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llvm-project/llvm/lib/IR/ConstantFold.cpp

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//===- ConstantFold.cpp - LLVM constant folder ----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements folding of constants for LLVM. This implements the
// (internal) ConstantFold.h interface, which is used by the
// ConstantExpr::get* methods to automatically fold constants when possible.
//
// The current constant folding implementation is implemented in two pieces: the
// pieces that don't need DataLayout, and the pieces that do. This is to avoid
// a dependence in IR on Target.
//
//===----------------------------------------------------------------------===//
#include "ConstantFold.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/MathExtras.h"
using namespace llvm;
using namespace llvm::PatternMatch;
//===----------------------------------------------------------------------===//
// ConstantFold*Instruction Implementations
//===----------------------------------------------------------------------===//
/// Convert the specified vector Constant node to the specified vector type.
/// At this point, we know that the elements of the input vector constant are
/// all simple integer or FP values.
static Constant *BitCastConstantVector(Constant *CV, VectorType *DstTy) {
if (CV->isAllOnesValue()) return Constant::getAllOnesValue(DstTy);
if (CV->isNullValue()) return Constant::getNullValue(DstTy);
// If this cast changes element count then we can't handle it here:
// doing so requires endianness information. This should be handled by
// Analysis/ConstantFolding.cpp
unsigned NumElts = DstTy->getNumElements();
if (NumElts != CV->getType()->getVectorNumElements())
return nullptr;
Type *DstEltTy = DstTy->getElementType();
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(CV->getContext(), 32);
for (unsigned i = 0; i != NumElts; ++i) {
Constant *C =
ConstantExpr::getExtractElement(CV, ConstantInt::get(Ty, i));
C = ConstantExpr::getBitCast(C, DstEltTy);
Result.push_back(C);
}
return ConstantVector::get(Result);
}
/// This function determines which opcode to use to fold two constant cast
/// expressions together. It uses CastInst::isEliminableCastPair to determine
/// the opcode. Consequently its just a wrapper around that function.
/// @brief Determine if it is valid to fold a cast of a cast
static unsigned
foldConstantCastPair(
unsigned opc, ///< opcode of the second cast constant expression
ConstantExpr *Op, ///< the first cast constant expression
Type *DstTy ///< destination type of the first cast
) {
assert(Op && Op->isCast() && "Can't fold cast of cast without a cast!");
assert(DstTy && DstTy->isFirstClassType() && "Invalid cast destination type");
assert(CastInst::isCast(opc) && "Invalid cast opcode");
// The types and opcodes for the two Cast constant expressions
Type *SrcTy = Op->getOperand(0)->getType();
Type *MidTy = Op->getType();
Instruction::CastOps firstOp = Instruction::CastOps(Op->getOpcode());
Instruction::CastOps secondOp = Instruction::CastOps(opc);
// Assume that pointers are never more than 64 bits wide, and only use this
// for the middle type. Otherwise we could end up folding away illegal
// bitcasts between address spaces with different sizes.
IntegerType *FakeIntPtrTy = Type::getInt64Ty(DstTy->getContext());
// Let CastInst::isEliminableCastPair do the heavy lifting.
return CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, DstTy,
nullptr, FakeIntPtrTy, nullptr);
}
static Constant *FoldBitCast(Constant *V, Type *DestTy) {
Type *SrcTy = V->getType();
if (SrcTy == DestTy)
return V; // no-op cast
// Check to see if we are casting a pointer to an aggregate to a pointer to
// the first element. If so, return the appropriate GEP instruction.
if (PointerType *PTy = dyn_cast<PointerType>(V->getType()))
if (PointerType *DPTy = dyn_cast<PointerType>(DestTy))
if (PTy->getAddressSpace() == DPTy->getAddressSpace()
&& PTy->getElementType()->isSized()) {
SmallVector<Value*, 8> IdxList;
Value *Zero =
Constant::getNullValue(Type::getInt32Ty(DPTy->getContext()));
IdxList.push_back(Zero);
Type *ElTy = PTy->getElementType();
while (ElTy != DPTy->getElementType()) {
if (StructType *STy = dyn_cast<StructType>(ElTy)) {
if (STy->getNumElements() == 0) break;
ElTy = STy->getElementType(0);
IdxList.push_back(Zero);
} else if (SequentialType *STy =
dyn_cast<SequentialType>(ElTy)) {
ElTy = STy->getElementType();
IdxList.push_back(Zero);
} else {
break;
}
}
if (ElTy == DPTy->getElementType())
// This GEP is inbounds because all indices are zero.
return ConstantExpr::getInBoundsGetElementPtr(PTy->getElementType(),
V, IdxList);
}
// Handle casts from one vector constant to another. We know that the src
// and dest type have the same size (otherwise its an illegal cast).
if (VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) {
if (VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) {
assert(DestPTy->getBitWidth() == SrcTy->getBitWidth() &&
"Not cast between same sized vectors!");
SrcTy = nullptr;
// First, check for null. Undef is already handled.
if (isa<ConstantAggregateZero>(V))
return Constant::getNullValue(DestTy);
// Handle ConstantVector and ConstantAggregateVector.
return BitCastConstantVector(V, DestPTy);
}
// Canonicalize scalar-to-vector bitcasts into vector-to-vector bitcasts
// This allows for other simplifications (although some of them
// can only be handled by Analysis/ConstantFolding.cpp).
if (isa<ConstantInt>(V) || isa<ConstantFP>(V))
return ConstantExpr::getBitCast(ConstantVector::get(V), DestPTy);
}
// Finally, implement bitcast folding now. The code below doesn't handle
// bitcast right.
if (isa<ConstantPointerNull>(V)) // ptr->ptr cast.
return ConstantPointerNull::get(cast<PointerType>(DestTy));
// Handle integral constant input.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
if (DestTy->isIntegerTy())
// Integral -> Integral. This is a no-op because the bit widths must
// be the same. Consequently, we just fold to V.
return V;
// See note below regarding the PPC_FP128 restriction.
if (DestTy->isFloatingPointTy() && !DestTy->isPPC_FP128Ty())
return ConstantFP::get(DestTy->getContext(),
APFloat(DestTy->getFltSemantics(),
CI->getValue()));
// Otherwise, can't fold this (vector?)
return nullptr;
}
// Handle ConstantFP input: FP -> Integral.
if (ConstantFP *FP = dyn_cast<ConstantFP>(V)) {
// PPC_FP128 is really the sum of two consecutive doubles, where the first
// double is always stored first in memory, regardless of the target
// endianness. The memory layout of i128, however, depends on the target
// endianness, and so we can't fold this without target endianness
// information. This should instead be handled by
// Analysis/ConstantFolding.cpp
if (FP->getType()->isPPC_FP128Ty())
return nullptr;
// Make sure dest type is compatible with the folded integer constant.
if (!DestTy->isIntegerTy())
return nullptr;
return ConstantInt::get(FP->getContext(),
FP->getValueAPF().bitcastToAPInt());
}
return nullptr;
}
/// V is an integer constant which only has a subset of its bytes used.
/// The bytes used are indicated by ByteStart (which is the first byte used,
/// counting from the least significant byte) and ByteSize, which is the number
/// of bytes used.
///
/// This function analyzes the specified constant to see if the specified byte
/// range can be returned as a simplified constant. If so, the constant is
/// returned, otherwise null is returned.
static Constant *ExtractConstantBytes(Constant *C, unsigned ByteStart,
unsigned ByteSize) {
assert(C->getType()->isIntegerTy() &&
(cast<IntegerType>(C->getType())->getBitWidth() & 7) == 0 &&
"Non-byte sized integer input");
unsigned CSize = cast<IntegerType>(C->getType())->getBitWidth()/8;
assert(ByteSize && "Must be accessing some piece");
assert(ByteStart+ByteSize <= CSize && "Extracting invalid piece from input");
assert(ByteSize != CSize && "Should not extract everything");
// Constant Integers are simple.
if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
APInt V = CI->getValue();
if (ByteStart)
V = V.lshr(ByteStart*8);
V = V.trunc(ByteSize*8);
return ConstantInt::get(CI->getContext(), V);
}
// In the input is a constant expr, we might be able to recursively simplify.
// If not, we definitely can't do anything.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE) return nullptr;
switch (CE->getOpcode()) {
default: return nullptr;
case Instruction::Or: {
Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
if (!RHS)
return nullptr;
// X | -1 -> -1.
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS))
if (RHSC->isAllOnesValue())
return RHSC;
Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
if (!LHS)
return nullptr;
return ConstantExpr::getOr(LHS, RHS);
}
case Instruction::And: {
Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
if (!RHS)
return nullptr;
// X & 0 -> 0.
if (RHS->isNullValue())
return RHS;
Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
if (!LHS)
return nullptr;
return ConstantExpr::getAnd(LHS, RHS);
}
case Instruction::LShr: {
ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
if (!Amt)
return nullptr;
unsigned ShAmt = Amt->getZExtValue();
// Cannot analyze non-byte shifts.
if ((ShAmt & 7) != 0)
return nullptr;
ShAmt >>= 3;
// If the extract is known to be all zeros, return zero.
if (ByteStart >= CSize-ShAmt)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If the extract is known to be fully in the input, extract it.
if (ByteStart+ByteSize+ShAmt <= CSize)
return ExtractConstantBytes(CE->getOperand(0), ByteStart+ShAmt, ByteSize);
// TODO: Handle the 'partially zero' case.
return nullptr;
}
case Instruction::Shl: {
ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
if (!Amt)
return nullptr;
unsigned ShAmt = Amt->getZExtValue();
// Cannot analyze non-byte shifts.
if ((ShAmt & 7) != 0)
return nullptr;
ShAmt >>= 3;
// If the extract is known to be all zeros, return zero.
if (ByteStart+ByteSize <= ShAmt)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If the extract is known to be fully in the input, extract it.
if (ByteStart >= ShAmt)
return ExtractConstantBytes(CE->getOperand(0), ByteStart-ShAmt, ByteSize);
// TODO: Handle the 'partially zero' case.
