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llvm-mirror/lib/Transforms/InstCombine/InstCombineCasts.cpp
Datta Nagraj 9ca79457ad [InstCombine] Eliminate casts to optimize ctlz operation 
If a ctlz operation is performed on higher datatype and then
downcasted, then this can be optimized by doing a ctlz operation
on a lower datatype and adding the difference bitsize to the result
of ctlz to provide the same output:

https://alive2.llvm.org/ce/z/8uup9M

The original problem is shown in
https://llvm.org/PR50173

Differential Revision: https://reviews.llvm.org/D103788
2021-06-23 11:19:12 -04:00

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//===- InstCombineCasts.cpp -----------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the visit functions for cast operations.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Transforms/InstCombine/InstCombiner.h"
#include <numeric>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
/// Analyze 'Val', seeing if it is a simple linear expression.
/// If so, decompose it, returning some value X, such that Val is
/// X*Scale+Offset.
///
static Value *decomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
uint64_t &Offset) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
Offset = CI->getZExtValue();
Scale = 0;
return ConstantInt::get(Val->getType(), 0);
}
if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
// Cannot look past anything that might overflow.
OverflowingBinaryOperator *OBI = dyn_cast<OverflowingBinaryOperator>(Val);
if (OBI && !OBI->hasNoUnsignedWrap() && !OBI->hasNoSignedWrap()) {
Scale = 1;
Offset = 0;
return Val;
}
if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
if (I->getOpcode() == Instruction::Shl) {
// This is a value scaled by '1 << the shift amt'.
Scale = UINT64_C(1) << RHS->getZExtValue();
Offset = 0;
return I->getOperand(0);
}
if (I->getOpcode() == Instruction::Mul) {
// This value is scaled by 'RHS'.
Scale = RHS->getZExtValue();
Offset = 0;
return I->getOperand(0);
}
if (I->getOpcode() == Instruction::Add) {
// We have X+C. Check to see if we really have (X*C2)+C1,
// where C1 is divisible by C2.
unsigned SubScale;
Value *SubVal =
decomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
Offset += RHS->getZExtValue();
Scale = SubScale;
return SubVal;
}
}
}
// Otherwise, we can't look past this.
Scale = 1;
Offset = 0;
return Val;
}
/// If we find a cast of an allocation instruction, try to eliminate the cast by
/// moving the type information into the alloc.
Instruction *InstCombinerImpl::PromoteCastOfAllocation(BitCastInst &CI,
AllocaInst &AI) {
PointerType *PTy = cast<PointerType>(CI.getType());
IRBuilderBase::InsertPointGuard Guard(Builder);
Builder.SetInsertPoint(&AI);
// Get the type really allocated and the type casted to.
Type *AllocElTy = AI.getAllocatedType();
Type *CastElTy = PTy->getElementType();
if (!AllocElTy->isSized() || !CastElTy->isSized()) return nullptr;
// This optimisation does not work for cases where the cast type
// is scalable and the allocated type is not. This because we need to
// know how many times the casted type fits into the allocated type.
// For the opposite case where the allocated type is scalable and the
// cast type is not this leads to poor code quality due to the
// introduction of 'vscale' into the calculations. It seems better to
// bail out for this case too until we've done a proper cost-benefit
// analysis.
bool AllocIsScalable = isa<ScalableVectorType>(AllocElTy);
bool CastIsScalable = isa<ScalableVectorType>(CastElTy);
if (AllocIsScalable != CastIsScalable) return nullptr;
Align AllocElTyAlign = DL.getABITypeAlign(AllocElTy);
Align CastElTyAlign = DL.getABITypeAlign(CastElTy);
if (CastElTyAlign < AllocElTyAlign) return nullptr;
// If the allocation has multiple uses, only promote it if we are strictly
// increasing the alignment of the resultant allocation. If we keep it the
// same, we open the door to infinite loops of various kinds.
if (!AI.hasOneUse() && CastElTyAlign == AllocElTyAlign) return nullptr;
// The alloc and cast types should be either both fixed or both scalable.
uint64_t AllocElTySize = DL.getTypeAllocSize(AllocElTy).getKnownMinSize();
uint64_t CastElTySize = DL.getTypeAllocSize(CastElTy).getKnownMinSize();
if (CastElTySize == 0 || AllocElTySize == 0) return nullptr;
// If the allocation has multiple uses, only promote it if we're not
// shrinking the amount of memory being allocated.
uint64_t AllocElTyStoreSize = DL.getTypeStoreSize(AllocElTy).getKnownMinSize();
uint64_t CastElTyStoreSize = DL.getTypeStoreSize(CastElTy).getKnownMinSize();
if (!AI.hasOneUse() && CastElTyStoreSize < AllocElTyStoreSize) return nullptr;
// See if we can satisfy the modulus by pulling a scale out of the array
// size argument.
unsigned ArraySizeScale;
uint64_t ArrayOffset;
Value *NumElements = // See if the array size is a decomposable linear expr.
decomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
// If we can now satisfy the modulus, by using a non-1 scale, we really can
// do the xform.
if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
(AllocElTySize*ArrayOffset ) % CastElTySize != 0) return nullptr;
// We don't currently support arrays of scalable types.
assert(!AllocIsScalable || (ArrayOffset == 1 && ArraySizeScale == 0));
unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
Value *Amt = nullptr;
if (Scale == 1) {
Amt = NumElements;
} else {
Amt = ConstantInt::get(AI.getArraySize()->getType(), Scale);
// Insert before the alloca, not before the cast.
Amt = Builder.CreateMul(Amt, NumElements);
}
if (uint64_t Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
Value *Off = ConstantInt::get(AI.getArraySize()->getType(),
Offset, true);
Amt = Builder.CreateAdd(Amt, Off);
}
AllocaInst *New = Builder.CreateAlloca(CastElTy, Amt);
New->setAlignment(AI.getAlign());
New->takeName(&AI);
New->setUsedWithInAlloca(AI.isUsedWithInAlloca());
// If the allocation has multiple real uses, insert a cast and change all
// things that used it to use the new cast. This will also hack on CI, but it
// will die soon.
if (!AI.hasOneUse()) {
// New is the allocation instruction, pointer typed. AI is the original
// allocation instruction, also pointer typed. Thus, cast to use is BitCast.
Value *NewCast = Builder.CreateBitCast(New, AI.getType(), "tmpcast");
replaceInstUsesWith(AI, NewCast);
eraseInstFromFunction(AI);
}
return replaceInstUsesWith(CI, New);
}
/// Given an expression that CanEvaluateTruncated or CanEvaluateSExtd returns
/// true for, actually insert the code to evaluate the expression.
Value *InstCombinerImpl::EvaluateInDifferentType(Value *V, Type *Ty,
bool isSigned) {
if (Constant *C = dyn_cast<Constant>(V)) {
C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
// If we got a constantexpr back, try to simplify it with DL info.
return ConstantFoldConstant(C, DL, &TLI);
}
// Otherwise, it must be an instruction.
Instruction *I = cast<Instruction>(V);
Instruction *Res = nullptr;
unsigned Opc = I->getOpcode();
switch (Opc) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::AShr:
case Instruction::LShr:
case Instruction::Shl:
case Instruction::UDiv:
case Instruction::URem: {
Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
break;
}
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
// If the source type of the cast is the type we're trying for then we can
// just return the source. There's no need to insert it because it is not
// new.
if (I->getOperand(0)->getType() == Ty)
return I->getOperand(0);
// Otherwise, must be the same type of cast, so just reinsert a new one.
// This also handles the case of zext(trunc(x)) -> zext(x).
Res = CastInst::CreateIntegerCast(I->getOperand(0), Ty,
Opc == Instruction::SExt);
break;
case Instruction::Select: {
Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
Res = SelectInst::Create(I->getOperand(0), True, False);
break;
}
case Instruction::PHI: {
PHINode *OPN = cast<PHINode>(I);
PHINode *NPN = PHINode::Create(Ty, OPN->getNumIncomingValues());
for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
Value *V =
EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
NPN->addIncoming(V, OPN->getIncomingBlock(i));
}
Res = NPN;
break;
}
default:
// TODO: Can handle more cases here.
llvm_unreachable("Unreachable!");
}
Res->takeName(I);
return InsertNewInstWith(Res, *I);
}
Instruction::CastOps
InstCombinerImpl::isEliminableCastPair(const CastInst *CI1,
const CastInst *CI2) {
Type *SrcTy = CI1->getSrcTy();
Type *MidTy = CI1->getDestTy();
Type *DstTy = CI2->getDestTy();
Instruction::CastOps firstOp = CI1->getOpcode();
Instruction::CastOps secondOp = CI2->getOpcode();
Type *SrcIntPtrTy =
SrcTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(SrcTy) : nullptr;
Type *MidIntPtrTy =
MidTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(MidTy) : nullptr;
Type *DstIntPtrTy =
DstTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(DstTy) : nullptr;
unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy,
DstTy, SrcIntPtrTy, MidIntPtrTy,
DstIntPtrTy);
// We don't want to form an inttoptr or ptrtoint that converts to an integer
// type that differs from the pointer size.
if ((Res == Instruction::IntToPtr && SrcTy != DstIntPtrTy) ||
(Res == Instruction::PtrToInt && DstTy != SrcIntPtrTy))
Res = 0;
return Instruction::CastOps(Res);
}
/// Implement the transforms common to all CastInst visitors.
Instruction *InstCombinerImpl::commonCastTransforms(CastInst &CI) {
Value *Src = CI.getOperand(0);
Type *Ty = CI.getType();
// Try to eliminate a cast of a cast.
if (auto *CSrc = dyn_cast<CastInst>(Src)) { // A->B->C cast
if (Instruction::CastOps NewOpc = isEliminableCastPair(CSrc, &CI)) {
// The first cast (CSrc) is eliminable so we need to fix up or replace
// the second cast (CI). CSrc will then have a good chance of being dead.
auto *Res = CastInst::Create(NewOpc, CSrc->getOperand(0), Ty);
// Point debug users of the dying cast to the new one.
if (CSrc->hasOneUse())
replaceAllDbgUsesWith(*CSrc, *Res, CI, DT);
return Res;
}
}
if (auto *Sel = dyn_cast<SelectInst>(Src)) {
// We are casting a select. Try to fold the cast into the select if the
// select does not have a compare instruction with matching operand types
// or the select is likely better done in a narrow type.
// Creating a select with operands that are different sizes than its
// condition may inhibit other folds and lead to worse codegen.
auto *Cmp = dyn_cast<CmpInst>(Sel->getCondition());
if (!Cmp || Cmp->getOperand(0)->getType() != Sel->getType() ||
(CI.getOpcode() == Instruction::Trunc &&
shouldChangeType(CI.getSrcTy(), CI.getType()))) {
if (Instruction *NV = FoldOpIntoSelect(CI, Sel)) {
replaceAllDbgUsesWith(*Sel, *NV, CI, DT);
return NV;
}
}
}
// If we are casting a PHI, then fold the cast into the PHI.
if (auto *PN = dyn_cast<PHINode>(Src)) {
// Don't do this if it would create a PHI node with an illegal type from a
// legal type.
if (!Src->getType()->isIntegerTy() || !CI.getType()->isIntegerTy() ||
shouldChangeType(CI.getSrcTy(), CI.getType()))
if (Instruction *NV = foldOpIntoPhi(CI, PN))
return NV;
}
// Canonicalize a unary shuffle after the cast if neither operation changes
// the size or element size of the input vector.
// TODO: We could allow size-changing ops if that doesn't harm codegen.
// cast (shuffle X, Mask) --> shuffle (cast X), Mask
Value *X;
ArrayRef<int> Mask;
if (match(Src, m_OneUse(m_Shuffle(m_Value(X), m_Undef(), m_Mask(Mask))))) {
// TODO: Allow scalable vectors?
auto *SrcTy = dyn_cast<FixedVectorType>(X->getType());
auto *DestTy = dyn_cast<FixedVectorType>(Ty);
if (SrcTy && DestTy &&
SrcTy->getNumElements() == DestTy->getNumElements() &&
SrcTy->getPrimitiveSizeInBits() == DestTy->getPrimitiveSizeInBits()) {
Value *CastX = Builder.CreateCast(CI.getOpcode(), X, DestTy);
return new ShuffleVectorInst(CastX, UndefValue::get(DestTy), Mask);
}
}
return nullptr;
}
/// Constants and extensions/truncates from the destination type are always
/// free to be evaluated in that type. This is a helper for canEvaluate*.
static bool canAlwaysEvaluateInType(Value *V, Type *Ty) {
if (isa<Constant>(V))
return true;
Value *X;
if ((match(V, m_ZExtOrSExt(m_Value(X))) || match(V, m_Trunc(m_Value(X)))) &&
X->getType() == Ty)
return true;
return false;
}
/// Filter out values that we can not evaluate in the destination type for free.
/// This is a helper for canEvaluate*.
static bool canNotEvaluateInType(Value *V, Type *Ty) {
assert(!isa<Constant>(V) && "Constant should already be handled.");
if (!isa<Instruction>(V))
return true;
// We don't extend or shrink something that has multiple uses -- doing so
// would require duplicating the instruction which isn't profitable.
if (!V->hasOneUse())
return true;
return false;
}
/// Return true if we can evaluate the specified expression tree as type Ty
/// instead of its larger type, and arrive with the same value.
/// This is used by code that tries to eliminate truncates.
///
/// Ty will always be a type smaller than V. We should return true if trunc(V)
/// can be computed by computing V in the smaller type. If V is an instruction,
/// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only
/// makes sense if x and y can be efficiently truncated.
///
/// This function works on both vectors and scalars.
