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//===- InstCombineVectorOps.cpp -------------------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 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/SmallBitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.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 "llvm/Transforms/InstCombine/InstCombiner.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
"Number of aggregate reconstructions turned into reuse of the "
"original aggregate");
/// 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_InsertElt(m_Value(), m_Value(), m_ConstantInt())))
return IsConstantExtractIndex;
if (match(V, m_OneUse(m_Load(m_Value()))))
return true;
if (match(V, m_OneUse(m_UnOp())))
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 *InstCombinerImpl::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())
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"),
Value *newPHIUser = InsertNewInstWith(
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]
auto *SrcTy = cast<VectorType>(X->getType());
Type *DestTy = Ext.getType();
ElementCount NumSrcElts = SrcTy->getElementCount();
ElementCount NumElts =
if (NumSrcElts == NumElts)
if (Value *Elt = findScalarElement(X, ExtIndexC))
return new BitCastInst(Elt, DestTy);
assert(NumSrcElts.isScalable() == NumElts.isScalable() &&
"Src and Dst must be the same sort of vector type");
// 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.getKnownMinValue() < NumElts.getKnownMinValue()) {
Value *Scalar;
uint64_t InsIndexC;
if (!match(X, m_InsertElt(m_Value(), m_Value(Scalar),
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.getKnownMinValue() / NumSrcElts.getKnownMinValue();
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;
/// Find elements of V demanded by UserInstr.
static APInt findDemandedEltsBySingleUser(Value *V, Instruction *UserInstr) {
unsigned VWidth = cast<FixedVectorType>(V->getType())->getNumElements();
// Conservatively assume that all elements are needed.
APInt UsedElts(APInt::getAllOnesValue(VWidth));
switch (UserInstr->getOpcode()) {
case Instruction::ExtractElement: {
ExtractElementInst *EEI = cast<ExtractElementInst>(UserInstr);
assert(EEI->getVectorOperand() == V);
ConstantInt *EEIIndexC = dyn_cast<ConstantInt>(EEI->getIndexOperand());
if (EEIIndexC && EEIIndexC->getValue().ult(VWidth)) {
UsedElts = APInt::getOneBitSet(VWidth, EEIIndexC->getZExtValue());
case Instruction::ShuffleVector: {
ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(UserInstr);
unsigned MaskNumElts =
UsedElts = APInt(VWidth, 0);
for (unsigned i = 0; i < MaskNumElts; i++) {
unsigned MaskVal = Shuffle->getMaskValue(i);
if (MaskVal == -1u || MaskVal >= 2 * VWidth)
if (Shuffle->getOperand(0) == V && (MaskVal < VWidth))
if (Shuffle->getOperand(1) == V &&
((MaskVal >= VWidth) && (MaskVal < 2 * VWidth)))
UsedElts.setBit(MaskVal - VWidth);
return UsedElts;
/// Find union of elements of V demanded by all its users.
/// If it is known by querying findDemandedEltsBySingleUser that
/// no user demands an element of V, then the corresponding bit
/// remains unset in the returned value.
static APInt findDemandedEltsByAllUsers(Value *V) {
unsigned VWidth = cast<FixedVectorType>(V->getType())->getNumElements();
APInt UnionUsedElts(VWidth, 0);
for (const Use &U : V->uses()) {
if (Instruction *I = dyn_cast<Instruction>(U.getUser())) {
UnionUsedElts |= findDemandedEltsBySingleUser(V, I);
} else {
UnionUsedElts = APInt::getAllOnesValue(VWidth);
if (UnionUsedElts.isAllOnesValue())
return UnionUsedElts;
Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
Value *SrcVec = EI.getVectorOperand();
Value *Index = EI.getIndexOperand();
if (Value *V = SimplifyExtractElementInst(SrcVec, Index,
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) {
ElementCount EC = EI.getVectorOperandType()->getElementCount();
unsigned NumElts = EC.getKnownMinValue();
// InstSimplify should handle cases where the index is invalid.
// For fixed-length vector, it's invalid to extract out-of-range element.
if (!EC.isScalable() && IndexC->getValue().uge(NumElts))
return nullptr;
// This instruction only demands the single element from the input vector.
// Skip for scalable type, the number of elements is unknown at
// compile-time.
if (!EC.isScalable() && NumElts != 1) {
// If the input vector has a single use, simplify it based on this use
// property.
if (SrcVec->hasOneUse()) {
APInt UndefElts(NumElts, 0);
APInt DemandedElts(NumElts, 0);
if (Value *V =
SimplifyDemandedVectorElts(SrcVec, DemandedElts, UndefElts))
return replaceOperand(EI, 0, V);
} else {
// If the input vector has multiple uses, simplify it based on a union
// of all elements used.
APInt DemandedElts = findDemandedEltsByAllUsers(SrcVec);
if (!DemandedElts.isAllOnesValue()) {
APInt UndefElts(NumElts, 0);
if (Value *V = SimplifyDemandedVectorElts(
SrcVec, DemandedElts, UndefElts, 0 /* Depth */,
true /* AllowMultipleUsers */)) {
if (V != SrcVec) {
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;
// TODO come up with a n-ary matcher that subsumes both unary and
// binary matchers.
UnaryOperator *UO;
if (match(SrcVec, m_UnOp(UO)) && cheapToScalarize(SrcVec, IndexC)) {
// extelt (unop X), Index --> unop (extelt X, Index)
Value *X = UO->getOperand(0);
Value *E = Builder.CreateExtractElement(X, Index);
return UnaryOperator::CreateWithCopiedFlags(UO->getOpcode(), E, UO);
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)
return replaceOperand(EI, 0, IE->getOperand(0));
} 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.
