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llvm-project/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

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//===- InstCombineVectorOps.cpp -------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements instcombine for ExtractElement, InsertElement and
// ShuffleVector.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Transforms/InstCombine/InstCombineWorklist.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
/// Return true if the value is cheaper to scalarize than it is to leave as a
/// vector operation. IsConstantExtractIndex indicates whether we are extracting
/// one known element from a vector constant.
///
/// FIXME: It's possible to create more instructions than previously existed.
static bool cheapToScalarize(Value *V, bool IsConstantExtractIndex) {
// If we can pick a scalar constant value out of a vector, that is free.
if (auto *C = dyn_cast<Constant>(V))
return IsConstantExtractIndex || C->getSplatValue();
// An insertelement to the same constant index as our extract will simplify
// to the scalar inserted element. An insertelement to a different constant
// index is irrelevant to our extract.
if (match(V, m_InsertElement(m_Value(), m_Value(), m_ConstantInt())))
return IsConstantExtractIndex;
if (match(V, m_OneUse(m_Load(m_Value()))))
return true;
Value *V0, *V1;
if (match(V, m_OneUse(m_BinOp(m_Value(V0), m_Value(V1)))))
if (cheapToScalarize(V0, IsConstantExtractIndex) ||
cheapToScalarize(V1, IsConstantExtractIndex))
return true;
CmpInst::Predicate UnusedPred;
if (match(V, m_OneUse(m_Cmp(UnusedPred, m_Value(V0), m_Value(V1)))))
if (cheapToScalarize(V0, IsConstantExtractIndex) ||
cheapToScalarize(V1, IsConstantExtractIndex))
return true;
return false;
}
// If we have a PHI node with a vector type that is only used to feed
// itself and be an operand of extractelement at a constant location,
// try to replace the PHI of the vector type with a PHI of a scalar type.
Instruction *InstCombiner::scalarizePHI(ExtractElementInst &EI, PHINode *PN) {
SmallVector<Instruction *, 2> Extracts;
// The users we want the PHI to have are:
// 1) The EI ExtractElement (we already know this)
// 2) Possibly more ExtractElements with the same index.
// 3) Another operand, which will feed back into the PHI.
Instruction *PHIUser = nullptr;
for (auto U : PN->users()) {
if (ExtractElementInst *EU = dyn_cast<ExtractElementInst>(U)) {
if (EI.getIndexOperand() == EU->getIndexOperand())
Extracts.push_back(EU);
else
return nullptr;
} else if (!PHIUser) {
PHIUser = cast<Instruction>(U);
} else {
return nullptr;
}
}
if (!PHIUser)
return nullptr;
// Verify that this PHI user has one use, which is the PHI itself,
// and that it is a binary operation which is cheap to scalarize.
// otherwise return nullptr.
if (!PHIUser->hasOneUse() || !(PHIUser->user_back() == PN) ||
!(isa<BinaryOperator>(PHIUser)) || !cheapToScalarize(PHIUser, true))
return nullptr;
// Create a scalar PHI node that will replace the vector PHI node
// just before the current PHI node.
PHINode *scalarPHI = cast<PHINode>(InsertNewInstWith(
PHINode::Create(EI.getType(), PN->getNumIncomingValues(), ""), *PN));
// Scalarize each PHI operand.
for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) {
Value *PHIInVal = PN->getIncomingValue(i);
BasicBlock *inBB = PN->getIncomingBlock(i);
Value *Elt = EI.getIndexOperand();
// If the operand is the PHI induction variable:
if (PHIInVal == PHIUser) {
// Scalarize the binary operation. Its first operand is the
// scalar PHI, and the second operand is extracted from the other
// vector operand.
BinaryOperator *B0 = cast<BinaryOperator>(PHIUser);
unsigned opId = (B0->getOperand(0) == PN) ? 1 : 0;
Value *Op = InsertNewInstWith(
ExtractElementInst::Create(B0->getOperand(opId), Elt,
B0->getOperand(opId)->getName() + ".Elt"),
*B0);
Value *newPHIUser = InsertNewInstWith(
BinaryOperator::CreateWithCopiedFlags(B0->getOpcode(),
scalarPHI, Op, B0), *B0);
scalarPHI->addIncoming(newPHIUser, inBB);
} else {
// Scalarize PHI input:
Instruction *newEI = ExtractElementInst::Create(PHIInVal, Elt, "");
// Insert the new instruction into the predecessor basic block.
Instruction *pos = dyn_cast<Instruction>(PHIInVal);
BasicBlock::iterator InsertPos;
if (pos && !isa<PHINode>(pos)) {
InsertPos = ++pos->getIterator();
} else {
InsertPos = inBB->getFirstInsertionPt();
}
InsertNewInstWith(newEI, *InsertPos);
scalarPHI->addIncoming(newEI, inBB);
}
}
for (auto E : Extracts)
replaceInstUsesWith(*E, scalarPHI);
return &EI;
}
static Instruction *foldBitcastExtElt(ExtractElementInst &Ext,
InstCombiner::BuilderTy &Builder,
bool IsBigEndian) {
Value *X;
uint64_t ExtIndexC;
if (!match(Ext.getVectorOperand(), m_BitCast(m_Value(X))) ||
!X->getType()->isVectorTy() ||
!match(Ext.getIndexOperand(), m_ConstantInt(ExtIndexC)))
return nullptr;
// If this extractelement is using a bitcast from a vector of the same number
// of elements, see if we can find the source element from the source vector:
// extelt (bitcast VecX), IndexC --> bitcast X[IndexC]
Type *SrcTy = X->getType();
Type *DestTy = Ext.getType();
unsigned NumSrcElts = SrcTy->getVectorNumElements();
unsigned NumElts = Ext.getVectorOperandType()->getNumElements();
if (NumSrcElts == NumElts)
if (Value *Elt = findScalarElement(X, ExtIndexC))
return new BitCastInst(Elt, DestTy);
// If the source elements are wider than the destination, try to shift and
// truncate a subset of scalar bits of an insert op.
if (NumSrcElts < NumElts) {
Value *Scalar;
uint64_t InsIndexC;
if (!match(X, m_InsertElement(m_Value(), m_Value(Scalar),
m_ConstantInt(InsIndexC))))
return nullptr;
// The extract must be from the subset of vector elements that we inserted
// into. Example: if we inserted element 1 of a <2 x i64> and we are
// extracting an i16 (narrowing ratio = 4), then this extract must be from 1
// of elements 4-7 of the bitcasted vector.
unsigned NarrowingRatio = NumElts / NumSrcElts;
if (ExtIndexC / NarrowingRatio != InsIndexC)
return nullptr;
// We are extracting part of the original scalar. How that scalar is
// inserted into the vector depends on the endian-ness. Example:
// Vector Byte Elt Index: 0 1 2 3 4 5 6 7
// +--+--+--+--+--+--+--+--+
// inselt <2 x i32> V, <i32> S, 1: |V0|V1|V2|V3|S0|S1|S2|S3|
// extelt <4 x i16> V', 3: | |S2|S3|
// +--+--+--+--+--+--+--+--+
// If this is little-endian, S2|S3 are the MSB of the 32-bit 'S' value.
// If this is big-endian, S2|S3 are the LSB of the 32-bit 'S' value.
// In this example, we must right-shift little-endian. Big-endian is just a
// truncate.
unsigned Chunk = ExtIndexC % NarrowingRatio;
if (IsBigEndian)
Chunk = NarrowingRatio - 1 - Chunk;
// Bail out if this is an FP vector to FP vector sequence. That would take
// more instructions than we started with unless there is no shift, and it
// may not be handled as well in the backend.
bool NeedSrcBitcast = SrcTy->getScalarType()->isFloatingPointTy();
bool NeedDestBitcast = DestTy->isFloatingPointTy();
if (NeedSrcBitcast && NeedDestBitcast)
return nullptr;
unsigned SrcWidth = SrcTy->getScalarSizeInBits();
unsigned DestWidth = DestTy->getPrimitiveSizeInBits();
unsigned ShAmt = Chunk * DestWidth;
// TODO: This limitation is more strict than necessary. We could sum the
// number of new instructions and subtract the number eliminated to know if
// we can proceed.
if (!X->hasOneUse() || !Ext.getVectorOperand()->hasOneUse())
if (NeedSrcBitcast || NeedDestBitcast)
return nullptr;
if (NeedSrcBitcast) {
Type *SrcIntTy = IntegerType::getIntNTy(Scalar->getContext(), SrcWidth);
Scalar = Builder.CreateBitCast(Scalar, SrcIntTy);
}
if (ShAmt) {
// Bail out if we could end with more instructions than we started with.
if (!Ext.getVectorOperand()->hasOneUse())
return nullptr;
Scalar = Builder.CreateLShr(Scalar, ShAmt);
}
if (NeedDestBitcast) {
Type *DestIntTy = IntegerType::getIntNTy(Scalar->getContext(), DestWidth);
return new BitCastInst(Builder.CreateTrunc(Scalar, DestIntTy), DestTy);
}
return new TruncInst(Scalar, DestTy);
}
return nullptr;
}
Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
Value *SrcVec = EI.getVectorOperand();
Value *Index = EI.getIndexOperand();
if (Value *V = SimplifyExtractElementInst(SrcVec, Index,
SQ.getWithInstruction(&EI)))
return replaceInstUsesWith(EI, V);
// If extracting a specified index from the vector, see if we can recursively
// find a previously computed scalar that was inserted into the vector.
auto *IndexC = dyn_cast<ConstantInt>(Index);
if (IndexC) {
unsigned NumElts = EI.getVectorOperandType()->getNumElements();
// InstSimplify should handle cases where the index is invalid.
if (!IndexC->getValue().ule(NumElts))
return nullptr;
// This instruction only demands the single element from the input vector.
