded, TD))
return 0;
APInt ResultVal(IntType->getBitWidth(), 0);
for (unsigned i = 0; i != BytesLoaded; ++i) {
ResultVal <<= 8;
ResultVal |= APInt(IntType->getBitWidth(), RawBytes[BytesLoaded-1-i]);
}
return ConstantInt::get(IntType->getContext(), ResultVal);
}
/// ConstantFoldLoadFromConstPtr - 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 TargetData *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 0;
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;
}
// Instead of loading constant c string, use corresponding integer value
// directly if string length is small enough.
std::string Str;
if (TD && GetConstantStringInfo(CE->getOperand(0), Str) && !Str.empty()) {
unsigned StrLen = Str.length();
const Type *Ty = cast<PointerType>(CE->getType())->getElementType();
unsigned NumBits = Ty->getPrimitiveSizeInBits();
// Replace LI with immediate integer store.
if ((NumBits >> 3) == StrLen + 1) {
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;
}
return ConstantInt::get(CE->getContext(), StrVal);
}
}
// 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>(CE->getUnderlyingObject())){
if (GV->isConstant() && GV->hasDefinitiveInitializer()) {
const 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. We
// currently don't do any of this for big endian systems. It can be
// generalized in the future if someone is interested.
if (TD && TD->isLittleEndian())
return FoldReinterpretLoadFromConstPtr(CE, *TD);
return 0;
}
static Constant *ConstantFoldLoadInst(const LoadInst *LI, const TargetData *TD){
if (LI->isVolatile()) return 0;
if (Constant *C = dyn_cast<Constant>(LI->getOperand(0)))
return ConstantFoldLoadFromConstPtr(C, TD);
return 0;
}
/// SymbolicallyEvaluateBinop - 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 TD,
/// otherwise TD is null.
static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
Constant *Op1, const TargetData *TD){
// 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 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 && TD) {
GlobalValue *GV1, *GV2;
int64_t Offs1, Offs2;
if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD))
if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) &&
GV1 == GV2) {
// (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
return ConstantInt::get(Op0->getType(), Offs1-Offs2);
}
}
return 0;
}
/// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
/// constant expression, do so.
static Constant *SymbolicallyEvaluateGEP(Constant *const *Ops, unsigned NumOps,
const Type *ResultTy,
const TargetData *TD) {
Constant *Ptr = Ops[0];
if (!TD || !cast<PointerType>(Ptr->getType())->getElementType()->isSized())
return 0;
unsigned BitWidth =
TD->getTypeSizeInBits(TD->getIntPtrType(Ptr->getContext()));
APInt BasePtr(BitWidth, 0);
bool BaseIsInt = true;
if (!Ptr->isNullValue()) {
// If this is a inttoptr from a constant int, we can fold this as the base,
// otherwise we can't.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
if (CE->getOpcode() == Instruction::IntToPtr)
if (ConstantInt *Base = dyn_cast<ConstantInt>(CE->getOperand(0))) {
BasePtr = Base->getValue();
BasePtr.zextOrTrunc(BitWidth);
}
if (BasePtr == 0)
BaseIsInt = false;
}
// 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; i != NumOps; ++i)
if (!isa<ConstantInt>(Ops[i]))
return 0;
APInt Offset = APInt(BitWidth,
TD->getIndexedOffset(Ptr->getType(),
(Value**)Ops+1, NumOps-1));
// 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.
if (BaseIsInt) {
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.
const Type *Ty = Ptr->getType();
SmallVector<Constant*, 32> NewIdxs;
do {
if (const SequentialType *ATy = dyn_cast<SequentialType>(Ty)) {
// The only pointer indexing we'll do is on the first index of the GEP.
if (isa<PointerType>(ATy) && !NewIdxs.empty())
break;
// Determine which element of the array the offset points into.