///
static bool canEvaluateTruncated(Value *V, Type *Ty, InstCombinerImpl &IC,
Instruction *CxtI) {
if (canAlwaysEvaluateInType(V, Ty))
return true;
if (canNotEvaluateInType(V, Ty))
return false;
auto *I = cast<Instruction>(V);
Type *OrigTy = V->getType();
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// These operators can all arbitrarily be extended or truncated.
return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
case Instruction::UDiv:
case Instruction::URem: {
// UDiv and URem can be truncated if all the truncated bits are zero.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
assert(BitWidth < OrigBitWidth && "Unexpected bitwidths!");
APInt Mask = APInt::getBitsSetFrom(OrigBitWidth, BitWidth);
if (IC.MaskedValueIsZero(I->getOperand(0), Mask, 0, CxtI) &&
IC.MaskedValueIsZero(I->getOperand(1), Mask, 0, CxtI)) {
return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
}
break;
}
case Instruction::Shl: {
// If we are truncating the result of this SHL, and if it's a shift of an
// inrange amount, we can always perform a SHL in a smaller type.
uint32_t BitWidth = Ty->getScalarSizeInBits();
KnownBits AmtKnownBits =
llvm::computeKnownBits(I->getOperand(1), IC.getDataLayout());
if (AmtKnownBits.getMaxValue().ult(BitWidth))
return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
break;
}
case Instruction::LShr: {
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
// TODO: It is enough to check that the bits we would be shifting in are
// zero - use AmtKnownBits.getMaxValue().
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
KnownBits AmtKnownBits =
llvm::computeKnownBits(I->getOperand(1), IC.getDataLayout());
APInt ShiftedBits = APInt::getBitsSetFrom(OrigBitWidth, BitWidth);
if (AmtKnownBits.getMaxValue().ult(BitWidth) &&
IC.MaskedValueIsZero(I->getOperand(0), ShiftedBits, 0, CxtI)) {
return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
}
break;
}
case Instruction::AShr: {
// If this is a truncate of an arithmetic shr, we can truncate it to a
// smaller ashr iff we know that all the bits from the sign bit of the
// original type and the sign bit of the truncate type are similar.
// TODO: It is enough to check that the bits we would be shifting in are
// similar to sign bit of the truncate type.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
KnownBits AmtKnownBits =
llvm::computeKnownBits(I->getOperand(1), IC.getDataLayout());
unsigned ShiftedBits = OrigBitWidth - BitWidth;
if (AmtKnownBits.getMaxValue().ult(BitWidth) &&
ShiftedBits < IC.ComputeNumSignBits(I->getOperand(0), 0, CxtI))
return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
break;
}
case Instruction::Trunc:
// trunc(trunc(x)) -> trunc(x)
return true;
case Instruction::ZExt:
case Instruction::SExt:
// trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest
// trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest
return true;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
return canEvaluateTruncated(SI->getTrueValue(), Ty, IC, CxtI) &&
canEvaluateTruncated(SI->getFalseValue(), Ty, IC, CxtI);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (Value *IncValue : PN->incoming_values())
if (!canEvaluateTruncated(IncValue, Ty, IC, CxtI))
return false;
return true;
}
default:
// TODO: Can handle more cases here.
break;
}
return false;
}
/// Given a vector that is bitcast to an integer, optionally logically
/// right-shifted, and truncated, convert it to an extractelement.
/// Example (big endian):
/// trunc (lshr (bitcast <4 x i32> %X to i128), 32) to i32
/// --->
/// extractelement <4 x i32> %X, 1
static Instruction *foldVecTruncToExtElt(TruncInst &Trunc,
InstCombinerImpl &IC) {
Value *TruncOp = Trunc.getOperand(0);
Type *DestType = Trunc.getType();
if (!TruncOp->hasOneUse() || !isa<IntegerType>(DestType))
return nullptr;
Value *VecInput = nullptr;
ConstantInt *ShiftVal = nullptr;
if (!match(TruncOp, m_CombineOr(m_BitCast(m_Value(VecInput)),
m_LShr(m_BitCast(m_Value(VecInput)),
m_ConstantInt(ShiftVal)))) ||
!isa<VectorType>(VecInput->getType()))
return nullptr;
VectorType *VecType = cast<VectorType>(VecInput->getType());
unsigned VecWidth = VecType->getPrimitiveSizeInBits();
unsigned DestWidth = DestType->getPrimitiveSizeInBits();
unsigned ShiftAmount = ShiftVal ? ShiftVal->getZExtValue() : 0;
if ((VecWidth % DestWidth != 0) || (ShiftAmount % DestWidth != 0))
return nullptr;
// If the element type of the vector doesn't match the result type,
// bitcast it to a vector type that we can extract from.
unsigned NumVecElts = VecWidth / DestWidth;
if (VecType->getElementType() != DestType) {
VecType = FixedVectorType::get(DestType, NumVecElts);
VecInput = IC.Builder.CreateBitCast(VecInput, VecType, "bc");
}
unsigned Elt = ShiftAmount / DestWidth;
if (IC.getDataLayout().isBigEndian())
Elt = NumVecElts - 1 - Elt;
return ExtractElementInst::Create(VecInput, IC.Builder.getInt32(Elt));
}
/// Funnel/Rotate left/right may occur in a wider type than necessary because of
/// type promotion rules. Try to narrow the inputs and convert to funnel shift.
Instruction *InstCombinerImpl::narrowFunnelShift(TruncInst &Trunc) {
assert((isa<VectorType>(Trunc.getSrcTy()) ||
shouldChangeType(Trunc.getSrcTy(), Trunc.getType())) &&
"Don't narrow to an illegal scalar type");
// Bail out on strange types. It is possible to handle some of these patterns
// even with non-power-of-2 sizes, but it is not a likely scenario.
Type *DestTy = Trunc.getType();
unsigned NarrowWidth = DestTy->getScalarSizeInBits();
unsigned WideWidth = Trunc.getSrcTy()->getScalarSizeInBits();
if (!isPowerOf2_32(NarrowWidth))
return nullptr;
// First, find an or'd pair of opposite shifts:
// trunc (or (lshr ShVal0, ShAmt0), (shl ShVal1, ShAmt1))
BinaryOperator *Or0, *Or1;
if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
return nullptr;
Value *ShVal0, *ShVal1, *ShAmt0, *ShAmt1;
if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal0), m_Value(ShAmt0)))) ||
!match(Or1, m_OneUse(m_LogicalShift(m_Value(ShVal1), m_Value(ShAmt1)))) ||
Or0->getOpcode() == Or1->getOpcode())
return nullptr;
// Canonicalize to or(shl(ShVal0, ShAmt0), lshr(ShVal1, ShAmt1)).
if (Or0->getOpcode() == BinaryOperator::LShr) {
std::swap(Or0, Or1);
std::swap(ShVal0, ShVal1);
std::swap(ShAmt0, ShAmt1);
}
assert(Or0->getOpcode() == BinaryOperator::Shl &&
Or1->getOpcode() == BinaryOperator::LShr &&
"Illegal or(shift,shift) pair");
// Match the shift amount operands for a funnel/rotate pattern. This always
// matches a subtraction on the R operand.
auto matchShiftAmount = [&](Value *L, Value *R, unsigned Width) -> Value * {
// The shift amounts may add up to the narrow bit width:
// (shl ShVal0, L) | (lshr ShVal1, Width - L)
// If this is a funnel shift (different operands are shifted), then the
// shift amount can not over-shift (create poison) in the narrow type.
unsigned MaxShiftAmountWidth = Log2_32(NarrowWidth);
APInt HiBitMask = ~APInt::getLowBitsSet(WideWidth, MaxShiftAmountWidth);
if (ShVal0 == ShVal1 || MaskedValueIsZero(L, HiBitMask))
if (match(R, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(L)))))
return L;
// The following patterns currently only work for rotation patterns.
// TODO: Add more general funnel-shift compatible patterns.
if (ShVal0 != ShVal1)
return nullptr;
// The shift amount may be masked with negation:
// (shl ShVal0, (X & (Width - 1))) | (lshr ShVal1, ((-X) & (Width - 1)))
Value *X;
unsigned Mask = Width - 1;
if (match(L, m_And(m_Value(X), m_SpecificInt(Mask))) &&
match(R, m_And(m_Neg(m_Specific(X)), m_SpecificInt(Mask))))
return X;
// Same as above, but the shift amount may be extended after masking:
if (match(L, m_ZExt(m_And(m_Value(X), m_SpecificInt(Mask)))) &&
match(R, m_ZExt(m_And(m_Neg(m_Specific(X)), m_SpecificInt(Mask)))))
return X;
return nullptr;
};
Value *ShAmt = matchShiftAmount(ShAmt0, ShAmt1, NarrowWidth);
bool IsFshl = true; // Sub on LSHR.
if (!ShAmt) {
ShAmt = matchShiftAmount(ShAmt1, ShAmt0, NarrowWidth);
IsFshl = false; // Sub on SHL.
}
if (!ShAmt)
return nullptr;
// The right-shifted value must have high zeros in the wide type (for example
// from 'zext', 'and' or 'shift'). High bits of the left-shifted value are
// truncated, so those do not matter.
APInt HiBitMask = APInt::getHighBitsSet(WideWidth, WideWidth - NarrowWidth);
if (!MaskedValueIsZero(ShVal1, HiBitMask, 0, &Trunc))
return nullptr;
// We have an unnecessarily wide rotate!
// trunc (or (shl ShVal0, ShAmt), (lshr ShVal1, BitWidth - ShAmt))
// Narrow the inputs and convert to funnel shift intrinsic:
// llvm.fshl.i8(trunc(ShVal), trunc(ShVal), trunc(ShAmt))
Value *NarrowShAmt = Builder.CreateTrunc(ShAmt, DestTy);
Value *X, *Y;
X = Y = Builder.CreateTrunc(ShVal0, DestTy);
if (ShVal0 != ShVal1)
Y = Builder.CreateTrunc(ShVal1, DestTy);
Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
Function *F = Intrinsic::getDeclaration(Trunc.getModule(), IID, DestTy);
return CallInst::Create(F, {X, Y, NarrowShAmt});
}
/// Try to narrow the width of math or bitwise logic instructions by pulling a
/// truncate ahead of binary operators.
/// TODO: Transforms for truncated shifts should be moved into here.
Instruction *InstCombinerImpl::narrowBinOp(TruncInst &Trunc) {
Type *SrcTy = Trunc.getSrcTy();
Type *DestTy = Trunc.getType();
if (!isa<VectorType>(SrcTy) && !shouldChangeType(SrcTy, DestTy))
return nullptr;
BinaryOperator *BinOp;
if (!match(Trunc.getOperand(0), m_OneUse(m_BinOp(BinOp))))
return nullptr;
Value *BinOp0 = BinOp->getOperand(0);
Value *BinOp1 = BinOp->getOperand(1);
switch (BinOp->getOpcode()) {
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul: {
Constant *C;
if (match(BinOp0, m_Constant(C))) {
// trunc (binop C, X) --> binop (trunc C', X)
Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
Value *TruncX = Builder.CreateTrunc(BinOp1, DestTy);
return BinaryOperator::Create(BinOp->getOpcode(), NarrowC, TruncX);
}
if (match(BinOp1, m_Constant(C))) {
// trunc (binop X, C) --> binop (trunc X, C')
Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
Value *TruncX = Builder.CreateTrunc(BinOp0, DestTy);
return BinaryOperator::Create(BinOp->getOpcode(), TruncX, NarrowC);
}
Value *X;
if (match(BinOp0, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
// trunc (binop (ext X), Y) --> binop X, (trunc Y)
Value *NarrowOp1 = Builder.CreateTrunc(BinOp1, DestTy);
return BinaryOperator::Create(BinOp->getOpcode(), X, NarrowOp1);
}
if (match(BinOp1, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
// trunc (binop Y, (ext X)) --> binop (trunc Y), X
Value *NarrowOp0 = Builder.CreateTrunc(BinOp0, DestTy);
return BinaryOperator::Create(BinOp->getOpcode(), NarrowOp0, X);
}
break;
}
default: break;
}
if (Instruction *NarrowOr = narrowFunnelShift(Trunc))
return NarrowOr;
return nullptr;
}
/// Try to narrow the width of a splat shuffle. This could be generalized to any
/// shuffle with a constant operand, but we limit the transform to avoid
/// creating a shuffle type that targets may not be able to lower effectively.
static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
InstCombiner::BuilderTy &Builder) {
auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
if (Shuf && Shuf->hasOneUse() && match(Shuf->getOperand(1), m_Undef()) &&
is_splat(Shuf->getShuffleMask()) &&
Shuf->getType() == Shuf->getOperand(0)->getType()) {
// trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef, SplatMask
Constant *NarrowUndef = UndefValue::get(Trunc.getType());
Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());
return new ShuffleVectorInst(NarrowOp, NarrowUndef, Shuf->getShuffleMask());
}
return nullptr;
}
/// Try to narrow the width of an insert element. This could be generalized for
/// any vector constant, but we limit the transform to insertion into undef to
/// avoid potential backend problems from unsupported insertion widths. This
/// could also be extended to handle the case of inserting a scalar constant
/// into a vector variable.
static Instruction *shrinkInsertElt(CastInst &Trunc,
InstCombiner::BuilderTy &Builder) {
Instruction::CastOps Opcode = Trunc.getOpcode();
assert((Opcode == Instruction::Trunc || Opcode == Instruction::FPTrunc) &&
"Unexpected instruction for shrinking");
auto *InsElt = dyn_cast<InsertElementInst>(Trunc.getOperand(0));
if (!InsElt || !InsElt->hasOneUse())
return nullptr;
Type *DestTy = Trunc.getType();
Type *DestScalarTy = DestTy->getScalarType();
Value *VecOp = InsElt->getOperand(0);
Value *ScalarOp = InsElt->getOperand(1);
Value *Index = InsElt->getOperand(2);
if (match(VecOp, m_Undef())) {
// trunc (inselt undef, X, Index) --> inselt undef, (trunc X), Index
// fptrunc (inselt undef, X, Index) --> inselt undef, (fptrunc X), Index
UndefValue *NarrowUndef = UndefValue::get(DestTy);
Value *NarrowOp = Builder.CreateCast(Opcode, ScalarOp, DestScalarTy);
return InsertElementInst::Create(NarrowUndef, NarrowOp, Index);
}
return nullptr;
}
Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
if (Instruction *Result = commonCastTransforms(Trunc))
return Result;
Value *Src = Trunc.getOperand(0);
Type *DestTy = Trunc.getType(), *SrcTy = Src->getType();
unsigned DestWidth = DestTy->getScalarSizeInBits();
unsigned SrcWidth = SrcTy->getScalarSizeInBits();
// Attempt to truncate the entire input expression tree to the destination
// type. Only do this if the dest type is a simple type, don't convert the
// expression tree to something weird like i93 unless the source is also
// strange.
if ((DestTy->isVectorTy() || shouldChangeType(SrcTy, DestTy)) &&
canEvaluateTruncated(Src, DestTy, *this, &Trunc)) {
// If this cast is a truncate, evaluting in a different type always
// eliminates the cast, so it is always a win.