// If the input vector has a single use, simplify it based on this use
// property.
if (SrcVec->hasOneUse() && NumElts != 1) {
APInt UndefElts(NumElts, 0);
APInt DemandedElts(NumElts, 0);
DemandedElts.setBit(IndexC->getZExtValue());
if (Value *V = SimplifyDemandedVectorElts(SrcVec, DemandedElts,
UndefElts)) {
EI.setOperand(0, V);
return &EI;
}
}
if (Instruction *I = foldBitcastExtElt(EI, Builder, DL.isBigEndian()))
return I;
// If there's a vector PHI feeding a scalar use through this extractelement
// instruction, try to scalarize the PHI.
if (auto *Phi = dyn_cast<PHINode>(SrcVec))
if (Instruction *ScalarPHI = scalarizePHI(EI, Phi))
return ScalarPHI;
}
BinaryOperator *BO;
if (match(SrcVec, m_BinOp(BO)) && cheapToScalarize(SrcVec, IndexC)) {
// extelt (binop X, Y), Index --> binop (extelt X, Index), (extelt Y, Index)
Value *X = BO->getOperand(0), *Y = BO->getOperand(1);
Value *E0 = Builder.CreateExtractElement(X, Index);
Value *E1 = Builder.CreateExtractElement(Y, Index);
return BinaryOperator::CreateWithCopiedFlags(BO->getOpcode(), E0, E1, BO);
}
Value *X, *Y;
CmpInst::Predicate Pred;
if (match(SrcVec, m_Cmp(Pred, m_Value(X), m_Value(Y))) &&
cheapToScalarize(SrcVec, IndexC)) {
// extelt (cmp X, Y), Index --> cmp (extelt X, Index), (extelt Y, Index)
Value *E0 = Builder.CreateExtractElement(X, Index);
Value *E1 = Builder.CreateExtractElement(Y, Index);
return CmpInst::Create(cast<CmpInst>(SrcVec)->getOpcode(), Pred, E0, E1);
}
if (auto *I = dyn_cast<Instruction>(SrcVec)) {
if (auto *IE = dyn_cast<InsertElementInst>(I)) {
// Extracting the inserted element?
if (IE->getOperand(2) == Index)
return replaceInstUsesWith(EI, IE->getOperand(1));
// If the inserted and extracted elements are constants, they must not
// be the same value, extract from the pre-inserted value instead.
if (isa<Constant>(IE->getOperand(2)) && IndexC) {
Worklist.AddValue(SrcVec);
EI.setOperand(0, IE->getOperand(0));
return &EI;
}
} else if (auto *SVI = dyn_cast<ShuffleVectorInst>(I)) {
// If this is extracting an element from a shufflevector, figure out where
// it came from and extract from the appropriate input element instead.
if (auto *Elt = dyn_cast<ConstantInt>(Index)) {
int SrcIdx = SVI->getMaskValue(Elt->getZExtValue());
Value *Src;
unsigned LHSWidth =
SVI->getOperand(0)->getType()->getVectorNumElements();
if (SrcIdx < 0)
return replaceInstUsesWith(EI, UndefValue::get(EI.getType()));
if (SrcIdx < (int)LHSWidth)
Src = SVI->getOperand(0);
else {
SrcIdx -= LHSWidth;
Src = SVI->getOperand(1);
}
Type *Int32Ty = Type::getInt32Ty(EI.getContext());
return ExtractElementInst::Create(Src,
ConstantInt::get(Int32Ty,
SrcIdx, false));
}
} else if (auto *CI = dyn_cast<CastInst>(I)) {
// Canonicalize extractelement(cast) -> cast(extractelement).
// Bitcasts can change the number of vector elements, and they cost
// nothing.
if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast)) {
Value *EE = Builder.CreateExtractElement(CI->getOperand(0), Index);
Worklist.AddValue(EE);
return CastInst::Create(CI->getOpcode(), EE, EI.getType());
}
}
}
return nullptr;
}
/// If V is a shuffle of values that ONLY returns elements from either LHS or
/// RHS, return the shuffle mask and true. Otherwise, return false.
static bool collectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
SmallVectorImpl<Constant*> &Mask) {
assert(LHS->getType() == RHS->getType() &&
"Invalid CollectSingleShuffleElements");
unsigned NumElts = V->getType()->getVectorNumElements();
if (isa<UndefValue>(V)) {
Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
return true;
}
if (V == LHS) {
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
return true;
}
if (V == RHS) {
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()),
i+NumElts));
return true;
}
if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(V)) {
// If this is an insert of an extract from some other vector, include it.
Value *VecOp = IEI->getOperand(0);
Value *ScalarOp = IEI->getOperand(1);
Value *IdxOp = IEI->getOperand(2);
if (!isa<ConstantInt>(IdxOp))
return false;
unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
if (isa<UndefValue>(ScalarOp)) { // inserting undef into vector.
// We can handle this if the vector we are inserting into is
// transitively ok.
if (collectSingleShuffleElements(VecOp, LHS, RHS, Mask)) {
// If so, update the mask to reflect the inserted undef.
Mask[InsertedIdx] = UndefValue::get(Type::getInt32Ty(V->getContext()));
return true;
}
} else if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)){
if (isa<ConstantInt>(EI->getOperand(1))) {
unsigned ExtractedIdx =
cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
unsigned NumLHSElts = LHS->getType()->getVectorNumElements();
// This must be extracting from either LHS or RHS.
if (EI->getOperand(0) == LHS || EI->getOperand(0) == RHS) {
// We can handle this if the vector we are inserting into is
// transitively ok.
if (collectSingleShuffleElements(VecOp, LHS, RHS, Mask)) {
// If so, update the mask to reflect the inserted value.
if (EI->getOperand(0) == LHS) {
Mask[InsertedIdx % NumElts] =
ConstantInt::get(Type::getInt32Ty(V->getContext()),
ExtractedIdx);
} else {
assert(EI->getOperand(0) == RHS);
Mask[InsertedIdx % NumElts] =
ConstantInt::get(Type::getInt32Ty(V->getContext()),
ExtractedIdx + NumLHSElts);
}
return true;
}
}
}
}
}
return false;
}
/// If we have insertion into a vector that is wider than the vector that we
/// are extracting from, try to widen the source vector to allow a single
/// shufflevector to replace one or more insert/extract pairs.
static void replaceExtractElements(InsertElementInst *InsElt,
ExtractElementInst *ExtElt,
InstCombiner &IC) {
VectorType *InsVecType = InsElt->getType();
VectorType *ExtVecType = ExtElt->getVectorOperandType();
unsigned NumInsElts = InsVecType->getVectorNumElements();
unsigned NumExtElts = ExtVecType->getVectorNumElements();
// The inserted-to vector must be wider than the extracted-from vector.
if (InsVecType->getElementType() != ExtVecType->getElementType() ||
NumExtElts >= NumInsElts)
return;
// Create a shuffle mask to widen the extended-from vector using undefined
// values. The mask selects all of the values of the original vector followed
// by as many undefined values as needed to create a vector of the same length
// as the inserted-to vector.
SmallVector<Constant *, 16> ExtendMask;
IntegerType *IntType = Type::getInt32Ty(InsElt->getContext());
for (unsigned i = 0; i < NumExtElts; ++i)
ExtendMask.push_back(ConstantInt::get(IntType, i));
for (unsigned i = NumExtElts; i < NumInsElts; ++i)
ExtendMask.push_back(UndefValue::get(IntType));
Value *ExtVecOp = ExtElt->getVectorOperand();
auto *ExtVecOpInst = dyn_cast<Instruction>(ExtVecOp);
BasicBlock *InsertionBlock = (ExtVecOpInst && !isa<PHINode>(ExtVecOpInst))
? ExtVecOpInst->getParent()
: ExtElt->getParent();
// TODO: This restriction matches the basic block check below when creating
// new extractelement instructions. If that limitation is removed, this one
// could also be removed. But for now, we just bail out to ensure that we
// will replace the extractelement instruction that is feeding our
// insertelement instruction. This allows the insertelement to then be
// replaced by a shufflevector. If the insertelement is not replaced, we can
// induce infinite looping because there's an optimization for extractelement
// that will delete our widening shuffle. This would trigger another attempt
// here to create that shuffle, and we spin forever.
if (InsertionBlock != InsElt->getParent())
return;
// TODO: This restriction matches the check in visitInsertElementInst() and
// prevents an infinite loop caused by not turning the extract/insert pair
// into a shuffle. We really should not need either check, but we're lacking
// folds for shufflevectors because we're afraid to generate shuffle masks
// that the backend can't handle.
if (InsElt->hasOneUse() && isa<InsertElementInst>(InsElt->user_back()))
return;
auto *WideVec = new ShuffleVectorInst(ExtVecOp, UndefValue::get(ExtVecType),
ConstantVector::get(ExtendMask));
// Insert the new shuffle after the vector operand of the extract is defined
// (as long as it's not a PHI) or at the start of the basic block of the
// extract, so any subsequent extracts in the same basic block can use it.