APInt ElemSize(BitWidth, TD->getTypeAllocSize(ATy->getElementType()));
if (ElemSize == 0)
return 0;
APInt NewIdx = Offset.udiv(ElemSize);
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(TD->getIntPtrType(Ty->getContext()),
NewIdx));
Ty = ATy->getElementType();
} else if (const StructType *STy = dyn_cast<StructType>(Ty)) {
// Determine which field of the struct the offset points into. The
// getZExtValue is at least as safe as the StructLayout API because we
// know the offset is within the struct at this point.
const StructLayout &SL = *TD->getStructLayout(STy);
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 != cast<PointerType>(ResultTy)->getElementType());
// 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 0;
// Create a GEP.
Constant *C =
ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
assert(cast<PointerType>(C->getType())->getElementType() == 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 != cast<PointerType>(ResultTy)->getElementType())
C = FoldBitCast(C, ResultTy, *TD);
return C;
}
//===----------------------------------------------------------------------===//
// Constant Folding public APIs
//===----------------------------------------------------------------------===//
/// ConstantFoldInstruction - Attempt to constant fold the specified
/// instruction. If successful, the constant result is returned, if not, null
/// is returned. Note that 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 TargetData *TD) {
if (PHINode *PN = dyn_cast<PHINode>(I)) {
if (PN->getNumIncomingValues() == 0)
return UndefValue::get(PN->getType());
Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
if (Result == 0) return 0;
// Handle PHI nodes specially here...
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
return 0; // Not all the same incoming constants...
// If we reach here, all incoming values are the same constant.
return Result;
}
// 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)
if (Constant *Op = dyn_cast<Constant>(*i))
Ops.push_back(Op);
else
return 0; // All operands not constant!
if (const CmpInst *CI = dyn_cast<CmpInst>(I))
return ConstantFoldCompareInstOperands(CI->getPredicate(), Ops[0], Ops[1],
TD);
if (const LoadInst *LI = dyn_cast<LoadInst>(I))
return ConstantFoldLoadInst(LI, TD);
return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
Ops.data(), Ops.size(), TD);
}
/// ConstantFoldConstantExpression - Attempt to fold the constant expression
/// using the specified TargetData. If successful, the constant result is
/// result is returned, if not, null is returned.
Constant *llvm::ConstantFoldConstantExpression(ConstantExpr *CE,
const TargetData *TD) {
SmallVector<Constant*, 8> Ops;
for (User::op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i)
Ops.push_back(cast<Constant>(*i));
if (CE->isCompare())
return ConstantFoldCompareInstOperands(CE->getPredicate(), Ops[0], Ops[1],
TD);
return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(),
Ops.data(), Ops.size(), TD);
}
/// ConstantFoldInstOperands - 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.
///
Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, const Type *DestTy,
Constant* const* Ops, unsigned NumOps,
const TargetData *TD) {
// 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 0;
case Instruction::Call:
if (Function *F = dyn_cast<Function>(Ops[0]))
if (canConstantFoldCallTo(F))
return ConstantFoldCall(F, Ops+1, NumOps-1);
return 0;
case Instruction::ICmp:
case Instruction::FCmp:
llvm_unreachable("This function is invalid for compares: no predicate specified");
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();
if (TD->getPointerSizeInBits() < InWidth) {
Constant *Mask =
ConstantInt::get(CE->getContext(), APInt::getLowBitsSet(InWidth,
TD->getPointerSizeInBits()));
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. 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 &&
TD->getPointerSizeInBits() <=
CE->getType()->getScalarSizeInBits()) {
if (CE->getOpcode() == Instruction::PtrToInt)
return FoldBitCast(CE->getOperand(0), DestTy, *TD);
// If there's a constant offset added to the integer value before
// it is casted back to a pointer, see if the expression can be
// converted into a GEP.