LLVM_DEBUG(
dbgs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid cast: "
<< Trunc << '\n');
Value *Res = EvaluateInDifferentType(Src, DestTy, false);
assert(Res->getType() == DestTy);
return replaceInstUsesWith(Trunc, Res);
}
// For integer types, check if we can shorten the entire input expression to
// DestWidth * 2, which won't allow removing the truncate, but reducing the
// width may enable further optimizations, e.g. allowing for larger
// vectorization factors.
if (auto *DestITy = dyn_cast<IntegerType>(DestTy)) {
if (DestWidth * 2 < SrcWidth) {
auto *NewDestTy = DestITy->getExtendedType();
if (shouldChangeType(SrcTy, NewDestTy) &&
canEvaluateTruncated(Src, NewDestTy, *this, &Trunc)) {
LLVM_DEBUG(
dbgs() << "ICE: EvaluateInDifferentType converting expression type"
" to reduce the width of operand of"
<< Trunc << '\n');
Value *Res = EvaluateInDifferentType(Src, NewDestTy, false);
return new TruncInst(Res, DestTy);
}
}
}
// Test if the trunc is the user of a select which is part of a
// minimum or maximum operation. If so, don't do any more simplification.
// Even simplifying demanded bits can break the canonical form of a
// min/max.
Value *LHS, *RHS;
if (SelectInst *Sel = dyn_cast<SelectInst>(Src))
if (matchSelectPattern(Sel, LHS, RHS).Flavor != SPF_UNKNOWN)
return nullptr;
// See if we can simplify any instructions used by the input whose sole
// purpose is to compute bits we don't care about.
if (SimplifyDemandedInstructionBits(Trunc))
return &Trunc;
if (DestWidth == 1) {
Value *Zero = Constant::getNullValue(SrcTy);
if (DestTy->isIntegerTy()) {
// Canonicalize trunc x to i1 -> icmp ne (and x, 1), 0 (scalar only).
// TODO: We canonicalize to more instructions here because we are probably
// lacking equivalent analysis for trunc relative to icmp. There may also
// be codegen concerns. If those trunc limitations were removed, we could
// remove this transform.
Value *And = Builder.CreateAnd(Src, ConstantInt::get(SrcTy, 1));
return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
}
// For vectors, we do not canonicalize all truncs to icmp, so optimize
// patterns that would be covered within visitICmpInst.
Value *X;
Constant *C;
if (match(Src, m_OneUse(m_LShr(m_Value(X), m_Constant(C))))) {
// trunc (lshr X, C) to i1 --> icmp ne (and X, C'), 0
Constant *One = ConstantInt::get(SrcTy, APInt(SrcWidth, 1));
Constant *MaskC = ConstantExpr::getShl(One, C);
Value *And = Builder.CreateAnd(X, MaskC);
return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
}
if (match(Src, m_OneUse(m_c_Or(m_LShr(m_Value(X), m_Constant(C)),
m_Deferred(X))))) {
// trunc (or (lshr X, C), X) to i1 --> icmp ne (and X, C'), 0
Constant *One = ConstantInt::get(SrcTy, APInt(SrcWidth, 1));
Constant *MaskC = ConstantExpr::getShl(One, C);
MaskC = ConstantExpr::getOr(MaskC, One);
Value *And = Builder.CreateAnd(X, MaskC);
return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
}
}
Value *A, *B;
Constant *C;
if (match(Src, m_LShr(m_SExt(m_Value(A)), m_Constant(C)))) {
unsigned AWidth = A->getType()->getScalarSizeInBits();
unsigned MaxShiftAmt = SrcWidth - std::max(DestWidth, AWidth);
auto *OldSh = cast<Instruction>(Src);
bool IsExact = OldSh->isExact();
// If the shift is small enough, all zero bits created by the shift are
// removed by the trunc.
if (match(C, m_SpecificInt_ICMP(ICmpInst::ICMP_ULE,
APInt(SrcWidth, MaxShiftAmt)))) {
// trunc (lshr (sext A), C) --> ashr A, C
if (A->getType() == DestTy) {
Constant *MaxAmt = ConstantInt::get(SrcTy, DestWidth - 1, false);
Constant *ShAmt = ConstantExpr::getUMin(C, MaxAmt);
ShAmt = ConstantExpr::getTrunc(ShAmt, A->getType());
ShAmt = Constant::mergeUndefsWith(ShAmt, C);
return IsExact ? BinaryOperator::CreateExactAShr(A, ShAmt)
: BinaryOperator::CreateAShr(A, ShAmt);
}
// The types are mismatched, so create a cast after shifting:
// trunc (lshr (sext A), C) --> sext/trunc (ashr A, C)
if (Src->hasOneUse()) {
Constant *MaxAmt = ConstantInt::get(SrcTy, AWidth - 1, false);
Constant *ShAmt = ConstantExpr::getUMin(C, MaxAmt);
ShAmt = ConstantExpr::getTrunc(ShAmt, A->getType());
Value *Shift = Builder.CreateAShr(A, ShAmt, "", IsExact);
return CastInst::CreateIntegerCast(Shift, DestTy, true);
}
}
// TODO: Mask high bits with 'and'.
}
// trunc (*shr (trunc A), C) --> trunc(*shr A, C)
if (match(Src, m_OneUse(m_Shr(m_Trunc(m_Value(A)), m_Constant(C))))) {
unsigned MaxShiftAmt = SrcWidth - DestWidth;
// If the shift is small enough, all zero/sign bits created by the shift are
// removed by the trunc.
if (match(C, m_SpecificInt_ICMP(ICmpInst::ICMP_ULE,
APInt(SrcWidth, MaxShiftAmt)))) {
auto *OldShift = cast<Instruction>(Src);
bool IsExact = OldShift->isExact();
auto *ShAmt = ConstantExpr::getIntegerCast(C, A->getType(), true);
ShAmt = Constant::mergeUndefsWith(ShAmt, C);
Value *Shift =
OldShift->getOpcode() == Instruction::AShr
? Builder.CreateAShr(A, ShAmt, OldShift->getName(), IsExact)
: Builder.CreateLShr(A, ShAmt, OldShift->getName(), IsExact);
return CastInst::CreateTruncOrBitCast(Shift, DestTy);
}
}
if (Instruction *I = narrowBinOp(Trunc))
return I;
if (Instruction *I = shrinkSplatShuffle(Trunc, Builder))
return I;
if (Instruction *I = shrinkInsertElt(Trunc, Builder))
return I;
if (Src->hasOneUse() &&
(isa<VectorType>(SrcTy) || shouldChangeType(SrcTy, DestTy))) {
// Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the
// dest type is native and cst < dest size.
if (match(Src, m_Shl(m_Value(A), m_Constant(C))) &&
!match(A, m_Shr(m_Value(), m_Constant()))) {
// Skip shifts of shift by constants. It undoes a combine in
// FoldShiftByConstant and is the extend in reg pattern.
APInt Threshold = APInt(C->getType()->getScalarSizeInBits(), DestWidth);
if (match(C, m_SpecificInt_ICMP(ICmpInst::ICMP_ULT, Threshold))) {
Value *NewTrunc = Builder.CreateTrunc(A, DestTy, A->getName() + ".tr");
return BinaryOperator::Create(Instruction::Shl, NewTrunc,
ConstantExpr::getTrunc(C, DestTy));
}
}
}
if (Instruction *I = foldVecTruncToExtElt(Trunc, *this))
return I;
// Whenever an element is extracted from a vector, and then truncated,
// canonicalize by converting it to a bitcast followed by an
// extractelement.
//
// Example (little endian):
// trunc (extractelement <4 x i64> %X, 0) to i32
// --->
// extractelement <8 x i32> (bitcast <4 x i64> %X to <8 x i32>), i32 0
Value *VecOp;
ConstantInt *Cst;
if (match(Src, m_OneUse(m_ExtractElt(m_Value(VecOp), m_ConstantInt(Cst))))) {
auto *VecOpTy = cast<VectorType>(VecOp->getType());
auto VecElts = VecOpTy->getElementCount();
// A badly fit destination size would result in an invalid cast.
if (SrcWidth % DestWidth == 0) {
uint64_t TruncRatio = SrcWidth / DestWidth;
uint64_t BitCastNumElts = VecElts.getKnownMinValue() * TruncRatio;
uint64_t VecOpIdx = Cst->getZExtValue();
uint64_t NewIdx = DL.isBigEndian() ? (VecOpIdx + 1) * TruncRatio - 1
: VecOpIdx * TruncRatio;
assert(BitCastNumElts <= std::numeric_limits<uint32_t>::max() &&
"overflow 32-bits");
auto *BitCastTo =
VectorType::get(DestTy, BitCastNumElts, VecElts.isScalable());
Value *BitCast = Builder.CreateBitCast(VecOp, BitCastTo);
return ExtractElementInst::Create(BitCast, Builder.getInt32(NewIdx));
}
}
// trunc (ctlz_i32(zext(A), B) --> add(ctlz_i16(A, B), C)
if (match(Src, m_OneUse(m_Intrinsic<Intrinsic::ctlz>(m_ZExt(m_Value(A)),
m_Value(B))))) {
unsigned AWidth = A->getType()->getScalarSizeInBits();
if (AWidth == DestWidth && AWidth > Log2_32(SrcWidth)) {
Value *WidthDiff = ConstantInt::get(A->getType(), SrcWidth - AWidth);
Value *NarrowCtlz =
Builder.CreateIntrinsic(Intrinsic::ctlz, {Trunc.getType()}, {A, B});
return BinaryOperator::CreateAdd(NarrowCtlz, WidthDiff);
}
}
return nullptr;
}
/// Transform (zext icmp) to bitwise / integer operations in order to
/// eliminate it. If DoTransform is false, just test whether the given
/// (zext icmp) can be transformed.
Instruction *InstCombinerImpl::transformZExtICmp(ICmpInst *Cmp, ZExtInst &Zext,
bool DoTransform) {
// If we are just checking for a icmp eq of a single bit and zext'ing it
// to an integer, then shift the bit to the appropriate place and then
// cast to integer to avoid the comparison.
const APInt *Op1CV;
if (match(Cmp->getOperand(1), m_APInt(Op1CV))) {
// zext (x <s 0) to i32 --> x>>u31 true if signbit set.
// zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear.
if ((Cmp->getPredicate() == ICmpInst::ICMP_SLT && Op1CV->isNullValue()) ||
(Cmp->getPredicate() == ICmpInst::ICMP_SGT && Op1CV->isAllOnesValue())) {
if (!DoTransform) return Cmp;
Value *In = Cmp->getOperand(0);
Value *Sh = ConstantInt::get(In->getType(),
In->getType()->getScalarSizeInBits() - 1);
In = Builder.CreateLShr(In, Sh, In->getName() + ".lobit");
if (In->getType() != Zext.getType())
In = Builder.CreateIntCast(In, Zext.getType(), false /*ZExt*/);
if (Cmp->getPredicate() == ICmpInst::ICMP_SGT) {
Constant *One = ConstantInt::get(In->getType(), 1);
In = Builder.CreateXor(In, One, In->getName() + ".not");
}
return replaceInstUsesWith(Zext, In);
}
// zext (X == 0) to i32 --> X^1 iff X has only the low bit set.
// zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
// zext (X == 1) to i32 --> X iff X has only the low bit set.
// zext (X == 2) to i32 --> X>>1 iff X has only the 2nd bit set.
// zext (X != 0) to i32 --> X iff X has only the low bit set.
// zext (X != 0) to i32 --> X>>1 iff X has only the 2nd bit set.
// zext (X != 1) to i32 --> X^1 iff X has only the low bit set.
// zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
if ((Op1CV->isNullValue() || Op1CV->isPowerOf2()) &&
// This only works for EQ and NE
Cmp->isEquality()) {
// If Op1C some other power of two, convert:
KnownBits Known = computeKnownBits(Cmp->getOperand(0), 0, &Zext);
APInt KnownZeroMask(~Known.Zero);
if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
if (!DoTransform) return Cmp;
bool isNE = Cmp->getPredicate() == ICmpInst::ICMP_NE;
if (!Op1CV->isNullValue() && (*Op1CV != KnownZeroMask)) {
// (X&4) == 2 --> false
// (X&4) != 2 --> true
Constant *Res = ConstantInt::get(Zext.getType(), isNE);
return replaceInstUsesWith(Zext, Res);
}
uint32_t ShAmt = KnownZeroMask.logBase2();
Value *In = Cmp->getOperand(0);
if (ShAmt) {
// Perform a logical shr by shiftamt.
// Insert the shift to put the result in the low bit.
In = Builder.CreateLShr(In, ConstantInt::get(In->getType(), ShAmt),
In->getName() + ".lobit");
}
if (!Op1CV->isNullValue() == isNE) { // Toggle the low bit.