// TODO: Insert before the earliest ExtractElementInst that is replaced.
if (ExtVecOpInst && !isa<PHINode>(ExtVecOpInst))
WideVec->insertAfter(ExtVecOpInst);
else
IC.InsertNewInstWith(WideVec, *ExtElt->getParent()->getFirstInsertionPt());
// Replace extracts from the original narrow vector with extracts from the new
// wide vector.
for (User *U : ExtVecOp->users()) {
ExtractElementInst *OldExt = dyn_cast<ExtractElementInst>(U);
if (!OldExt || OldExt->getParent() != WideVec->getParent())
continue;
auto *NewExt = ExtractElementInst::Create(WideVec, OldExt->getOperand(1));
NewExt->insertAfter(OldExt);
IC.replaceInstUsesWith(*OldExt, NewExt);
}
}
/// We are building a shuffle to create V, which is a sequence of insertelement,
/// extractelement pairs. If PermittedRHS is set, then we must either use it or
/// not rely on the second vector source. Return a std::pair containing the
/// left and right vectors of the proposed shuffle (or 0), and set the Mask
/// parameter as required.
///
/// Note: we intentionally don't try to fold earlier shuffles since they have
/// often been chosen carefully to be efficiently implementable on the target.
using ShuffleOps = std::pair<Value *, Value *>;
static ShuffleOps collectShuffleElements(Value *V,
SmallVectorImpl<Constant *> &Mask,
Value *PermittedRHS,
InstCombiner &IC) {
assert(V->getType()->isVectorTy() && "Invalid shuffle!");
unsigned NumElts = V->getType()->getVectorNumElements();
if (isa<UndefValue>(V)) {
Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
return std::make_pair(
PermittedRHS ? UndefValue::get(PermittedRHS->getType()) : V, nullptr);
}
if (isa<ConstantAggregateZero>(V)) {
Mask.assign(NumElts, ConstantInt::get(Type::getInt32Ty(V->getContext()),0));
return std::make_pair(V, nullptr);
}
if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(V)) {
// If this is an insert of an extract from some other vector, include it.
Value *VecOp = IEI->getOperand(0);
Value *ScalarOp = IEI->getOperand(1);
Value *IdxOp = IEI->getOperand(2);
if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp)) {
unsigned ExtractedIdx =
cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
// Either the extracted from or inserted into vector must be RHSVec,
// otherwise we'd end up with a shuffle of three inputs.
if (EI->getOperand(0) == PermittedRHS || PermittedRHS == nullptr) {
Value *RHS = EI->getOperand(0);
ShuffleOps LR = collectShuffleElements(VecOp, Mask, RHS, IC);
assert(LR.second == nullptr || LR.second == RHS);
if (LR.first->getType() != RHS->getType()) {
// Although we are giving up for now, see if we can create extracts
// that match the inserts for another round of combining.
replaceExtractElements(IEI, EI, IC);
// We tried our best, but we can't find anything compatible with RHS
// further up the chain. Return a trivial shuffle.
for (unsigned i = 0; i < NumElts; ++i)
Mask[i] = ConstantInt::get(Type::getInt32Ty(V->getContext()), i);
return std::make_pair(V, nullptr);
}
unsigned NumLHSElts = RHS->getType()->getVectorNumElements();
Mask[InsertedIdx % NumElts] =
ConstantInt::get(Type::getInt32Ty(V->getContext()),
NumLHSElts+ExtractedIdx);
return std::make_pair(LR.first, RHS);
}
if (VecOp == PermittedRHS) {
// We've gone as far as we can: anything on the other side of the
// extractelement will already have been converted into a shuffle.
unsigned NumLHSElts =
EI->getOperand(0)->getType()->getVectorNumElements();
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(ConstantInt::get(
Type::getInt32Ty(V->getContext()),
i == InsertedIdx ? ExtractedIdx : NumLHSElts + i));
return std::make_pair(EI->getOperand(0), PermittedRHS);
}
// If this insertelement is a chain that comes from exactly these two
// vectors, return the vector and the effective shuffle.
if (EI->getOperand(0)->getType() == PermittedRHS->getType() &&
collectSingleShuffleElements(IEI, EI->getOperand(0), PermittedRHS,
Mask))
return std::make_pair(EI->getOperand(0), PermittedRHS);
}
}
}
// Otherwise, we can't do anything fancy. Return an identity vector.
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
return std::make_pair(V, nullptr);
}
/// Try to find redundant insertvalue instructions, like the following ones:
/// %0 = insertvalue { i8, i32 } undef, i8 %x, 0
/// %1 = insertvalue { i8, i32 } %0, i8 %y, 0
/// Here the second instruction inserts values at the same indices, as the
/// first one, making the first one redundant.
/// It should be transformed to:
/// %0 = insertvalue { i8, i32 } undef, i8 %y, 0
Instruction *InstCombiner::visitInsertValueInst(InsertValueInst &I) {
bool IsRedundant = false;
ArrayRef<unsigned int> FirstIndices = I.getIndices();
// If there is a chain of insertvalue instructions (each of them except the
// last one has only one use and it's another insertvalue insn from this
// chain), check if any of the 'children' uses the same indices as the first
// instruction. In this case, the first one is redundant.
Value *V = &I;
unsigned Depth = 0;
while (V->hasOneUse() && Depth < 10) {
User *U = V->user_back();
auto UserInsInst = dyn_cast<InsertValueInst>(U);
if (!UserInsInst || U->getOperand(0) != V)
break;
if (UserInsInst->getIndices() == FirstIndices) {
IsRedundant = true;
break;
}
V = UserInsInst;
Depth++;
}
if (IsRedundant)
return replaceInstUsesWith(I, I.getOperand(0));
return nullptr;
}
static bool isShuffleEquivalentToSelect(ShuffleVectorInst &Shuf) {
int MaskSize = Shuf.getMask()->getType()->getVectorNumElements();
int VecSize = Shuf.getOperand(0)->getType()->getVectorNumElements();
// A vector select does not change the size of the operands.
if (MaskSize != VecSize)
return false;
// Each mask element must be undefined or choose a vector element from one of
// the source operands without crossing vector lanes.
for (int i = 0; i != MaskSize; ++i) {
int Elt = Shuf.getMaskValue(i);
if (Elt != -1 && Elt != i && Elt != i + VecSize)
return false;
}
return true;
}
// Turn a chain of inserts that splats a value into a canonical insert + shuffle
// splat. That is:
// insertelt(insertelt(insertelt(insertelt X, %k, 0), %k, 1), %k, 2) ... ->
// shufflevector(insertelt(X, %k, 0), undef, zero)
static Instruction *foldInsSequenceIntoBroadcast(InsertElementInst &InsElt) {
// We are interested in the last insert in a chain. So, if this insert
// has a single user, and that user is an insert, bail.
if (InsElt.hasOneUse() && isa<InsertElementInst>(InsElt.user_back()))
return nullptr;
VectorType *VT = cast<VectorType>(InsElt.getType());
int NumElements = VT->getNumElements();
// Do not try to do this for a one-element vector, since that's a nop,
// and will cause an inf-loop.
if (NumElements == 1)
return nullptr;
Value *SplatVal = InsElt.getOperand(1);
InsertElementInst *CurrIE = &InsElt;
SmallVector<bool, 16> ElementPresent(NumElements, false);
InsertElementInst *FirstIE = nullptr;
// Walk the chain backwards, keeping track of which indices we inserted into,
// until we hit something that isn't an insert of the splatted value.
while (CurrIE) {
auto *Idx = dyn_cast<ConstantInt>(CurrIE->getOperand(2));
if (!Idx || CurrIE->getOperand(1) != SplatVal)
return nullptr;
auto *NextIE = dyn_cast<InsertElementInst>(CurrIE->getOperand(0));
// Check none of the intermediate steps have any additional uses, except
// for the root insertelement instruction, which can be re-used, if it
// inserts at position 0.
if (CurrIE != &InsElt &&
(!CurrIE->hasOneUse() && (NextIE != nullptr || !Idx->isZero())))
return nullptr;
ElementPresent[Idx->getZExtValue()] = true;
FirstIE = CurrIE;
CurrIE = NextIE;
}
// Make sure we've seen an insert into every element.
if (llvm::any_of(ElementPresent, [](bool Present) { return !Present; }))
return nullptr;
// All right, create the insert + shuffle.
Instruction *InsertFirst;
if (cast<ConstantInt>(FirstIE->getOperand(2))->isZero())
InsertFirst = FirstIE;
else
InsertFirst = InsertElementInst::Create(
UndefValue::get(VT), SplatVal,
ConstantInt::get(Type::getInt32Ty(InsElt.getContext()), 0),
"", &InsElt);
Constant *ZeroMask = ConstantAggregateZero::get(
VectorType::get(Type::getInt32Ty(InsElt.getContext()), NumElements));
return new ShuffleVectorInst(InsertFirst, UndefValue::get(VT), ZeroMask);
}
/// If we have an insertelement instruction feeding into another insertelement
/// and the 2nd is inserting a constant into the vector, canonicalize that
/// constant insertion before the insertion of a variable:
///
/// insertelement (insertelement X, Y, IdxC1), ScalarC, IdxC2 -->
/// insertelement (insertelement X, ScalarC, IdxC2), Y, IdxC1
///
/// This has the potential of eliminating the 2nd insertelement instruction
/// via constant folding of the scalar constant into a vector constant.
static Instruction *hoistInsEltConst(InsertElementInst &InsElt2,
InstCombiner::BuilderTy &Builder) {
auto *InsElt1 = dyn_cast<InsertElementInst>(InsElt2.getOperand(0));
if (!InsElt1 || !InsElt1->hasOneUse())
return nullptr;
Value *X, *Y;
Constant *ScalarC;
ConstantInt *IdxC1, *IdxC2;
if (match(InsElt1->getOperand(0), m_Value(X)) &&
match(InsElt1->getOperand(1), m_Value(Y)) && !isa<Constant>(Y) &&
match(InsElt1->getOperand(2), m_ConstantInt(IdxC1)) &&
match(InsElt2.getOperand(1), m_Constant(ScalarC)) &&
match(InsElt2.getOperand(2), m_ConstantInt(IdxC2)) && IdxC1 != IdxC2) {
Value *NewInsElt1 = Builder.CreateInsertElement(X, ScalarC, IdxC2);
return InsertElementInst::Create(NewInsElt1, Y, IdxC1);
}
return nullptr;
}
/// insertelt (shufflevector X, CVec, Mask|insertelt X, C1, CIndex1), C, CIndex
/// --> shufflevector X, CVec', Mask'
static Instruction *foldConstantInsEltIntoShuffle(InsertElementInst &InsElt) {
auto *Inst = dyn_cast<Instruction>(InsElt.getOperand(0));
// Bail out if the parent has more than one use. In that case, we'd be
// replacing the insertelt with a shuffle, and that's not a clear win.
if (!Inst || !Inst->hasOneUse())
return nullptr;
if (auto *Shuf = dyn_cast<ShuffleVectorInst>(InsElt.getOperand(0))) {
// The shuffle must have a constant vector operand. The insertelt must have
// a constant scalar being inserted at a constant position in the vector.