if (CE->getOpcode() == Instruction::Add)
if (ConstantInt *L = dyn_cast<ConstantInt>(CE->getOperand(0)))
if (ConstantExpr *R = dyn_cast<ConstantExpr>(CE->getOperand(1)))
if (R->getOpcode() == Instruction::PtrToInt)
if (GlobalVariable *GV =
dyn_cast<GlobalVariable>(R->getOperand(0))) {
const PointerType *GVTy = cast<PointerType>(GV->getType());
if (const ArrayType *AT =
dyn_cast<ArrayType>(GVTy->getElementType())) {
const Type *ElTy = AT->getElementType();
uint64_t AllocSize = TD->getTypeAllocSize(ElTy);
APInt PSA(L->getValue().getBitWidth(), AllocSize);
if (ElTy == cast<PointerType>(DestTy)->getElementType() &&
L->getValue().urem(PSA) == 0) {
APInt ElemIdx = L->getValue().udiv(PSA);
if (ElemIdx.ult(APInt(ElemIdx.getBitWidth(),
AT->getNumElements()))) {
Constant *Index[] = {
Constant::getNullValue(CE->getType()),
ConstantInt::get(ElTy->getContext(), ElemIdx)
};
return
ConstantExpr::getGetElementPtr(GV, &Index[0], 2);
}
}
}
}
}
}
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:
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 = SymbolicallyEvaluateGEP(Ops, NumOps, DestTy, TD))
return C;
return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1);
}
}
/// ConstantFoldCompareInstOperands - 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 TargetData *TD) {
// 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()) {
const Type *IntPtrTy = TD->getIntPtrType(CE0->getContext());
if (CE0->getOpcode() == Instruction::IntToPtr) {
// 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);
}
// 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 &&
CE0->getType() == IntPtrTy) {
Constant *C = CE0->getOperand(0);
Constant *Null = Constant::getNullValue(C->getType());
return ConstantFoldCompareInstOperands(Predicate, C, Null, TD);
}
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops1)) {
if (TD && CE0->getOpcode() == CE1->getOpcode()) {
const Type *IntPtrTy = TD->getIntPtrType(CE0->getContext());
if (CE0->getOpcode() == Instruction::IntToPtr) {
// 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);
}
// 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 &&
CE0->getType() == IntPtrTy &&
CE0->getOperand(0)->getType() == CE1->getOperand(0)->getType()))
return ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(0),
CE1->getOperand(0), TD);
}
}
}
return ConstantExpr::getCompare(Predicate, Ops0, Ops1);
}
/// ConstantFoldLoadThroughGEPConstantExpr - 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) != Constant::getNullValue(CE->getOperand(1)->getType()))
return 0; // Do not allow stepping over the value!
// Loop over all of the operands, tracking down which value we are
// addressing...
gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
for (++I; I != E; ++I)
if (const StructType *STy = dyn_cast<StructType>(*I)) {
ConstantInt *CU = cast<ConstantInt>(I.getOperand());
assert(CU->getZExtValue() < STy->getNumElements() &&
"Struct index out of range!");
unsigned El = (unsigned)CU->getZExtValue();
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
C = CS->getOperand(El);
} else if (isa<ConstantAggregateZero>(C)) {
C = Constant::getNullValue(STy->getElementType(El));
} else if (isa<UndefValue>(C)) {
C = UndefValue::get(STy->getElementType(El));
} else {
return 0;
}
} else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
if (CI->getZExtValue() >= ATy->getNumElements())
return 0;
if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
C = CA->getOperand(CI->getZExtValue());
else if (isa<ConstantAggregateZero>(C))
C = Constant::getNullValue(ATy->getElementType());
else if (isa<UndefValue>(C))
C = UndefValue::get(ATy->getElementType());
else
return 0;
} else if (const VectorType *VTy = dyn_cast<VectorType>(*I)) {
if (CI->getZExtValue() >= VTy->getNumElements())
return 0;
if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
C = CP->getOperand(CI->getZExtValue());
else if (isa<ConstantAggregateZero>(C))
C = Constant::getNullValue(VTy->getElementType());
else if (isa<UndefValue>(C))
C = UndefValue::get(VTy->getElementType());
else
return 0;
} else {
return 0;
}
} else {
return 0;
}
return C;
}
//===----------------------------------------------------------------------===//
// Constant Folding for Calls
//
/// canConstantFoldCallTo - Return true if its even possible to fold a call to
/// the specified function.