Constant *One = ConstantInt::get(In->getType(), 1);
In = Builder.CreateXor(In, One);
}
if (Zext.getType() == In->getType())
return replaceInstUsesWith(Zext, In);
Value *IntCast = Builder.CreateIntCast(In, Zext.getType(), false);
return replaceInstUsesWith(Zext, IntCast);
}
}
}
if (Cmp->isEquality() && Zext.getType() == Cmp->getOperand(0)->getType()) {
// Test if a bit is clear/set using a shifted-one mask:
// zext (icmp eq (and X, (1 << ShAmt)), 0) --> and (lshr (not X), ShAmt), 1
// zext (icmp ne (and X, (1 << ShAmt)), 0) --> and (lshr X, ShAmt), 1
Value *X, *ShAmt;
if (Cmp->hasOneUse() && match(Cmp->getOperand(1), m_ZeroInt()) &&
match(Cmp->getOperand(0),
m_OneUse(m_c_And(m_Shl(m_One(), m_Value(ShAmt)), m_Value(X))))) {
if (!DoTransform)
return Cmp;
if (Cmp->getPredicate() == ICmpInst::ICMP_EQ)
X = Builder.CreateNot(X);
Value *Lshr = Builder.CreateLShr(X, ShAmt);
Value *And1 = Builder.CreateAnd(Lshr, ConstantInt::get(X->getType(), 1));
return replaceInstUsesWith(Zext, And1);
}
// icmp ne A, B is equal to xor A, B when A and B only really have one bit.
// It is also profitable to transform icmp eq into not(xor(A, B)) because
// that may lead to additional simplifications.
if (IntegerType *ITy = dyn_cast<IntegerType>(Zext.getType())) {
Value *LHS = Cmp->getOperand(0);
Value *RHS = Cmp->getOperand(1);
KnownBits KnownLHS = computeKnownBits(LHS, 0, &Zext);
KnownBits KnownRHS = computeKnownBits(RHS, 0, &Zext);
if (KnownLHS.Zero == KnownRHS.Zero && KnownLHS.One == KnownRHS.One) {
APInt KnownBits = KnownLHS.Zero | KnownLHS.One;
APInt UnknownBit = ~KnownBits;
if (UnknownBit.countPopulation() == 1) {
if (!DoTransform) return Cmp;
Value *Result = Builder.CreateXor(LHS, RHS);
// Mask off any bits that are set and won't be shifted away.
if (KnownLHS.One.uge(UnknownBit))
Result = Builder.CreateAnd(Result,
ConstantInt::get(ITy, UnknownBit));
// Shift the bit we're testing down to the lsb.
Result = Builder.CreateLShr(
Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
if (Cmp->getPredicate() == ICmpInst::ICMP_EQ)
Result = Builder.CreateXor(Result, ConstantInt::get(ITy, 1));
Result->takeName(Cmp);
return replaceInstUsesWith(Zext, Result);
}
}
}
}
return nullptr;
}
/// Determine if the specified value can be computed in the specified wider type
/// and produce the same low bits. If not, return false.
///
/// If this function returns true, it can also return a non-zero number of bits
/// (in BitsToClear) which indicates that the value it computes is correct for
/// the zero extend, but that the additional BitsToClear bits need to be zero'd
/// out. For example, to promote something like:
///
/// %B = trunc i64 %A to i32
/// %C = lshr i32 %B, 8
/// %E = zext i32 %C to i64
///
/// CanEvaluateZExtd for the 'lshr' will return true, and BitsToClear will be
/// set to 8 to indicate that the promoted value needs to have bits 24-31
/// cleared in addition to bits 32-63. Since an 'and' will be generated to
/// clear the top bits anyway, doing this has no extra cost.
///
/// This function works on both vectors and scalars.
static bool canEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear,
InstCombinerImpl &IC, Instruction *CxtI) {
BitsToClear = 0;
if (canAlwaysEvaluateInType(V, Ty))
return true;
if (canNotEvaluateInType(V, Ty))
return false;
auto *I = cast<Instruction>(V);
unsigned Tmp;
switch (I->getOpcode()) {
case Instruction::ZExt: // zext(zext(x)) -> zext(x).
case Instruction::SExt: // zext(sext(x)) -> sext(x).
case Instruction::Trunc: // zext(trunc(x)) -> trunc(x) or zext(x)
return true;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI) ||
!canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI))
return false;
// These can all be promoted if neither operand has 'bits to clear'.
if (BitsToClear == 0 && Tmp == 0)
return true;
// If the operation is an AND/OR/XOR and the bits to clear are zero in the
// other side, BitsToClear is ok.
if (Tmp == 0 && I->isBitwiseLogicOp()) {
// We use MaskedValueIsZero here for generality, but the case we care
// about the most is constant RHS.
unsigned VSize = V->getType()->getScalarSizeInBits();
if (IC.MaskedValueIsZero(I->getOperand(1),
APInt::getHighBitsSet(VSize, BitsToClear),
0, CxtI)) {
// If this is an And instruction and all of the BitsToClear are
// known to be zero we can reset BitsToClear.
if (I->getOpcode() == Instruction::And)
BitsToClear = 0;
return true;
}
}
// Otherwise, we don't know how to analyze this BitsToClear case yet.
return false;
case Instruction::Shl: {
// We can promote shl(x, cst) if we can promote x. Since shl overwrites the
// upper bits we can reduce BitsToClear by the shift amount.
const APInt *Amt;
if (match(I->getOperand(1), m_APInt(Amt))) {
if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
return false;
uint64_t ShiftAmt = Amt->getZExtValue();
BitsToClear = ShiftAmt < BitsToClear ? BitsToClear - ShiftAmt : 0;
return true;
}
return false;
}
case Instruction::LShr: {
// We can promote lshr(x, cst) if we can promote x. This requires the
// ultimate 'and' to clear out the high zero bits we're clearing out though.
const APInt *Amt;
if (match(I->getOperand(1), m_APInt(Amt))) {
if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
return false;
BitsToClear += Amt->getZExtValue();
if (BitsToClear > V->getType()->getScalarSizeInBits())
BitsToClear = V->getType()->getScalarSizeInBits();
return true;
}
// Cannot promote variable LSHR.
return false;
}
case Instruction::Select:
if (!canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI) ||
!canEvaluateZExtd(I->getOperand(2), Ty, BitsToClear, IC, CxtI) ||
// TODO: If important, we could handle the case when the BitsToClear are
// known zero in the disagreeing side.
Tmp != BitsToClear)
return false;
return true;
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
if (!canEvaluateZExtd(PN->getIncomingValue(0), Ty, BitsToClear, IC, CxtI))
return false;
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
if (!canEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp, IC, CxtI) ||
// TODO: If important, we could handle the case when the BitsToClear
// are known zero in the disagreeing input.
Tmp != BitsToClear)
return false;
return true;
}
default:
// TODO: Can handle more cases here.
return false;
}
}
Instruction *InstCombinerImpl::visitZExt(ZExtInst &CI) {
// If this zero extend is only used by a truncate, let the truncate be
// eliminated before we try to optimize this zext.
if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
return nullptr;
// If one of the common conversion will work, do it.
if (Instruction *Result = commonCastTransforms(CI))
return Result;
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType(), *DestTy = CI.getType();
// Try to extend the entire expression tree to the wide destination type.
unsigned BitsToClear;
if (shouldChangeType(SrcTy, DestTy) &&
canEvaluateZExtd(Src, DestTy, BitsToClear, *this, &CI)) {
assert(BitsToClear <= SrcTy->getScalarSizeInBits() &&
"Can't clear more bits than in SrcTy");
// Okay, we can transform this! Insert the new expression now.
LLVM_DEBUG(
dbgs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid zero extend: "
<< CI << '\n');
Value *Res = EvaluateInDifferentType(Src, DestTy, false);
assert(Res->getType() == DestTy);
// Preserve debug values referring to Src if the zext is its last use.
if (auto *SrcOp = dyn_cast<Instruction>(Src))
if (SrcOp->hasOneUse())
replaceAllDbgUsesWith(*SrcOp, *Res, CI, DT);
uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear;
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
// If the high bits are already filled with zeros, just replace this
// cast with the result.
if (MaskedValueIsZero(Res,
APInt::getHighBitsSet(DestBitSize,
DestBitSize-SrcBitsKept),
0, &CI))
return replaceInstUsesWith(CI, Res);
// We need to emit an AND to clear the high bits.
Constant *C = ConstantInt::get(Res->getType(),
APInt::getLowBitsSet(DestBitSize, SrcBitsKept));
return BinaryOperator::CreateAnd(Res, C);
}
// If this is a TRUNC followed by a ZEXT then we are dealing with integral
// types and if the sizes are just right we can convert this into a logical
// 'and' which will be much cheaper than the pair of casts.
if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast
// TODO: Subsume this into EvaluateInDifferentType.
// Get the sizes of the types involved. We know that the intermediate type
// will be smaller than A or C, but don't know the relation between A and C.
Value *A = CSrc->getOperand(0);
unsigned SrcSize = A->getType()->getScalarSizeInBits();
unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
unsigned DstSize = CI.getType()->getScalarSizeInBits();
// If we're actually extending zero bits, then if
// SrcSize < DstSize: zext(a & mask)
// SrcSize == DstSize: a & mask
// SrcSize > DstSize: trunc(a) & mask
if (SrcSize < DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
Constant *AndConst = ConstantInt::get(A->getType(), AndValue);
Value *And = Builder.CreateAnd(A, AndConst, CSrc->getName() + ".mask");
return new ZExtInst(And, CI.getType());
}
if (SrcSize == DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(),
AndValue));
}
if (SrcSize > DstSize) {
Value *Trunc = Builder.CreateTrunc(A, CI.getType());
APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
return BinaryOperator::CreateAnd(Trunc,
ConstantInt::get(Trunc->getType(),
AndValue));
}
}
if (ICmpInst *Cmp = dyn_cast<ICmpInst>(Src))
return transformZExtICmp(Cmp, CI);
BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
if (SrcI && SrcI->getOpcode() == Instruction::Or) {
// zext (or icmp, icmp) -> or (zext icmp), (zext icmp) if at least one
// of the (zext icmp) can be eliminated. If so, immediately perform the
// according elimination.
ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
LHS->getOperand(0)->getType() == RHS->getOperand(0)->getType() &&
(transformZExtICmp(LHS, CI, false) ||
transformZExtICmp(RHS, CI, false))) {
// zext (or icmp, icmp) -> or (zext icmp), (zext icmp)
Value *LCast = Builder.CreateZExt(LHS, CI.getType(), LHS->getName());
Value *RCast = Builder.CreateZExt(RHS, CI.getType(), RHS->getName());
Value *Or = Builder.CreateOr(LCast, RCast, CI.getName());
if (auto *OrInst = dyn_cast<Instruction>(Or))
Builder.SetInsertPoint(OrInst);
// Perform the elimination.
if (auto *LZExt = dyn_cast<ZExtInst>(LCast))
transformZExtICmp(LHS, *LZExt);
if (auto *RZExt = dyn_cast<ZExtInst>(RCast))
transformZExtICmp(RHS, *RZExt);
return replaceInstUsesWith(CI, Or);
}
}
// zext(trunc(X) & C) -> (X & zext(C)).
Constant *C;
Value *X;
if (SrcI &&
match(SrcI, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Constant(C)))) &&
X->getType() == CI.getType())
return BinaryOperator::CreateAnd(X, ConstantExpr::getZExt(C, CI.getType()));
// zext((trunc(X) & C) ^ C) -> ((X & zext(C)) ^ zext(C)).
Value *And;
if (SrcI && match(SrcI, m_OneUse(m_Xor(m_Value(And), m_Constant(C)))) &&
match(And, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Specific(C)))) &&
X->getType() == CI.getType()) {
Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
return BinaryOperator::CreateXor(Builder.CreateAnd(X, ZC), ZC);
}
return nullptr;
}
/// Transform (sext icmp) to bitwise / integer operations to eliminate the icmp.
Instruction *InstCombinerImpl::transformSExtICmp(ICmpInst *ICI,
Instruction &CI) {
Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1);
ICmpInst::Predicate Pred = ICI->getPredicate();
// Don't bother if Op1 isn't of vector or integer type.
if (!Op1->getType()->isIntOrIntVectorTy())
return nullptr;
if ((Pred == ICmpInst::ICMP_SLT && match(Op1, m_ZeroInt())) ||
(Pred == ICmpInst::ICMP_SGT && match(Op1, m_AllOnes()))) {
// (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if negative
// (x >s -1) ? -1 : 0 -> not (ashr x, 31) -> all ones if positive
Value *Sh = ConstantInt::get(Op0->getType(),
Op0->getType()->getScalarSizeInBits() - 1);
Value *In = Builder.CreateAShr(Op0, Sh, Op0->getName() + ".lobit");
if (In->getType() != CI.getType())
In = Builder.CreateIntCast(In, CI.getType(), true /*SExt*/);
if (Pred == ICmpInst::ICMP_SGT)
In = Builder.CreateNot(In, In->getName() + ".not");
return replaceInstUsesWith(CI, In);
}
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If we know that only one bit of the LHS of the icmp can be set and we
// have an equality comparison with zero or a power of 2, we can transform
// the icmp and sext into bitwise/integer operations.
if (ICI->hasOneUse() &&
ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
KnownBits Known = computeKnownBits(Op0, 0, &CI);
APInt KnownZeroMask(~Known.Zero);
if (KnownZeroMask.isPowerOf2()) {
Value *In = ICI->getOperand(0);
// If the icmp tests for a known zero bit we can constant fold it.
if (!Op1C->isZero() && Op1C->getValue() != KnownZeroMask) {
Value *V = Pred == ICmpInst::ICMP_NE ?
ConstantInt::getAllOnesValue(CI.getType()) :
ConstantInt::getNullValue(CI.getType());
return replaceInstUsesWith(CI, V);
}
if (!Op1C->isZero() == (Pred == ICmpInst::ICMP_NE)) {
// sext ((x & 2^n) == 0) -> (x >> n) - 1
// sext ((x & 2^n) != 2^n) -> (x >> n) - 1
unsigned ShiftAmt = KnownZeroMask.countTrailingZeros();
// Perform a right shift to place the desired bit in the LSB.
if (ShiftAmt)
In = Builder.CreateLShr(In,
ConstantInt::get(In->getType(), ShiftAmt));
// At this point "In" is either 1 or 0. Subtract 1 to turn
// {1, 0} -> {0, -1}.