return nullptr;
}
case Instruction::ZExt: {
unsigned SrcBitSize =
cast<IntegerType>(CE->getOperand(0)->getType())->getBitWidth();
// If extracting something that is completely zero, return 0.
if (ByteStart*8 >= SrcBitSize)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If exactly extracting the input, return it.
if (ByteStart == 0 && ByteSize*8 == SrcBitSize)
return CE->getOperand(0);
// If extracting something completely in the input, if if the input is a
// multiple of 8 bits, recurse.
if ((SrcBitSize&7) == 0 && (ByteStart+ByteSize)*8 <= SrcBitSize)
return ExtractConstantBytes(CE->getOperand(0), ByteStart, ByteSize);
// Otherwise, if extracting a subset of the input, which is not multiple of
// 8 bits, do a shift and trunc to get the bits.
if ((ByteStart+ByteSize)*8 < SrcBitSize) {
assert((SrcBitSize&7) && "Shouldn't get byte sized case here");
Constant *Res = CE->getOperand(0);
if (ByteStart)
Res = ConstantExpr::getLShr(Res,
ConstantInt::get(Res->getType(), ByteStart*8));
return ConstantExpr::getTrunc(Res, IntegerType::get(C->getContext(),
ByteSize*8));
}
// TODO: Handle the 'partially zero' case.
return nullptr;
}
}
}
/// Return a ConstantExpr with type DestTy for sizeof on Ty, with any known
/// factors factored out. If Folded is false, return null if no factoring was
/// possible, to avoid endlessly bouncing an unfoldable expression back into the
/// top-level folder.
static Constant *getFoldedSizeOf(Type *Ty, Type *DestTy,
bool Folded) {
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Constant *N = ConstantInt::get(DestTy, ATy->getNumElements());
Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
return ConstantExpr::getNUWMul(E, N);
}
if (StructType *STy = dyn_cast<StructType>(Ty))
if (!STy->isPacked()) {
unsigned NumElems = STy->getNumElements();
// An empty struct has size zero.
if (NumElems == 0)
return ConstantExpr::getNullValue(DestTy);
// Check for a struct with all members having the same size.
Constant *MemberSize =
getFoldedSizeOf(STy->getElementType(0), DestTy, true);
bool AllSame = true;
for (unsigned i = 1; i != NumElems; ++i)
if (MemberSize !=
getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
AllSame = false;
break;
}
if (AllSame) {
Constant *N = ConstantInt::get(DestTy, NumElems);
return ConstantExpr::getNUWMul(MemberSize, N);
}
}
// Pointer size doesn't depend on the pointee type, so canonicalize them
// to an arbitrary pointee.
if (PointerType *PTy = dyn_cast<PointerType>(Ty))
if (!PTy->getElementType()->isIntegerTy(1))
return
getFoldedSizeOf(PointerType::get(IntegerType::get(PTy->getContext(), 1),
PTy->getAddressSpace()),
DestTy, true);
// If there's no interesting folding happening, bail so that we don't create
// a constant that looks like it needs folding but really doesn't.
if (!Folded)
return nullptr;
// Base case: Get a regular sizeof expression.
Constant *C = ConstantExpr::getSizeOf(Ty);
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
DestTy, false),
C, DestTy);
return C;
}
/// Return a ConstantExpr with type DestTy for alignof on Ty, with any known
/// factors factored out. If Folded is false, return null if no factoring was
/// possible, to avoid endlessly bouncing an unfoldable expression back into the
/// top-level folder.
static Constant *getFoldedAlignOf(Type *Ty, Type *DestTy,
bool Folded) {
// The alignment of an array is equal to the alignment of the
// array element. Note that this is not always true for vectors.
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Constant *C = ConstantExpr::getAlignOf(ATy->getElementType());
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
DestTy,
false),
C, DestTy);
return C;
}
if (StructType *STy = dyn_cast<StructType>(Ty)) {
// Packed structs always have an alignment of 1.
if (STy->isPacked())
return ConstantInt::get(DestTy, 1);
// Otherwise, struct alignment is the maximum alignment of any member.
// Without target data, we can't compare much, but we can check to see
// if all the members have the same alignment.
unsigned NumElems = STy->getNumElements();
// An empty struct has minimal alignment.
if (NumElems == 0)
return ConstantInt::get(DestTy, 1);
// Check for a struct with all members having the same alignment.
Constant *MemberAlign =
getFoldedAlignOf(STy->getElementType(0), DestTy, true);
bool AllSame = true;
for (unsigned i = 1; i != NumElems; ++i)
if (MemberAlign != getFoldedAlignOf(STy->getElementType(i), DestTy, true)) {
AllSame = false;
break;
}
if (AllSame)
return MemberAlign;
}
// Pointer alignment doesn't depend on the pointee type, so canonicalize them
// to an arbitrary pointee.
if (PointerType *PTy = dyn_cast<PointerType>(Ty))
if (!PTy->getElementType()->isIntegerTy(1))
return
getFoldedAlignOf(PointerType::get(IntegerType::get(PTy->getContext(),
1),
PTy->getAddressSpace()),
DestTy, true);
// If there's no interesting folding happening, bail so that we don't create
// a constant that looks like it needs folding but really doesn't.
if (!Folded)
return nullptr;
// Base case: Get a regular alignof expression.
Constant *C = ConstantExpr::getAlignOf(Ty);
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
DestTy, false),
C, DestTy);
return C;
}
/// Return a ConstantExpr with type DestTy for offsetof on Ty and FieldNo, with
/// any known factors factored out. If Folded is false, return null if no
/// factoring was possible, to avoid endlessly bouncing an unfoldable expression
/// back into the top-level folder.
static Constant *getFoldedOffsetOf(Type *Ty, Constant *FieldNo,
Type *DestTy,
bool Folded) {
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo, false,
DestTy, false),
FieldNo, DestTy);
Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
return ConstantExpr::getNUWMul(E, N);
}
if (StructType *STy = dyn_cast<StructType>(Ty))
if (!STy->isPacked()) {
unsigned NumElems = STy->getNumElements();
// An empty struct has no members.
if (NumElems == 0)
return nullptr;
// Check for a struct with all members having the same size.
Constant *MemberSize =
getFoldedSizeOf(STy->getElementType(0), DestTy, true);
bool AllSame = true;
for (unsigned i = 1; i != NumElems; ++i)
if (MemberSize !=
getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
AllSame = false;
break;
}
if (AllSame) {
Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo,
false,
DestTy,
false),
FieldNo, DestTy);
return ConstantExpr::getNUWMul(MemberSize, N);
}
}
// If there's no interesting folding happening, bail so that we don't create
// a constant that looks like it needs folding but really doesn't.
if (!Folded)
return nullptr;
// Base case: Get a regular offsetof expression.
Constant *C = ConstantExpr::getOffsetOf(Ty, FieldNo);
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
DestTy, false),
C, DestTy);
return C;
}
Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
Type *DestTy) {
if (isa<UndefValue>(V)) {
// zext(undef) = 0, because the top bits will be zero.
// sext(undef) = 0, because the top bits will all be the same.
// [us]itofp(undef) = 0, because the result value is bounded.
if (opc == Instruction::ZExt || opc == Instruction::SExt ||
opc == Instruction::UIToFP || opc == Instruction::SIToFP)
return Constant::getNullValue(DestTy);
return UndefValue::get(DestTy);
}
if (V->isNullValue() && !DestTy->isX86_MMXTy() &&
opc != Instruction::AddrSpaceCast)
return Constant::getNullValue(DestTy);
// If the cast operand is a constant expression, there's a few things we can
// do to try to simplify it.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (CE->isCast()) {
// Try hard to fold cast of cast because they are often eliminable.
if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy))
return ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy);
} else if (CE->getOpcode() == Instruction::GetElementPtr &&
// Do not fold addrspacecast (gep 0, .., 0). It might make the
// addrspacecast uncanonicalized.
opc != Instruction::AddrSpaceCast &&
// Do not fold bitcast (gep) with inrange index, as this loses
// information.
!cast<GEPOperator>(CE)->getInRangeIndex().hasValue()) {
// If all of the indexes in the GEP are null values, there is no pointer
// adjustment going on. We might as well cast the source pointer.
bool isAllNull = true;
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
if (!CE->getOperand(i)->isNullValue()) {
isAllNull = false;
break;
}
if (isAllNull)
// This is casting one pointer type to another, always BitCast
return ConstantExpr::getPointerCast(CE->getOperand(0), DestTy);
}
}
// If the cast operand is a constant vector, perform the cast by
// operating on each element. In the cast of bitcasts, the element
// count may be mismatched; don't attempt to handle that here.
if ((isa<ConstantVector>(V) || isa<ConstantDataVector>(V)) &&
DestTy->isVectorTy() &&
DestTy->getVectorNumElements() == V->getType()->getVectorNumElements()) {
SmallVector<Constant*, 16> res;
VectorType *DestVecTy = cast<VectorType>(DestTy);
Type *DstEltTy = DestVecTy->getElementType();
Type *Ty = IntegerType::get(V->getContext(), 32);
for (unsigned i = 0, e = V->getType()->getVectorNumElements(); i != e; ++i) {
Constant *C =
ConstantExpr::getExtractElement(V, ConstantInt::get(Ty, i));
res.push_back(ConstantExpr::getCast(opc, C, DstEltTy));
}
return ConstantVector::get(res);
}
// We actually have to do a cast now. Perform the cast according to the
// opcode specified.
switch (opc) {
default:
llvm_unreachable("Failed to cast constant expression");
case Instruction::FPTrunc:
case Instruction::FPExt:
if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
bool ignored;
APFloat Val = FPC->getValueAPF();
Val.convert(DestTy->isHalfTy() ? APFloat::IEEEhalf() :
DestTy->isFloatTy() ? APFloat::IEEEsingle() :
DestTy->isDoubleTy() ? APFloat::IEEEdouble() :
DestTy->isX86_FP80Ty() ? APFloat::x87DoubleExtended() :
DestTy->isFP128Ty() ? APFloat::IEEEquad() :
DestTy->isPPC_FP128Ty() ? APFloat::PPCDoubleDouble() :
APFloat::Bogus(),
APFloat::rmNearestTiesToEven, &ignored);
return ConstantFP::get(V->getContext(), Val);
}
return nullptr; // Can't fold.
