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llvm-6502/lib/Analysis/ConstantFolding.cpp
Torok Edwin c25e7581b9 assert(0) -> LLVM_UNREACHABLE. 
Make llvm_unreachable take an optional string, thus moving the cerr<< out of
line.
LLVM_UNREACHABLE is now a simple wrapper that makes the message go away for
NDEBUG builds.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75379 91177308-0d34-0410-b5e6-96231b3b80d8
2009-07-11 20:10:48 +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 Context->getConstantInt(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;
uint64_t BasePtr = 0;
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->getZExtValue();
if (BasePtr == 0)
return 0;
}
// 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 false;
uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
(Value**)Ops+1, NumOps-1);
Constant *C = Context->getConstantInt(TD->getIntPtrType(), Offset+BasePtr);
return Context->getConstantExprIntToPtr(C, ResultTy);
}
/// 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 = Context->getVectorType(
Context->getIntegerType(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 Context->getConstantExprBitCast(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 = Context->getVectorType(
Context->getIntegerType(FPWidth), NumSrcElt);
// Ask VMCore to do the conversion now that #elts line up.
C = Context->getConstantExprBitCast(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 = Context->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 = Context->getConstantExprZExt(Src, Elt->getType());
// Shift it to the right place, depending on endianness.
Src = Context->getConstantExprShl(Src,
Context->getConstantInt(Src->getType(), ShiftAmt));
ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize;
// Mix it in.
Elt = Context->getConstantExprOr(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 = Context->getConstantExprLShr(Src,
Context->getConstantInt(Src->getType(), ShiftAmt));
ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize;
// Truncate and remember this piece.
Result.push_back(Context->getConstantExprTrunc(Elt, DstEltTy));
}
}
}
return Context->getConstantVector(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 Context->getUndef(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 Context->getConstantExpr(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 =
Context->getConstantInt(APInt::getLowBitsSet(InWidth,
TD->getPointerSizeInBits()));
Input = Context->getConstantExprAnd(Input, Mask);
}
// Do a zext or trunc to get to the dest size.
return Context->getConstantExprIntegerCast(Input, DestTy, false);
}
}
return Context->getConstantExprCast(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 : Context->getConstantExprBitCast(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[] = {
Context->getNullValue(CE->getType()),
Context->getConstantInt(ElemIdx)
};
return
Context->getConstantExprGetElementPtr(GV, &Index[0], 2);
}
}
}
}
}
}
return Context->getConstantExprCast(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 Context->getConstantExprCast(Opcode, Ops[0], DestTy);
case Instruction::BitCast:
if (TD)
if (Constant *C = FoldBitCast(Ops[0], DestTy, *TD, Context))
return C;
return Context->getConstantExprBitCast(Ops[0], DestTy);
case Instruction::Select:
return Context->getConstantExprSelect(Ops[0], Ops[1], Ops[2]);
case Instruction::ExtractElement:
return Context->getConstantExprExtractElement(Ops[0], Ops[1]);
case Instruction::InsertElement:
return Context->getConstantExprInsertElement(Ops[0], Ops[1], Ops[2]);
case Instruction::ShuffleVector:
return Context->getConstantExprShuffleVector(Ops[0], Ops[1], Ops[2]);
case Instruction::GetElementPtr:
if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, DestTy, Context, TD))
return C;
return Context->getConstantExprGetElementPtr(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();
if (CE0->getOpcode() == Instruction::IntToPtr) {
// Convert the integer value to the right size to ensure we get the
// proper extension or truncation.
Constant *C = Context->getConstantExprIntegerCast(CE0->getOperand(0),
IntPtrTy, false);
Constant *NewOps[] = { C, Context->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, Context->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();
if (CE0->getOpcode() == Instruction::IntToPtr) {
// Convert the integer value to the right size to ensure we get the
// proper extension or truncation.