// Restrict the following transformation to fixed-length vector.
if (isa<FixedVectorType>(SVI->getType()) && isa<ConstantInt>(Index)) {
int SrcIdx =
Value *Src;
unsigned LHSWidth = cast<FixedVectorType>(SVI->getOperand(0)->getType())
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);
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<int> &Mask) {
assert(LHS->getType() == RHS->getType() &&
"Invalid CollectSingleShuffleElements");
unsigned NumElts = cast<FixedVectorType>(V->getType())->getNumElements();
if (isa<UndefValue>(V)) {
Mask.assign(NumElts, -1);
return true;
if (V == LHS) {
for (unsigned i = 0; i != NumElts; ++i)
return true;
if (V == RHS) {
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(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] = -1;
return true;
} else if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)){
if (isa<ConstantInt>(EI->getOperand(1))) {
unsigned ExtractedIdx =
unsigned NumLHSElts =
// 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] = ExtractedIdx;
} else {
assert(EI->getOperand(0) == RHS);
Mask[InsertedIdx % NumElts] = 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,
InstCombinerImpl &IC) {
auto *InsVecType = cast<FixedVectorType>(InsElt->getType());
auto *ExtVecType = cast<FixedVectorType>(ExtElt->getVectorOperandType());
unsigned NumInsElts = InsVecType->getNumElements();
unsigned NumExtElts = ExtVecType->getNumElements();
// The inserted-to vector must be wider than the extracted-from vector.
if (InsVecType->getElementType() != ExtVecType->getElementType() ||
NumExtElts >= NumInsElts)
// 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<int, 16> ExtendMask;
for (unsigned i = 0; i < NumExtElts; ++i)
for (unsigned i = NumExtElts; i < NumInsElts; ++i)
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())
// 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()))
auto *WideVec =
new ShuffleVectorInst(ExtVecOp, UndefValue::get(ExtVecType), 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))
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())
auto *NewExt = ExtractElementInst::Create(WideVec, OldExt->getOperand(1));
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<int> &Mask,
Value *PermittedRHS,
InstCombinerImpl &IC) {
assert(V->getType()->isVectorTy() && "Invalid shuffle!");
unsigned NumElts = cast<FixedVectorType>(V->getType())->getNumElements();
if (isa<UndefValue>(V)) {
Mask.assign(NumElts, -1);
return std::make_pair(
PermittedRHS ? UndefValue::get(PermittedRHS->getType()) : V, nullptr);
if (isa<ConstantAggregateZero>(V)) {
Mask.assign(NumElts, 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 =
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] = i;
return std::make_pair(V, nullptr);
unsigned NumLHSElts =
Mask[InsertedIdx % NumElts] = 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 =
for (unsigned i = 0; i != NumElts; ++i)
Mask.push_back(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,
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)
return std::make_pair(V, nullptr);
/// Look for chain of insertvalue's that fully define an aggregate, and trace
/// back the values inserted, see if they are all were extractvalue'd from
/// the same source aggregate from the exact same element indexes.
/// If they were, just reuse the source aggregate.
/// This potentially deals with PHI indirections.
Instruction *InstCombinerImpl::foldAggregateConstructionIntoAggregateReuse(
InsertValueInst &OrigIVI) {
Type *AggTy = OrigIVI.getType();
unsigned NumAggElts;
switch (AggTy->getTypeID()) {
case Type::StructTyID:
NumAggElts = AggTy->getStructNumElements();
case Type::ArrayTyID:
NumAggElts = AggTy->getArrayNumElements();
llvm_unreachable("Unhandled aggregate type?");
// Arbitrary aggregate size cut-off. Motivation for limit of 2 is to be able
// to handle clang C++ exception struct (which is hardcoded as {i8*, i32}),
// FIXME: any interesting patterns to be caught with larger limit?
assert(NumAggElts > 0 && "Aggregate should have elements.");
if (NumAggElts > 2)
return nullptr;
static constexpr auto NotFound = None;
static constexpr auto FoundMismatch = nullptr;
// Try to find a value of each element of an aggregate.
// FIXME: deal with more complex, not one-dimensional, aggregate types
SmallVector<Optional<Value *>, 2> AggElts(NumAggElts, NotFound);
// Do we know values for each element of the aggregate?
auto KnowAllElts = [&AggElts]() {
return all_of(AggElts,
[](Optional<Value *> Elt) { return Elt != NotFound; });
int Depth = 0;
// Arbitrary `insertvalue` visitation depth limit. Let's be okay with
// every element being overwritten twice, which should never happen.
static const int DepthLimit = 2 * NumAggElts;
// Recurse up the chain of `insertvalue` aggregate operands until either we've
// reconstructed full initializer or can't visit any more `insertvalue`'s.
for (InsertValueInst *CurrIVI = &OrigIVI;
Depth < DepthLimit && CurrIVI && !KnowAllElts();
CurrIVI = dyn_cast<InsertValueInst>(CurrIVI->getAggregateOperand()),
++Depth) {
Value *InsertedValue = CurrIVI->getInsertedValueOperand();
ArrayRef<unsigned int> Indices = CurrIVI->getIndices();
// Don't bother with more than single-level aggregates.
if (Indices.size() != 1)
return nullptr; // FIXME: deal with more complex aggregates?
// Now, we may have already previously recorded the value for this element
// of an aggregate. If we did, that means the CurrIVI will later be
// overwritten with the already-recorded value. But if not, let's record it!
Optional<Value *> &Elt = AggElts[Indices.front()];
Elt = Elt.getValueOr(InsertedValue);
// FIXME: should we handle chain-terminating undef base operand?
// Was that sufficient to deduce the full initializer for the aggregate?
if (!KnowAllElts())
return nullptr; // Give up then.
// We now want to find the source[s] of the aggregate elements we've found.
// And with "source" we mean the original aggregate[s] from which
// the inserted elements were extracted. This may require PHI translation.
enum class AggregateDescription {
/// When analyzing the value that was inserted into an aggregate, we did
/// not manage to find defining `extractvalue` instruction to analyze.
/// When analyzing the value that was inserted into an aggregate, we did
/// manage to find defining `extractvalue` instruction[s], and everything
/// matched perfectly - aggregate type, element insertion/extraction index.