case Instruction::FPToUI:
case Instruction::FPToSI:
if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
const APFloat &V = FPC->getValueAPF();
bool ignored;
uint64_t x[2];
uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
if (APFloat::opInvalidOp ==
V.convertToInteger(x, DestBitWidth, opc==Instruction::FPToSI,
APFloat::rmTowardZero, &ignored)) {
// Undefined behavior invoked - the destination type can't represent
// the input constant.
return UndefValue::get(DestTy);
}
APInt Val(DestBitWidth, x);
return ConstantInt::get(FPC->getContext(), Val);
}
return nullptr; // Can't fold.
case Instruction::IntToPtr: //always treated as unsigned
if (V->isNullValue()) // Is it an integral null value?
return ConstantPointerNull::get(cast<PointerType>(DestTy));
return nullptr; // Other pointer types cannot be casted
case Instruction::PtrToInt: // always treated as unsigned
// Is it a null pointer value?
if (V->isNullValue())
return ConstantInt::get(DestTy, 0);
// If this is a sizeof-like expression, pull out multiplications by
// known factors to expose them to subsequent folding. If it's an
// alignof-like expression, factor out known factors.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::GetElementPtr &&
CE->getOperand(0)->isNullValue()) {
GEPOperator *GEPO = cast<GEPOperator>(CE);
Type *Ty = GEPO->getSourceElementType();
if (CE->getNumOperands() == 2) {
// Handle a sizeof-like expression.
Constant *Idx = CE->getOperand(1);
bool isOne = isa<ConstantInt>(Idx) && cast<ConstantInt>(Idx)->isOne();
if (Constant *C = getFoldedSizeOf(Ty, DestTy, !isOne)) {
Idx = ConstantExpr::getCast(CastInst::getCastOpcode(Idx, true,
DestTy, false),
Idx, DestTy);
return ConstantExpr::getMul(C, Idx);
}
} else if (CE->getNumOperands() == 3 &&
CE->getOperand(1)->isNullValue()) {
// Handle an alignof-like expression.
if (StructType *STy = dyn_cast<StructType>(Ty))
if (!STy->isPacked()) {
ConstantInt *CI = cast<ConstantInt>(CE->getOperand(2));
if (CI->isOne() &&
STy->getNumElements() == 2 &&
STy->getElementType(0)->isIntegerTy(1)) {
return getFoldedAlignOf(STy->getElementType(1), DestTy, false);
}
}
// Handle an offsetof-like expression.
if (Ty->isStructTy() || Ty->isArrayTy()) {
if (Constant *C = getFoldedOffsetOf(Ty, CE->getOperand(2),
DestTy, false))
return C;
}
}
}
// Other pointer types cannot be casted
return nullptr;
case Instruction::UIToFP:
case Instruction::SIToFP:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
const APInt &api = CI->getValue();
APFloat apf(DestTy->getFltSemantics(),
APInt::getNullValue(DestTy->getPrimitiveSizeInBits()));
if (APFloat::opOverflow &
apf.convertFromAPInt(api, opc==Instruction::SIToFP,
APFloat::rmNearestTiesToEven)) {
// Undefined behavior invoked - the destination type can't represent
// the input constant.
return UndefValue::get(DestTy);
}
return ConstantFP::get(V->getContext(), apf);
}
return nullptr;
case Instruction::ZExt:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth();
return ConstantInt::get(V->getContext(),
CI->getValue().zext(BitWidth));
}
return nullptr;
case Instruction::SExt:
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth();
return ConstantInt::get(V->getContext(),
CI->getValue().sext(BitWidth));
}
return nullptr;
case Instruction::Trunc: {
if (V->getType()->isVectorTy())
return nullptr;
uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
return ConstantInt::get(V->getContext(),
CI->getValue().trunc(DestBitWidth));
}
// The input must be a constantexpr. See if we can simplify this based on
// the bytes we are demanding. Only do this if the source and dest are an
// even multiple of a byte.
if ((DestBitWidth & 7) == 0 &&
(cast<IntegerType>(V->getType())->getBitWidth() & 7) == 0)
if (Constant *Res = ExtractConstantBytes(V, 0, DestBitWidth / 8))
return Res;
return nullptr;
}
case Instruction::BitCast:
return FoldBitCast(V, DestTy);
case Instruction::AddrSpaceCast:
return nullptr;
}
}
Constant *llvm::ConstantFoldSelectInstruction(Constant *Cond,
Constant *V1, Constant *V2) {
// Check for i1 and vector true/false conditions.
if (Cond->isNullValue()) return V2;
if (Cond->isAllOnesValue()) return V1;
// If the condition is a vector constant, fold the result elementwise.
if (ConstantVector *CondV = dyn_cast<ConstantVector>(Cond)) {
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(CondV->getContext(), 32);
for (unsigned i = 0, e = V1->getType()->getVectorNumElements(); i != e;++i){
Constant *V;
Constant *V1Element = ConstantExpr::getExtractElement(V1,
ConstantInt::get(Ty, i));
Constant *V2Element = ConstantExpr::getExtractElement(V2,
ConstantInt::get(Ty, i));
Constant *Cond = dyn_cast<Constant>(CondV->getOperand(i));
if (V1Element == V2Element) {
V = V1Element;
} else if (isa<UndefValue>(Cond)) {
V = isa<UndefValue>(V1Element) ? V1Element : V2Element;
} else {
if (!isa<ConstantInt>(Cond)) break;
V = Cond->isNullValue() ? V2Element : V1Element;
}
Result.push_back(V);
}
// If we were able to build the vector, return it.
if (Result.size() == V1->getType()->getVectorNumElements())
return ConstantVector::get(Result);
}
if (isa<UndefValue>(Cond)) {
if (isa<UndefValue>(V1)) return V1;
return V2;
}
if (isa<UndefValue>(V1)) return V2;
if (isa<UndefValue>(V2)) return V1;
if (V1 == V2) return V1;
if (ConstantExpr *TrueVal = dyn_cast<ConstantExpr>(V1)) {
if (TrueVal->getOpcode() == Instruction::Select)
if (TrueVal->getOperand(0) == Cond)
return ConstantExpr::getSelect(Cond, TrueVal->getOperand(1), V2);
}
if (ConstantExpr *FalseVal = dyn_cast<ConstantExpr>(V2)) {
if (FalseVal->getOpcode() == Instruction::Select)
if (FalseVal->getOperand(0) == Cond)
return ConstantExpr::getSelect(Cond, V1, FalseVal->getOperand(2));
}
return nullptr;
}
Constant *llvm::ConstantFoldExtractElementInstruction(Constant *Val,
Constant *Idx) {
if (isa<UndefValue>(Val)) // ee(undef, x) -> undef
return UndefValue::get(Val->getType()->getVectorElementType());
if (Val->isNullValue()) // ee(zero, x) -> zero
return Constant::getNullValue(Val->getType()->getVectorElementType());
// ee({w,x,y,z}, undef) -> undef
if (isa<UndefValue>(Idx))
return UndefValue::get(Val->getType()->getVectorElementType());
if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx)) {
// ee({w,x,y,z}, wrong_value) -> undef
if (CIdx->uge(Val->getType()->getVectorNumElements()))
return UndefValue::get(Val->getType()->getVectorElementType());
return Val->getAggregateElement(CIdx->getZExtValue());
}
return nullptr;
}
Constant *llvm::ConstantFoldInsertElementInstruction(Constant *Val,
Constant *Elt,
Constant *Idx) {
if (isa<UndefValue>(Idx))
return UndefValue::get(Val->getType());
ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx);
if (!CIdx) return nullptr;
unsigned NumElts = Val->getType()->getVectorNumElements();
if (CIdx->uge(NumElts))
return UndefValue::get(Val->getType());
SmallVector<Constant*, 16> Result;
Result.reserve(NumElts);
auto *Ty = Type::getInt32Ty(Val->getContext());
uint64_t IdxVal = CIdx->getZExtValue();
for (unsigned i = 0; i != NumElts; ++i) {
if (i == IdxVal) {
Result.push_back(Elt);
continue;
}
Constant *C = ConstantExpr::getExtractElement(Val, ConstantInt::get(Ty, i));
Result.push_back(C);
}
return ConstantVector::get(Result);
}
Constant *llvm::ConstantFoldShuffleVectorInstruction(Constant *V1,
Constant *V2,
Constant *Mask) {
unsigned MaskNumElts = Mask->getType()->getVectorNumElements();
Type *EltTy = V1->getType()->getVectorElementType();
// Undefined shuffle mask -> undefined value.
if (isa<UndefValue>(Mask))
return UndefValue::get(VectorType::get(EltTy, MaskNumElts));
// Don't break the bitcode reader hack.
if (isa<ConstantExpr>(Mask)) return nullptr;
unsigned SrcNumElts = V1->getType()->getVectorNumElements();
// Loop over the shuffle mask, evaluating each element.