Constant *ShufConstVec, *InsEltScalar;
uint64_t InsEltIndex;
if (!match(Shuf->getOperand(1), m_Constant(ShufConstVec)) ||
!match(InsElt.getOperand(1), m_Constant(InsEltScalar)) ||
!match(InsElt.getOperand(2), m_ConstantInt(InsEltIndex)))
return nullptr;
// Adding an element to an arbitrary shuffle could be expensive, but a
// shuffle that selects elements from vectors without crossing lanes is
// assumed cheap.
// If we're just adding a constant into that shuffle, it will still be
// cheap.
if (!isShuffleEquivalentToSelect(*Shuf))
return nullptr;
// From the above 'select' check, we know that the mask has the same number
// of elements as the vector input operands. We also know that each constant
// input element is used in its lane and can not be used more than once by
// the shuffle. Therefore, replace the constant in the shuffle's constant
// vector with the insertelt constant. Replace the constant in the shuffle's
// mask vector with the insertelt index plus the length of the vector
// (because the constant vector operand of a shuffle is always the 2nd
// operand).
Constant *Mask = Shuf->getMask();
unsigned NumElts = Mask->getType()->getVectorNumElements();
SmallVector<Constant *, 16> NewShufElts(NumElts);
SmallVector<Constant *, 16> NewMaskElts(NumElts);
for (unsigned I = 0; I != NumElts; ++I) {
if (I == InsEltIndex) {
NewShufElts[I] = InsEltScalar;
Type *Int32Ty = Type::getInt32Ty(Shuf->getContext());
NewMaskElts[I] = ConstantInt::get(Int32Ty, InsEltIndex + NumElts);
} else {
// Copy over the existing values.
NewShufElts[I] = ShufConstVec->getAggregateElement(I);
NewMaskElts[I] = Mask->getAggregateElement(I);
}
}
// Create new operands for a shuffle that includes the constant of the
// original insertelt. The old shuffle will be dead now.
return new ShuffleVectorInst(Shuf->getOperand(0),
ConstantVector::get(NewShufElts),
ConstantVector::get(NewMaskElts));
} else if (auto *IEI = dyn_cast<InsertElementInst>(Inst)) {
// Transform sequences of insertelements ops with constant data/indexes into
// a single shuffle op.
unsigned NumElts = InsElt.getType()->getNumElements();
uint64_t InsertIdx[2];
Constant *Val[2];
if (!match(InsElt.getOperand(2), m_ConstantInt(InsertIdx[0])) ||
!match(InsElt.getOperand(1), m_Constant(Val[0])) ||
!match(IEI->getOperand(2), m_ConstantInt(InsertIdx[1])) ||
!match(IEI->getOperand(1), m_Constant(Val[1])))
return nullptr;
SmallVector<Constant *, 16> Values(NumElts);
SmallVector<Constant *, 16> Mask(NumElts);
auto ValI = std::begin(Val);
// Generate new constant vector and mask.
// We have 2 values/masks from the insertelements instructions. Insert them
// into new value/mask vectors.
for (uint64_t I : InsertIdx) {
if (!Values[I]) {
assert(!Mask[I]);
Values[I] = *ValI;
Mask[I] = ConstantInt::get(Type::getInt32Ty(InsElt.getContext()),
NumElts + I);
}
++ValI;
}
// Remaining values are filled with 'undef' values.
for (unsigned I = 0; I < NumElts; ++I) {
if (!Values[I]) {
assert(!Mask[I]);
Values[I] = UndefValue::get(InsElt.getType()->getElementType());
Mask[I] = ConstantInt::get(Type::getInt32Ty(InsElt.getContext()), I);
}
}
// Create new operands for a shuffle that includes the constant of the
// original insertelt.
return new ShuffleVectorInst(IEI->getOperand(0),
ConstantVector::get(Values),
ConstantVector::get(Mask));
}
return nullptr;
}
Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
Value *VecOp = IE.getOperand(0);
Value *ScalarOp = IE.getOperand(1);
Value *IdxOp = IE.getOperand(2);
if (auto *V = SimplifyInsertElementInst(
VecOp, ScalarOp, IdxOp, SQ.getWithInstruction(&IE)))
return replaceInstUsesWith(IE, V);
// Inserting an undef or into an undefined place, remove this.
if (isa<UndefValue>(ScalarOp) || isa<UndefValue>(IdxOp))
replaceInstUsesWith(IE, VecOp);
// If the inserted element was extracted from some other vector and both
// indexes are constant, try to turn this into a shuffle.
uint64_t InsertedIdx, ExtractedIdx;
Value *ExtVecOp;
if (match(IdxOp, m_ConstantInt(InsertedIdx)) &&
match(ScalarOp, m_ExtractElement(m_Value(ExtVecOp),
m_ConstantInt(ExtractedIdx)))) {
unsigned NumInsertVectorElts = IE.getType()->getNumElements();
unsigned NumExtractVectorElts = ExtVecOp->getType()->getVectorNumElements();
if (ExtractedIdx >= NumExtractVectorElts) // Out of range extract.
return replaceInstUsesWith(IE, VecOp);
if (InsertedIdx >= NumInsertVectorElts) // Out of range insert.
return replaceInstUsesWith(IE, UndefValue::get(IE.getType()));
// If we are extracting a value from a vector, then inserting it right
// back into the same place, just use the input vector.
if (ExtVecOp == VecOp && ExtractedIdx == InsertedIdx)
return replaceInstUsesWith(IE, VecOp);
// TODO: Looking at the user(s) to determine if this insert is a
// fold-to-shuffle opportunity does not match the usual instcombine
// constraints. We should decide if the transform is worthy based only
// on this instruction and its operands, but that may not work currently.
//
// Here, we are trying to avoid creating shuffles before reaching
// the end of a chain of extract-insert pairs. This is complicated because
// we do not generally form arbitrary shuffle masks in instcombine
// (because those may codegen poorly), but collectShuffleElements() does
// exactly that.
//
// The rules for determining what is an acceptable target-independent
// shuffle mask are fuzzy because they evolve based on the backend's
// capabilities and real-world impact.
auto isShuffleRootCandidate = [](InsertElementInst &Insert) {
if (!Insert.hasOneUse())
return true;
auto *InsertUser = dyn_cast<InsertElementInst>(Insert.user_back());
if (!InsertUser)
return true;
return false;
};
// Try to form a shuffle from a chain of extract-insert ops.
if (isShuffleRootCandidate(IE)) {
SmallVector<Constant*, 16> Mask;
ShuffleOps LR = collectShuffleElements(&IE, Mask, nullptr, *this);
// The proposed shuffle may be trivial, in which case we shouldn't
// perform the combine.
if (LR.first != &IE && LR.second != &IE) {
// We now have a shuffle of LHS, RHS, Mask.
if (LR.second == nullptr)
LR.second = UndefValue::get(LR.first->getType());
return new ShuffleVectorInst(LR.first, LR.second,
ConstantVector::get(Mask));
}
}
}
unsigned VWidth = VecOp->getType()->getVectorNumElements();
APInt UndefElts(VWidth, 0);
APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
if (Value *V = SimplifyDemandedVectorElts(&IE, AllOnesEltMask, UndefElts)) {
if (V != &IE)
return replaceInstUsesWith(IE, V);
return &IE;
}
if (Instruction *Shuf = foldConstantInsEltIntoShuffle(IE))
return Shuf;
if (Instruction *NewInsElt = hoistInsEltConst(IE, Builder))
return NewInsElt;
// Turn a sequence of inserts that broadcasts a scalar into a single
// insert + shufflevector.
if (Instruction *Broadcast = foldInsSequenceIntoBroadcast(IE))
return Broadcast;
return nullptr;
}
/// Return true if we can evaluate the specified expression tree if the vector
/// elements were shuffled in a different order.
static bool canEvaluateShuffled(Value *V, ArrayRef<int> Mask,
unsigned Depth = 5) {
// We can always reorder the elements of a constant.
if (isa<Constant>(V))
return true;
// We won't reorder vector arguments. No IPO here.
