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e56a94ef91
llvm-6502/lib/Analysis/ConstantFolding.cpp
Dan Gohman e56a94ef91 Remove the API for creating ConstantExprs with the nsw, nuw, inbounds, 
and exact flags. Because ConstantExprs are uniqued, creating an
expression with this flag causes all expressions with the same operands
to have the same flag, which may not be safe. Add, sub, mul, and sdiv
ConstantExprs are usually folded anyway, so the main interesting flag
here is inbounds, and the constant folder already knows how to set the
inbounds flag automatically in most cases, so there isn't an urgent need
for the API support.

This can be reconsidered in the future, but for now just removing these
API bits eliminates a source of potential trouble with little downside.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80959 91177308-0d34-0410-b5e6-96231b3b80d8
2009-09-03 22:17:40 +00:00

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//===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions determines the possibility of performing constant
// folding.
//
//===----------------------------------------------------------------------===//
#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/LLVMContext.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Target/TargetData.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
//===----------------------------------------------------------------------===//
/// 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;
}
/// 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,
LLVMContext &Context){
// 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,
LLVMContext &Context,
const TargetData *TD) {
Constant *Ptr = Ops[0];
if (!TD || !cast<PointerType>(Ptr->getType())->getElementType()->isSized())
return 0;
unsigned BitWidth = TD->getTypeSizeInBits(TD->getIntPtrType(Context));
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(Context, 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(Context), 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(Context), 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 the GEP constant expr.
Constant *C = ConstantExpr::getGetElementPtr(Ptr,
&NewIdxs[0], NewIdxs.size());
assert(cast<PointerType>(C->getType())->getElementType() == Ty &&
"Computed GetElementPtr has unexpected type!");
// If the base is the start of a GlobalVariable and all the array indices
// remain in their static bounds, the GEP is inbounds. We can check that
// all indices are in bounds by just checking the first index only
// because we've just normalized all the indices. We can mutate the
// Constant in place because we've proven that the indices are in bounds,
// so they'll always be in bounds.
if (isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue())
if (GEPOperator *GEP = dyn_cast<GEPOperator>(C))
GEP->setIsInBounds(true);
// 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 = ConstantExpr::getBitCast(C, ResultTy);
return C;
}
/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with
/// targetdata. Return 0 if unfoldable.
static Constant *FoldBitCast(Constant *C, const Type *DestTy,
const TargetData &TD, LLVMContext &Context) {
// If this is a bitcast from constant vector -> vector, fold it.
if (ConstantVector *CV = dyn_cast<ConstantVector>(C)) {
if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
// If the element types match, VMCore can fold it.
unsigned NumDstElt = DestVTy->getNumElements();
unsigned NumSrcElt = CV->getNumOperands();
if (NumDstElt == NumSrcElt)
return 0;
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(Context, FPWidth), NumDstElt);
// Recursively handle this integer conversion, if possible.
C = FoldBitCast(C, DestIVTy, TD, Context);
if (!C) return 0;
// 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(Context, 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) return 0; // If VMCore wasn't able to fold it, bail out.
}
// 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) return 0; // Reject constantexpr elements.
// 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) return 0; // Reject constantexpr elements.
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());
}
}
return 0;
}
//===----------------------------------------------------------------------===//
// 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, LLVMContext &Context,
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.data(), Ops.size(),
Context, TD);
else
return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
Ops.data(), Ops.size(), Context, 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,
LLVMContext &Context,
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.data(), Ops.size(),
Context, TD);
else
return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(),
Ops.data(), Ops.size(), Context, 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,
LLVMContext &Context,
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,
Context))
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(Context, 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) {
Constant *Input = CE->getOperand(0);
Constant *C = FoldBitCast(Input, DestTy, *TD, Context);
return C ? C : ConstantExpr::getBitCast(Input, DestTy);
}
// 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(Context, 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)
if (Constant *C = FoldBitCast(Ops[0], DestTy, *TD, Context))
return C;
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, Context, 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*const * Ops,
unsigned NumOps,
LLVMContext &Context,
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>(Ops[0])) {
if (TD && Ops[1]->isNullValue()) {
const Type *IntPtrTy = TD->getIntPtrType(Context);
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 *NewOps[] = { C, Constant::getNullValue(C->getType()) };
return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
Context, 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 *NewOps[] = { C, Constant::getNullValue(C->getType()) };
// FIXME!