SmallVector<Constant*, 32> Result;
for (unsigned i = 0; i != MaskNumElts; ++i) {
int Elt = ShuffleVectorInst::getMaskValue(Mask, i);
if (Elt == -1) {
Result.push_back(UndefValue::get(EltTy));
continue;
}
Constant *InElt;
if (unsigned(Elt) >= SrcNumElts*2)
InElt = UndefValue::get(EltTy);
else if (unsigned(Elt) >= SrcNumElts) {
Type *Ty = IntegerType::get(V2->getContext(), 32);
InElt =
ConstantExpr::getExtractElement(V2,
ConstantInt::get(Ty, Elt - SrcNumElts));
} else {
Type *Ty = IntegerType::get(V1->getContext(), 32);
InElt = ConstantExpr::getExtractElement(V1, ConstantInt::get(Ty, Elt));
}
Result.push_back(InElt);
}
return ConstantVector::get(Result);
}
Constant *llvm::ConstantFoldExtractValueInstruction(Constant *Agg,
ArrayRef<unsigned> Idxs) {
// Base case: no indices, so return the entire value.
if (Idxs.empty())
return Agg;
if (Constant *C = Agg->getAggregateElement(Idxs[0]))
return ConstantFoldExtractValueInstruction(C, Idxs.slice(1));
return nullptr;
}
Constant *llvm::ConstantFoldInsertValueInstruction(Constant *Agg,
Constant *Val,
ArrayRef<unsigned> Idxs) {
// Base case: no indices, so replace the entire value.
if (Idxs.empty())
return Val;
unsigned NumElts;
if (StructType *ST = dyn_cast<StructType>(Agg->getType()))
NumElts = ST->getNumElements();
else
NumElts = cast<SequentialType>(Agg->getType())->getNumElements();
SmallVector<Constant*, 32> Result;
for (unsigned i = 0; i != NumElts; ++i) {
Constant *C = Agg->getAggregateElement(i);
if (!C) return nullptr;
if (Idxs[0] == i)
C = ConstantFoldInsertValueInstruction(C, Val, Idxs.slice(1));
Result.push_back(C);
}
if (StructType *ST = dyn_cast<StructType>(Agg->getType()))
return ConstantStruct::get(ST, Result);
if (ArrayType *AT = dyn_cast<ArrayType>(Agg->getType()))
return ConstantArray::get(AT, Result);
return ConstantVector::get(Result);
}
Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
Constant *C1, Constant *C2) {
assert(Instruction::isBinaryOp(Opcode) && "Non-binary instruction detected");
// Handle UndefValue up front.
if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
switch (static_cast<Instruction::BinaryOps>(Opcode)) {
case Instruction::Xor:
if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
// Handle undef ^ undef -> 0 special case. This is a common
// idiom (misuse).
return Constant::getNullValue(C1->getType());
LLVM_FALLTHROUGH;
case Instruction::Add:
case Instruction::Sub:
return UndefValue::get(C1->getType());
case Instruction::And:
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef & undef -> undef
return C1;
return Constant::getNullValue(C1->getType()); // undef & X -> 0
case Instruction::Mul: {
// undef * undef -> undef
if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
return C1;
const APInt *CV;
// X * undef -> undef if X is odd
if (match(C1, m_APInt(CV)) || match(C2, m_APInt(CV)))
if ((*CV)[0])
return UndefValue::get(C1->getType());
// X * undef -> 0 otherwise
return Constant::getNullValue(C1->getType());
}
case Instruction::SDiv:
case Instruction::UDiv:
// X / undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef / 0 -> undef
// undef / 1 -> undef
if (match(C2, m_Zero()) || match(C2, m_One()))
return C1;
// undef / X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::URem:
case Instruction::SRem:
// X % undef -> undef
if (match(C2, m_Undef()))
return C2;
// undef % 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef % X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::Or: // X | undef -> -1
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef | undef -> undef
return C1;
return Constant::getAllOnesValue(C1->getType()); // undef | X -> ~0
case Instruction::LShr:
// X >>l undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>l 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef >>l X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::AShr:
// X >>a undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>a 0 -> undef
if (match(C2, m_Zero()))
return C1;
// TODO: undef >>a X -> undef if the shift is exact
// undef >>a X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::Shl:
// X << undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef << 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef << X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::FAdd:
case Instruction::FSub:
case Instruction::FMul:
case Instruction::FDiv:
case Instruction::FRem:
// TODO: UNDEF handling for binary float instructions.
return nullptr;
case Instruction::BinaryOpsEnd:
llvm_unreachable("Invalid BinaryOp");
}
}
// At this point neither constant should be an UndefValue.
assert(!isa<UndefValue>(C1) && !isa<UndefValue>(C2) &&
"Unexpected UndefValue");
// Handle simplifications when the RHS is a constant int.
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
switch (Opcode) {
case Instruction::Add:
if (CI2->equalsInt(0)) return C1; // X + 0 == X
break;
case Instruction::Sub:
if (CI2->equalsInt(0)) return C1; // X - 0 == X
break;
case Instruction::Mul:
if (CI2->equalsInt(0)) return C2; // X * 0 == 0
if (CI2->equalsInt(1))
return C1; // X * 1 == X
break;
case Instruction::UDiv:
case Instruction::SDiv:
if (CI2->equalsInt(1))
return C1; // X / 1 == X
if (CI2->equalsInt(0))
return UndefValue::get(CI2->getType()); // X / 0 == undef
break;
case Instruction::URem:
case Instruction::SRem:
if (CI2->equalsInt(1))
return Constant::getNullValue(CI2->getType()); // X % 1 == 0
if (CI2->equalsInt(0))
return UndefValue::get(CI2->getType()); // X % 0 == undef
break;
case Instruction::And:
if (CI2->isZero()) return C2; // X & 0 == 0
if (CI2->isAllOnesValue())
return C1; // X & -1 == X
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
// (zext i32 to i64) & 4294967295 -> (zext i32 to i64)
if (CE1->getOpcode() == Instruction::ZExt) {
unsigned DstWidth = CI2->getType()->getBitWidth();
unsigned SrcWidth =
CE1->getOperand(0)->getType()->getPrimitiveSizeInBits();
APInt PossiblySetBits(APInt::getLowBitsSet(DstWidth, SrcWidth));
if ((PossiblySetBits & CI2->getValue()) == PossiblySetBits)
return C1;
}
// If and'ing the address of a global with a constant, fold it.
if (CE1->getOpcode() == Instruction::PtrToInt &&
isa<GlobalValue>(CE1->getOperand(0))) {
GlobalValue *GV = cast<GlobalValue>(CE1->getOperand(0));
// Functions are at least 4-byte aligned.
unsigned GVAlign = GV->getAlignment();
if (isa<Function>(GV))
GVAlign = std::max(GVAlign, 4U);
if (GVAlign > 1) {
unsigned DstWidth = CI2->getType()->getBitWidth();
unsigned SrcWidth = std::min(DstWidth, Log2_32(GVAlign));
APInt BitsNotSet(APInt::getLowBitsSet(DstWidth, SrcWidth));
// If checking bits we know are clear, return zero.
if ((CI2->getValue() & BitsNotSet) == CI2->getValue())
return Constant::getNullValue(CI2->getType());
}
}
}
break;
case Instruction::Or:
if (CI2->equalsInt(0)) return C1; // X | 0 == X
if (CI2->isAllOnesValue())
return C2; // X | -1 == -1
break;
case Instruction::Xor:
if (CI2->equalsInt(0)) return C1; // X ^ 0 == X
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
switch (CE1->getOpcode()) {
default: break;
case Instruction::ICmp:
case Instruction::FCmp:
// cmp pred ^ true -> cmp !pred
assert(CI2->equalsInt(1));
CmpInst::Predicate pred = (CmpInst::Predicate)CE1->getPredicate();
pred = CmpInst::getInversePredicate(pred);
return ConstantExpr::getCompare(pred, CE1->getOperand(0),
CE1->getOperand(1));
}
}
break;
case Instruction::AShr:
// ashr (zext C to Ty), C2 -> lshr (zext C, CSA), C2
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1))
if (CE1->getOpcode() == Instruction::ZExt) // Top bits known zero.
return ConstantExpr::getLShr(C1, C2);
break;
}
} else if (isa<ConstantInt>(C1)) {
// If C1 is a ConstantInt and C2 is not, swap the operands.
if (Instruction::isCommutative(Opcode))
return ConstantExpr::get(Opcode, C2, C1);
}
if (ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) {
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
const APInt &C1V = CI1->getValue();
const APInt &C2V = CI2->getValue();
switch (Opcode) {
default:
break;
case Instruction::Add:
return ConstantInt::get(CI1->getContext(), C1V + C2V);
case Instruction::Sub:
return ConstantInt::get(CI1->getContext(), C1V - C2V);
case Instruction::Mul:
return ConstantInt::get(CI1->getContext(), C1V * C2V);
case Instruction::UDiv:
assert(!CI2->isNullValue() && "Div by zero handled above");
return ConstantInt::get(CI1->getContext(), C1V.udiv(C2V));
case Instruction::SDiv:
assert(!CI2->isNullValue() && "Div by zero handled above");
if (C2V.isAllOnesValue() && C1V.isMinSignedValue())
return UndefValue::get(CI1->getType()); // MIN_INT / -1 -> undef
return ConstantInt::get(CI1->getContext(), C1V.sdiv(C2V));
case Instruction::URem:
assert(!CI2->isNullValue() && "Div by zero handled above");
return ConstantInt::get(CI1->getContext(), C1V.urem(C2V));
case Instruction::SRem:
assert(!CI2->isNullValue() && "Div by zero handled above");
if (C2V.isAllOnesValue() && C1V.isMinSignedValue())
return UndefValue::get(CI1->getType()); // MIN_INT % -1 -> undef
return ConstantInt::get(CI1->getContext(), C1V.srem(C2V));
case Instruction::And:
return ConstantInt::get(CI1->getContext(), C1V & C2V);
case Instruction::Or:
return ConstantInt::get(CI1->getContext(), C1V | C2V);
case Instruction::Xor:
return ConstantInt::get(CI1->getContext(), C1V ^ C2V);
case Instruction::Shl:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.shl(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
case Instruction::LShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.lshr(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
case Instruction::AShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.ashr(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
}
}
switch (Opcode) {
case Instruction::SDiv:
case Instruction::UDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::Shl:
if (CI1->equalsInt(0)) return C1;
break;
default:
break;
}
} else if (ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) {
if (ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) {
const APFloat &C1V = CFP1->getValueAPF();
const APFloat &C2V = CFP2->getValueAPF();
APFloat C3V = C1V; // copy for modification
switch (Opcode) {
default:
break;
case Instruction::FAdd:
(void)C3V.add(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FSub:
(void)C3V.subtract(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FMul:
(void)C3V.multiply(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FDiv:
(void)C3V.divide(C2V, APFloat::rmNearestTiesToEven);
return ConstantFP::get(C1->getContext(), C3V);
case Instruction::FRem:
(void)C3V.mod(C2V);
return ConstantFP::get(C1->getContext(), C3V);
}
}
} else if (VectorType *VTy = dyn_cast<VectorType>(C1->getType())) {
// Perform elementwise folding.