/// When analyzing the value that was inserted into an aggregate, we did
/// manage to find defining `extractvalue` instruction, but there was
/// a mismatch: either the source type from which the extraction was didn't
/// match the aggregate type into which the insertion was,
/// or the extraction/insertion channels mismatched,
/// or different elements had different source aggregates.
auto Describe = [](Optional<Value *> SourceAggregate) {
if (SourceAggregate == NotFound)
return AggregateDescription::NotFound;
if (*SourceAggregate == FoundMismatch)
return AggregateDescription::FoundMismatch;
return AggregateDescription::Found;
// Given the value \p Elt that was being inserted into element \p EltIdx of an
// aggregate AggTy, see if \p Elt was originally defined by an
// appropriate extractvalue (same element index, same aggregate type).
// If found, return the source aggregate from which the extraction was.
// If \p PredBB is provided, does PHI translation of an \p Elt first.
auto FindSourceAggregate =
[&](Value *Elt, unsigned EltIdx, Optional<BasicBlock *> UseBB,
Optional<BasicBlock *> PredBB) -> Optional<Value *> {
// For now(?), only deal with, at most, a single level of PHI indirection.
if (UseBB && PredBB)
Elt = Elt->DoPHITranslation(*UseBB, *PredBB);
// FIXME: deal with multiple levels of PHI indirection?
// Did we find an extraction?
auto *EVI = dyn_cast<ExtractValueInst>(Elt);
if (!EVI)
return NotFound;
Value *SourceAggregate = EVI->getAggregateOperand();
// Is the extraction from the same type into which the insertion was?
if (SourceAggregate->getType() != AggTy)
return FoundMismatch;
// And the element index doesn't change between extraction and insertion?
if (EVI->getNumIndices() != 1 || EltIdx != EVI->getIndices().front())
return FoundMismatch;
return SourceAggregate; // AggregateDescription::Found
// Given elements AggElts that were constructing an aggregate OrigIVI,
// see if we can find appropriate source aggregate for each of the elements,
// and see it's the same aggregate for each element. If so, return it.
auto FindCommonSourceAggregate =
[&](Optional<BasicBlock *> UseBB,
Optional<BasicBlock *> PredBB) -> Optional<Value *> {
Optional<Value *> SourceAggregate;
for (auto I : enumerate(AggElts)) {
assert(Describe(SourceAggregate) != AggregateDescription::FoundMismatch &&
"We don't store nullptr in SourceAggregate!");
assert((Describe(SourceAggregate) == AggregateDescription::Found) ==
(I.index() != 0) &&
"SourceAggregate should be valid after the the first element,");
// For this element, is there a plausible source aggregate?
// FIXME: we could special-case undef element, IFF we know that in the
// source aggregate said element isn't poison.
Optional<Value *> SourceAggregateForElement =
FindSourceAggregate(*I.value(), I.index(), UseBB, PredBB);
// Okay, what have we found? Does that correlate with previous findings?
// Regardless of whether or not we have previously found source
// aggregate for previous elements (if any), if we didn't find one for
// this element, passthrough whatever we have just found.
if (Describe(SourceAggregateForElement) != AggregateDescription::Found)
return SourceAggregateForElement;
// Okay, we have found source aggregate for this element.
// Let's see what we already know from previous elements, if any.
switch (Describe(SourceAggregate)) {
case AggregateDescription::NotFound:
// This is apparently the first element that we have examined.
SourceAggregate = SourceAggregateForElement; // Record the aggregate!
continue; // Great, now look at next element.
case AggregateDescription::Found:
// We have previously already successfully examined other elements.
// Is this the same source aggregate we've found for other elements?
if (*SourceAggregateForElement != *SourceAggregate)
return FoundMismatch;
continue; // Still the same aggregate, look at next element.
case AggregateDescription::FoundMismatch:
llvm_unreachable("Can't happen. We would have early-exited then.");
assert(Describe(SourceAggregate) == AggregateDescription::Found &&
"Must be a valid Value");
return *SourceAggregate;
Optional<Value *> SourceAggregate;
// Can we find the source aggregate without looking at predecessors?
SourceAggregate = FindCommonSourceAggregate(/*UseBB=*/None, /*PredBB=*/None);
if (Describe(SourceAggregate) != AggregateDescription::NotFound) {
if (Describe(SourceAggregate) == AggregateDescription::FoundMismatch)
return nullptr; // Conflicting source aggregates!
return replaceInstUsesWith(OrigIVI, *SourceAggregate);
// Okay, apparently we need to look at predecessors.
// We should be smart about picking the "use" basic block, which will be the
// merge point for aggregate, where we'll insert the final PHI that will be
// used instead of OrigIVI. Basic block of OrigIVI is *not* the right choice.
// We should look in which blocks each of the AggElts is being defined,
// they all should be defined in the same basic block.
BasicBlock *UseBB = nullptr;
for (const Optional<Value *> &Elt : AggElts) {
// If this element's value was not defined by an instruction, ignore it.
auto *I = dyn_cast<Instruction>(*Elt);
if (!I)
// Otherwise, in which basic block is this instruction located?
BasicBlock *BB = I->getParent();
// If it's the first instruction we've encountered, record the basic block.
if (!UseBB) {
UseBB = BB;
// Otherwise, this must be the same basic block we've seen previously.
if (UseBB != BB)
return nullptr;
// If *all* of the elements are basic-block-independent, meaning they are
// either function arguments, or constant expressions, then if we didn't
// handle them without predecessor-aware handling, we won't handle them now.
if (!UseBB)
return nullptr;
// If we didn't manage to find source aggregate without looking at
// predecessors, and there are no predecessors to look at, then we're done.
if (pred_empty(UseBB))
return nullptr;
// Arbitrary predecessor count limit.
static const int PredCountLimit = 64;
// Cache the (non-uniqified!) list of predecessors in a vector,
// checking the limit at the same time for efficiency.
SmallVector<BasicBlock *, 4> Preds; // May have duplicates!
for (BasicBlock *Pred : predecessors(UseBB)) {
// Don't bother if there are too many predecessors.
if (Preds.size() >= PredCountLimit) // FIXME: only count duplicates once?
return nullptr;
// For each predecessor, what is the source aggregate,
// from which all the elements were originally extracted from?