Constant *C0 = Context->getConstantExprIntegerCast(CE0->getOperand(0),
IntPtrTy, false);
Constant *C1 = Context->getConstantExprIntegerCast(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 Context->getConstantExprCompare(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) != Context->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 = Context->getNullValue(STy->getElementType(El));
} else if (isa<UndefValue>(C)) {
C = Context->getUndef(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 = Context->getNullValue(ATy->getElementType());
else if (isa<UndefValue>(C))
C = Context->getUndef(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 = Context->getNullValue(PTy->getElementType());
else if (isa<UndefValue>(C))
C = Context->getUndef(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;
const char *Str = F->getNameStart();
unsigned Len = F->getNameLen();
// 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 (Str[0]) {
default: return false;
case 'a':
if (Len == 4)
return !strcmp(Str, "acos") || !strcmp(Str, "asin") ||
!strcmp(Str, "atan");
else if (Len == 5)
return !strcmp(Str, "atan2");
return false;
case 'c':
if (Len == 3)
return !strcmp(Str, "cos");
else if (Len == 4)
return !strcmp(Str, "ceil") || !strcmp(Str, "cosf") ||
!strcmp(Str, "cosh");
return false;
case 'e':
if (Len == 3)
return !strcmp(Str, "exp");
return false;
case 'f':
if (Len == 4)
return !strcmp(Str, "fabs") || !strcmp(Str, "fmod");
else if (Len == 5)
return !strcmp(Str, "floor");
return false;
break;
case 'l':
if (Len == 3 && !strcmp(Str, "log"))
return true;
if (Len == 5 && !strcmp(Str, "log10"))
return true;
return false;
case 'p':
if (Len == 3 && !strcmp(Str, "pow"))
return true;
return false;
case 's':
if (Len == 3)
return !strcmp(Str, "sin");
if (Len == 4)
return !strcmp(Str, "sinh") || !strcmp(Str, "sqrt") ||
!strcmp(Str, "sinf");
if (Len == 5)
return !strcmp(Str, "sqrtf");
return false;
case 't':
if (Len == 3 && !strcmp(Str, "tan"))
return true;
else if (Len == 4 && !strcmp(Str, "tanh"))
return true;
return false;
}
}
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::FloatTy)
return Context->getConstantFP(APFloat((float)V));
if (Ty == Type::DoubleTy)
return Context->getConstantFP(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::FloatTy)
return Context->getConstantFP(APFloat((float)V));
if (Ty == Type::DoubleTy)
return Context->getConstantFP(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();
const char *Str = F->getNameStart();
unsigned Len = F->getNameLen();
const Type *Ty = F->getReturnType();
if (NumOperands == 1) {
if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy)
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::FloatTy ? (double)Op->getValueAPF().convertToFloat():
Op->getValueAPF().convertToDouble();
switch (Str[0]) {
case 'a':
if (Len == 4 && !strcmp(Str, "acos"))
return ConstantFoldFP(acos, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "asin"))
return ConstantFoldFP(asin, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "atan"))
return ConstantFoldFP(atan, V, Ty, Context);
break;
case 'c':
if (Len == 4 && !strcmp(Str, "ceil"))
return ConstantFoldFP(ceil, V, Ty, Context);
else if (Len == 3 && !strcmp(Str, "cos"))
return ConstantFoldFP(cos, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "cosh"))
return ConstantFoldFP(cosh, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "cosf"))
return ConstantFoldFP(cos, V, Ty, Context);
break;
case 'e':
if (Len == 3 && !strcmp(Str, "exp"))
return ConstantFoldFP(exp, V, Ty, Context);
break;
case 'f':
if (Len == 4 && !strcmp(Str, "fabs"))
return ConstantFoldFP(fabs, V, Ty, Context);
else if (Len == 5 && !strcmp(Str, "floor"))
return ConstantFoldFP(floor, V, Ty, Context);
break;
case 'l':
if (Len == 3 && !strcmp(Str, "log") && V > 0)
return ConstantFoldFP(log, V, Ty, Context);
else if (Len == 5 && !strcmp(Str, "log10") && V > 0)
return ConstantFoldFP(log10, V, Ty, Context);
else if (!strcmp(Str, "llvm.sqrt.f32") ||
!strcmp(Str, "llvm.sqrt.f64")) {
if (V >= -0.0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else // Undefined
return Context->getNullValue(Ty);
}
break;
case 's':
if (Len == 3 && !strcmp(Str, "sin"))
return ConstantFoldFP(sin, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "sinh"))
return ConstantFoldFP(sinh, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "sqrt") && V >= 0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else if (Len == 5 && !strcmp(Str, "sqrtf") && V >= 0)
return ConstantFoldFP(sqrt, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "sinf"))
return ConstantFoldFP(sin, V, Ty, Context);
break;
case 't':
if (Len == 3 && !strcmp(Str, "tan"))
return ConstantFoldFP(tan, V, Ty, Context);
else if (Len == 4 && !strcmp(Str, "tanh"))
return ConstantFoldFP(tanh, V, Ty, Context);
break;
default:
break;
}
} else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
if (Len > 11 && !memcmp(Str, "llvm.bswap", 10))
return Context->getConstantInt(Op->getValue().byteSwap());
else if (Len > 11 && !memcmp(Str, "llvm.ctpop", 10))
return Context->getConstantInt(Ty, Op->getValue().countPopulation());
else if (Len > 10 && !memcmp(Str, "llvm.cttz", 9))
return Context->getConstantInt(Ty, Op->getValue().countTrailingZeros());
else if (Len > 10 && !memcmp(Str, "llvm.ctlz", 9))
return Context->getConstantInt(Ty, Op->getValue().countLeadingZeros());
}
} else if (NumOperands == 2) {
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy)
return 0;
double Op1V = Ty==Type::FloatTy ?
(double)Op1->getValueAPF().convertToFloat():
Op1->getValueAPF().convertToDouble();
if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
double Op2V = Ty==Type::FloatTy ?
(double)Op2->getValueAPF().convertToFloat():
Op2->getValueAPF().convertToDouble();
if (Len == 3 && !strcmp(Str, "pow")) {
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty, Context);
} else if (Len == 4 && !strcmp(Str, "fmod")) {
return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty, Context);
} else if (Len == 5 && !strcmp(Str, "atan2")) {
return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty, Context);
}
} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
if (!strcmp(Str, "llvm.powi.f32")) {
return Context->getConstantFP(APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
} else if (!strcmp(Str, "llvm.powi.f64")) {
return Context->getConstantFP(APFloat((double)std::pow((double)Op1V,
(int)Op2C->getZExtValue())));
}
}
}
}
return 0;
}
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