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(VTy->getContext(), 32);
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);
// If any element of a divisor vector is zero, the whole op is undef.
if ((Opcode == Instruction::SDiv || Opcode == Instruction::UDiv ||
Opcode == Instruction::SRem || Opcode == Instruction::URem) &&
RHS->isNullValue())
return UndefValue::get(VTy);
Result.push_back(ConstantExpr::get(Opcode, LHS, RHS));
}
return ConstantVector::get(Result);
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
// Given ((a + b) + c), if (b + c) folds to something interesting, return
// (a + (b + c)).
if (Instruction::isAssociative(Opcode) && CE1->getOpcode() == Opcode) {
Constant *T = ConstantExpr::get(Opcode, CE1->getOperand(1), C2);
if (!isa<ConstantExpr>(T) || cast<ConstantExpr>(T)->getOpcode() != Opcode)
return ConstantExpr::get(Opcode, CE1->getOperand(0), T);
}
} else if (isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flop them around and fold the
// other way if possible.
if (Instruction::isCommutative(Opcode))
return ConstantFoldBinaryInstruction(Opcode, C2, C1);
}
// i1 can be simplified in many cases.
if (C1->getType()->isIntegerTy(1)) {
switch (Opcode) {
case Instruction::Add:
case Instruction::Sub:
return ConstantExpr::getXor(C1, C2);
case Instruction::Mul:
return ConstantExpr::getAnd(C1, C2);
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
// We can assume that C2 == 0. If it were one the result would be
// undefined because the shift value is as large as the bitwidth.
return C1;
case Instruction::SDiv:
case Instruction::UDiv:
// We can assume that C2 == 1. If it were zero the result would be
// undefined through division by zero.
return C1;
case Instruction::URem:
case Instruction::SRem:
// We can assume that C2 == 1. If it were zero the result would be
// undefined through division by zero.
return ConstantInt::getFalse(C1->getContext());
default:
break;
}
}
// We don't know how to fold this.
return nullptr;
}
/// This type is zero-sized if it's an array or structure of zero-sized types.
/// The only leaf zero-sized type is an empty structure.
static bool isMaybeZeroSizedType(Type *Ty) {
if (StructType *STy = dyn_cast<StructType>(Ty)) {
if (STy->isOpaque()) return true; // Can't say.
// If all of elements have zero size, this does too.
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
if (!isMaybeZeroSizedType(STy->getElementType(i))) return false;
return true;
} else if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
return isMaybeZeroSizedType(ATy->getElementType());
}
return false;
}
/// Compare the two constants as though they were getelementptr indices.
/// This allows coercion of the types to be the same thing.
///
/// If the two constants are the "same" (after coercion), return 0. If the
/// first is less than the second, return -1, if the second is less than the
/// first, return 1. If the constants are not integral, return -2.
///
static int IdxCompare(Constant *C1, Constant *C2, Type *ElTy) {
if (C1 == C2) return 0;
// Ok, we found a different index. If they are not ConstantInt, we can't do
// anything with them.
if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2))
return -2; // don't know!
// We cannot compare the indices if they don't fit in an int64_t.
if (cast<ConstantInt>(C1)->getValue().getActiveBits() > 64 ||
cast<ConstantInt>(C2)->getValue().getActiveBits() > 64)
return -2; // don't know!
// Ok, we have two differing integer indices. Sign extend them to be the same
// type.
int64_t C1Val = cast<ConstantInt>(C1)->getSExtValue();
int64_t C2Val = cast<ConstantInt>(C2)->getSExtValue();
if (C1Val == C2Val) return 0; // They are equal
// If the type being indexed over is really just a zero sized type, there is
// no pointer difference being made here.
if (isMaybeZeroSizedType(ElTy))
return -2; // dunno.
// If they are really different, now that they are the same type, then we
// found a difference!
if (C1Val < C2Val)
return -1;
else
return 1;
}
/// This function determines if there is anything we can decide about the two
/// constants provided. This doesn't need to handle simple things like
/// ConstantFP comparisons, but should instead handle ConstantExprs.
/// If we can determine that the two constants have a particular relation to
/// each other, we should return the corresponding FCmpInst predicate,
/// otherwise return FCmpInst::BAD_FCMP_PREDICATE. This is used below in
/// ConstantFoldCompareInstruction.
///
/// To simplify this code we canonicalize the relation so that the first
/// operand is always the most "complex" of the two. We consider ConstantFP
/// to be the simplest, and ConstantExprs to be the most complex.
static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
assert(V1->getType() == V2->getType() &&
"Cannot compare values of different types!");
// Handle degenerate case quickly
if (V1 == V2) return FCmpInst::FCMP_OEQ;
if (!isa<ConstantExpr>(V1)) {
if (!isa<ConstantExpr>(V2)) {
// Simple case, use the standard constant folder.
ConstantInt *R = nullptr;
R = dyn_cast<ConstantInt>(
ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, V1, V2));
if (R && !R->isZero())
return FCmpInst::FCMP_OEQ;
R = dyn_cast<ConstantInt>(
ConstantExpr::getFCmp(FCmpInst::FCMP_OLT, V1, V2));
if (R && !R->isZero())
return FCmpInst::FCMP_OLT;
R = dyn_cast<ConstantInt>(
ConstantExpr::getFCmp(FCmpInst::FCMP_OGT, V1, V2));
if (R && !R->isZero())
return FCmpInst::FCMP_OGT;
// Nothing more we can do
return FCmpInst::BAD_FCMP_PREDICATE;
}
// If the first operand is simple and second is ConstantExpr, swap operands.
FCmpInst::Predicate SwappedRelation = evaluateFCmpRelation(V2, V1);
if (SwappedRelation != FCmpInst::BAD_FCMP_PREDICATE)
return FCmpInst::getSwappedPredicate(SwappedRelation);
} else {
// Ok, the LHS is known to be a constantexpr. The RHS can be any of a
// constantexpr or a simple constant.
ConstantExpr *CE1 = cast<ConstantExpr>(V1);
switch (CE1->getOpcode()) {
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::UIToFP:
case Instruction::SIToFP:
// We might be able to do something with these but we don't right now.
break;
default:
break;
}
}
// There are MANY other foldings that we could perform here. They will
// probably be added on demand, as they seem needed.
return FCmpInst::BAD_FCMP_PREDICATE;
}
static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
auto isGlobalUnsafeForEquality = [](const GlobalValue *GV) {
if (GV->hasExternalWeakLinkage() || GV->hasWeakAnyLinkage())
return true;
if (const auto *GVar = dyn_cast<GlobalVariable>(GV)) {
Type *Ty = GVar->getValueType();
// A global with opaque type might end up being zero sized.
if (!Ty->isSized())
return true;
// A global with an empty type might lie at the address of any other
// global.
if (Ty->isEmptyTy())
return true;
}
return false;
};
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!isGlobalUnsafeForEquality(GV1) && !isGlobalUnsafeForEquality(GV2))
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}
/// This function determines if there is anything we can decide about the two
/// constants provided. This doesn't need to handle simple things like integer
/// comparisons, but should instead handle ConstantExprs and GlobalValues.
/// If we can determine that the two constants have a particular relation to
/// each other, we should return the corresponding ICmp predicate, otherwise
/// return ICmpInst::BAD_ICMP_PREDICATE.
///
/// To simplify this code we canonicalize the relation so that the first
/// operand is always the most "complex" of the two. We consider simple
/// constants (like ConstantInt) to be the simplest, followed by
/// GlobalValues, followed by ConstantExpr's (the most complex).
///
static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
bool isSigned) {
assert(V1->getType() == V2->getType() &&
"Cannot compare different types of values!");
if (V1 == V2) return ICmpInst::ICMP_EQ;
if (!isa<ConstantExpr>(V1) && !isa<GlobalValue>(V1) &&
!isa<BlockAddress>(V1)) {
if (!isa<GlobalValue>(V2) && !isa<ConstantExpr>(V2) &&
!isa<BlockAddress>(V2)) {
// We distilled this down to a simple case, use the standard constant
// folder.
ConstantInt *R = nullptr;
ICmpInst::Predicate pred = ICmpInst::ICMP_EQ;
R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, V1, V2));
if (R && !R->isZero())
return pred;
pred = isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, V1, V2));
if (R && !R->isZero())
return pred;
pred = isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, V1, V2));
if (R && !R->isZero())
return pred;
// If we couldn't figure it out, bail.
return ICmpInst::BAD_ICMP_PREDICATE;
}
// If the first operand is simple, swap operands.
ICmpInst::Predicate SwappedRelation =
evaluateICmpRelation(V2, V1, isSigned);
if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE)
return ICmpInst::getSwappedPredicate(SwappedRelation);
} else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V1)) {
if (isa<ConstantExpr>(V2)) { // Swap as necessary.
ICmpInst::Predicate SwappedRelation =
evaluateICmpRelation(V2, V1, isSigned);
if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE)
return ICmpInst::getSwappedPredicate(SwappedRelation);
return ICmpInst::BAD_ICMP_PREDICATE;
}
// Now we know that the RHS is a GlobalValue, BlockAddress or simple
// constant (which, since the types must match, means that it's a
// ConstantPointerNull).
if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
return areGlobalsPotentiallyEqual(GV, GV2);
} else if (isa<BlockAddress>(V2)) {
return ICmpInst::ICMP_NE; // Globals never equal labels.
} else {
assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!");
// GlobalVals can never be null unless they have external weak linkage.
// We don't try to evaluate aliases here.
if (!GV->hasExternalWeakLinkage() && !isa<GlobalAlias>(GV))
return ICmpInst::ICMP_NE;
}
} else if (const BlockAddress *BA = dyn_cast<BlockAddress>(V1)) {
if (isa<ConstantExpr>(V2)) { // Swap as necessary.