// Note that we want for the map to have stable iteration order!
SmallDenseMap<BasicBlock *, Value *, 4> SourceAggregates;
for (BasicBlock *Pred : Preds) {
std::pair<decltype(SourceAggregates)::iterator, bool> IV =
SourceAggregates.insert({Pred, nullptr});
// Did we already evaluate this predecessor?
if (!IV.second)
// Let's hope that when coming from predecessor Pred, all elements of the
// aggregate produced by OrigIVI must have been originally extracted from
// the same aggregate. Is that so? Can we find said original aggregate?
SourceAggregate = FindCommonSourceAggregate(UseBB, Pred);
if (Describe(SourceAggregate) != AggregateDescription::Found)
return nullptr; // Give up.
IV.first->second = *SourceAggregate;
// All good! Now we just need to thread the source aggregates here.
// Note that we have to insert the new PHI here, ourselves, because we can't
// rely on InstCombinerImpl::run() inserting it into the right basic block.
// Note that the same block can be a predecessor more than once,
// and we need to preserve that invariant for the PHI node.
BuilderTy::InsertPointGuard Guard(Builder);
auto *PHI =
Builder.CreatePHI(AggTy, Preds.size(), OrigIVI.getName() + ".merged");
for (BasicBlock *Pred : Preds)
PHI->addIncoming(SourceAggregates[Pred], Pred);
return replaceInstUsesWith(OrigIVI, PHI);
/// 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 *InstCombinerImpl::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)
if (UserInsInst->getIndices() == FirstIndices) {
IsRedundant = true;
V = UserInsInst;
if (IsRedundant)
return replaceInstUsesWith(I, I.getOperand(0));
if (Instruction *NewI = foldAggregateConstructionIntoAggregateReuse(I))
return NewI;
return nullptr;
static bool isShuffleEquivalentToSelect(ShuffleVectorInst &Shuf) {
// Can not analyze scalable type, the number of elements is not a compile-time
// constant.
if (isa<ScalableVectorType>(Shuf.getOperand(0)->getType()))
return false;
int MaskSize = Shuf.getShuffleMask().size();
int VecSize =
// 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 an insert + shuffle:
/// insertelt(insertelt(insertelt(insertelt X, %k, 0), %k, 1), %k, 2) ... ->
/// shufflevector(insertelt(X, %k, 0), undef, zero)
static Instruction *foldInsSequenceIntoSplat(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 *VecTy = InsElt.getType();
// Can not handle scalable type, the number of elements is not a compile-time
// constant.
if (isa<ScalableVectorType>(VecTy))
return nullptr;
unsigned NumElements = cast<FixedVectorType>(VecTy)->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;
SmallBitVector 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;
// If this is just a single insertelement (not a sequence), we are done.
if (FirstIE == &InsElt)
return nullptr;
// If we are not inserting into an undef vector, make sure we've seen an
// insert into every element.
// TODO: If the base vector is not undef, it might be better to create a splat
// and then a select-shuffle (blend) with the base vector.
if (!isa<UndefValue>(FirstIE->getOperand(0)))
if (!ElementPresent.all())
return nullptr;
// Create the insert + shuffle.
Type *Int32Ty = Type::getInt32Ty(InsElt.getContext());
UndefValue *UndefVec = UndefValue::get(VecTy);
Constant *Zero = ConstantInt::get(Int32Ty, 0);
if (!cast<ConstantInt>(FirstIE->getOperand(2))->isZero())
FirstIE = InsertElementInst::Create(UndefVec, SplatVal, Zero, "", &InsElt);
// Splat from element 0, but replace absent elements with undef in the mask.
SmallVector<int, 16> Mask(NumElements, 0);
for (unsigned i = 0; i != NumElements; ++i)
if (!ElementPresent[i])
Mask[i] = -1;
return new ShuffleVectorInst(FirstIE, UndefVec, Mask);
/// Try to fold an insert element into an existing splat shuffle by changing
/// the shuffle's mask to include the index of this insert element.
static Instruction *foldInsEltIntoSplat(InsertElementInst &InsElt) {
// Check if the vector operand of this insert is a canonical splat shuffle.
auto *Shuf = dyn_cast<ShuffleVectorInst>(InsElt.getOperand(0));
if (!Shuf || !Shuf->isZeroEltSplat())
return nullptr;
// Bail out early if shuffle is scalable type. The number of elements in
// shuffle mask is unknown at compile-time.
if (isa<ScalableVectorType>(Shuf->getType()))
return nullptr;
// Check for a constant insertion index.
uint64_t IdxC;
if (!match(InsElt.getOperand(2), m_ConstantInt(IdxC)))
return nullptr;
// Check if the splat shuffle's input is the same as this insert's scalar op.
Value *X = InsElt.getOperand(1);
Value *Op0 = Shuf->getOperand(0);
if (!match(Op0, m_InsertElt(m_Undef(), m_Specific(X), m_ZeroInt())))
return nullptr;
// Replace the shuffle mask element at the index of this insert with a zero.
// For example:
// inselt (shuf (inselt undef, X, 0), undef, <0,undef,0,undef>), X, 1
// --> shuf (inselt undef, X, 0), undef, <0,0,0,undef>
unsigned NumMaskElts =
SmallVector<int, 16> NewMask(NumMaskElts);
for (unsigned i = 0; i != NumMaskElts; ++i)
NewMask[i] = i == IdxC ? 0 : Shuf->getMaskValue(i);
return new ShuffleVectorInst(Op0, UndefValue::get(Op0->getType()), NewMask);
/// Try to fold an extract+insert element into an existing identity shuffle by
/// changing the shuffle's mask to include the index of this insert element.
static Instruction *foldInsEltIntoIdentityShuffle(InsertElementInst &InsElt) {
// Check if the vector operand of this insert is an identity shuffle.
auto *Shuf = dyn_cast<ShuffleVectorInst>(InsElt.getOperand(0));
if (!Shuf || !isa<UndefValue>(Shuf->getOperand(1)) ||
!(Shuf->isIdentityWithExtract() || Shuf->isIdentityWithPadding()))
return nullptr;
// Bail out early if shuffle is scalable type. The number of elements in
// shuffle mask is unknown at compile-time.
if (isa<ScalableVectorType>(Shuf->getType()))
return nullptr;
// Check for a constant insertion index.
uint64_t IdxC;
if (!match(InsElt.getOperand(2), m_ConstantInt(IdxC)))
return nullptr;
// Check if this insert's scalar op is extracted from the identity shuffle's
// input vector.