In = Builder.CreateAdd(In,
ConstantInt::getAllOnesValue(In->getType()),
"sext");
} else {
// sext ((x & 2^n) != 0) -> (x << bitwidth-n) a>> bitwidth-1
// sext ((x & 2^n) == 2^n) -> (x << bitwidth-n) a>> bitwidth-1
unsigned ShiftAmt = KnownZeroMask.countLeadingZeros();
// Perform a left shift to place the desired bit in the MSB.
if (ShiftAmt)
In = Builder.CreateShl(In,
ConstantInt::get(In->getType(), ShiftAmt));
// Distribute the bit over the whole bit width.
In = Builder.CreateAShr(In, ConstantInt::get(In->getType(),
KnownZeroMask.getBitWidth() - 1), "sext");
}
if (CI.getType() == In->getType())
return replaceInstUsesWith(CI, In);
return CastInst::CreateIntegerCast(In, CI.getType(), true/*SExt*/);
}
}
}
return nullptr;
}
/// Return true if we can take the specified value and return it as type Ty
/// without inserting any new casts and without changing the value of the common
/// low bits. This is used by code that tries to promote integer operations to
/// a wider types will allow us to eliminate the extension.
///
/// This function works on both vectors and scalars.
///
static bool canEvaluateSExtd(Value *V, Type *Ty) {
assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
"Can't sign extend type to a smaller type");
if (canAlwaysEvaluateInType(V, Ty))
return true;
if (canNotEvaluateInType(V, Ty))
return false;
auto *I = cast<Instruction>(V);
switch (I->getOpcode()) {
case Instruction::SExt: // sext(sext(x)) -> sext(x)
case Instruction::ZExt: // sext(zext(x)) -> zext(x)
case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x)
return true;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
// These operators can all arbitrarily be extended if their inputs can.
return canEvaluateSExtd(I->getOperand(0), Ty) &&
canEvaluateSExtd(I->getOperand(1), Ty);
//case Instruction::Shl: TODO
//case Instruction::LShr: TODO
case Instruction::Select:
return canEvaluateSExtd(I->getOperand(1), Ty) &&
canEvaluateSExtd(I->getOperand(2), Ty);
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (Value *IncValue : PN->incoming_values())
if (!canEvaluateSExtd(IncValue, Ty)) return false;
return true;
}
default:
// TODO: Can handle more cases here.
break;
}
return false;
}
Instruction *InstCombinerImpl::visitSExt(SExtInst &CI) {
// If this sign extend is only used by a truncate, let the truncate be
// eliminated before we try to optimize this sext.
if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
return nullptr;
if (Instruction *I = commonCastTransforms(CI))
return I;
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType(), *DestTy = CI.getType();
unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
unsigned DestBitSize = DestTy->getScalarSizeInBits();
// If we know that the value being extended is positive, we can use a zext
// instead.
KnownBits Known = computeKnownBits(Src, 0, &CI);
if (Known.isNonNegative())
return CastInst::Create(Instruction::ZExt, Src, DestTy);
// Try to extend the entire expression tree to the wide destination type.
if (shouldChangeType(SrcTy, DestTy) && canEvaluateSExtd(Src, DestTy)) {
// Okay, we can transform this! Insert the new expression now.
LLVM_DEBUG(
dbgs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid sign extend: "
<< CI << '\n');
Value *Res = EvaluateInDifferentType(Src, DestTy, true);
assert(Res->getType() == DestTy);
// If the high bits are already filled with sign bit, just replace this
// cast with the result.
if (ComputeNumSignBits(Res, 0, &CI) > DestBitSize - SrcBitSize)
return replaceInstUsesWith(CI, Res);
// We need to emit a shl + ashr to do the sign extend.
Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
return BinaryOperator::CreateAShr(Builder.CreateShl(Res, ShAmt, "sext"),
ShAmt);
}
Value *X;
if (match(Src, m_Trunc(m_Value(X)))) {
// If the input has more sign bits than bits truncated, then convert
// directly to final type.
unsigned XBitSize = X->getType()->getScalarSizeInBits();
if (ComputeNumSignBits(X, 0, &CI) > XBitSize - SrcBitSize)
return CastInst::CreateIntegerCast(X, DestTy, /* isSigned */ true);
// If input is a trunc from the destination type, then convert into shifts.
if (Src->hasOneUse() && X->getType() == DestTy) {
// sext (trunc X) --> ashr (shl X, C), C
Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
}
// If we are replacing shifted-in high zero bits with sign bits, convert
// the logic shift to arithmetic shift and eliminate the cast to
// intermediate type:
// sext (trunc (lshr Y, C)) --> sext/trunc (ashr Y, C)
Value *Y;
if (Src->hasOneUse() &&
match(X, m_LShr(m_Value(Y),
m_SpecificIntAllowUndef(XBitSize - SrcBitSize)))) {
Value *Ashr = Builder.CreateAShr(Y, XBitSize - SrcBitSize);
return CastInst::CreateIntegerCast(Ashr, DestTy, /* isSigned */ true);
}
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
return transformSExtICmp(ICI, CI);
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then
// use a sext for the whole extension. Since we don't, look deeper and check
// for a truncate. If the source and dest are the same type, eliminate the
// trunc and extend and just do shifts. For example, turn:
// %a = trunc i32 %i to i8
// %b = shl i8 %a, C
// %c = ashr i8 %b, C
// %d = sext i8 %c to i32
// into:
// %a = shl i32 %i, 32-(8-C)
// %d = ashr i32 %a, 32-(8-C)
Value *A = nullptr;
// TODO: Eventually this could be subsumed by EvaluateInDifferentType.
Constant *BA = nullptr, *CA = nullptr;
if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_Constant(BA)),
m_Constant(CA))) &&
BA->isElementWiseEqual(CA) && A->getType() == DestTy) {
Constant *WideCurrShAmt = ConstantExpr::getSExt(CA, DestTy);
Constant *NumLowbitsLeft = ConstantExpr::getSub(
ConstantInt::get(DestTy, SrcTy->getScalarSizeInBits()), WideCurrShAmt);
Constant *NewShAmt = ConstantExpr::getSub(
ConstantInt::get(DestTy, DestTy->getScalarSizeInBits()),
NumLowbitsLeft);
NewShAmt =
Constant::mergeUndefsWith(Constant::mergeUndefsWith(NewShAmt, BA), CA);
A = Builder.CreateShl(A, NewShAmt, CI.getName());
return BinaryOperator::CreateAShr(A, NewShAmt);
}
return nullptr;
}
/// Return a Constant* for the specified floating-point constant if it fits
/// in the specified FP type without changing its value.
static bool fitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
bool losesInfo;
APFloat F = CFP->getValueAPF();
(void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
return !losesInfo;
}
static Type *shrinkFPConstant(ConstantFP *CFP) {
if (CFP->getType() == Type::getPPC_FP128Ty(CFP->getContext()))
return nullptr; // No constant folding of this.
// See if the value can be truncated to half and then reextended.
if (fitsInFPType(CFP, APFloat::IEEEhalf()))
return Type::getHalfTy(CFP->getContext());
// See if the value can be truncated to float and then reextended.
if (fitsInFPType(CFP, APFloat::IEEEsingle()))
return Type::getFloatTy(CFP->getContext());
if (CFP->getType()->isDoubleTy())
return nullptr; // Won't shrink.
if (fitsInFPType(CFP, APFloat::IEEEdouble()))
return Type::getDoubleTy(CFP->getContext());
// Don't try to shrink to various long double types.
return nullptr;
}
// Determine if this is a vector of ConstantFPs and if so, return the minimal
// type we can safely truncate all elements to.
// TODO: Make these support undef elements.
static Type *shrinkFPConstantVector(Value *V) {
auto *CV = dyn_cast<Constant>(V);
auto *CVVTy = dyn_cast<FixedVectorType>(V->getType());
if (!CV || !CVVTy)
return nullptr;
Type *MinType = nullptr;
unsigned NumElts = CVVTy->getNumElements();
// For fixed-width vectors we find the minimal type by looking
// through the constant values of the vector.
for (unsigned i = 0; i != NumElts; ++i) {
auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
if (!CFP)
return nullptr;
Type *T = shrinkFPConstant(CFP);
if (!T)
return nullptr;
// If we haven't found a type yet or this type has a larger mantissa than
// our previous type, this is our new minimal type.
if (!MinType || T->getFPMantissaWidth() > MinType->getFPMantissaWidth())
MinType = T;
}
// Make a vector type from the minimal type.
return FixedVectorType::get(MinType, NumElts);
}
/// Find the minimum FP type we can safely truncate to.
static Type *getMinimumFPType(Value *V) {
if (auto *FPExt = dyn_cast<FPExtInst>(V))
return FPExt->getOperand(0)->getType();
// If this value is a constant, return the constant in the smallest FP type
// that can accurately represent it. This allows us to turn
// (float)((double)X+2.0) into x+2.0f.
if (auto *CFP = dyn_cast<ConstantFP>(V))
if (Type *T = shrinkFPConstant(CFP))
return T;
// We can only correctly find a minimum type for a scalable vector when it is
// a splat. For splats of constant values the fpext is wrapped up as a
// ConstantExpr.
if (auto *FPCExt = dyn_cast<ConstantExpr>(V))
if (FPCExt->getOpcode() == Instruction::FPExt)
return FPCExt->getOperand(0)->getType();
// Try to shrink a vector of FP constants. This returns nullptr on scalable
// vectors
if (Type *T = shrinkFPConstantVector(V))
return T;
return V->getType();
}
/// Return true if the cast from integer to FP can be proven to be exact for all
/// possible inputs (the conversion does not lose any precision).
static bool isKnownExactCastIntToFP(CastInst &I) {
CastInst::CastOps Opcode = I.getOpcode();
assert((Opcode == CastInst::SIToFP || Opcode == CastInst::UIToFP) &&
"Unexpected cast");
Value *Src = I.getOperand(0);
Type *SrcTy = Src->getType();
Type *FPTy = I.getType();
bool IsSigned = Opcode == Instruction::SIToFP;
int SrcSize = (int)SrcTy->getScalarSizeInBits() - IsSigned;
// Easy case - if the source integer type has less bits than the FP mantissa,
// then the cast must be exact.
int DestNumSigBits = FPTy->getFPMantissaWidth();
if (SrcSize <= DestNumSigBits)
return true;
// Cast from FP to integer and back to FP is independent of the intermediate
// integer width because of poison on overflow.
Value *F;
if (match(Src, m_FPToSI(m_Value(F))) || match(Src, m_FPToUI(m_Value(F)))) {
// If this is uitofp (fptosi F), the source needs an extra bit to avoid
// potential rounding of negative FP input values.
int SrcNumSigBits = F->getType()->getFPMantissaWidth();
if (!IsSigned && match(Src, m_FPToSI(m_Value())))
SrcNumSigBits++;
// [su]itofp (fpto[su]i F) --> exact if the source type has less or equal
// significant bits than the destination (and make sure neither type is
// weird -- ppc_fp128).
if (SrcNumSigBits > 0 && DestNumSigBits > 0 &&
SrcNumSigBits <= DestNumSigBits)
return true;
}
// TODO:
// Try harder to find if the source integer type has less significant bits.
// For example, compute number of sign bits or compute low bit mask.
return false;
}
Instruction *InstCombinerImpl::visitFPTrunc(FPTruncInst &FPT) {
if (Instruction *I = commonCastTransforms(FPT))
return I;
// If we have fptrunc(OpI (fpextend x), (fpextend y)), we would like to
// simplify this expression to avoid one or more of the trunc/extend
// operations if we can do so without changing the numerical results.
//
// The exact manner in which the widths of the operands interact to limit
// what we can and cannot do safely varies from operation to operation, and
// is explained below in the various case statements.
Type *Ty = FPT.getType();
auto *BO = dyn_cast<BinaryOperator>(FPT.getOperand(0));
if (BO && BO->hasOneUse()) {
Type *LHSMinType = getMinimumFPType(BO->getOperand(0));
Type *RHSMinType = getMinimumFPType(BO->getOperand(1));
unsigned OpWidth = BO->getType()->getFPMantissaWidth();
unsigned LHSWidth = LHSMinType->getFPMantissaWidth();
unsigned RHSWidth = RHSMinType->getFPMantissaWidth();
unsigned SrcWidth = std::max(LHSWidth, RHSWidth);
unsigned DstWidth = Ty->getFPMantissaWidth();
switch (BO->getOpcode()) {
default: break;
case Instruction::FAdd:
case Instruction::FSub:
// For addition and subtraction, the infinitely precise result can
// essentially be arbitrarily wide; proving that double rounding
// will not occur because the result of OpI is exact (as we will for
// FMul, for example) is hopeless. However, we *can* nonetheless
// frequently know that double rounding cannot occur (or that it is
// innocuous) by taking advantage of the specific structure of
// infinitely-precise results that admit double rounding.
//
// Specifically, if OpWidth >= 2*DstWdith+1 and DstWidth is sufficient
// to represent both sources, we can guarantee that the double
// rounding is innocuous (See p50 of Figueroa's 2000 PhD thesis,
// "A Rigorous Framework for Fully Supporting the IEEE Standard ..."
// for proof of this fact).
//
// Note: Figueroa does not consider the case where DstFormat !=
// SrcFormat. It's possible (likely even!) that this analysis
// could be tightened for those cases, but they are rare (the main
// case of interest here is (float)((double)float + float)).
if (OpWidth >= 2*DstWidth+1 && DstWidth >= SrcWidth) {
Value *LHS = Builder.CreateFPTrunc(BO->getOperand(0), Ty);
Value *RHS = Builder.CreateFPTrunc(BO->getOperand(1), Ty);
Instruction *RI = BinaryOperator::Create(BO->getOpcode(), LHS, RHS);
RI->copyFastMathFlags(BO);
return RI;
}
break;
case Instruction::FMul:
// For multiplication, the infinitely precise result has at most
// LHSWidth + RHSWidth significant bits; if OpWidth is sufficient
// that such a value can be exactly represented, then no double
// rounding can possibly occur; we can safely perform the operation
// in the destination format if it can represent both sources.
if (OpWidth >= LHSWidth + RHSWidth && DstWidth >= SrcWidth) {
Value *LHS = Builder.CreateFPTrunc(BO->getOperand(0), Ty);
Value *RHS = Builder.CreateFPTrunc(BO->getOperand(1), Ty);
return BinaryOperator::CreateFMulFMF(LHS, RHS, BO);
}
break;
case Instruction::FDiv:
// For division, we use again use the bound from Figueroa's
// dissertation. I am entirely certain that this bound can be
// tightened in the unbalanced operand case by an analysis based on
// the diophantine rational approximation bound, but the well-known
// condition used here is a good conservative first pass.