ICmpInst::Predicate SwappedRelation =
evaluateICmpRelation(V2, V1, isSigned);
if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE)
return ICmpInst::getSwappedPredicate(SwappedRelation);
return ICmpInst::BAD_ICMP_PREDICATE;
}
// Now we know that the RHS is a GlobalValue, BlockAddress or simple
// constant (which, since the types must match, means that it is a
// ConstantPointerNull).
if (const BlockAddress *BA2 = dyn_cast<BlockAddress>(V2)) {
// Block address in another function can't equal this one, but block
// addresses in the current function might be the same if blocks are
// empty.
if (BA2->getFunction() != BA->getFunction())
return ICmpInst::ICMP_NE;
} else {
// Block addresses aren't null, don't equal the address of globals.
assert((isa<ConstantPointerNull>(V2) || isa<GlobalValue>(V2)) &&
"Canonicalization guarantee!");
return ICmpInst::ICMP_NE;
}
} else {
// Ok, the LHS is known to be a constantexpr. The RHS can be any of a
// constantexpr, a global, block address, or a simple constant.
ConstantExpr *CE1 = cast<ConstantExpr>(V1);
Constant *CE1Op0 = CE1->getOperand(0);
switch (CE1->getOpcode()) {
case Instruction::Trunc:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
break; // We can't evaluate floating point casts or truncations.
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::BitCast:
case Instruction::ZExt:
case Instruction::SExt:
// We can't evaluate floating point casts or truncations.
if (CE1Op0->getType()->isFloatingPointTy())
break;
// If the cast is not actually changing bits, and the second operand is a
// null pointer, do the comparison with the pre-casted value.
if (V2->isNullValue() &&
(CE1->getType()->isPointerTy() || CE1->getType()->isIntegerTy())) {
if (CE1->getOpcode() == Instruction::ZExt) isSigned = false;
if (CE1->getOpcode() == Instruction::SExt) isSigned = true;
return evaluateICmpRelation(CE1Op0,
Constant::getNullValue(CE1Op0->getType()),
isSigned);
}
break;
case Instruction::GetElementPtr: {
GEPOperator *CE1GEP = cast<GEPOperator>(CE1);
// Ok, since this is a getelementptr, we know that the constant has a
// pointer type. Check the various cases.
if (isa<ConstantPointerNull>(V2)) {
// If we are comparing a GEP to a null pointer, check to see if the base
// of the GEP equals the null pointer.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) {
if (GV->hasExternalWeakLinkage())
// Weak linkage GVals could be zero or not. We're comparing that
// to null pointer so its greater-or-equal
return isSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
else
// If its not weak linkage, the GVal must have a non-zero address
// so the result is greater-than
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
} else if (isa<ConstantPointerNull>(CE1Op0)) {
// If we are indexing from a null pointer, check to see if we have any
// non-zero indices.
for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i)
if (!CE1->getOperand(i)->isNullValue())
// Offsetting from null, must not be equal.
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
// Only zero indexes from null, must still be zero.
return ICmpInst::ICMP_EQ;
}
// Otherwise, we can't really say if the first operand is null or not.
} else if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
if (isa<ConstantPointerNull>(CE1Op0)) {
if (GV2->hasExternalWeakLinkage())
// Weak linkage GVals could be zero or not. We're comparing it to
// a null pointer, so its less-or-equal
return isSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
else
// If its not weak linkage, the GVal must have a non-zero address
// so the result is less-than
return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
} else if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) {
if (GV == GV2) {
// If this is a getelementptr of the same global, then it must be
// different. Because the types must match, the getelementptr could
// only have at most one index, and because we fold getelementptr's
// with a single zero index, it must be nonzero.
assert(CE1->getNumOperands() == 2 &&
!CE1->getOperand(1)->isNullValue() &&
"Surprising getelementptr!");
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
} else {
if (CE1GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(GV, GV2);
return ICmpInst::BAD_ICMP_PREDICATE;
}
}
} else {
ConstantExpr *CE2 = cast<ConstantExpr>(V2);
Constant *CE2Op0 = CE2->getOperand(0);
// There are MANY other foldings that we could perform here. They will
// probably be added on demand, as they seem needed.
switch (CE2->getOpcode()) {
default: break;
case Instruction::GetElementPtr:
// By far the most common case to handle is when the base pointers are
// obviously to the same global.
if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) {
// Don't know relative ordering, but check for inequality.
if (CE1Op0 != CE2Op0) {
GEPOperator *CE2GEP = cast<GEPOperator>(CE2);
if (CE1GEP->hasAllZeroIndices() && CE2GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(cast<GlobalValue>(CE1Op0),
cast<GlobalValue>(CE2Op0));
return ICmpInst::BAD_ICMP_PREDICATE;
}
// Ok, we know that both getelementptr instructions are based on the
// same global. From this, we can precisely determine the relative
// ordering of the resultant pointers.
unsigned i = 1;
// The logic below assumes that the result of the comparison
// can be determined by finding the first index that differs.
// This doesn't work if there is over-indexing in any
// subsequent indices, so check for that case first.
if (!CE1->isGEPWithNoNotionalOverIndexing() ||
!CE2->isGEPWithNoNotionalOverIndexing())
return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal.
// Compare all of the operands the GEP's have in common.
gep_type_iterator GTI = gep_type_begin(CE1);
for (;i != CE1->getNumOperands() && i != CE2->getNumOperands();
++i, ++GTI)
switch (IdxCompare(CE1->getOperand(i),
CE2->getOperand(i), GTI.getIndexedType())) {
case -1: return isSigned ? ICmpInst::ICMP_SLT:ICmpInst::ICMP_ULT;
case 1: return isSigned ? ICmpInst::ICMP_SGT:ICmpInst::ICMP_UGT;
case -2: return ICmpInst::BAD_ICMP_PREDICATE;
}
// Ok, we ran out of things they have in common. If any leftovers
// are non-zero then we have a difference, otherwise we are equal.
for (; i < CE1->getNumOperands(); ++i)
if (!CE1->getOperand(i)->isNullValue()) {
if (isa<ConstantInt>(CE1->getOperand(i)))
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
else
return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal.
}
for (; i < CE2->getNumOperands(); ++i)
if (!CE2->getOperand(i)->isNullValue()) {
if (isa<ConstantInt>(CE2->getOperand(i)))
return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
else
return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal.
}
return ICmpInst::ICMP_EQ;
}
}
}
}
default:
break;
}
}
return ICmpInst::BAD_ICMP_PREDICATE;
}
Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
Constant *C1, Constant *C2) {
Type *ResultTy;
if (VectorType *VT = dyn_cast<VectorType>(C1->getType()))
ResultTy = VectorType::get(Type::getInt1Ty(C1->getContext()),
VT->getNumElements());
else
ResultTy = Type::getInt1Ty(C1->getContext());
// Fold FCMP_FALSE/FCMP_TRUE unconditionally.
if (pred == FCmpInst::FCMP_FALSE)
return Constant::getNullValue(ResultTy);
if (pred == FCmpInst::FCMP_TRUE)
return Constant::getAllOnesValue(ResultTy);
// Handle some degenerate cases first
if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
CmpInst::Predicate Predicate = CmpInst::Predicate(pred);
bool isIntegerPredicate = ICmpInst::isIntPredicate(Predicate);
// For EQ and NE, we can always pick a value for the undef to make the
// predicate pass or fail, so we can return undef.
// Also, if both operands are undef, we can return undef for int comparison.
if (ICmpInst::isEquality(Predicate) || (isIntegerPredicate && C1 == C2))
return UndefValue::get(ResultTy);
// Otherwise, for integer compare, pick the same value as the non-undef
// operand, and fold it to true or false.
if (isIntegerPredicate)
return ConstantInt::get(ResultTy, CmpInst::isTrueWhenEqual(Predicate));
// Choosing NaN for the undef will always make unordered comparison succeed
// and ordered comparison fails.
return ConstantInt::get(ResultTy, CmpInst::isUnordered(Predicate));
}
// icmp eq/ne(null,GV) -> false/true
if (C1->isNullValue()) {
if (const GlobalValue *GV = dyn_cast<GlobalValue>(C2))
// Don't try to evaluate aliases. External weak GV can be null.
if (!isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage()) {
if (pred == ICmpInst::ICMP_EQ)
return ConstantInt::getFalse(C1->getContext());
else if (pred == ICmpInst::ICMP_NE)
return ConstantInt::getTrue(C1->getContext());
}
// icmp eq/ne(GV,null) -> false/true
} else if (C2->isNullValue()) {
if (const GlobalValue *GV = dyn_cast<GlobalValue>(C1))
// Don't try to evaluate aliases. External weak GV can be null.
if (!isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage()) {
if (pred == ICmpInst::ICMP_EQ)
return ConstantInt::getFalse(C1->getContext());
else if (pred == ICmpInst::ICMP_NE)
return ConstantInt::getTrue(C1->getContext());
}
}
// If the comparison is a comparison between two i1's, simplify it.