Value *Scalar = InsElt.getOperand(1);
Value *X = Shuf->getOperand(0);
if (!match(Scalar, m_ExtractElt(m_Specific(X), m_SpecificInt(IdxC))))
return nullptr;
// Replace the shuffle mask element at the index of this extract+insert with
// that same index value.
// For example:
// inselt (shuf X, IdMask), (extelt X, IdxC), IdxC --> shuf X, IdMask'
unsigned NumMaskElts =
SmallVector<int, 16> NewMask(NumMaskElts);
ArrayRef<int> OldMask = Shuf->getShuffleMask();
for (unsigned i = 0; i != NumMaskElts; ++i) {
if (i != IdxC) {
// All mask elements besides the inserted element remain the same.
NewMask[i] = OldMask[i];
} else if (OldMask[i] == (int)IdxC) {
// If the mask element was already set, there's nothing to do
// (demanded elements analysis may unset it later).
return nullptr;
} else {
assert(OldMask[i] == UndefMaskElem &&
"Unexpected shuffle mask element for identity shuffle");
NewMask[i] = IdxC;
return new ShuffleVectorInst(X, Shuf->getOperand(1), NewMask);
/// 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).
ArrayRef<int> Mask = Shuf->getShuffleMask();
unsigned NumElts = Mask.size();
SmallVector<Constant *, 16> NewShufElts(NumElts);
SmallVector<int, 16> NewMaskElts(NumElts);
for (unsigned I = 0; I != NumElts; ++I) {
if (I == InsEltIndex) {
NewShufElts[I] = InsEltScalar;
NewMaskElts[I] = InsEltIndex + NumElts;
} else {
// Copy over the existing values.
NewShufElts[I] = ShufConstVec->getAggregateElement(I);
NewMaskElts[I] = Mask[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), NewMaskElts);
} else if (auto *IEI = dyn_cast<InsertElementInst>(Inst)) {
// Transform sequences of insertelements ops with constant data/indexes into
// a single shuffle op.
// Can not handle scalable type, the number of elements needed to create
// shuffle mask is not a compile-time constant.
if (isa<ScalableVectorType>(InsElt.getType()))
return nullptr;
unsigned NumElts =
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<int, 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]) {
Values[I] = *ValI;
Mask[I] = NumElts + I;
// Remaining values are filled with 'undef' values.
for (unsigned I = 0; I < NumElts; ++I) {
if (!Values[I]) {
Values[I] = UndefValue::get(InsElt.getType()->getElementType());
Mask[I] = I;
// Create new operands for a shuffle that includes the constant of the
// original insertelt.
return new ShuffleVectorInst(IEI->getOperand(0),
ConstantVector::get(Values), Mask);
return nullptr;
Instruction *InstCombinerImpl::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);
// If the scalar is bitcast and inserted into undef, do the insert in the
// source type followed by bitcast.
// TODO: Generalize for insert into any constant, not just undef?
Value *ScalarSrc;
if (match(VecOp, m_Undef()) &&
match(ScalarOp, m_OneUse(m_BitCast(m_Value(ScalarSrc)))) &&
(ScalarSrc->getType()->isIntegerTy() ||
ScalarSrc->getType()->isFloatingPointTy())) {
// inselt undef, (bitcast ScalarSrc), IdxOp -->
// bitcast (inselt undef, ScalarSrc, IdxOp)
Type *ScalarTy = ScalarSrc->getType();
Type *VecTy = VectorType::get(ScalarTy, IE.getType()->getElementCount());
UndefValue *NewUndef = UndefValue::get(VecTy);
Value *NewInsElt = Builder.CreateInsertElement(NewUndef, ScalarSrc, IdxOp);
return new BitCastInst(NewInsElt, IE.getType());
// If the vector and scalar are both bitcast from the same element type, do
// the insert in that source type followed by bitcast.
Value *VecSrc;
if (match(VecOp, m_BitCast(m_Value(VecSrc))) &&
match(ScalarOp, m_BitCast(m_Value(ScalarSrc))) &&
(VecOp->hasOneUse() || ScalarOp->hasOneUse()) &&
VecSrc->getType()->isVectorTy() && !ScalarSrc->getType()->isVectorTy() &&
cast<VectorType>(VecSrc->getType())->getElementType() ==
ScalarSrc->getType()) {
// inselt (bitcast VecSrc), (bitcast ScalarSrc), IdxOp -->
// bitcast (inselt VecSrc, ScalarSrc, IdxOp)
Value *NewInsElt = Builder.CreateInsertElement(VecSrc, ScalarSrc, IdxOp);
return new BitCastInst(NewInsElt, IE.getType());
// If the inserted element was extracted from some other fixed-length vector
// and both indexes are valid constants, try to turn this into a shuffle.