bool
llvm::canConstantFoldCallTo(const Function *F) {
switch (F->getIntrinsicID()) {
case Intrinsic::sqrt:
case Intrinsic::powi:
case Intrinsic::bswap:
case Intrinsic::ctpop:
case Intrinsic::ctlz:
case Intrinsic::cttz:
case Intrinsic::uadd_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
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";
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 *ConstantFoldFP(double (*NativeFP)(double), double V,
const Type *Ty) {
errno = 0;
V = NativeFP(V);
if (errno != 0) {
errno = 0;
return 0;
}
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 float/double");
return 0; // dummy return to suppress warning
}
static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
double V, double W, const Type *Ty) {
errno = 0;
V = NativeFP(V, W);
if (errno != 0) {
errno = 0;
return 0;
}
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 float/double");
return 0; // dummy return to suppress warning
}
/// ConstantFoldCall - Attempt to constant fold a call to the specified function
/// with the specified arguments, returning null if unsuccessful.
Constant *
llvm::ConstantFoldCall(Function *F,
Constant *const *Operands, unsigned NumOperands) {
if (!F->hasName()) return 0;
StringRef Name = F->getName();
const Type *Ty = F->getReturnType();
if (NumOperands == 1) {
if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
if (!Ty->isFloatTy() && !Ty->isDoubleTy())
return 0;
/// 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 = Ty->isFloatTy() ? (double)Op->getValueAPF().convertToFloat() :
Op->getValueAPF().convertToDouble();
switch (Name[0]) {
case 'a':
if (Name == "acos")
return ConstantFoldFP(acos, V, Ty);
else if (Name == "asin")
return ConstantFoldFP(asin, V, Ty);
else if (Name == "atan")
return ConstantFoldFP(atan, V, Ty);
break;
case 'c':
if (Name == "ceil")
return ConstantFoldFP(ceil, V, Ty);
else if (Name == "cos")
return ConstantFoldFP(cos, V, Ty);
else if (Name == "cosh")
return ConstantFoldFP(cosh, V, Ty);
else if (Name == "cosf")
return ConstantFoldFP(cos, V, Ty);
break;
case 'e':
if (Name == "exp")
return ConstantFoldFP(exp, V, Ty);
break;
case 'f':
if (Name == "fabs")
return ConstantFoldFP(fabs, V, Ty);
else if (Name == "floor")
return ConstantFoldFP(floor, V, Ty);
break;
case 'l':
if (Name == "log" && V > 0)
return ConstantFoldFP(log, V, Ty);
else if (Name == "log10" && V > 0)
return ConstantFoldFP(log10, V, Ty);
else if (Name == "llvm.sqrt.f32" ||
Name == "llvm.sqrt.f64") {
if (V >= -0.0)
return ConstantFoldFP(sqrt, V, Ty);
else // Undefined
return Constant::getNullValue(Ty);
}
break;
case 's':
if (Name == "sin")
return ConstantFoldFP(sin, V, Ty);
else if (Name == "sinh")
return ConstantFoldFP(sinh, V, Ty);
else if (Name == "sqrt" && V >= 0)
return ConstantFoldFP(sqrt, V, Ty);
else if (Name == "sqrtf" && V >= 0)
return ConstantFoldFP(sqrt, V, Ty);
else if (Name == "sinf")
return ConstantFoldFP(sin, V, Ty);
break;
case 't':
if (Name == "tan")
return ConstantFoldFP(tan, V, Ty);
else if (Name == "tanh")
return ConstantFoldFP(tanh, V, Ty);
break;
default:
break;
}
return 0;
}
if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
if (Name.startswith("llvm.bswap"))
return ConstantInt::get(F->getContext(), Op->getValue().byteSwap());
else if (Name.startswith("llvm.ctpop"))
return ConstantInt::get(Ty, Op->getValue().countPopulation());
else if (Name.startswith("llvm.cttz"))
return ConstantInt::get(Ty, Op->getValue().countTrailingZeros());
else if (Name.startswith("llvm.ctlz"))
return ConstantInt::get(Ty, Op->getValue().countLeadingZeros());
return 0;
}
return 0;
}
if (NumOperands == 2) {
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
if (!Ty->isFloatTy() && !Ty->isDoubleTy())
return 0;
double Op1V = Ty->isFloatTy() ?