return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
Context, TD);
}
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops[1])) {
if (TD && CE0->getOpcode() == CE1->getOpcode()) {
const Type *IntPtrTy = TD->getIntPtrType(Context);
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);
Constant *NewOps[] = { C0, C1 };
return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
Context, 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())) {
Constant *NewOps[] = {
CE0->getOperand(0), CE1->getOperand(0)
};
return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
Context, TD);
}
}
}
}
return ConstantExpr::getCompare(Predicate, Ops[0], Ops[1]);
}
/// 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,
LLVMContext &Context) {
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 *PTy = dyn_cast<VectorType>(*I)) {
if (CI->getZExtValue() >= PTy->getNumElements())
return 0;
if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
C = CP->getOperand(CI->getZExtValue());
else if (isa<ConstantAggregateZero>(C))
C = Constant::getNullValue(PTy->getElementType());
else if (isa<UndefValue>(C))
C = UndefValue::get(PTy->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:
return true;
default: 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, LLVMContext &Context) {
errno = 0;
V = NativeFP(V);
if (errno != 0) {
errno = 0;
return 0;
}
if (Ty == Type::getFloatTy(Context))
return ConstantFP::get(Context, APFloat((float)V));
if (Ty == Type::getDoubleTy(Context))
return ConstantFP::get(Context, 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,
LLVMContext &Context) {
errno = 0;
V = NativeFP(V, W);
if (errno != 0) {
errno = 0;
return 0;
}
if (Ty == Type::getFloatTy(Context))
return ConstantFP::get(Context, APFloat((float)V));
if (Ty == Type::getDoubleTy(Context))
return ConstantFP::get(Context, 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;
LLVMContext &Context = F->getContext();
StringRef Name = F->getName();
const Type *Ty = F->getReturnType();
if (NumOperands == 1) {
if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
if (Ty!=Type::getFloatTy(F->getContext()) &&
Ty!=Type::getDoubleTy(Context))
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==Type::getFloatTy(F->getContext()) ?
(double)Op->getValueAPF().convertToFloat():
Op->getValueAPF().convertToDouble();
switch (Name[0]) {
case 'a':
if (Name == "acos")
return ConstantFoldFP(acos, V, Ty, Context);
else if (Name == "asin")
return ConstantFoldFP(asin, V, Ty, Context);
else if (Name == "atan")
return ConstantFoldFP(atan, V, Ty, Context);
break;
case 'c':
if (Name == "ceil")
return ConstantFoldFP(ceil, V, Ty, Context);
else if (Name == "cos")
return ConstantFoldFP(cos, V, Ty, Context);
else if (Name == "cosh")
return ConstantFoldFP(cosh, V, Ty, Context);
else if (Name == "cosf")
return ConstantFoldFP(cos, V, Ty, Context);
break;
case 'e':
if (Name == "exp")
return ConstantFoldFP(exp, V, Ty, Context);
break;
case 'f':
if (Name == "fabs")
return ConstantFoldFP(fabs, V, Ty, Context);
else if (Name == "floor")
return ConstantFoldFP(floor, V, Ty, Context);
break;
case 'l':
if (Name == "log" && V > 0)
return ConstantFoldFP(log, V, Ty, Context);
else if (Name == "log10" && V > 0)
return ConstantFoldFP(log10, V, Ty, Context);
else if (Name == "llvm.sqrt.f32" ||
Name == "llvm.sqrt.f64") {
if (V >= -0.0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else // Undefined
return Constant::getNullValue(Ty);
}
break;
case 's':
if (Name == "sin")
return ConstantFoldFP(sin, V, Ty, Context);
else if (Name == "sinh")
return ConstantFoldFP(sinh, V, Ty, Context);
else if (Name == "sqrt" && V >= 0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else if (Name == "sqrtf" && V >= 0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else if (Name == "sinf")
return ConstantFoldFP(sin, V, Ty, Context);
break;
case 't':
if (Name == "tan")
return ConstantFoldFP(tan, V, Ty, Context);
else if (Name == "tanh")
return ConstantFoldFP(tanh, V, Ty, Context);
break;
default:
break;
}
} else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
if (Name.startswith("llvm.bswap"))
return ConstantInt::get(Context, 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());
}
} else if (NumOperands == 2) {
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
if (Ty!=Type::getFloatTy(F->getContext()) &&
Ty!=Type::getDoubleTy(Context))
return 0;
double Op1V = Ty==Type::getFloatTy(F->getContext()) ?
(double)Op1->getValueAPF().convertToFloat():
Op1->getValueAPF().convertToDouble();
if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
double Op2V = Ty==Type::getFloatTy(F->getContext()) ?
(double)Op2->getValueAPF().convertToFloat():
Op2->getValueAPF().convertToDouble();
if (Name == "pow") {
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty, Context);
} else if (Name == "fmod") {
return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty, Context);
} else if (Name == "atan2") {
return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty, Context);
}
} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
if (Name == "llvm.powi.f32") {
return ConstantFP::get(Context, APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
} else if (Name == "llvm.powi.f64") {
return ConstantFP::get(Context, APFloat((double)std::pow((double)Op1V,
(int)Op2C->getZExtValue())));
}
}
}
}
return 0;
}
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