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// Two users may expect different orders of the elements. Don't try it.
if (!I->hasOneUse())
return false;
if (Depth == 0) return false;
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::ICmp:
case Instruction::FCmp:
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::GetElementPtr: {
// Bail out if we would create longer vector ops. We could allow creating
// longer vector ops, but that may result in more expensive codegen. We
// would also need to limit the transform to avoid undefined behavior for
// integer div/rem.
Type *ITy = I->getType();
if (ITy->isVectorTy() && Mask.size() > ITy->getVectorNumElements())
return false;
for (Value *Operand : I->operands()) {
if (!canEvaluateShuffled(Operand, Mask, Depth - 1))
return false;
}
return true;
}
case Instruction::InsertElement: {
ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(2));
if (!CI) return false;
int ElementNumber = CI->getLimitedValue();
// Verify that 'CI' does not occur twice in Mask. A single 'insertelement'
// can't put an element into multiple indices.
bool SeenOnce = false;
for (int i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] == ElementNumber) {
if (SeenOnce)
return false;
SeenOnce = true;
}
}
return canEvaluateShuffled(I->getOperand(0), Mask, Depth - 1);
}
}
return false;
}
/// Rebuild a new instruction just like 'I' but with the new operands given.
/// In the event of type mismatch, the type of the operands is correct.
static Value *buildNew(Instruction *I, ArrayRef<Value*> NewOps) {
// We don't want to use the IRBuilder here because we want the replacement
// instructions to appear next to 'I', not the builder's insertion point.
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
BinaryOperator *BO = cast<BinaryOperator>(I);
assert(NewOps.size() == 2 && "binary operator with #ops != 2");
BinaryOperator *New =
BinaryOperator::Create(cast<BinaryOperator>(I)->getOpcode(),
NewOps[0], NewOps[1], "", BO);
if (isa<OverflowingBinaryOperator>(BO)) {
New->setHasNoUnsignedWrap(BO->hasNoUnsignedWrap());
New->setHasNoSignedWrap(BO->hasNoSignedWrap());
}
if (isa<PossiblyExactOperator>(BO)) {
New->setIsExact(BO->isExact());
}
if (isa<FPMathOperator>(BO))
New->copyFastMathFlags(I);
return New;
}
case Instruction::ICmp:
assert(NewOps.size() == 2 && "icmp with #ops != 2");
return new ICmpInst(I, cast<ICmpInst>(I)->getPredicate(),
NewOps[0], NewOps[1]);
case Instruction::FCmp:
assert(NewOps.size() == 2 && "fcmp with #ops != 2");
return new FCmpInst(I, cast<FCmpInst>(I)->getPredicate(),
NewOps[0], NewOps[1]);
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPTrunc:
case Instruction::FPExt: {
// It's possible that the mask has a different number of elements from
// the original cast. We recompute the destination type to match the mask.
Type *DestTy =
VectorType::get(I->getType()->getScalarType(),
NewOps[0]->getType()->getVectorNumElements());
assert(NewOps.size() == 1 && "cast with #ops != 1");
return CastInst::Create(cast<CastInst>(I)->getOpcode(), NewOps[0], DestTy,
"", I);
}
case Instruction::GetElementPtr: {
Value *Ptr = NewOps[0];
ArrayRef<Value*> Idx = NewOps.slice(1);
GetElementPtrInst *GEP = GetElementPtrInst::Create(
cast<GetElementPtrInst>(I)->getSourceElementType(), Ptr, Idx, "", I);
GEP->setIsInBounds(cast<GetElementPtrInst>(I)->isInBounds());
return GEP;
}
}
llvm_unreachable("failed to rebuild vector instructions");
}
static Value *evaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask) {
// Mask.size() does not need to be equal to the number of vector elements.
assert(V->getType()->isVectorTy() && "can't reorder non-vector elements");
Type *EltTy = V->getType()->getScalarType();
Type *I32Ty = IntegerType::getInt32Ty(V->getContext());
if (isa<UndefValue>(V))
return UndefValue::get(VectorType::get(EltTy, Mask.size()));
if (isa<ConstantAggregateZero>(V))
return ConstantAggregateZero::get(VectorType::get(EltTy, Mask.size()));
if (Constant *C = dyn_cast<Constant>(V)) {
SmallVector<Constant *, 16> MaskValues;
for (int i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] == -1)
MaskValues.push_back(UndefValue::get(I32Ty));
else
MaskValues.push_back(ConstantInt::get(I32Ty, Mask[i]));
}
return ConstantExpr::getShuffleVector(C, UndefValue::get(C->getType()),
ConstantVector::get(MaskValues));
}
Instruction *I = cast<Instruction>(V);
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::ICmp:
case Instruction::FCmp:
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::Select:
case Instruction::GetElementPtr: {
SmallVector<Value*, 8> NewOps;
bool NeedsRebuild = (Mask.size() != I->getType()->getVectorNumElements());
for (int i = 0, e = I->getNumOperands(); i != e; ++i) {
Value *V = evaluateInDifferentElementOrder(I->getOperand(i), Mask);
NewOps.push_back(V);
NeedsRebuild |= (V != I->getOperand(i));
}
if (NeedsRebuild) {
return buildNew(I, NewOps);
}
return I;
}
case Instruction::InsertElement: {
int Element = cast<ConstantInt>(I->getOperand(2))->getLimitedValue();
// The insertelement was inserting at Element. Figure out which element
// that becomes after shuffling. The answer is guaranteed to be unique
// by CanEvaluateShuffled.
bool Found = false;
int Index = 0;
for (int e = Mask.size(); Index != e; ++Index) {
if (Mask[Index] == Element) {
Found = true;
break;
}
}
// If element is not in Mask, no need to handle the operand 1 (element to
// be inserted). Just evaluate values in operand 0 according to Mask.
if (!Found)
return evaluateInDifferentElementOrder(I->getOperand(0), Mask);
Value *V = evaluateInDifferentElementOrder(I->getOperand(0), Mask);
return InsertElementInst::Create(V, I->getOperand(1),
ConstantInt::get(I32Ty, Index), "", I);
}
}
llvm_unreachable("failed to reorder elements of vector instruction!");
}
static void recognizeIdentityMask(const SmallVectorImpl<int> &Mask,
bool &isLHSID, bool &isRHSID) {
isLHSID = isRHSID = true;
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] < 0) continue; // Ignore undef values.
// Is this an identity shuffle of the LHS value?
isLHSID &= (Mask[i] == (int)i);
// Is this an identity shuffle of the RHS value?
isRHSID &= (Mask[i]-e == i);
}
}
// Returns true if the shuffle is extracting a contiguous range of values from
// LHS, for example:
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// Input: |AA|BB|CC|DD|EE|FF|GG|HH|II|JJ|KK|LL|MM|NN|OO|PP|
// Shuffles to: |EE|FF|GG|HH|
// +--+--+--+--+
static bool isShuffleExtractingFromLHS(ShuffleVectorInst &SVI,
SmallVector<int, 16> &Mask) {
unsigned LHSElems = SVI.getOperand(0)->getType()->getVectorNumElements();
unsigned MaskElems = Mask.size();
unsigned BegIdx = Mask.front();
unsigned EndIdx = Mask.back();
if (BegIdx > EndIdx || EndIdx >= LHSElems || EndIdx - BegIdx != MaskElems - 1)
return false;
for (unsigned I = 0; I != MaskElems; ++I)
if (static_cast<unsigned>(Mask[I]) != BegIdx + I)
return false;
return true;
}
/// These are the ingredients in an alternate form binary operator as described
/// below.
struct BinopElts {
BinaryOperator::BinaryOps Opcode;
Value *Op0;
Value *Op1;
BinopElts(BinaryOperator::BinaryOps Opc = (BinaryOperator::BinaryOps)0,
Value *V0 = nullptr, Value *V1 = nullptr) :
Opcode(Opc), Op0(V0), Op1(V1) {}
operator bool() const { return Opcode != 0; }
};
/// Binops may be transformed into binops with different opcodes and operands.
/// Reverse the usual canonicalization to enable folds with the non-canonical
/// form of the binop. If a transform is possible, return the elements of the
/// new binop. If not, return invalid elements.
static BinopElts getAlternateBinop(BinaryOperator *BO, const DataLayout &DL) {
Value *BO0 = BO->getOperand(0), *BO1 = BO->getOperand(1);
Type *Ty = BO->getType();
switch (BO->getOpcode()) {
case Instruction::Shl: {
// shl X, C --> mul X, (1 << C)
Constant *C;
if (match(BO1, m_Constant(C))) {
Constant *ShlOne = ConstantExpr::getShl(ConstantInt::get(Ty, 1), C);
return { Instruction::Mul, BO0, ShlOne };
}
break;
}
case Instruction::Or: {
// or X, C --> add X, C (when X and C have no common bits set)
const APInt *C;
if (match(BO1, m_APInt(C)) && MaskedValueIsZero(BO0, *C, DL))
return { Instruction::Add, BO0, BO1 };
break;
}
default:
break;
}
return {};
}
static Instruction *foldSelectShuffleWith1Binop(ShuffleVectorInst &Shuf) {
assert(Shuf.isSelect() && "Must have select-equivalent shuffle");
// Are we shuffling together some value and that same value after it has been
// modified by a binop with a constant?
Value *Op0 = Shuf.getOperand(0), *Op1 = Shuf.getOperand(1);
Constant *C;
bool Op0IsBinop;
if (match(Op0, m_BinOp(m_Specific(Op1), m_Constant(C))))
Op0IsBinop = true;
else if (match(Op1, m_BinOp(m_Specific(Op0), m_Constant(C))))
Op0IsBinop = false;
else
return nullptr;
// The identity constant for a binop leaves a variable operand unchanged. For
// a vector, this is a splat of something like 0, -1, or 1.