// Can not handle scalable vector type, the number of elements needed to
// create shuffle mask is not a compile-time constant.
uint64_t InsertedIdx, ExtractedIdx;
Value *ExtVecOp;
if (isa<FixedVectorType>(IE.getType()) &&
match(IdxOp, m_ConstantInt(InsertedIdx)) &&
m_ExtractElt(m_Value(ExtVecOp), m_ConstantInt(ExtractedIdx))) &&
isa<FixedVectorType>(ExtVecOp->getType()) &&
ExtractedIdx <
cast<FixedVectorType>(ExtVecOp->getType())->getNumElements()) {
// 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<int, 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, Mask);
if (auto VecTy = dyn_cast<FixedVectorType>(VecOp->getType())) {
unsigned VWidth = VecTy->getNumElements();
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;
if (Instruction *Broadcast = foldInsSequenceIntoSplat(IE))
return Broadcast;
if (Instruction *Splat = foldInsEltIntoSplat(IE))
return Splat;
if (Instruction *IdentityShuf = foldInsEltIntoIdentityShuffle(IE))
return IdentityShuf;
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::UDiv:
case Instruction::SDiv:
case Instruction::URem:
case Instruction::SRem:
// Propagating an undefined shuffle mask element to integer div/rem is not
// allowed because those opcodes can create immediate undefined behavior
// from an undefined element in an operand.
if (llvm::is_contained(Mask, -1))
return false;
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::FDiv:
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.
Type *ITy = I->getType();
if (ITy->isVectorTy() &&
Mask.size() > cast<FixedVectorType>(ITy)->getNumElements())
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 =
NewOps[0], NewOps[1], "", BO);
if (isa<OverflowingBinaryOperator>(BO)) {
if (isa<PossiblyExactOperator>(BO)) {
if (isa<FPMathOperator>(BO))
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(
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);
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(FixedVectorType::get(EltTy, Mask.size()));
if (isa<ConstantAggregateZero>(V))
return ConstantAggregateZero::get(FixedVectorType::get(EltTy, Mask.size()));
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getShuffleVector(C, UndefValue::get(C->getType()),
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() !=
for (int i = 0, e = I->getNumOperands(); i != e; ++i) {
Value *V;
// Recursively call evaluateInDifferentElementOrder on vector arguments
// as well. E.g. GetElementPtr may have scalar operands even if the
// return value is a vector, so we need to examine the operand type.
if (I->getOperand(i)->getType()->isVectorTy())
V = evaluateInDifferentElementOrder(I->getOperand(i), Mask);
V = I->getOperand(i);
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;
// 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!");
// Returns true if the shuffle is extracting a contiguous range of values from
// LHS, for example:
// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// Shuffles to: |EE|FF|GG|HH|
// +--+--+--+--+
static bool isShuffleExtractingFromLHS(ShuffleVectorInst &SVI,
ArrayRef<int> Mask) {
unsigned LHSElems =
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 };
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 };
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;
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.
ArrayRef<int> Mask = Shuf.getShuffleMask();
Constant *NewC = Op0IsBinop ? ConstantExpr::getShuffleVector(C, IdC, Mask) :
ConstantExpr::getShuffleVector(IdC, C, Mask);
bool MightCreatePoisonOrUB =
is_contained(Mask, UndefMaskElem) &&
(Instruction::isIntDivRem(BOpcode) || Instruction::isShift(BOpcode));
if (MightCreatePoisonOrUB)
NewC = InstCombiner::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);
// 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 (is_contained(Mask, UndefMaskElem) && !MightCreatePoisonOrUB)
return NewBO;
/// If we have an insert of a scalar to a non-zero element of an undefined
/// vector and then shuffle that value, that's the same as inserting to the zero
/// element and shuffling. Splatting from the zero element is recognized as the
/// canonical form of splat.
static Instruction *canonicalizeInsertSplat(ShuffleVectorInst &Shuf,
InstCombiner::BuilderTy &Builder) {
Value *Op0 = Shuf.getOperand(0), *Op1 = Shuf.getOperand(1);
ArrayRef<int> Mask = Shuf.getShuffleMask();
Value *X;
uint64_t IndexC;
// Match a shuffle that is a splat to a non-zero element.
if (!match(Op0, m_OneUse(m_InsertElt(m_Undef(), m_Value(X),
m_ConstantInt(IndexC)))) ||
!match(Op1, m_Undef()) || match(Mask, m_ZeroMask()) || IndexC == 0)
return nullptr;
// Insert into element 0 of an undef vector.
UndefValue *UndefVec = UndefValue::get(Shuf.getType());
Constant *Zero = Builder.getInt32(0);
Value *NewIns = Builder.CreateInsertElement(UndefVec, X, Zero);
// Splat from element 0. Any mask element that is undefined remains undefined.
// For example:
// shuf (inselt undef, X, 2), undef, <2,2,undef>
// --> shuf (inselt undef, X, 0), undef, <0,0,undef>
unsigned NumMaskElts =
SmallVector<int, 16> NewMask(NumMaskElts, 0);
for (unsigned i = 0; i != NumMaskElts; ++i)
if (Mask[i] == UndefMaskElem)
NewMask[i] = Mask[i];
return new ShuffleVectorInst(NewIns, UndefVec, NewMask);
/// 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;
// Canonicalize to choose from operand 0 first unless operand 1 is undefined.
// Commuting undef to operand 0 conflicts with another canonicalization.
unsigned NumElts = cast<FixedVectorType>(Shuf.getType())->getNumElements();
if (!isa<UndefValue>(Shuf.getOperand(1)) &&
Shuf.getMaskValue(0) >= (int)NumElts) {
// TODO: Can we assert that both operands of a shuffle-select are not undef
// (otherwise, it would have been folded by instsimplify?
return &Shuf;
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;
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.
ArrayRef<int> Mask = Shuf.getShuffleMask();
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 =
is_contained(Mask, UndefMaskElem) &&
(Instruction::isIntDivRem(BOpc) || Instruction::isShift(BOpc));
if (MightCreatePoisonOrUB)
NewC = InstCombiner::getSafeVectorConstantForBinop(BOpc, NewC,
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.
if (DropNSW)
if (is_contained(Mask, UndefMaskElem) && !MightCreatePoisonOrUB)
return NewBO;
/// Convert a narrowing shuffle of a bitcasted vector into a vector truncate.
/// Example (little endian):
/// shuf (bitcast <4 x i16> X to <8 x i8>), <0, 2, 4, 6> --> trunc X to <4 x i8>
static Instruction *foldTruncShuffle(ShuffleVectorInst &Shuf,
bool IsBigEndian) {
// This must be a bitcasted shuffle of 1 vector integer operand.