// TODO: Tighten bound via rigorous analysis of the unbalanced case.
if (OpWidth >= 2*DstWidth && DstWidth >= SrcWidth) {
Value *LHS = Builder.CreateFPTrunc(BO->getOperand(0), Ty);
Value *RHS = Builder.CreateFPTrunc(BO->getOperand(1), Ty);
return BinaryOperator::CreateFDivFMF(LHS, RHS, BO);
}
break;
case Instruction::FRem: {
// Remainder is straightforward. Remainder is always exact, so the
// type of OpI doesn't enter into things at all. We simply evaluate
// in whichever source type is larger, then convert to the
// destination type.
if (SrcWidth == OpWidth)
break;
Value *LHS, *RHS;
if (LHSWidth == SrcWidth) {
LHS = Builder.CreateFPTrunc(BO->getOperand(0), LHSMinType);
RHS = Builder.CreateFPTrunc(BO->getOperand(1), LHSMinType);
} else {
LHS = Builder.CreateFPTrunc(BO->getOperand(0), RHSMinType);
RHS = Builder.CreateFPTrunc(BO->getOperand(1), RHSMinType);
}
Value *ExactResult = Builder.CreateFRemFMF(LHS, RHS, BO);
return CastInst::CreateFPCast(ExactResult, Ty);
}
}
}
// (fptrunc (fneg x)) -> (fneg (fptrunc x))
Value *X;
Instruction *Op = dyn_cast<Instruction>(FPT.getOperand(0));
if (Op && Op->hasOneUse()) {
// FIXME: The FMF should propagate from the fptrunc, not the source op.
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
if (isa<FPMathOperator>(Op))
Builder.setFastMathFlags(Op->getFastMathFlags());
if (match(Op, m_FNeg(m_Value(X)))) {
Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
}
// If we are truncating a select that has an extended operand, we can
// narrow the other operand and do the select as a narrow op.
Value *Cond, *X, *Y;
if (match(Op, m_Select(m_Value(Cond), m_FPExt(m_Value(X)), m_Value(Y))) &&
X->getType() == Ty) {
// fptrunc (select Cond, (fpext X), Y --> select Cond, X, (fptrunc Y)
Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
Value *Sel = Builder.CreateSelect(Cond, X, NarrowY, "narrow.sel", Op);
return replaceInstUsesWith(FPT, Sel);
}
if (match(Op, m_Select(m_Value(Cond), m_Value(Y), m_FPExt(m_Value(X)))) &&
X->getType() == Ty) {
// fptrunc (select Cond, Y, (fpext X) --> select Cond, (fptrunc Y), X
Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
Value *Sel = Builder.CreateSelect(Cond, NarrowY, X, "narrow.sel", Op);
return replaceInstUsesWith(FPT, Sel);
}
}
if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::ceil:
case Intrinsic::fabs:
case Intrinsic::floor:
case Intrinsic::nearbyint:
case Intrinsic::rint:
case Intrinsic::round:
case Intrinsic::roundeven:
case Intrinsic::trunc: {
Value *Src = II->getArgOperand(0);
if (!Src->hasOneUse())
break;
// Except for fabs, this transformation requires the input of the unary FP
// operation to be itself an fpext from the type to which we're
// truncating.
if (II->getIntrinsicID() != Intrinsic::fabs) {
FPExtInst *FPExtSrc = dyn_cast<FPExtInst>(Src);
if (!FPExtSrc || FPExtSrc->getSrcTy() != Ty)
break;
}
// Do unary FP operation on smaller type.
// (fptrunc (fabs x)) -> (fabs (fptrunc x))
Value *InnerTrunc = Builder.CreateFPTrunc(Src, Ty);
Function *Overload = Intrinsic::getDeclaration(FPT.getModule(),
II->getIntrinsicID(), Ty);
SmallVector<OperandBundleDef, 1> OpBundles;
II->getOperandBundlesAsDefs(OpBundles);
CallInst *NewCI =
CallInst::Create(Overload, {InnerTrunc}, OpBundles, II->getName());
NewCI->copyFastMathFlags(II);
return NewCI;
}
}
}
if (Instruction *I = shrinkInsertElt(FPT, Builder))
return I;
Value *Src = FPT.getOperand(0);
if (isa<SIToFPInst>(Src) || isa<UIToFPInst>(Src)) {
auto *FPCast = cast<CastInst>(Src);
if (isKnownExactCastIntToFP(*FPCast))
return CastInst::Create(FPCast->getOpcode(), FPCast->getOperand(0), Ty);
}
return nullptr;
}
Instruction *InstCombinerImpl::visitFPExt(CastInst &FPExt) {
// If the source operand is a cast from integer to FP and known exact, then
// cast the integer operand directly to the destination type.
Type *Ty = FPExt.getType();
Value *Src = FPExt.getOperand(0);
if (isa<SIToFPInst>(Src) || isa<UIToFPInst>(Src)) {
auto *FPCast = cast<CastInst>(Src);
if (isKnownExactCastIntToFP(*FPCast))
return CastInst::Create(FPCast->getOpcode(), FPCast->getOperand(0), Ty);
}
return commonCastTransforms(FPExt);
}
/// fpto{s/u}i({u/s}itofp(X)) --> X or zext(X) or sext(X) or trunc(X)
/// This is safe if the intermediate type has enough bits in its mantissa to
/// accurately represent all values of X. For example, this won't work with
/// i64 -> float -> i64.
Instruction *InstCombinerImpl::foldItoFPtoI(CastInst &FI) {
if (!isa<UIToFPInst>(FI.getOperand(0)) && !isa<SIToFPInst>(FI.getOperand(0)))
return nullptr;
auto *OpI = cast<CastInst>(FI.getOperand(0));
Value *X = OpI->getOperand(0);
Type *XType = X->getType();
Type *DestType = FI.getType();
bool IsOutputSigned = isa<FPToSIInst>(FI);
// Since we can assume the conversion won't overflow, our decision as to
// whether the input will fit in the float should depend on the minimum
// of the input range and output range.
// This means this is also safe for a signed input and unsigned output, since
// a negative input would lead to undefined behavior.
if (!isKnownExactCastIntToFP(*OpI)) {
// The first cast may not round exactly based on the source integer width
// and FP width, but the overflow UB rules can still allow this to fold.
// If the destination type is narrow, that means the intermediate FP value
// must be large enough to hold the source value exactly.
// For example, (uint8_t)((float)(uint32_t 16777217) is undefined behavior.
int OutputSize = (int)DestType->getScalarSizeInBits() - IsOutputSigned;
if (OutputSize > OpI->getType()->getFPMantissaWidth())
return nullptr;
}
if (DestType->getScalarSizeInBits() > XType->getScalarSizeInBits()) {
bool IsInputSigned = isa<SIToFPInst>(OpI);
if (IsInputSigned && IsOutputSigned)
return new SExtInst(X, DestType);
return new ZExtInst(X, DestType);
}
if (DestType->getScalarSizeInBits() < XType->getScalarSizeInBits())
return new TruncInst(X, DestType);
assert(XType == DestType && "Unexpected types for int to FP to int casts");
return replaceInstUsesWith(FI, X);
}
Instruction *InstCombinerImpl::visitFPToUI(FPToUIInst &FI) {
if (Instruction *I = foldItoFPtoI(FI))
return I;
return commonCastTransforms(FI);
}
Instruction *InstCombinerImpl::visitFPToSI(FPToSIInst &FI) {
if (Instruction *I = foldItoFPtoI(FI))
return I;
return commonCastTransforms(FI);
}
Instruction *InstCombinerImpl::visitUIToFP(CastInst &CI) {
return commonCastTransforms(CI);
}
Instruction *InstCombinerImpl::visitSIToFP(CastInst &CI) {
return commonCastTransforms(CI);
}
Instruction *InstCombinerImpl::visitIntToPtr(IntToPtrInst &CI) {
// If the source integer type is not the intptr_t type for this target, do a
// trunc or zext to the intptr_t type, then inttoptr of it. This allows the
// cast to be exposed to other transforms.
unsigned AS = CI.getAddressSpace();
if (CI.getOperand(0)->getType()->getScalarSizeInBits() !=
DL.getPointerSizeInBits(AS)) {
Type *Ty = CI.getOperand(0)->getType()->getWithNewType(
DL.getIntPtrType(CI.getContext(), AS));
Value *P = Builder.CreateZExtOrTrunc(CI.getOperand(0), Ty);
return new IntToPtrInst(P, CI.getType());
}
if (Instruction *I = commonCastTransforms(CI))
return I;
return nullptr;
}
/// Implement the transforms for cast of pointer (bitcast/ptrtoint)
Instruction *InstCombinerImpl::commonPointerCastTransforms(CastInst &CI) {
Value *Src = CI.getOperand(0);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
// If casting the result of a getelementptr instruction with no offset, turn
// this into a cast of the original pointer!
if (GEP->hasAllZeroIndices() &&
// If CI is an addrspacecast and GEP changes the poiner type, merging
// GEP into CI would undo canonicalizing addrspacecast with different
// pointer types, causing infinite loops.
(!isa<AddrSpaceCastInst>(CI) ||
GEP->getType() == GEP->getPointerOperandType())) {
// Changing the cast operand is usually not a good idea but it is safe
// here because the pointer operand is being replaced with another
// pointer operand so the opcode doesn't need to change.
return replaceOperand(CI, 0, GEP->getOperand(0));
}
}
return commonCastTransforms(CI);
}
Instruction *InstCombinerImpl::visitPtrToInt(PtrToIntInst &CI) {
// If the destination integer type is not the intptr_t type for this target,
// do a ptrtoint to intptr_t then do a trunc or zext. This allows the cast
// to be exposed to other transforms.
Value *SrcOp = CI.getPointerOperand();
Type *SrcTy = SrcOp->getType();
Type *Ty = CI.getType();
unsigned AS = CI.getPointerAddressSpace();
unsigned TySize = Ty->getScalarSizeInBits();
unsigned PtrSize = DL.getPointerSizeInBits(AS);
if (TySize != PtrSize) {
Type *IntPtrTy =
SrcTy->getWithNewType(DL.getIntPtrType(CI.getContext(), AS));
Value *P = Builder.CreatePtrToInt(SrcOp, IntPtrTy);
return CastInst::CreateIntegerCast(P, Ty, /*isSigned=*/false);
}
Value *Vec, *Scalar, *Index;
if (match(SrcOp, m_OneUse(m_InsertElt(m_IntToPtr(m_Value(Vec)),
m_Value(Scalar), m_Value(Index)))) &&
Vec->getType() == Ty) {
assert(Vec->getType()->getScalarSizeInBits() == PtrSize && "Wrong type");
// Convert the scalar to int followed by insert to eliminate one cast:
// p2i (ins (i2p Vec), Scalar, Index --> ins Vec, (p2i Scalar), Index
Value *NewCast = Builder.CreatePtrToInt(Scalar, Ty->getScalarType());
return InsertElementInst::Create(Vec, NewCast, Index);
}
return commonPointerCastTransforms(CI);
}
/// This input value (which is known to have vector type) is being zero extended
/// or truncated to the specified vector type. Since the zext/trunc is done
/// using an integer type, we have a (bitcast(cast(bitcast))) pattern,
/// endianness will impact which end of the vector that is extended or
/// truncated.
///
/// A vector is always stored with index 0 at the lowest address, which
/// corresponds to the most significant bits for a big endian stored integer and
/// the least significant bits for little endian. A trunc/zext of an integer
/// impacts the big end of the integer. Thus, we need to add/remove elements at
/// the front of the vector for big endian targets, and the back of the vector
/// for little endian targets.
///
/// Try to replace it with a shuffle (and vector/vector bitcast) if possible.
///
/// The source and destination vector types may have different element types.
static Instruction *
optimizeVectorResizeWithIntegerBitCasts(Value *InVal, VectorType *DestTy,
InstCombinerImpl &IC) {
// We can only do this optimization if the output is a multiple of the input
// element size, or the input is a multiple of the output element size.
// Convert the input type to have the same element type as the output.
VectorType *SrcTy = cast<VectorType>(InVal->getType());
if (SrcTy->getElementType() != DestTy->getElementType()) {
// The input types don't need to be identical, but for now they must be the
// same size. There is no specific reason we couldn't handle things like
// <4 x i16> -> <4 x i32> by bitcasting to <2 x i32> but haven't gotten
// there yet.
if (SrcTy->getElementType()->getPrimitiveSizeInBits() !=
DestTy->getElementType()->getPrimitiveSizeInBits())
return nullptr;
SrcTy =
FixedVectorType::get(DestTy->getElementType(),
cast<FixedVectorType>(SrcTy)->getNumElements());
InVal = IC.Builder.CreateBitCast(InVal, SrcTy);
}
bool IsBigEndian = IC.getDataLayout().isBigEndian();
unsigned SrcElts = cast<FixedVectorType>(SrcTy)->getNumElements();
unsigned DestElts = cast<FixedVectorType>(DestTy)->getNumElements();
assert(SrcElts != DestElts && "Element counts should be different.");
// Now that the element types match, get the shuffle mask and RHS of the
// shuffle to use, which depends on whether we're increasing or decreasing the
// size of the input.