// If there's no identity constant for this binop, we're done.
auto *BO = cast<BinaryOperator>(Op0IsBinop ? Op0 : Op1);
BinaryOperator::BinaryOps BOpcode = BO->getOpcode();
Constant *IdC = ConstantExpr::getBinOpIdentity(BOpcode, Shuf.getType(), true);
if (!IdC)
return nullptr;
// Shuffle identity constants into the lanes that return the original value.
// Example: shuf (mul X, {-1,-2,-3,-4}), X, {0,5,6,3} --> mul X, {-1,1,1,-4}
// Example: shuf X, (add X, {-1,-2,-3,-4}), {0,1,6,7} --> add X, {0,0,-3,-4}
// The existing binop constant vector remains in the same operand position.
Constant *Mask = Shuf.getMask();
Constant *NewC = Op0IsBinop ? ConstantExpr::getShuffleVector(C, IdC, Mask) :
ConstantExpr::getShuffleVector(IdC, C, Mask);
bool MightCreatePoisonOrUB =
Mask->containsUndefElement() &&
(Instruction::isIntDivRem(BOpcode) || Instruction::isShift(BOpcode));
if (MightCreatePoisonOrUB)
NewC = getSafeVectorConstantForBinop(BOpcode, NewC, true);
// shuf (bop X, C), X, M --> bop X, C'
// shuf X, (bop X, C), M --> bop X, C'
Value *X = Op0IsBinop ? Op1 : Op0;
Instruction *NewBO = BinaryOperator::Create(BOpcode, X, NewC);
NewBO->copyIRFlags(BO);
// An undef shuffle mask element may propagate as an undef constant element in
// the new binop. That would produce poison where the original code might not.
// If we already made a safe constant, then there's no danger.
if (Mask->containsUndefElement() && !MightCreatePoisonOrUB)
NewBO->dropPoisonGeneratingFlags();
return NewBO;
}
/// Try to fold shuffles that are the equivalent of a vector select.
static Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf,
InstCombiner::BuilderTy &Builder,
const DataLayout &DL) {
if (!Shuf.isSelect())
return nullptr;
if (Instruction *I = foldSelectShuffleWith1Binop(Shuf))
return I;
BinaryOperator *B0, *B1;
if (!match(Shuf.getOperand(0), m_BinOp(B0)) ||
!match(Shuf.getOperand(1), m_BinOp(B1)))
return nullptr;
Value *X, *Y;
Constant *C0, *C1;
bool ConstantsAreOp1;
if (match(B0, m_BinOp(m_Value(X), m_Constant(C0))) &&
match(B1, m_BinOp(m_Value(Y), m_Constant(C1))))
ConstantsAreOp1 = true;
else if (match(B0, m_BinOp(m_Constant(C0), m_Value(X))) &&
match(B1, m_BinOp(m_Constant(C1), m_Value(Y))))
ConstantsAreOp1 = false;
else
return nullptr;
// We need matching binops to fold the lanes together.
BinaryOperator::BinaryOps Opc0 = B0->getOpcode();
BinaryOperator::BinaryOps Opc1 = B1->getOpcode();
bool DropNSW = false;
if (ConstantsAreOp1 && Opc0 != Opc1) {
// TODO: We drop "nsw" if shift is converted into multiply because it may
// not be correct when the shift amount is BitWidth - 1. We could examine
// each vector element to determine if it is safe to keep that flag.
if (Opc0 == Instruction::Shl || Opc1 == Instruction::Shl)
DropNSW = true;
if (BinopElts AltB0 = getAlternateBinop(B0, DL)) {
assert(isa<Constant>(AltB0.Op1) && "Expecting constant with alt binop");
Opc0 = AltB0.Opcode;
C0 = cast<Constant>(AltB0.Op1);
} else if (BinopElts AltB1 = getAlternateBinop(B1, DL)) {
assert(isa<Constant>(AltB1.Op1) && "Expecting constant with alt binop");
Opc1 = AltB1.Opcode;
C1 = cast<Constant>(AltB1.Op1);
}
}
if (Opc0 != Opc1)
return nullptr;
// The opcodes must be the same. Use a new name to make that clear.
BinaryOperator::BinaryOps BOpc = Opc0;
// Select the constant elements needed for the single binop.
Constant *Mask = Shuf.getMask();
Constant *NewC = ConstantExpr::getShuffleVector(C0, C1, Mask);
// We are moving a binop after a shuffle. When a shuffle has an undefined
// mask element, the result is undefined, but it is not poison or undefined
// behavior. That is not necessarily true for div/rem/shift.
bool MightCreatePoisonOrUB =
Mask->containsUndefElement() &&
(Instruction::isIntDivRem(BOpc) || Instruction::isShift(BOpc));
if (MightCreatePoisonOrUB)
NewC = getSafeVectorConstantForBinop(BOpc, NewC, ConstantsAreOp1);
Value *V;
if (X == Y) {
// Remove a binop and the shuffle by rearranging the constant:
// shuffle (op V, C0), (op V, C1), M --> op V, C'
// shuffle (op C0, V), (op C1, V), M --> op C', V
V = X;
} else {
// If there are 2 different variable operands, we must create a new shuffle
// (select) first, so check uses to ensure that we don't end up with more
// instructions than we started with.
if (!B0->hasOneUse() && !B1->hasOneUse())
return nullptr;
// If we use the original shuffle mask and op1 is *variable*, we would be
// putting an undef into operand 1 of div/rem/shift. This is either UB or
// poison. We do not have to guard against UB when *constants* are op1
// because safe constants guarantee that we do not overflow sdiv/srem (and
// there's no danger for other opcodes).
// TODO: To allow this case, create a new shuffle mask with no undefs.
if (MightCreatePoisonOrUB && !ConstantsAreOp1)
return nullptr;
// Note: In general, we do not create new shuffles in InstCombine because we
// do not know if a target can lower an arbitrary shuffle optimally. In this
// case, the shuffle uses the existing mask, so there is no additional risk.
// Select the variable vectors first, then perform the binop:
// shuffle (op X, C0), (op Y, C1), M --> op (shuffle X, Y, M), C'
// shuffle (op C0, X), (op C1, Y), M --> op C', (shuffle X, Y, M)
V = Builder.CreateShuffleVector(X, Y, Mask);
}
Instruction *NewBO = ConstantsAreOp1 ? BinaryOperator::Create(BOpc, V, NewC) :
BinaryOperator::Create(BOpc, NewC, V);
// Flags are intersected from the 2 source binops. But there are 2 exceptions:
// 1. If we changed an opcode, poison conditions might have changed.
// 2. If the shuffle had undef mask elements, the new binop might have undefs
// where the original code did not. But if we already made a safe constant,
// then there's no danger.
NewBO->copyIRFlags(B0);
NewBO->andIRFlags(B1);
if (DropNSW)
NewBO->setHasNoSignedWrap(false);
if (Mask->containsUndefElement() && !MightCreatePoisonOrUB)
NewBO->dropPoisonGeneratingFlags();
return NewBO;
}
/// Match a shuffle-select-shuffle pattern where the shuffles are widening and
/// narrowing (concatenating with undef and extracting back to the original
/// length). This allows replacing the wide select with a narrow select.
static Instruction *narrowVectorSelect(ShuffleVectorInst &Shuf,
InstCombiner::BuilderTy &Builder) {
// This must be a narrowing identity shuffle. It extracts the 1st N elements
// of the 1st vector operand of a shuffle.
if (!match(Shuf.getOperand(1), m_Undef()) || !Shuf.isIdentityWithExtract())
return nullptr;
// The vector being shuffled must be a vector select that we can eliminate.
// TODO: The one-use requirement could be eased if X and/or Y are constants.
Value *Cond, *X, *Y;
if (!match(Shuf.getOperand(0),
m_OneUse(m_Select(m_Value(Cond), m_Value(X), m_Value(Y)))))
return nullptr;
// We need a narrow condition value. It must be extended with undef elements
// and have the same number of elements as this shuffle.
unsigned NarrowNumElts = Shuf.getType()->getVectorNumElements();
Value *NarrowCond;
if (!match(Cond, m_OneUse(m_ShuffleVector(m_Value(NarrowCond), m_Undef(),
m_Constant()))) ||
NarrowCond->getType()->getVectorNumElements() != NarrowNumElts ||
!cast<ShuffleVectorInst>(Cond)->isIdentityWithPadding())
return nullptr;
// shuf (sel (shuf NarrowCond, undef, WideMask), X, Y), undef, NarrowMask) -->
// sel NarrowCond, (shuf X, undef, NarrowMask), (shuf Y, undef, NarrowMask)
Value *Undef = UndefValue::get(X->getType());
Value *NarrowX = Builder.CreateShuffleVector(X, Undef, Shuf.getMask());
Value *NarrowY = Builder.CreateShuffleVector(Y, Undef, Shuf.getMask());
return SelectInst::Create(NarrowCond, NarrowX, NarrowY);
}
/// Try to combine 2 shuffles into 1 shuffle by concatenating a shuffle mask.
static Instruction *foldIdentityExtractShuffle(ShuffleVectorInst &Shuf) {
Value *Op0 = Shuf.getOperand(0), *Op1 = Shuf.getOperand(1);
if (!Shuf.isIdentityWithExtract() || !isa<UndefValue>(Op1))
return nullptr;
Value *X, *Y;
Constant *Mask;
if (!match(Op0, m_ShuffleVector(m_Value(X), m_Value(Y), m_Constant(Mask))))
return nullptr;
// We are extracting a subvector from a shuffle. Remove excess elements from
// the 1st shuffle mask to eliminate the extract.
