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43421b3dd7
llvm-6502/lib/Analysis/ConstantFolding.cpp
Dale Johannesen 43421b3dd7 Next round of APFloat changes. 
Use APFloat in UpgradeParser and AsmParser.
Change all references to ConstantFP to use the
APFloat interface rather than double.  Remove
the ConstantFP double interfaces.
Use APFloat functions for constant folding arithmetic
and comparisons.
(There are still way too many places APFloat is
just a wrapper around host float/double, but we're
getting there.)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41747 91177308-0d34-0410-b5e6-96231b3b80d8
2007-09-06 18:13:44 +00:00

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//===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Target/TargetData.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 (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) {
ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(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.getTypeSize(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){
// 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);
}
}
// TODO: Fold icmp setne/seteq as well.
return 0;
}
/// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
/// constant expression, do so.
static Constant *SymbolicallyEvaluateGEP(Constant** Ops, unsigned NumOps,
const Type *ResultTy,
const TargetData *TD) {
Constant *Ptr = Ops[0];
if (!cast<PointerType>(Ptr->getType())->getElementType()->isSized())
return 0;
if (TD && Ptr->isNullValue()) {
// 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'
bool isFoldableGEP = true;
for (unsigned i = 1; i != NumOps; ++i)
if (!isa<ConstantInt>(Ops[i])) {
isFoldableGEP = false;
break;
}
if (isFoldableGEP) {
uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
(Value**)Ops+1, NumOps-1);
Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset);
return ConstantExpr::getIntToPtr(C, ResultTy);
}
}
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, const TargetData *TD) {
if (PHINode *PN = dyn_cast<PHINode>(I)) {
if (PN->getNumIncomingValues() == 0)
return Constant::getNullValue(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 (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
Ops.push_back(Op);
else
return 0; // All operands not constant!
return ConstantFoldInstOperands(I, &Ops[0], 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(const Instruction* I,
Constant** Ops, unsigned NumOps,
const TargetData *TD) {
unsigned Opc = I->getOpcode();
const Type *DestTy = I->getType();
// Handle easy binops first.
if (isa<BinaryOperator>(I)) {
if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1]))
if (Constant *C = SymbolicallyEvaluateBinop(I->getOpcode(), Ops[0],
Ops[1], TD))
return C;
return ConstantExpr::get(Opc, Ops[0], Ops[1]);
}
switch (Opc) {
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:
return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
Ops[1]);
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()->getPrimitiveSizeInBits();
Constant *Mask =
ConstantInt::get(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, I->getType(), false);
}
}
// FALL THROUGH.
case Instruction::IntToPtr:
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::BitCast:
return ConstantExpr::getCast(Opc, 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, I->getType(), TD))
return C;
return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-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) {
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(Function *F) {
switch (F->getIntrinsicID()) {
case Intrinsic::sqrt_f32:
case Intrinsic::sqrt_f64:
case Intrinsic::powi_f32:
case Intrinsic::powi_f64:
case Intrinsic::bswap:
case Intrinsic::ctpop:
case Intrinsic::ctlz:
case Intrinsic::cttz:
return true;
default: break;
}
const ValueName *NameVal = F->getValueName();
if (NameVal == 0) return false;
const char *Str = NameVal->getKeyData();
unsigned Len = NameVal->getKeyLength();
// 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");
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) {
errno = 0;
V = NativeFP(V);
if (errno == 0) {
if (Ty==Type::FloatTy)