if (C1->getType()->isIntegerTy(1)) {
switch(pred) {
case ICmpInst::ICMP_EQ:
if (isa<ConstantInt>(C2))
return ConstantExpr::getXor(C1, ConstantExpr::getNot(C2));
return ConstantExpr::getXor(ConstantExpr::getNot(C1), C2);
case ICmpInst::ICMP_NE:
return ConstantExpr::getXor(C1, C2);
default:
break;
}
}
if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) {
const APInt &V1 = cast<ConstantInt>(C1)->getValue();
const APInt &V2 = cast<ConstantInt>(C2)->getValue();
switch (pred) {
default: llvm_unreachable("Invalid ICmp Predicate");
case ICmpInst::ICMP_EQ: return ConstantInt::get(ResultTy, V1 == V2);
case ICmpInst::ICMP_NE: return ConstantInt::get(ResultTy, V1 != V2);
case ICmpInst::ICMP_SLT: return ConstantInt::get(ResultTy, V1.slt(V2));
case ICmpInst::ICMP_SGT: return ConstantInt::get(ResultTy, V1.sgt(V2));
case ICmpInst::ICMP_SLE: return ConstantInt::get(ResultTy, V1.sle(V2));
case ICmpInst::ICMP_SGE: return ConstantInt::get(ResultTy, V1.sge(V2));
case ICmpInst::ICMP_ULT: return ConstantInt::get(ResultTy, V1.ult(V2));
case ICmpInst::ICMP_UGT: return ConstantInt::get(ResultTy, V1.ugt(V2));
case ICmpInst::ICMP_ULE: return ConstantInt::get(ResultTy, V1.ule(V2));
case ICmpInst::ICMP_UGE: return ConstantInt::get(ResultTy, V1.uge(V2));
}
} else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) {
const APFloat &C1V = cast<ConstantFP>(C1)->getValueAPF();
const APFloat &C2V = cast<ConstantFP>(C2)->getValueAPF();
APFloat::cmpResult R = C1V.compare(C2V);
switch (pred) {
default: llvm_unreachable("Invalid FCmp Predicate");
case FCmpInst::FCMP_FALSE: return Constant::getNullValue(ResultTy);
case FCmpInst::FCMP_TRUE: return Constant::getAllOnesValue(ResultTy);
case FCmpInst::FCMP_UNO:
return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered);
case FCmpInst::FCMP_ORD:
return ConstantInt::get(ResultTy, R!=APFloat::cmpUnordered);
case FCmpInst::FCMP_UEQ:
return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
R==APFloat::cmpEqual);
case FCmpInst::FCMP_OEQ:
return ConstantInt::get(ResultTy, R==APFloat::cmpEqual);
case FCmpInst::FCMP_UNE:
return ConstantInt::get(ResultTy, R!=APFloat::cmpEqual);
case FCmpInst::FCMP_ONE:
return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan ||
R==APFloat::cmpGreaterThan);
case FCmpInst::FCMP_ULT:
return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
R==APFloat::cmpLessThan);
case FCmpInst::FCMP_OLT:
return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan);
case FCmpInst::FCMP_UGT:
return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
R==APFloat::cmpGreaterThan);
case FCmpInst::FCMP_OGT:
return ConstantInt::get(ResultTy, R==APFloat::cmpGreaterThan);
case FCmpInst::FCMP_ULE:
return ConstantInt::get(ResultTy, R!=APFloat::cmpGreaterThan);
case FCmpInst::FCMP_OLE:
return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan ||
R==APFloat::cmpEqual);
case FCmpInst::FCMP_UGE:
return ConstantInt::get(ResultTy, R!=APFloat::cmpLessThan);
case FCmpInst::FCMP_OGE:
return ConstantInt::get(ResultTy, R==APFloat::cmpGreaterThan ||
R==APFloat::cmpEqual);
}
} else if (C1->getType()->isVectorTy()) {
// If we can constant fold the comparison of each element, constant fold
// the whole vector comparison.
SmallVector<Constant*, 4> ResElts;
Type *Ty = IntegerType::get(C1->getContext(), 32);
// Compare the elements, producing an i1 result or constant expr.
for (unsigned i = 0, e = C1->getType()->getVectorNumElements(); i != e;++i){
Constant *C1E =
ConstantExpr::getExtractElement(C1, ConstantInt::get(Ty, i));
Constant *C2E =
ConstantExpr::getExtractElement(C2, ConstantInt::get(Ty, i));
ResElts.push_back(ConstantExpr::getCompare(pred, C1E, C2E));
}
return ConstantVector::get(ResElts);
}
if (C1->getType()->isFloatingPointTy() &&
// Only call evaluateFCmpRelation if we have a constant expr to avoid
// infinite recursive loop
(isa<ConstantExpr>(C1) || isa<ConstantExpr>(C2))) {
int Result = -1; // -1 = unknown, 0 = known false, 1 = known true.
switch (evaluateFCmpRelation(C1, C2)) {
default: llvm_unreachable("Unknown relation!");
case FCmpInst::FCMP_UNO:
case FCmpInst::FCMP_ORD:
case FCmpInst::FCMP_UEQ:
case FCmpInst::FCMP_UNE:
case FCmpInst::FCMP_ULT:
case FCmpInst::FCMP_UGT:
case FCmpInst::FCMP_ULE:
case FCmpInst::FCMP_UGE:
case FCmpInst::FCMP_TRUE:
case FCmpInst::FCMP_FALSE:
case FCmpInst::BAD_FCMP_PREDICATE:
break; // Couldn't determine anything about these constants.
case FCmpInst::FCMP_OEQ: // We know that C1 == C2
Result = (pred == FCmpInst::FCMP_UEQ || pred == FCmpInst::FCMP_OEQ ||
pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE ||
pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE);
break;
case FCmpInst::FCMP_OLT: // We know that C1 < C2
Result = (pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE ||
pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT ||
pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE);
break;
case FCmpInst::FCMP_OGT: // We know that C1 > C2
Result = (pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE ||
pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT ||
pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE);
break;
case FCmpInst::FCMP_OLE: // We know that C1 <= C2
// We can only partially decide this relation.
if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT)
Result = 0;
else if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT)
Result = 1;
break;
case FCmpInst::FCMP_OGE: // We known that C1 >= C2
// We can only partially decide this relation.
if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT)
Result = 0;
else if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT)
Result = 1;
break;
case FCmpInst::FCMP_ONE: // We know that C1 != C2
// We can only partially decide this relation.
if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ)
Result = 0;
else if (pred == FCmpInst::FCMP_ONE || pred == FCmpInst::FCMP_UNE)
Result = 1;
break;
}
// If we evaluated the result, return it now.
if (Result != -1)
return ConstantInt::get(ResultTy, Result);
} else {
// Evaluate the relation between the two constants, per the predicate.
int Result = -1; // -1 = unknown, 0 = known false, 1 = known true.
switch (evaluateICmpRelation(C1, C2,
CmpInst::isSigned((CmpInst::Predicate)pred))) {
default: llvm_unreachable("Unknown relational!");
case ICmpInst::BAD_ICMP_PREDICATE:
break; // Couldn't determine anything about these constants.
case ICmpInst::ICMP_EQ: // We know the constants are equal!
// If we know the constants are equal, we can decide the result of this
// computation precisely.
Result = ICmpInst::isTrueWhenEqual((ICmpInst::Predicate)pred);
break;
case ICmpInst::ICMP_ULT:
switch (pred) {
case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_ULE:
Result = 1; break;
case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_UGE:
Result = 0; break;
}
break;
case ICmpInst::ICMP_SLT:
switch (pred) {
case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_SLE:
Result = 1; break;
case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_SGE:
Result = 0; break;
}
break;
case ICmpInst::ICMP_UGT:
switch (pred) {
case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_UGE:
Result = 1; break;
case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_ULE:
Result = 0; break;
}
break;
case ICmpInst::ICMP_SGT:
switch (pred) {
case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_NE: case ICmpInst::ICMP_SGE:
Result = 1; break;
case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_SLE:
Result = 0; break;
}
break;
case ICmpInst::ICMP_ULE:
if (pred == ICmpInst::ICMP_UGT) Result = 0;
if (pred == ICmpInst::ICMP_ULT || pred == ICmpInst::ICMP_ULE) Result = 1;
break;
case ICmpInst::ICMP_SLE:
if (pred == ICmpInst::ICMP_SGT) Result = 0;
if (pred == ICmpInst::ICMP_SLT || pred == ICmpInst::ICMP_SLE) Result = 1;
break;
case ICmpInst::ICMP_UGE:
if (pred == ICmpInst::ICMP_ULT) Result = 0;
if (pred == ICmpInst::ICMP_UGT || pred == ICmpInst::ICMP_UGE) Result = 1;
break;
case ICmpInst::ICMP_SGE:
if (pred == ICmpInst::ICMP_SLT) Result = 0;
if (pred == ICmpInst::ICMP_SGT || pred == ICmpInst::ICMP_SGE) Result = 1;
break;
case ICmpInst::ICMP_NE:
if (pred == ICmpInst::ICMP_EQ) Result = 0;
if (pred == ICmpInst::ICMP_NE) Result = 1;
break;
}
// If we evaluated the result, return it now.
if (Result != -1)
return ConstantInt::get(ResultTy, Result);
// If the right hand side is a bitcast, try using its inverse to simplify
// it by moving it to the left hand side. We can't do this if it would turn
// a vector compare into a scalar compare or visa versa.
if (ConstantExpr *CE2 = dyn_cast<ConstantExpr>(C2)) {
Constant *CE2Op0 = CE2->getOperand(0);
if (CE2->getOpcode() == Instruction::BitCast &&
CE2->getType()->isVectorTy() == CE2Op0->getType()->isVectorTy()) {
Constant *Inverse = ConstantExpr::getBitCast(C1, CE2Op0->getType());
return ConstantExpr::getICmp(pred, Inverse, CE2Op0);
}
}
// If the left hand side is an extension, try eliminating it.
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
if ((CE1->getOpcode() == Instruction::SExt &&
ICmpInst::isSigned((ICmpInst::Predicate)pred)) ||
(CE1->getOpcode() == Instruction::ZExt &&
!ICmpInst::isSigned((ICmpInst::Predicate)pred))){
Constant *CE1Op0 = CE1->getOperand(0);
Constant *CE1Inverse = ConstantExpr::getTrunc(CE1, CE1Op0->getType());
if (CE1Inverse == CE1Op0) {
// Check whether we can safely truncate the right hand side.
Constant *C2Inverse = ConstantExpr::getTrunc(C2, CE1Op0->getType());
if (ConstantExpr::getCast(CE1->getOpcode(), C2Inverse,
C2->getType()) == C2)
return ConstantExpr::getICmp(pred, CE1Inverse, C2Inverse);
}
}
}
if ((!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) ||
(C1->isNullValue() && !C2->isNullValue())) {
// If C2 is a constant expr and C1 isn't, flip them around and fold the
// other way if possible.