//
// This transform is conservatively limited to identity extracts because we do
// not allow arbitrary shuffle mask creation as a target-independent transform
// (because we can't guarantee that will lower efficiently).
//
// If the extracting shuffle has an undef mask element, it transfers to the
// new shuffle mask. Otherwise, copy the original mask element. Example:
// shuf (shuf X, Y, <C0, C1, C2, undef, C4>), undef, <0, undef, 2, 3> -->
// shuf X, Y, <C0, undef, C2, undef>
unsigned NumElts = Shuf.getType()->getVectorNumElements();
SmallVector<Constant *, 16> NewMask(NumElts);
assert(NumElts < Mask->getType()->getVectorNumElements() &&
"Identity with extract must have less elements than its inputs");
for (unsigned i = 0; i != NumElts; ++i) {
Constant *ExtractMaskElt = Shuf.getMask()->getAggregateElement(i);
Constant *MaskElt = Mask->getAggregateElement(i);
NewMask[i] = isa<UndefValue>(ExtractMaskElt) ? ExtractMaskElt : MaskElt;
}
return new ShuffleVectorInst(X, Y, ConstantVector::get(NewMask));
}
/// Try to replace a shuffle with an insertelement.
static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf) {
Value *V0 = Shuf.getOperand(0), *V1 = Shuf.getOperand(1);
SmallVector<int, 16> Mask = Shuf.getShuffleMask();
// The shuffle must not change vector sizes.
// TODO: This restriction could be removed if the insert has only one use
// (because the transform would require a new length-changing shuffle).
int NumElts = Mask.size();
if (NumElts != (int)(V0->getType()->getVectorNumElements()))
return nullptr;
// shuffle (insert ?, Scalar, IndexC), V1, Mask --> insert V1, Scalar, IndexC'
auto isShufflingScalarIntoOp1 = [&](Value *&Scalar, ConstantInt *&IndexC) {
// We need an insertelement with a constant index.
if (!match(V0, m_InsertElement(m_Value(), m_Value(Scalar),
m_ConstantInt(IndexC))))
return false;
// Test the shuffle mask to see if it splices the inserted scalar into the
// operand 1 vector of the shuffle.
int NewInsIndex = -1;
for (int i = 0; i != NumElts; ++i) {
// Ignore undef mask elements.
if (Mask[i] == -1)
continue;
// The shuffle takes elements of operand 1 without lane changes.
if (Mask[i] == NumElts + i)
continue;
// The shuffle must choose the inserted scalar exactly once.
if (NewInsIndex != -1 || Mask[i] != IndexC->getSExtValue())
return false;
// The shuffle is placing the inserted scalar into element i.
NewInsIndex = i;
}
assert(NewInsIndex != -1 && "Did not fold shuffle with unused operand?");
// Index is updated to the potentially translated insertion lane.
IndexC = ConstantInt::get(IndexC->getType(), NewInsIndex);
return true;
};
// If the shuffle is unnecessary, insert the scalar operand directly into
// operand 1 of the shuffle. Example:
// shuffle (insert ?, S, 1), V1, <1, 5, 6, 7> --> insert V1, S, 0
Value *Scalar;
ConstantInt *IndexC;
if (isShufflingScalarIntoOp1(Scalar, IndexC))
return InsertElementInst::Create(V1, Scalar, IndexC);
// Try again after commuting shuffle. Example:
// shuffle V0, (insert ?, S, 0), <0, 1, 2, 4> -->
// shuffle (insert ?, S, 0), V0, <4, 5, 6, 0> --> insert V0, S, 3
std::swap(V0, V1);
ShuffleVectorInst::commuteShuffleMask(Mask, NumElts);
if (isShufflingScalarIntoOp1(Scalar, IndexC))
return InsertElementInst::Create(V1, Scalar, IndexC);
return nullptr;
}
Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
Value *LHS = SVI.getOperand(0);
Value *RHS = SVI.getOperand(1);
if (auto *V = SimplifyShuffleVectorInst(
LHS, RHS, SVI.getMask(), SVI.getType(), SQ.getWithInstruction(&SVI)))
return replaceInstUsesWith(SVI, V);
if (Instruction *I = foldSelectShuffle(SVI, Builder, DL))
return I;
if (Instruction *I = narrowVectorSelect(SVI, Builder))
return I;
unsigned VWidth = SVI.getType()->getVectorNumElements();
APInt UndefElts(VWidth, 0);
APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
if (V != &SVI)
return replaceInstUsesWith(SVI, V);
return &SVI;
}
if (Instruction *I = foldIdentityExtractShuffle(SVI))
return I;
// This transform has the potential to lose undef knowledge, so it is
// intentionally placed after SimplifyDemandedVectorElts().
if (Instruction *I = foldShuffleWithInsert(SVI))
return I;
SmallVector<int, 16> Mask = SVI.getShuffleMask();
Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
unsigned LHSWidth = LHS->getType()->getVectorNumElements();
bool MadeChange = false;
// Canonicalize shuffle(x ,x,mask) -> shuffle(x, undef,mask')
// Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
if (LHS == RHS || isa<UndefValue>(LHS)) {
// Remap any references to RHS to use LHS.
SmallVector<Constant*, 16> Elts;
for (unsigned i = 0, e = LHSWidth; i != VWidth; ++i) {
if (Mask[i] < 0) {
Elts.push_back(UndefValue::get(Int32Ty));
continue;
}
if ((Mask[i] >= (int)e && isa<UndefValue>(RHS)) ||
(Mask[i] < (int)e && isa<UndefValue>(LHS))) {
Mask[i] = -1; // Turn into undef.
Elts.push_back(UndefValue::get(Int32Ty));
} else {
Mask[i] = Mask[i] % e; // Force to LHS.
Elts.push_back(ConstantInt::get(Int32Ty, Mask[i]));
}
}
SVI.setOperand(0, SVI.getOperand(1));
SVI.setOperand(1, UndefValue::get(RHS->getType()));
SVI.setOperand(2, ConstantVector::get(Elts));
LHS = SVI.getOperand(0);
RHS = SVI.getOperand(1);
MadeChange = true;
}
if (VWidth == LHSWidth) {
// Analyze the shuffle, are the LHS or RHS and identity shuffles?
bool isLHSID, isRHSID;
recognizeIdentityMask(Mask, isLHSID, isRHSID);
// Eliminate identity shuffles.
if (isLHSID) return replaceInstUsesWith(SVI, LHS);
if (isRHSID) return replaceInstUsesWith(SVI, RHS);
}
if (isa<UndefValue>(RHS) && canEvaluateShuffled(LHS, Mask)) {
Value *V = evaluateInDifferentElementOrder(LHS, Mask);
return replaceInstUsesWith(SVI, V);
}
// SROA generates shuffle+bitcast when the extracted sub-vector is bitcast to
// a non-vector type. We can instead bitcast the original vector followed by
// an extract of the desired element:
//
// %sroa = shufflevector <16 x i8> %in, <16 x i8> undef,
// <4 x i32> <i32 0, i32 1, i32 2, i32 3>
// %1 = bitcast <4 x i8> %sroa to i32
// Becomes:
// %bc = bitcast <16 x i8> %in to <4 x i32>
// %ext = extractelement <4 x i32> %bc, i32 0
//
// If the shuffle is extracting a contiguous range of values from the input
// vector then each use which is a bitcast of the extracted size can be
// replaced. This will work if the vector types are compatible, and the begin
// index is aligned to a value in the casted vector type. If the begin index
// isn't aligned then we can shuffle the original vector (keeping the same
// vector type) before extracting.
//
// This code will bail out if the target type is fundamentally incompatible
// with vectors of the source type.
//
// Example of <16 x i8>, target type i32:
// Index range [4,8): v-----------v Will work.
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// <16 x i8>: | | | | | | | | | | | | | | | | |
// <4 x i32>: | | | | |
// +-----------+-----------+-----------+-----------+
// Index range [6,10): ^-----------^ Needs an extra shuffle.
// Target type i40: ^--------------^ Won't work, bail.
if (isShuffleExtractingFromLHS(SVI, Mask)) {
Value *V = LHS;
unsigned MaskElems = Mask.size();
VectorType *SrcTy = cast<VectorType>(V->getType());
unsigned VecBitWidth = SrcTy->getBitWidth();
unsigned SrcElemBitWidth = DL.getTypeSizeInBits(SrcTy->getElementType());
assert(SrcElemBitWidth && "vector elements must have a bitwidth");
unsigned SrcNumElems = SrcTy->getNumElements();
SmallVector<BitCastInst *, 8> BCs;
DenseMap<Type *, Value *> NewBCs;
for (User *U : SVI.users())
if (BitCastInst *BC = dyn_cast<BitCastInst>(U))
if (!BC->use_empty())
// Only visit bitcasts that weren't previously handled.