SmallVector<int, 16> ShuffleMaskStorage;
ArrayRef<int> ShuffleMask;
Value *V2;
// Produce an identify shuffle mask for the src vector.
ShuffleMaskStorage.resize(SrcElts);
std::iota(ShuffleMaskStorage.begin(), ShuffleMaskStorage.end(), 0);
if (SrcElts > DestElts) {
// If we're shrinking the number of elements (rewriting an integer
// truncate), just shuffle in the elements corresponding to the least
// significant bits from the input and use undef as the second shuffle
// input.
V2 = UndefValue::get(SrcTy);
// Make sure the shuffle mask selects the "least significant bits" by
// keeping elements from back of the src vector for big endian, and from the
// front for little endian.
ShuffleMask = ShuffleMaskStorage;
if (IsBigEndian)
ShuffleMask = ShuffleMask.take_back(DestElts);
else
ShuffleMask = ShuffleMask.take_front(DestElts);
} else {
// If we're increasing the number of elements (rewriting an integer zext),
// shuffle in all of the elements from InVal. Fill the rest of the result
// elements with zeros from a constant zero.
V2 = Constant::getNullValue(SrcTy);
// Use first elt from V2 when indicating zero in the shuffle mask.
uint32_t NullElt = SrcElts;
// Extend with null values in the "most significant bits" by adding elements
// in front of the src vector for big endian, and at the back for little
// endian.
unsigned DeltaElts = DestElts - SrcElts;
if (IsBigEndian)
ShuffleMaskStorage.insert(ShuffleMaskStorage.begin(), DeltaElts, NullElt);
else
ShuffleMaskStorage.append(DeltaElts, NullElt);
ShuffleMask = ShuffleMaskStorage;
}
return new ShuffleVectorInst(InVal, V2, ShuffleMask);
}
static bool isMultipleOfTypeSize(unsigned Value, Type *Ty) {
return Value % Ty->getPrimitiveSizeInBits() == 0;
}
static unsigned getTypeSizeIndex(unsigned Value, Type *Ty) {
return Value / Ty->getPrimitiveSizeInBits();
}
/// V is a value which is inserted into a vector of VecEltTy.
/// Look through the value to see if we can decompose it into
/// insertions into the vector. See the example in the comment for
/// OptimizeIntegerToVectorInsertions for the pattern this handles.
/// The type of V is always a non-zero multiple of VecEltTy's size.
/// Shift is the number of bits between the lsb of V and the lsb of
/// the vector.
///
/// This returns false if the pattern can't be matched or true if it can,
/// filling in Elements with the elements found here.
static bool collectInsertionElements(Value *V, unsigned Shift,
SmallVectorImpl<Value *> &Elements,
Type *VecEltTy, bool isBigEndian) {
assert(isMultipleOfTypeSize(Shift, VecEltTy) &&
"Shift should be a multiple of the element type size");
// Undef values never contribute useful bits to the result.
if (isa<UndefValue>(V)) return true;
// If we got down to a value of the right type, we win, try inserting into the
// right element.
if (V->getType() == VecEltTy) {
// Inserting null doesn't actually insert any elements.
if (Constant *C = dyn_cast<Constant>(V))
if (C->isNullValue())
return true;
unsigned ElementIndex = getTypeSizeIndex(Shift, VecEltTy);
if (isBigEndian)
ElementIndex = Elements.size() - ElementIndex - 1;
// Fail if multiple elements are inserted into this slot.
if (Elements[ElementIndex])
return false;
Elements[ElementIndex] = V;
return true;
}
if (Constant *C = dyn_cast<Constant>(V)) {
// Figure out the # elements this provides, and bitcast it or slice it up
// as required.
unsigned NumElts = getTypeSizeIndex(C->getType()->getPrimitiveSizeInBits(),
VecEltTy);
// If the constant is the size of a vector element, we just need to bitcast
// it to the right type so it gets properly inserted.
if (NumElts == 1)
return collectInsertionElements(ConstantExpr::getBitCast(C, VecEltTy),
Shift, Elements, VecEltTy, isBigEndian);
// Okay, this is a constant that covers multiple elements. Slice it up into
// pieces and insert each element-sized piece into the vector.
if (!isa<IntegerType>(C->getType()))
C = ConstantExpr::getBitCast(C, IntegerType::get(V->getContext(),
C->getType()->getPrimitiveSizeInBits()));
unsigned ElementSize = VecEltTy->getPrimitiveSizeInBits();
Type *ElementIntTy = IntegerType::get(C->getContext(), ElementSize);
for (unsigned i = 0; i != NumElts; ++i) {
unsigned ShiftI = Shift+i*ElementSize;
Constant *Piece = ConstantExpr::getLShr(C, ConstantInt::get(C->getType(),
ShiftI));
Piece = ConstantExpr::getTrunc(Piece, ElementIntTy);
if (!collectInsertionElements(Piece, ShiftI, Elements, VecEltTy,
isBigEndian))
return false;
}
return true;
}
if (!V->hasOneUse()) return false;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
switch (I->getOpcode()) {
default: return false; // Unhandled case.
case Instruction::BitCast:
return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
isBigEndian);
case Instruction::ZExt:
if (!isMultipleOfTypeSize(
I->getOperand(0)->getType()->getPrimitiveSizeInBits(),
VecEltTy))
return false;
return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
isBigEndian);
case Instruction::Or:
return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
isBigEndian) &&
collectInsertionElements(I->getOperand(1), Shift, Elements, VecEltTy,
isBigEndian);
case Instruction::Shl: {
// Must be shifting by a constant that is a multiple of the element size.
ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
if (!CI) return false;
Shift += CI->getZExtValue();
if (!isMultipleOfTypeSize(Shift, VecEltTy)) return false;
return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
isBigEndian);
}
}
}
/// If the input is an 'or' instruction, we may be doing shifts and ors to
/// assemble the elements of the vector manually.
/// Try to rip the code out and replace it with insertelements. This is to
/// optimize code like this:
///
/// %tmp37 = bitcast float %inc to i32
/// %tmp38 = zext i32 %tmp37 to i64
/// %tmp31 = bitcast float %inc5 to i32
/// %tmp32 = zext i32 %tmp31 to i64
/// %tmp33 = shl i64 %tmp32, 32
/// %ins35 = or i64 %tmp33, %tmp38
/// %tmp43 = bitcast i64 %ins35 to <2 x float>
///
/// Into two insertelements that do "buildvector{%inc, %inc5}".
static Value *optimizeIntegerToVectorInsertions(BitCastInst &CI,
InstCombinerImpl &IC) {
auto *DestVecTy = cast<FixedVectorType>(CI.getType());
Value *IntInput = CI.getOperand(0);
SmallVector<Value*, 8> Elements(DestVecTy->getNumElements());
if (!collectInsertionElements(IntInput, 0, Elements,
DestVecTy->getElementType(),
IC.getDataLayout().isBigEndian()))
return nullptr;
// If we succeeded, we know that all of the element are specified by Elements
// or are zero if Elements has a null entry. Recast this as a set of
// insertions.
Value *Result = Constant::getNullValue(CI.getType());
for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
if (!Elements[i]) continue; // Unset element.
Result = IC.Builder.CreateInsertElement(Result, Elements[i],
IC.Builder.getInt32(i));
}
return Result;
}
/// Canonicalize scalar bitcasts of extracted elements into a bitcast of the
/// vector followed by extract element. The backend tends to handle bitcasts of
/// vectors better than bitcasts of scalars because vector registers are
/// usually not type-specific like scalar integer or scalar floating-point.
static Instruction *canonicalizeBitCastExtElt(BitCastInst &BitCast,
InstCombinerImpl &IC) {
// TODO: Create and use a pattern matcher for ExtractElementInst.
auto *ExtElt = dyn_cast<ExtractElementInst>(BitCast.getOperand(0));
if (!ExtElt || !ExtElt->hasOneUse())
return nullptr;
// The bitcast must be to a vectorizable type, otherwise we can't make a new
// type to extract from.
Type *DestType = BitCast.getType();
if (!VectorType::isValidElementType(DestType))
return nullptr;
auto *NewVecType = VectorType::get(DestType, ExtElt->getVectorOperandType());
auto *NewBC = IC.Builder.CreateBitCast(ExtElt->getVectorOperand(),
NewVecType, "bc");
return ExtractElementInst::Create(NewBC, ExtElt->getIndexOperand());
}
/// Change the type of a bitwise logic operation if we can eliminate a bitcast.
static Instruction *foldBitCastBitwiseLogic(BitCastInst &BitCast,
InstCombiner::BuilderTy &Builder) {
Type *DestTy = BitCast.getType();
BinaryOperator *BO;
if (!DestTy->isIntOrIntVectorTy() ||
!match(BitCast.getOperand(0), m_OneUse(m_BinOp(BO))) ||
!BO->isBitwiseLogicOp())
return nullptr;
// FIXME: This transform is restricted to vector types to avoid backend
// problems caused by creating potentially illegal operations. If a fix-up is
// added to handle that situation, we can remove this check.
if (!DestTy->isVectorTy() || !BO->getType()->isVectorTy())
return nullptr;
Value *X;
if (match(BO->getOperand(0), m_OneUse(m_BitCast(m_Value(X)))) &&
X->getType() == DestTy && !isa<Constant>(X)) {
// bitcast(logic(bitcast(X), Y)) --> logic'(X, bitcast(Y))
Value *CastedOp1 = Builder.CreateBitCast(BO->getOperand(1), DestTy);
return BinaryOperator::Create(BO->getOpcode(), X, CastedOp1);
}
if (match(BO->getOperand(1), m_OneUse(m_BitCast(m_Value(X)))) &&
X->getType() == DestTy && !isa<Constant>(X)) {
// bitcast(logic(Y, bitcast(X))) --> logic'(bitcast(Y), X)
Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
return BinaryOperator::Create(BO->getOpcode(), CastedOp0, X);
}
// Canonicalize vector bitcasts to come before vector bitwise logic with a
// constant. This eases recognition of special constants for later ops.
// Example:
// icmp u/s (a ^ signmask), (b ^ signmask) --> icmp s/u a, b
Constant *C;
if (match(BO->getOperand(1), m_Constant(C))) {
// bitcast (logic X, C) --> logic (bitcast X, C')
Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
Value *CastedC = Builder.CreateBitCast(C, DestTy);
return BinaryOperator::Create(BO->getOpcode(), CastedOp0, CastedC);
}
return nullptr;
}
/// Change the type of a select if we can eliminate a bitcast.
static Instruction *foldBitCastSelect(BitCastInst &BitCast,
InstCombiner::BuilderTy &Builder) {
Value *Cond, *TVal, *FVal;
if (!match(BitCast.getOperand(0),
m_OneUse(m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))))
return nullptr;
// A vector select must maintain the same number of elements in its operands.
Type *CondTy = Cond->getType();
Type *DestTy = BitCast.getType();
if (auto *CondVTy = dyn_cast<VectorType>(CondTy))
if (!DestTy->isVectorTy() ||
CondVTy->getElementCount() !=
cast<VectorType>(DestTy)->getElementCount())
return nullptr;
// FIXME: This transform is restricted from changing the select between
// scalars and vectors to avoid backend problems caused by creating
// potentially illegal operations. If a fix-up is added to handle that
// situation, we can remove this check.
if (DestTy->isVectorTy() != TVal->getType()->isVectorTy())
return nullptr;
auto *Sel = cast<Instruction>(BitCast.getOperand(0));
Value *X;
if (match(TVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
!isa<Constant>(X)) {
// bitcast(select(Cond, bitcast(X), Y)) --> select'(Cond, X, bitcast(Y))
Value *CastedVal = Builder.CreateBitCast(FVal, DestTy);
return SelectInst::Create(Cond, X, CastedVal, "", nullptr, Sel);
}
if (match(FVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
!isa<Constant>(X)) {
// bitcast(select(Cond, Y, bitcast(X))) --> select'(Cond, bitcast(Y), X)
Value *CastedVal = Builder.CreateBitCast(TVal, DestTy);
return SelectInst::Create(Cond, CastedVal, X, "", nullptr, Sel);
}
return nullptr;
}
/// Check if all users of CI are StoreInsts.
static bool hasStoreUsersOnly(CastInst &CI) {
for (User *U : CI.users()) {
if (!isa<StoreInst>(U))
return false;
}
return true;
}
/// This function handles following case
///
/// A -> B cast
/// PHI
/// B -> A cast
///
/// All the related PHI nodes can be replaced by new PHI nodes with type A.
/// The uses of \p CI can be changed to the new PHI node corresponding to \p PN.
Instruction *InstCombinerImpl::optimizeBitCastFromPhi(CastInst &CI,
PHINode *PN) {
// BitCast used by Store can be handled in InstCombineLoadStoreAlloca.cpp.
if (hasStoreUsersOnly(CI))
return nullptr;
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType(); // Type B
Type *DestTy = CI.getType(); // Type A
SmallVector<PHINode *, 4> PhiWorklist;
SmallSetVector<PHINode *, 4> OldPhiNodes;
// Find all of the A->B casts and PHI nodes.
// We need to inspect all related PHI nodes, but PHIs can be cyclic, so
// OldPhiNodes is used to track all known PHI nodes, before adding a new
// PHI to PhiWorklist, it is checked against and added to OldPhiNodes first.
PhiWorklist.push_back(PN);
OldPhiNodes.insert(PN);
while (!PhiWorklist.empty()) {
auto *OldPN = PhiWorklist.pop_back_val();
for (Value *IncValue : OldPN->incoming_values()) {
if (isa<Constant>(IncValue))
continue;
if (auto *LI = dyn_cast<LoadInst>(IncValue)) {
// If there is a sequence of one or more load instructions, each loaded
// value is used as address of later load instruction, bitcast is
// necessary to change the value type, don't optimize it. For
// simplicity we give up if the load address comes from another load.
Value *Addr = LI->getOperand(0);
if (Addr == &CI || isa<LoadInst>(Addr))
return nullptr;
// Don't tranform "load <256 x i32>, <256 x i32>*" to
// "load x86_amx, x86_amx*", because x86_amx* is invalid.