// Also, if C1 is null and C2 isn't, flip them around.
pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
return ConstantExpr::getICmp(pred, C2, C1);
}
}
return nullptr;
}
/// Test whether the given sequence of *normalized* indices is "inbounds".
template<typename IndexTy>
static bool isInBoundsIndices(ArrayRef<IndexTy> Idxs) {
// No indices means nothing that could be out of bounds.
if (Idxs.empty()) return true;
// If the first index is zero, it's in bounds.
if (cast<Constant>(Idxs[0])->isNullValue()) return true;
// If the first index is one and all the rest are zero, it's in bounds,
// by the one-past-the-end rule.
if (!cast<ConstantInt>(Idxs[0])->isOne())
return false;
for (unsigned i = 1, e = Idxs.size(); i != e; ++i)
if (!cast<Constant>(Idxs[i])->isNullValue())
return false;
return true;
}
/// Test whether a given ConstantInt is in-range for a SequentialType.
static bool isIndexInRangeOfArrayType(uint64_t NumElements,
const ConstantInt *CI) {
// We cannot bounds check the index if it doesn't fit in an int64_t.
if (CI->getValue().getActiveBits() > 64)
return false;
// A negative index or an index past the end of our sequential type is
// considered out-of-range.
int64_t IndexVal = CI->getSExtValue();
if (IndexVal < 0 || (NumElements > 0 && (uint64_t)IndexVal >= NumElements))
return false;
// Otherwise, it is in-range.
return true;
}
Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
bool InBounds,
Optional<unsigned> InRangeIndex,
ArrayRef<Value *> Idxs) {
if (Idxs.empty()) return C;
Constant *Idx0 = cast<Constant>(Idxs[0]);
if ((Idxs.size() == 1 && Idx0->isNullValue()))
return C;
if (isa<UndefValue>(C)) {
Type *GEPTy = GetElementPtrInst::getGEPReturnType(
C, makeArrayRef((Value * const *)Idxs.data(), Idxs.size()));
return UndefValue::get(GEPTy);
}
if (C->isNullValue()) {
bool isNull = true;
for (unsigned i = 0, e = Idxs.size(); i != e; ++i)
if (!cast<Constant>(Idxs[i])->isNullValue()) {
isNull = false;
break;
}
if (isNull) {
PointerType *PtrTy = cast<PointerType>(C->getType()->getScalarType());
Type *Ty = GetElementPtrInst::getIndexedType(PointeeTy, Idxs);
assert(Ty && "Invalid indices for GEP!");
Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
GEPTy = VectorType::get(GEPTy, VT->getNumElements());
return Constant::getNullValue(GEPTy);
}
}
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
// Combine Indices - If the source pointer to this getelementptr instruction
// is a getelementptr instruction, combine the indices of the two
// getelementptr instructions into a single instruction.
//
if (CE->getOpcode() == Instruction::GetElementPtr) {
gep_type_iterator LastI = gep_type_end(CE);
for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
I != E; ++I)
LastI = I;
// We cannot combine indices if doing so would take us outside of an
// array or vector. Doing otherwise could trick us if we evaluated such a
// GEP as part of a load.
//
// e.g. Consider if the original GEP was:
// i8* getelementptr ({ [2 x i8], i32, i8, [3 x i8] }* @main.c,
// i32 0, i32 0, i64 0)
//
// If we then tried to offset it by '8' to get to the third element,
// an i8, we should *not* get:
// i8* getelementptr ({ [2 x i8], i32, i8, [3 x i8] }* @main.c,
// i32 0, i32 0, i64 8)
//
// This GEP tries to index array element '8 which runs out-of-bounds.
// Subsequent evaluation would get confused and produce erroneous results.
//
// The following prohibits such a GEP from being formed by checking to see
// if the index is in-range with respect to an array or vector.
bool PerformFold = false;
if (Idx0->isNullValue())
PerformFold = true;
else if (LastI.isSequential())
if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx0))
PerformFold =
!LastI.isBoundedSequential() ||
isIndexInRangeOfArrayType(LastI.getSequentialNumElements(), CI);
if (PerformFold) {
SmallVector<Value*, 16> NewIndices;
NewIndices.reserve(Idxs.size() + CE->getNumOperands());
NewIndices.append(CE->op_begin() + 1, CE->op_end() - 1);
// Add the last index of the source with the first index of the new GEP.
// Make sure to handle the case when they are actually different types.
Constant *Combined = CE->getOperand(CE->getNumOperands()-1);
// Otherwise it must be an array.
if (!Idx0->isNullValue()) {
Type *IdxTy = Combined->getType();
if (IdxTy != Idx0->getType()) {
unsigned CommonExtendedWidth =
std::max(IdxTy->getIntegerBitWidth(),
Idx0->getType()->getIntegerBitWidth());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
Type *CommonTy =
Type::getIntNTy(IdxTy->getContext(), CommonExtendedWidth);
Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, CommonTy);
Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, CommonTy);
Combined = ConstantExpr::get(Instruction::Add, C1, C2);
} else {
Combined =
ConstantExpr::get(Instruction::Add, Idx0, Combined);
}
}
NewIndices.push_back(Combined);
NewIndices.append(Idxs.begin() + 1, Idxs.end());
// The combined GEP normally inherits its index inrange attribute from
// the inner GEP, but if the inner GEP's last index was adjusted by the
// outer GEP, any inbounds attribute on that index is invalidated.
Optional<unsigned> IRIndex = cast<GEPOperator>(CE)->getInRangeIndex();
if (IRIndex && *IRIndex == CE->getNumOperands() - 2 && !Idx0->isNullValue())
IRIndex = None;
return ConstantExpr::getGetElementPtr(
cast<GEPOperator>(CE)->getSourceElementType(), CE->getOperand(0),
NewIndices, InBounds && cast<GEPOperator>(CE)->isInBounds(),
IRIndex);
}
}
// Attempt to fold casts to the same type away. For example, folding:
//
// i32* getelementptr ([2 x i32]* bitcast ([3 x i32]* %X to [2 x i32]*),
// i64 0, i64 0)
// into:
//
// i32* getelementptr ([3 x i32]* %X, i64 0, i64 0)
//
// Don't fold if the cast is changing address spaces.
if (CE->isCast() && Idxs.size() > 1 && Idx0->isNullValue()) {
PointerType *SrcPtrTy =
dyn_cast<PointerType>(CE->getOperand(0)->getType());
PointerType *DstPtrTy = dyn_cast<PointerType>(CE->getType());
if (SrcPtrTy && DstPtrTy) {
ArrayType *SrcArrayTy =
dyn_cast<ArrayType>(SrcPtrTy->getElementType());
ArrayType *DstArrayTy =
dyn_cast<ArrayType>(DstPtrTy->getElementType());
if (SrcArrayTy && DstArrayTy
&& SrcArrayTy->getElementType() == DstArrayTy->getElementType()
&& SrcPtrTy->getAddressSpace() == DstPtrTy->getAddressSpace())
return ConstantExpr::getGetElementPtr(SrcArrayTy,
(Constant *)CE->getOperand(0),
Idxs, InBounds, InRangeIndex);
}
}
}
// Check to see if any array indices are not within the corresponding
// notional array or vector bounds. If so, try to determine if they can be
// factored out into preceding dimensions.
SmallVector<Constant *, 8> NewIdxs;
Type *Ty = PointeeTy;
Type *Prev = C->getType();
bool Unknown = !isa<ConstantInt>(Idxs[0]);
for (unsigned i = 1, e = Idxs.size(); i != e;
Prev = Ty, Ty = cast<CompositeType>(Ty)->getTypeAtIndex(Idxs[i]), ++i) {
auto *CI = dyn_cast<ConstantInt>(Idxs[i]);
if (!CI) {
// We don't know if it's in range or not.
Unknown = true;
continue;
}
if (InRangeIndex && i == *InRangeIndex + 1) {
// If an index is marked inrange, we cannot apply this canonicalization to
// the following index, as that will cause the inrange index to point to
// the wrong element.
continue;
}
if (isa<StructType>(Ty)) {
// The verify makes sure that GEPs into a struct are in range.
continue;
}
auto *STy = cast<SequentialType>(Ty);
if (isa<VectorType>(STy)) {
// There can be awkward padding in after a non-power of two vector.
Unknown = true;
continue;
}
if (isIndexInRangeOfArrayType(STy->getNumElements(), CI))
// It's in range, skip to the next index.
continue;
if (isa<StructType>(Prev)) {
// It's out of range, but the prior dimension is a struct
// so we can't do anything about it.
Unknown = true;
continue;
}
if (CI->getSExtValue() < 0) {
// It's out of range and negative, don't try to factor it.
Unknown = true;
continue;
}
// It's out of range, but we can factor it into the prior
// dimension.
NewIdxs.resize(Idxs.size());
// Determine the number of elements in our sequential type.
uint64_t NumElements = STy->getArrayNumElements();
ConstantInt *Factor = ConstantInt::get(CI->getType(), NumElements);
NewIdxs[i] = ConstantExpr::getSRem(CI, Factor);
Constant *PrevIdx = NewIdxs[i-1] ? NewIdxs[i-1] :
cast<Constant>(Idxs[i - 1]);
Constant *Div = ConstantExpr::getSDiv(CI, Factor);
unsigned CommonExtendedWidth =
std::max(PrevIdx->getType()->getIntegerBitWidth(),
Div->getType()->getIntegerBitWidth());
CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
// Before adding, extend both operands to i64 to avoid
// overflow trouble.
if (!PrevIdx->getType()->isIntegerTy(CommonExtendedWidth))
PrevIdx = ConstantExpr::getSExt(
PrevIdx, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
if (!Div->getType()->isIntegerTy(CommonExtendedWidth))
Div = ConstantExpr::getSExt(
Div, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
NewIdxs[i - 1] = ConstantExpr::getAdd(PrevIdx, Div);
}
// If we did any factoring, start over with the adjusted indices.
if (!NewIdxs.empty()) {
for (unsigned i = 0, e = Idxs.size(); i != e; ++i)
if (!NewIdxs[i]) NewIdxs[i] = cast<Constant>(Idxs[i]);
return ConstantExpr::getGetElementPtr(PointeeTy, C, NewIdxs, InBounds,
InRangeIndex);
}
// If all indices are known integers and normalized, we can do a simple
// check for the "inbounds" property.
if (!Unknown && !InBounds)
if (auto *GV = dyn_cast<GlobalVariable>(C))
if (!GV->hasExternalWeakLinkage() && isInBoundsIndices(Idxs))
return ConstantExpr::getGetElementPtr(PointeeTy, C, Idxs,
/*InBounds=*/true, InRangeIndex);
return nullptr;
}
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