BCs.push_back(BC);
for (BitCastInst *BC : BCs) {
unsigned BegIdx = Mask.front();
Type *TgtTy = BC->getDestTy();
unsigned TgtElemBitWidth = DL.getTypeSizeInBits(TgtTy);
if (!TgtElemBitWidth)
continue;
unsigned TgtNumElems = VecBitWidth / TgtElemBitWidth;
bool VecBitWidthsEqual = VecBitWidth == TgtNumElems * TgtElemBitWidth;
bool BegIsAligned = 0 == ((SrcElemBitWidth * BegIdx) % TgtElemBitWidth);
if (!VecBitWidthsEqual)
continue;
if (!VectorType::isValidElementType(TgtTy))
continue;
VectorType *CastSrcTy = VectorType::get(TgtTy, TgtNumElems);
if (!BegIsAligned) {
// Shuffle the input so [0,NumElements) contains the output, and
// [NumElems,SrcNumElems) is undef.
SmallVector<Constant *, 16> ShuffleMask(SrcNumElems,
UndefValue::get(Int32Ty));
for (unsigned I = 0, E = MaskElems, Idx = BegIdx; I != E; ++Idx, ++I)
ShuffleMask[I] = ConstantInt::get(Int32Ty, Idx);
V = Builder.CreateShuffleVector(V, UndefValue::get(V->getType()),
ConstantVector::get(ShuffleMask),
SVI.getName() + ".extract");
BegIdx = 0;
}
unsigned SrcElemsPerTgtElem = TgtElemBitWidth / SrcElemBitWidth;
assert(SrcElemsPerTgtElem);
BegIdx /= SrcElemsPerTgtElem;
bool BCAlreadyExists = NewBCs.find(CastSrcTy) != NewBCs.end();
auto *NewBC =
BCAlreadyExists
? NewBCs[CastSrcTy]
: Builder.CreateBitCast(V, CastSrcTy, SVI.getName() + ".bc");
if (!BCAlreadyExists)
NewBCs[CastSrcTy] = NewBC;
auto *Ext = Builder.CreateExtractElement(
NewBC, ConstantInt::get(Int32Ty, BegIdx), SVI.getName() + ".extract");
// The shufflevector isn't being replaced: the bitcast that used it
// is. InstCombine will visit the newly-created instructions.
replaceInstUsesWith(*BC, Ext);
MadeChange = true;
}
}
// If the LHS is a shufflevector itself, see if we can combine it with this
// one without producing an unusual shuffle.
// Cases that might be simplified:
// 1.
// x1=shuffle(v1,v2,mask1)
// x=shuffle(x1,undef,mask)
// ==>
// x=shuffle(v1,undef,newMask)
// newMask[i] = (mask[i] < x1.size()) ? mask1[mask[i]] : -1
// 2.
// x1=shuffle(v1,undef,mask1)
// x=shuffle(x1,x2,mask)
// where v1.size() == mask1.size()
// ==>
// x=shuffle(v1,x2,newMask)
// newMask[i] = (mask[i] < x1.size()) ? mask1[mask[i]] : mask[i]
// 3.
// x2=shuffle(v2,undef,mask2)
// x=shuffle(x1,x2,mask)
// where v2.size() == mask2.size()
// ==>
// x=shuffle(x1,v2,newMask)
// newMask[i] = (mask[i] < x1.size())
// ? mask[i] : mask2[mask[i]-x1.size()]+x1.size()
// 4.
// x1=shuffle(v1,undef,mask1)
// x2=shuffle(v2,undef,mask2)
// x=shuffle(x1,x2,mask)
// where v1.size() == v2.size()
// ==>
// x=shuffle(v1,v2,newMask)
// newMask[i] = (mask[i] < x1.size())
// ? mask1[mask[i]] : mask2[mask[i]-x1.size()]+v1.size()
//
// Here we are really conservative:
// we are absolutely afraid of producing a shuffle mask not in the input
// program, because the code gen may not be smart enough to turn a merged
// shuffle into two specific shuffles: it may produce worse code. As such,
// we only merge two shuffles if the result is either a splat or one of the
// input shuffle masks. In this case, merging the shuffles just removes
// one instruction, which we know is safe. This is good for things like
// turning: (splat(splat)) -> splat, or
// merge(V[0..n], V[n+1..2n]) -> V[0..2n]
ShuffleVectorInst* LHSShuffle = dyn_cast<ShuffleVectorInst>(LHS);
ShuffleVectorInst* RHSShuffle = dyn_cast<ShuffleVectorInst>(RHS);
if (LHSShuffle)
if (!isa<UndefValue>(LHSShuffle->getOperand(1)) && !isa<UndefValue>(RHS))
LHSShuffle = nullptr;
if (RHSShuffle)
if (!isa<UndefValue>(RHSShuffle->getOperand(1)))
RHSShuffle = nullptr;
if (!LHSShuffle && !RHSShuffle)
return MadeChange ? &SVI : nullptr;
Value* LHSOp0 = nullptr;
Value* LHSOp1 = nullptr;
Value* RHSOp0 = nullptr;
unsigned LHSOp0Width = 0;
unsigned RHSOp0Width = 0;
if (LHSShuffle) {
LHSOp0 = LHSShuffle->getOperand(0);
LHSOp1 = LHSShuffle->getOperand(1);
LHSOp0Width = LHSOp0->getType()->getVectorNumElements();
}
if (RHSShuffle) {
RHSOp0 = RHSShuffle->getOperand(0);
RHSOp0Width = RHSOp0->getType()->getVectorNumElements();
}
Value* newLHS = LHS;
Value* newRHS = RHS;
if (LHSShuffle) {
// case 1
if (isa<UndefValue>(RHS)) {
newLHS = LHSOp0;
newRHS = LHSOp1;
}
// case 2 or 4
else if (LHSOp0Width == LHSWidth) {
newLHS = LHSOp0;
}
}
// case 3 or 4
if (RHSShuffle && RHSOp0Width == LHSWidth) {
newRHS = RHSOp0;
}
// case 4
if (LHSOp0 == RHSOp0) {
newLHS = LHSOp0;
newRHS = nullptr;
}
if (newLHS == LHS && newRHS == RHS)
return MadeChange ? &SVI : nullptr;
SmallVector<int, 16> LHSMask;
SmallVector<int, 16> RHSMask;
if (newLHS != LHS)
LHSMask = LHSShuffle->getShuffleMask();
if (RHSShuffle && newRHS != RHS)
RHSMask = RHSShuffle->getShuffleMask();
unsigned newLHSWidth = (newLHS != LHS) ? LHSOp0Width : LHSWidth;
SmallVector<int, 16> newMask;
bool isSplat = true;
int SplatElt = -1;
// Create a new mask for the new ShuffleVectorInst so that the new
// ShuffleVectorInst is equivalent to the original one.
for (unsigned i = 0; i < VWidth; ++i) {
int eltMask;
if (Mask[i] < 0) {
// This element is an undef value.
eltMask = -1;
} else if (Mask[i] < (int)LHSWidth) {
// This element is from left hand side vector operand.
//
// If LHS is going to be replaced (case 1, 2, or 4), calculate the
// new mask value for the element.
if (newLHS != LHS) {
eltMask = LHSMask[Mask[i]];
// If the value selected is an undef value, explicitly specify it
// with a -1 mask value.
if (eltMask >= (int)LHSOp0Width && isa<UndefValue>(LHSOp1))
eltMask = -1;
} else
eltMask = Mask[i];
} else {
// This element is from right hand side vector operand
//
// If the value selected is an undef value, explicitly specify it
// with a -1 mask value. (case 1)
if (isa<UndefValue>(RHS))
eltMask = -1;
// If RHS is going to be replaced (case 3 or 4), calculate the
// new mask value for the element.
else if (newRHS != RHS) {
eltMask = RHSMask[Mask[i]-LHSWidth];
// If the value selected is an undef value, explicitly specify it
// with a -1 mask value.
if (eltMask >= (int)RHSOp0Width) {
assert(isa<UndefValue>(RHSShuffle->getOperand(1))
&& "should have been check above");
eltMask = -1;
}
} else
eltMask = Mask[i]-LHSWidth;
// If LHS's width is changed, shift the mask value accordingly.
// If newRHS == nullptr, i.e. LHSOp0 == RHSOp0, we want to remap any
// references from RHSOp0 to LHSOp0, so we don't need to shift the mask.
// If newRHS == newLHS, we want to remap any references from newRHS to
// newLHS so that we can properly identify splats that may occur due to
// obfuscation across the two vectors.
if (eltMask >= 0 && newRHS != nullptr && newLHS != newRHS)
eltMask += newLHSWidth;
}
// Check if this could still be a splat.
if (eltMask >= 0) {
if (SplatElt >= 0 && SplatElt != eltMask)
isSplat = false;
SplatElt = eltMask;
}
newMask.push_back(eltMask);
}
// If the result mask is equal to one of the original shuffle masks,
// or is a splat, do the replacement.
if (isSplat || newMask == LHSMask || newMask == RHSMask || newMask == Mask) {
SmallVector<Constant*, 16> Elts;
for (unsigned i = 0, e = newMask.size(); i != e; ++i) {
if (newMask[i] < 0) {
Elts.push_back(UndefValue::get(Int32Ty));
} else {
Elts.push_back(ConstantInt::get(Int32Ty, newMask[i]));
}
}
if (!newRHS)
newRHS = UndefValue::get(newLHS->getType());
return new ShuffleVectorInst(newLHS, newRHS, ConstantVector::get(Elts));
}
// If the result mask is an identity, replace uses of this instruction with
// corresponding argument.
bool isLHSID, isRHSID;
recognizeIdentityMask(newMask, isLHSID, isRHSID);
if (isLHSID && VWidth == LHSOp0Width) return replaceInstUsesWith(SVI, newLHS);
if (isRHSID && VWidth == RHSOp0Width) return replaceInstUsesWith(SVI, newRHS);
return MadeChange ? &SVI : nullptr;
}
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