// TODO: Remove this check when bitcast between vector and x86_amx
// is replaced with a specific intrinsic.
if (DestTy->isX86_AMXTy())
return nullptr;
if (LI->hasOneUse() && LI->isSimple())
continue;
// If a LoadInst has more than one use, changing the type of loaded
// value may create another bitcast.
return nullptr;
}
if (auto *PNode = dyn_cast<PHINode>(IncValue)) {
if (OldPhiNodes.insert(PNode))
PhiWorklist.push_back(PNode);
continue;
}
auto *BCI = dyn_cast<BitCastInst>(IncValue);
// We can't handle other instructions.
if (!BCI)
return nullptr;
// Verify it's a A->B cast.
Type *TyA = BCI->getOperand(0)->getType();
Type *TyB = BCI->getType();
if (TyA != DestTy || TyB != SrcTy)
return nullptr;
}
}
// Check that each user of each old PHI node is something that we can
// rewrite, so that all of the old PHI nodes can be cleaned up afterwards.
for (auto *OldPN : OldPhiNodes) {
for (User *V : OldPN->users()) {
if (auto *SI = dyn_cast<StoreInst>(V)) {
if (!SI->isSimple() || SI->getOperand(0) != OldPN)
return nullptr;
} else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
// Verify it's a B->A cast.
Type *TyB = BCI->getOperand(0)->getType();
Type *TyA = BCI->getType();
if (TyA != DestTy || TyB != SrcTy)
return nullptr;
} else if (auto *PHI = dyn_cast<PHINode>(V)) {
// As long as the user is another old PHI node, then even if we don't
// rewrite it, the PHI web we're considering won't have any users
// outside itself, so it'll be dead.
if (OldPhiNodes.count(PHI) == 0)
return nullptr;
} else {
return nullptr;
}
}
}
// For each old PHI node, create a corresponding new PHI node with a type A.
SmallDenseMap<PHINode *, PHINode *> NewPNodes;
for (auto *OldPN : OldPhiNodes) {
Builder.SetInsertPoint(OldPN);
PHINode *NewPN = Builder.CreatePHI(DestTy, OldPN->getNumOperands());
NewPNodes[OldPN] = NewPN;
}
// Fill in the operands of new PHI nodes.
for (auto *OldPN : OldPhiNodes) {
PHINode *NewPN = NewPNodes[OldPN];
for (unsigned j = 0, e = OldPN->getNumOperands(); j != e; ++j) {
Value *V = OldPN->getOperand(j);
Value *NewV = nullptr;
if (auto *C = dyn_cast<Constant>(V)) {
NewV = ConstantExpr::getBitCast(C, DestTy);
} else if (auto *LI = dyn_cast<LoadInst>(V)) {
// Explicitly perform load combine to make sure no opposing transform
// can remove the bitcast in the meantime and trigger an infinite loop.
Builder.SetInsertPoint(LI);
NewV = combineLoadToNewType(*LI, DestTy);
// Remove the old load and its use in the old phi, which itself becomes
// dead once the whole transform finishes.
replaceInstUsesWith(*LI, PoisonValue::get(LI->getType()));
eraseInstFromFunction(*LI);
} else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
NewV = BCI->getOperand(0);
} else if (auto *PrevPN = dyn_cast<PHINode>(V)) {
NewV = NewPNodes[PrevPN];
}
assert(NewV);
NewPN->addIncoming(NewV, OldPN->getIncomingBlock(j));
}
}
// Traverse all accumulated PHI nodes and process its users,
// which are Stores and BitcCasts. Without this processing
// NewPHI nodes could be replicated and could lead to extra
// moves generated after DeSSA.
// If there is a store with type B, change it to type A.
// Replace users of BitCast B->A with NewPHI. These will help
// later to get rid off a closure formed by OldPHI nodes.
Instruction *RetVal = nullptr;
for (auto *OldPN : OldPhiNodes) {
PHINode *NewPN = NewPNodes[OldPN];
for (User *V : make_early_inc_range(OldPN->users())) {
if (auto *SI = dyn_cast<StoreInst>(V)) {
assert(SI->isSimple() && SI->getOperand(0) == OldPN);
Builder.SetInsertPoint(SI);
auto *NewBC =
cast<BitCastInst>(Builder.CreateBitCast(NewPN, SrcTy));
SI->setOperand(0, NewBC);
Worklist.push(SI);
assert(hasStoreUsersOnly(*NewBC));
}
else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
Type *TyB = BCI->getOperand(0)->getType();
Type *TyA = BCI->getType();
assert(TyA == DestTy && TyB == SrcTy);
(void) TyA;
(void) TyB;
Instruction *I = replaceInstUsesWith(*BCI, NewPN);
if (BCI == &CI)
RetVal = I;
} else if (auto *PHI = dyn_cast<PHINode>(V)) {
assert(OldPhiNodes.contains(PHI));
(void) PHI;
} else {
llvm_unreachable("all uses should be handled");
}
}
}
return RetVal;
}
static Instruction *convertBitCastToGEP(BitCastInst &CI, IRBuilderBase &Builder,
const DataLayout &DL) {
Value *Src = CI.getOperand(0);
PointerType *SrcPTy = cast<PointerType>(Src->getType());
PointerType *DstPTy = cast<PointerType>(CI.getType());
// Bitcasts involving opaque pointers cannot be converted into a GEP.
if (SrcPTy->isOpaque() || DstPTy->isOpaque())
return nullptr;
Type *DstElTy = DstPTy->getElementType();
Type *SrcElTy = SrcPTy->getElementType();
// When the type pointed to is not sized the cast cannot be
// turned into a gep.
if (!SrcElTy->isSized())
return nullptr;
// If the source and destination are pointers, and this cast is equivalent
// to a getelementptr X, 0, 0, 0... turn it into the appropriate gep.
// This can enhance SROA and other transforms that want type-safe pointers.
unsigned NumZeros = 0;
while (SrcElTy && SrcElTy != DstElTy) {
SrcElTy = GetElementPtrInst::getTypeAtIndex(SrcElTy, (uint64_t)0);
++NumZeros;
}
// If we found a path from the src to dest, create the getelementptr now.
if (SrcElTy == DstElTy) {
SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
GetElementPtrInst *GEP =
GetElementPtrInst::Create(SrcPTy->getElementType(), Src, Idxs);
// If the source pointer is dereferenceable, then assume it points to an
// allocated object and apply "inbounds" to the GEP.
bool CanBeNull, CanBeFreed;
if (Src->getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed)) {
// In a non-default address space (not 0), a null pointer can not be
// assumed inbounds, so ignore that case (dereferenceable_or_null).
// The reason is that 'null' is not treated differently in these address
// spaces, and we consequently ignore the 'gep inbounds' special case
// for 'null' which allows 'inbounds' on 'null' if the indices are
// zeros.
if (SrcPTy->getAddressSpace() == 0 || !CanBeNull)
GEP->setIsInBounds();
}
return GEP;
}
return nullptr;
}
Instruction *InstCombinerImpl::visitBitCast(BitCastInst &CI) {
// If the operands are integer typed then apply the integer transforms,
// otherwise just apply the common ones.
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType();
Type *DestTy = CI.getType();
// Get rid of casts from one type to the same type. These are useless and can
// be replaced by the operand.
if (DestTy == Src->getType())
return replaceInstUsesWith(CI, Src);
if (isa<PointerType>(SrcTy) && isa<PointerType>(DestTy)) {
// If we are casting a alloca to a pointer to a type of the same
// size, rewrite the allocation instruction to allocate the "right" type.
// There is no need to modify malloc calls because it is their bitcast that
// needs to be cleaned up.
if (AllocaInst *AI = dyn_cast<AllocaInst>(Src))
if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
return V;
if (Instruction *I = convertBitCastToGEP(CI, Builder, DL))
return I;
}
if (FixedVectorType *DestVTy = dyn_cast<FixedVectorType>(DestTy)) {
// Beware: messing with this target-specific oddity may cause trouble.
if (DestVTy->getNumElements() == 1 && SrcTy->isX86_MMXTy()) {
Value *Elem = Builder.CreateBitCast(Src, DestVTy->getElementType());
return InsertElementInst::Create(PoisonValue::get(DestTy), Elem,
Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
}
if (isa<IntegerType>(SrcTy)) {
// If this is a cast from an integer to vector, check to see if the input
// is a trunc or zext of a bitcast from vector. If so, we can replace all
// the casts with a shuffle and (potentially) a bitcast.
if (isa<TruncInst>(Src) || isa<ZExtInst>(Src)) {
CastInst *SrcCast = cast<CastInst>(Src);
if (BitCastInst *BCIn = dyn_cast<BitCastInst>(SrcCast->getOperand(0)))
if (isa<VectorType>(BCIn->getOperand(0)->getType()))
if (Instruction *I = optimizeVectorResizeWithIntegerBitCasts(
BCIn->getOperand(0), cast<VectorType>(DestTy), *this))
return I;
}
// If the input is an 'or' instruction, we may be doing shifts and ors to
// assemble the elements of the vector manually. Try to rip the code out
// and replace it with insertelements.
if (Value *V = optimizeIntegerToVectorInsertions(CI, *this))
return replaceInstUsesWith(CI, V);
}
}
if (FixedVectorType *SrcVTy = dyn_cast<FixedVectorType>(SrcTy)) {
if (SrcVTy->getNumElements() == 1) {
// If our destination is not a vector, then make this a straight
// scalar-scalar cast.
if (!DestTy->isVectorTy()) {
Value *Elem =
Builder.CreateExtractElement(Src,
Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
return CastInst::Create(Instruction::BitCast, Elem, DestTy);
}
// Otherwise, see if our source is an insert. If so, then use the scalar
// component directly:
// bitcast (inselt <1 x elt> V, X, 0) to <n x m> --> bitcast X to <n x m>
if (auto *InsElt = dyn_cast<InsertElementInst>(Src))
return new BitCastInst(InsElt->getOperand(1), DestTy);
}
}
if (auto *Shuf = dyn_cast<ShuffleVectorInst>(Src)) {
// Okay, we have (bitcast (shuffle ..)). Check to see if this is
// a bitcast to a vector with the same # elts.
Value *ShufOp0 = Shuf->getOperand(0);
Value *ShufOp1 = Shuf->getOperand(1);
auto ShufElts = cast<VectorType>(Shuf->getType())->getElementCount();
auto SrcVecElts = cast<VectorType>(ShufOp0->getType())->getElementCount();
if (Shuf->hasOneUse() && DestTy->isVectorTy() &&
cast<VectorType>(DestTy)->getElementCount() == ShufElts &&
ShufElts == SrcVecElts) {
BitCastInst *Tmp;
// If either of the operands is a cast from CI.getType(), then
// evaluating the shuffle in the casted destination's type will allow
// us to eliminate at least one cast.
if (((Tmp = dyn_cast<BitCastInst>(ShufOp0)) &&
Tmp->getOperand(0)->getType() == DestTy) ||
((Tmp = dyn_cast<BitCastInst>(ShufOp1)) &&
Tmp->getOperand(0)->getType() == DestTy)) {
Value *LHS = Builder.CreateBitCast(ShufOp0, DestTy);
Value *RHS = Builder.CreateBitCast(ShufOp1, DestTy);
// Return a new shuffle vector. Use the same element ID's, as we
// know the vector types match #elts.
return new ShuffleVectorInst(LHS, RHS, Shuf->getShuffleMask());
}
}
// A bitcasted-to-scalar and byte-reversing shuffle is better recognized as
// a byte-swap:
// bitcast <N x i8> (shuf X, undef, <N, N-1,...0>) --> bswap (bitcast X)
// TODO: We should match the related pattern for bitreverse.
if (DestTy->isIntegerTy() &&
DL.isLegalInteger(DestTy->getScalarSizeInBits()) &&
SrcTy->getScalarSizeInBits() == 8 &&
ShufElts.getKnownMinValue() % 2 == 0 && Shuf->hasOneUse() &&
Shuf->isReverse()) {
assert(ShufOp0->getType() == SrcTy && "Unexpected shuffle mask");
assert(match(ShufOp1, m_Undef()) && "Unexpected shuffle op");
Function *Bswap =
Intrinsic::getDeclaration(CI.getModule(), Intrinsic::bswap, DestTy);
Value *ScalarX = Builder.CreateBitCast(ShufOp0, DestTy);
return CallInst::Create(Bswap, { ScalarX });
}
}
// Handle the A->B->A cast, and there is an intervening PHI node.
if (PHINode *PN = dyn_cast<PHINode>(Src))
if (Instruction *I = optimizeBitCastFromPhi(CI, PN))
return I;
if (Instruction *I = canonicalizeBitCastExtElt(CI, *this))
return I;
if (Instruction *I = foldBitCastBitwiseLogic(CI, Builder))
return I;
if (Instruction *I = foldBitCastSelect(CI, Builder))
return I;
if (SrcTy->isPointerTy())
return commonPointerCastTransforms(CI);
return commonCastTransforms(CI);
}
Instruction *InstCombinerImpl::visitAddrSpaceCast(AddrSpaceCastInst &CI) {
// If the destination pointer element type is not the same as the source's
// first do a bitcast to the destination type, and then the addrspacecast.
// This allows the cast to be exposed to other transforms.
Value *Src = CI.getOperand(0);
PointerType *SrcTy = cast<PointerType>(Src->getType()->getScalarType());
PointerType *DestTy = cast<PointerType>(CI.getType()->getScalarType());
if (!SrcTy->hasSameElementTypeAs(DestTy)) {
Type *MidTy =
PointerType::getWithSamePointeeType(DestTy, SrcTy->getAddressSpace());
// Handle vectors of pointers.
if (VectorType *VT = dyn_cast<VectorType>(CI.getType()))
MidTy = VectorType::get(MidTy, VT->getElementCount());
Value *NewBitCast = Builder.CreateBitCast(Src, MidTy);
return new AddrSpaceCastInst(NewBitCast, CI.getType());
}
return commonPointerCastTransforms(CI);
}
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