return ConstantFP::get(Ty, APFloat((float)V));
else if (Ty==Type::DoubleTy)
return ConstantFP::get(Ty, APFloat(V));
else
assert(0);
}
errno = 0;
return 0;
}
static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
double V, double W,
const Type *Ty) {
errno = 0;
V = NativeFP(V, W);
if (errno == 0) {
if (Ty==Type::FloatTy)
return ConstantFP::get(Ty, APFloat((float)V));
else if (Ty==Type::DoubleTy)
return ConstantFP::get(Ty, APFloat(V));
else
assert(0);
}
errno = 0;
return 0;
}
/// 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** Operands, unsigned NumOperands) {
const ValueName *NameVal = F->getValueName();
if (NameVal == 0) return 0;
const char *Str = NameVal->getKeyData();
unsigned Len = NameVal->getKeyLength();
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);
else if (Len == 4 && !strcmp(Str, "asin"))
return ConstantFoldFP(asin, V, Ty);
else if (Len == 4 && !strcmp(Str, "atan"))
return ConstantFoldFP(atan, V, Ty);
break;
case 'c':
if (Len == 4 && !strcmp(Str, "ceil"))
return ConstantFoldFP(ceil, V, Ty);
else if (Len == 3 && !strcmp(Str, "cos"))
return ConstantFoldFP(cos, V, Ty);
else if (Len == 4 && !strcmp(Str, "cosh"))
return ConstantFoldFP(cosh, V, Ty);
break;
case 'e':
if (Len == 3 && !strcmp(Str, "exp"))
return ConstantFoldFP(exp, V, Ty);
break;
case 'f':
if (Len == 4 && !strcmp(Str, "fabs"))
return ConstantFoldFP(fabs, V, Ty);
else if (Len == 5 && !strcmp(Str, "floor"))
return ConstantFoldFP(floor, V, Ty);
break;
case 'l':
if (Len == 3 && !strcmp(Str, "log") && V > 0)
return ConstantFoldFP(log, V, Ty);
else if (Len == 5 && !strcmp(Str, "log10") && V > 0)
return ConstantFoldFP(log10, V, Ty);
else if (!strcmp(Str, "llvm.sqrt.f32") ||
!strcmp(Str, "llvm.sqrt.f64")) {
if (V >= -0.0)
return ConstantFoldFP(sqrt, V, Ty);
else // Undefined
return ConstantFP::get(Ty, Ty==Type::FloatTy ? APFloat(0.0f) :
APFloat(0.0));
}
break;
case 's':
if (Len == 3 && !strcmp(Str, "sin"))
return ConstantFoldFP(sin, V, Ty);
else if (Len == 4 && !strcmp(Str, "sinh"))
return ConstantFoldFP(sinh, V, Ty);
else if (Len == 4 && !strcmp(Str, "sqrt") && V >= 0)
return ConstantFoldFP(sqrt, V, Ty);
else if (Len == 5 && !strcmp(Str, "sqrtf") && V >= 0)
return ConstantFoldFP(sqrt, V, Ty);
break;
case 't':
if (Len == 3 && !strcmp(Str, "tan"))
return ConstantFoldFP(tan, V, Ty);
else if (Len == 4 && !strcmp(Str, "tanh"))
return ConstantFoldFP(tanh, V, Ty);
break;
default:
break;
}
} else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
if (Len > 11 && !memcmp(Str, "llvm.bswap", 10)) {
return ConstantInt::get(Op->getValue().byteSwap());
} else if (Len > 11 && !memcmp(Str, "llvm.ctpop", 10)) {
uint64_t ctpop = Op->getValue().countPopulation();
return ConstantInt::get(Ty, ctpop);
} else if (Len > 10 && !memcmp(Str, "llvm.cttz", 9)) {
uint64_t cttz = Op->getValue().countTrailingZeros();
return ConstantInt::get(Ty, cttz);
} else if (Len > 10 && !memcmp(Str, "llvm.ctlz", 9)) {
uint64_t ctlz = Op->getValue().countLeadingZeros();
return ConstantInt::get(Ty, ctlz);
}
}
} else if (NumOperands == 2) {
if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
double Op1V = Ty==Type::FloatTy ?
(double)Op1->getValueAPF().convertToFloat():
Op1->getValueAPF().convertToDouble();
if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy)
return 0;
double Op2V = Ty==Type::FloatTy ?
(double)Op2->getValueAPF().convertToFloat():
Op2->getValueAPF().convertToDouble();
if (Len == 3 && !strcmp(Str, "pow")) {
return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty);
} else if (Len == 4 && !strcmp(Str, "fmod")) {
return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty);
} else if (Len == 5 && !strcmp(Str, "atan2")) {
return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty);
}
} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
if (!strcmp(Str, "llvm.powi.f32")) {
return ConstantFP::get(Ty, APFloat((float)std::pow((float)Op1V,
(int)Op2C->getZExtValue())));
} else if (!strcmp(Str, "llvm.powi.f64")) {
return ConstantFP::get(Ty, APFloat((double)std::pow((double)Op1V,
(int)Op2C->getZExtValue())));
}
}
}
}
return 0;
}
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