Type *DestType = Shuf.getType();
Value *X;
if (!match(Shuf.getOperand(0), m_BitCast(m_Value(X))) ||
!match(Shuf.getOperand(1), m_Undef()) || !DestType->isIntOrIntVectorTy())
return nullptr;
// The source type must have the same number of elements as the shuffle,
// and the source element type must be larger than the shuffle element type.
Type *SrcType = X->getType();
if (!SrcType->isVectorTy() || !SrcType->isIntOrIntVectorTy() ||
cast<FixedVectorType>(SrcType)->getNumElements() !=
cast<FixedVectorType>(DestType)->getNumElements() ||
SrcType->getScalarSizeInBits() % DestType->getScalarSizeInBits() != 0)
return nullptr;
assert(Shuf.changesLength() && !Shuf.increasesLength() &&
"Expected a shuffle that decreases length");
// Last, check that the mask chooses the correct low bits for each narrow
// element in the result.
uint64_t TruncRatio =
SrcType->getScalarSizeInBits() / DestType->getScalarSizeInBits();
ArrayRef<int> Mask = Shuf.getShuffleMask();
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] == UndefMaskElem)
uint64_t LSBIndex = IsBigEndian ? (i + 1) * TruncRatio - 1 : i * TruncRatio;
assert(LSBIndex <= INT32_MAX && "Overflowed 32-bits");
if (Mask[i] != (int)LSBIndex)
return nullptr;
return new TruncInst(X, DestType);
/// 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 =
Value *NarrowCond;
if (!match(Cond, m_OneUse(m_Shuffle(m_Value(NarrowCond), m_Undef()))) ||
cast<FixedVectorType>(NarrowCond->getType())->getNumElements() !=
NarrowNumElts ||
return nullptr;
// shuf (sel (shuf NarrowCond, undef, WideMask), X, Y), undef, NarrowMask) -->
// sel NarrowCond, (shuf X, undef, NarrowMask), (shuf Y, undef, NarrowMask)
Value *NarrowX = Builder.CreateShuffleVector(X, Shuf.getShuffleMask());
Value *NarrowY = Builder.CreateShuffleVector(Y, Shuf.getShuffleMask());
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;
ArrayRef<int> Mask;
if (!match(Op0, m_Shuffle(m_Value(X), m_Value(Y), m_Mask(Mask))))
return nullptr;
// Be conservative with shuffle transforms. If we can't kill the 1st shuffle,
// then combining may result in worse codegen.
if (!Op0->hasOneUse())
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 = cast<FixedVectorType>(Shuf.getType())->getNumElements();
SmallVector<int, 16> NewMask(NumElts);
assert(NumElts < Mask.size() &&
"Identity with extract must have less elements than its inputs");
for (unsigned i = 0; i != NumElts; ++i) {
int ExtractMaskElt = Shuf.getMaskValue(i);
int MaskElt = Mask[i];
NewMask[i] = ExtractMaskElt == UndefMaskElem ? ExtractMaskElt : MaskElt;
return new ShuffleVectorInst(X, Y, NewMask);
/// Try to replace a shuffle with an insertelement or try to replace a shuffle
/// operand with the operand of an insertelement.
static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf,
InstCombinerImpl &IC) {
Value *V0 = Shuf.getOperand(0), *V1 = Shuf.getOperand(1);
SmallVector<int, 16> Mask;
// 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)(cast<FixedVectorType>(V0->getType())->getNumElements()))
return nullptr;
// This is a specialization of a fold in SimplifyDemandedVectorElts. We may
// not be able to handle it there if the insertelement has >1 use.
// If the shuffle has an insertelement operand but does not choose the
// inserted scalar element from that value, then we can replace that shuffle
// operand with the source vector of the insertelement.
Value *X;
uint64_t IdxC;
if (match(V0, m_InsertElt(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
// shuf (inselt X, ?, IdxC), ?, Mask --> shuf X, ?, Mask
if (!is_contained(Mask, (int)IdxC))
return IC.replaceOperand(Shuf, 0, X);
if (match(V1, m_InsertElt(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
// Offset the index constant by the vector width because we are checking for
// accesses to the 2nd vector input of the shuffle.
IdxC += NumElts;
// shuf ?, (inselt X, ?, IdxC), Mask --> shuf ?, X, Mask
if (!is_contained(Mask, (int)IdxC))
return IC.replaceOperand(Shuf, 1, X);
// 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_InsertElt(m_Value(), m_Value(Scalar),
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)
// The shuffle takes elements of operand 1 without lane changes.
if (Mask[i] == NumElts + i)
// 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;
static Instruction *foldIdentityPaddedShuffles(ShuffleVectorInst &Shuf) {
// Match the operands as identity with padding (also known as concatenation
// with undef) shuffles of the same source type. The backend is expected to
// recreate these concatenations from a shuffle of narrow operands.
auto *Shuffle0 = dyn_cast<ShuffleVectorInst>(Shuf.getOperand(0));
auto *Shuffle1 = dyn_cast<ShuffleVectorInst>(Shuf.getOperand(1));
if (!Shuffle0 || !Shuffle0->isIdentityWithPadding() ||
!Shuffle1 || !Shuffle1->isIdentityWithPadding())
return nullptr;
// We limit this transform to power-of-2 types because we expect that the
// backend can convert the simplified IR patterns to identical nodes as the
// original IR.
// TODO: If we can verify the same behavior for arbitrary types, the
// power-of-2 checks can be removed.