(double)Op1->getValueAPF().convertToFloat() :
Op1->getValueAPF().convertToDouble();
if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
if (Op2->getType() != Op1->getType())
return 0;
double Op2V = Ty->isFloatTy() ?
(double)Op2->getValueAPF().convertToFloat():
Op2->getValueAPF().convertToDouble();
if (Name == "pow")
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty);
if (Name == "fmod")
return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty);
if (Name == "atan2")
return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty);
} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
if (Name == "llvm.powi.f32")
return ConstantFP::get(F->getContext(),
APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
if (Name == "llvm.powi.f64")
return ConstantFP::get(F->getContext(),
APFloat((double)std::pow((double)Op1V,
(int)Op2C->getZExtValue())));
}
return 0;
}
if (ConstantInt *Op1 = dyn_cast<ConstantInt>(Operands[0])) {
if (ConstantInt *Op2 = dyn_cast<ConstantInt>(Operands[1])) {
switch (F->getIntrinsicID()) {
default: break;
case Intrinsic::uadd_with_overflow: {
Constant *Res = ConstantExpr::getAdd(Op1, Op2); // result.
Constant *Ops[] = {
Res, ConstantExpr::getICmp(CmpInst::ICMP_ULT, Res, Op1) // overflow.
};
return ConstantStruct::get(F->getContext(), Ops, 2, false);
}
case Intrinsic::usub_with_overflow: {
Constant *Res = ConstantExpr::getSub(Op1, Op2); // result.
Constant *Ops[] = {
Res, ConstantExpr::getICmp(CmpInst::ICMP_UGT, Res, Op1) // overflow.
};
return ConstantStruct::get(F->getContext(), Ops, 2, false);
}
case Intrinsic::sadd_with_overflow: {
Constant *Res = ConstantExpr::getAdd(Op1, Op2); // result.
Constant *Overflow = ConstantExpr::getSelect(
ConstantExpr::getICmp(CmpInst::ICMP_SGT,
ConstantInt::get(Op1->getType(), 0), Op1),
ConstantExpr::getICmp(CmpInst::ICMP_SGT, Res, Op2),
ConstantExpr::getICmp(CmpInst::ICMP_SLT, Res, Op2)); // overflow.
Constant *Ops[] = { Res, Overflow };
return ConstantStruct::get(F->getContext(), Ops, 2, false);
}
case Intrinsic::ssub_with_overflow: {
Constant *Res = ConstantExpr::getSub(Op1, Op2); // result.
Constant *Overflow = ConstantExpr::getSelect(
ConstantExpr::getICmp(CmpInst::ICMP_SGT,
ConstantInt::get(Op2->getType(), 0), Op2),
ConstantExpr::getICmp(CmpInst::ICMP_SLT, Res, Op1),
ConstantExpr::getICmp(CmpInst::ICMP_SGT, Res, Op1)); // overflow.
Constant *Ops[] = { Res, Overflow };
return ConstantStruct::get(F->getContext(), Ops, 2, false);
}
}
}
return 0;
}
return 0;
}
return 0;
}
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