Value *X = Shuffle0->getOperand(0);
Value *Y = Shuffle1->getOperand(0);
if (X->getType() != Y->getType() ||
!isPowerOf2_32(cast<FixedVectorType>(Shuf.getType())->getNumElements()) ||
cast<FixedVectorType>(Shuffle0->getType())->getNumElements()) ||
!isPowerOf2_32(cast<FixedVectorType>(X->getType())->getNumElements()) ||
isa<UndefValue>(X) || isa<UndefValue>(Y))
return nullptr;
assert(isa<UndefValue>(Shuffle0->getOperand(1)) &&
isa<UndefValue>(Shuffle1->getOperand(1)) &&
"Unexpected operand for identity shuffle");
// This is a shuffle of 2 widening shuffles. We can shuffle the narrow source
// operands directly by adjusting the shuffle mask to account for the narrower
// types:
// shuf (widen X), (widen Y), Mask --> shuf X, Y, Mask'
int NarrowElts = cast<FixedVectorType>(X->getType())->getNumElements();
int WideElts = cast<FixedVectorType>(Shuffle0->getType())->getNumElements();
assert(WideElts > NarrowElts && "Unexpected types for identity with padding");
ArrayRef<int> Mask = Shuf.getShuffleMask();
SmallVector<int, 16> NewMask(Mask.size(), -1);
for (int i = 0, e = Mask.size(); i != e; ++i) {
if (Mask[i] == -1)
// If this shuffle is choosing an undef element from 1 of the sources, that
// element is undef.
if (Mask[i] < WideElts) {
if (Shuffle0->getMaskValue(Mask[i]) == -1)
} else {
if (Shuffle1->getMaskValue(Mask[i] - WideElts) == -1)
// If this shuffle is choosing from the 1st narrow op, the mask element is
// the same. If this shuffle is choosing from the 2nd narrow op, the mask
// element is offset down to adjust for the narrow vector widths.
if (Mask[i] < WideElts) {
assert(Mask[i] < NarrowElts && "Unexpected shuffle mask");
NewMask[i] = Mask[i];
} else {
assert(Mask[i] < (WideElts + NarrowElts) && "Unexpected shuffle mask");
NewMask[i] = Mask[i] - (WideElts - NarrowElts);
return new ShuffleVectorInst(X, Y, NewMask);
Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
Value *LHS = SVI.getOperand(0);
Value *RHS = SVI.getOperand(1);
SimplifyQuery ShufQuery = SQ.getWithInstruction(&SVI);
if (auto *V = SimplifyShuffleVectorInst(LHS, RHS, SVI.getShuffleMask(),
SVI.getType(), ShufQuery))
return replaceInstUsesWith(SVI, V);
// Bail out for scalable vectors
if (isa<ScalableVectorType>(LHS->getType()))
return nullptr;
unsigned VWidth = cast<FixedVectorType>(SVI.getType())->getNumElements();
unsigned LHSWidth = cast<FixedVectorType>(LHS->getType())->getNumElements();
// shuffle (bitcast X), (bitcast Y), Mask --> bitcast (shuffle X, Y, Mask)
// if X and Y are of the same (vector) type, and the element size is not
// changed by the bitcasts, we can distribute the bitcasts through the
// shuffle, hopefully reducing the number of instructions. We make sure that
// at least one bitcast only has one use, so we don't *increase* the number of
// instructions here.
Value *X, *Y;
if (match(LHS, m_BitCast(m_Value(X))) && match(RHS, m_BitCast(m_Value(Y))) &&
X->getType()->isVectorTy() && X->getType() == Y->getType() &&
X->getType()->getScalarSizeInBits() ==
SVI.getType()->getScalarSizeInBits() &&
(LHS->hasOneUse() || RHS->hasOneUse())) {
Value *V = Builder.CreateShuffleVector(X, Y, SVI.getShuffleMask(),
SVI.getName() + ".uncasted");
return new BitCastInst(V, SVI.getType());
ArrayRef<int> Mask = SVI.getShuffleMask();
Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
// Peek through a bitcasted shuffle operand by scaling the mask. If the
// simulated shuffle can simplify, then this shuffle is unnecessary:
// shuf (bitcast X), undef, Mask --> bitcast X'
// TODO: This could be extended to allow length-changing shuffles.
// The transform might also be obsoleted if we allowed canonicalization
// of bitcasted shuffles.
if (match(LHS, m_BitCast(m_Value(X))) && match(RHS, m_Undef()) &&
X->getType()->isVectorTy() && VWidth == LHSWidth) {
// Try to create a scaled mask constant.
auto *XType = cast<FixedVectorType>(X->getType());
unsigned XNumElts = XType->getNumElements();
SmallVector<int, 16> ScaledMask;
if (XNumElts >= VWidth) {
assert(XNumElts % VWidth == 0 && "Unexpected vector bitcast");
narrowShuffleMaskElts(XNumElts / VWidth, Mask, ScaledMask);
} else {
assert(VWidth % XNumElts == 0 && "Unexpected vector bitcast");
if (!widenShuffleMaskElts(VWidth / XNumElts, Mask, ScaledMask))
if (!ScaledMask.empty()) {
// If the shuffled source vector simplifies, cast that value to this
// shuffle's type.
if (auto *V = SimplifyShuffleVectorInst(X, UndefValue::get(XType),
ScaledMask, XType, ShufQuery))
return BitCastInst::Create(Instruction::BitCast, V, SVI.getType());
// shuffle x, x, mask --> shuffle x, undef, mask'
if (LHS == RHS) {
assert(!isa<UndefValue>(RHS) && "Shuffle with 2 undef ops not simplified?");
// Remap any references to RHS to use LHS.
SmallVector<int, 16> Elts;
for (unsigned i = 0; i != VWidth; ++i) {
// Propagate undef elements or force mask to LHS.
if (Mask[i] < 0)
Elts.push_back(Mask[i] % LHSWidth);
return new ShuffleVectorInst(LHS, UndefValue::get(RHS->getType()), Elts);
// shuffle undef, x, mask --> shuffle x, undef, mask'
if (isa<UndefValue>(LHS)) {
return &SVI;
if (Instruction *I = canonicalizeInsertSplat(SVI, Builder))
return I;
if (Instruction *I = foldSelectShuffle(SVI, Builder, DL))
return I;
if (Instruction *I = foldTruncShuffle(SVI, DL.isBigEndian()))
return I;