// This function is *almost* as-is from instcombine, avoiding silly
// cases that should already have been optimized.
bool BackendCanonicalize::visitInsertElementInst(InsertElementInst &IE) {
Value *ScalarOp = IE.getOperand(1);
Value *IdxOp = IE.getOperand(2);
// If the inserted element was extracted from some other vector, and if the
// indexes are constant, try to turn this into a shufflevector operation.
if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp)) {
unsigned NumInsertVectorElts = IE.getType()->getNumElements();
unsigned NumExtractVectorElts =
EI->getOperand(0)->getType()->getVectorNumElements();
unsigned ExtractedIdx =
cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
if (ExtractedIdx >= NumExtractVectorElts) // Out of range extract.
return false;
if (InsertedIdx >= NumInsertVectorElts) // Out of range insert.
return false;
// If this insertelement isn't used by some other insertelement, turn it
// (and any insertelements it points to), into one big shuffle.
if (!IE.hasOneUse() || !isa<InsertElementInst>(IE.user_back())) {
typedef SmallVector<Constant *, 16> MaskT;
MaskT Mask;
Value *LHS, *RHS;
std::tie(LHS, RHS) = CollectShuffleElements(&IE, Mask, nullptr);
if (!RHS)
RHS = UndefValue::get(LHS->getType());
// We now have a shuffle of LHS, RHS, Mask.
if (isa<UndefValue>(LHS) && !isa<UndefValue>(RHS)) {
// Canonicalize shufflevector to always have undef on the RHS,
// and adjust the mask.
std::swap(LHS, RHS);
for (MaskT::iterator I = Mask.begin(), E = Mask.end(); I != E; ++I) {
unsigned Idx = cast<ConstantInt>(*I)->getZExtValue();
unsigned NewIdx = Idx >= NumInsertVectorElts
? Idx - NumInsertVectorElts
: Idx + NumInsertVectorElts;
*I = ConstantInt::get(Type::getInt32Ty(RHS->getContext()), NewIdx);
}
}
IRBuilder<> IRB(&IE);
IE.replaceAllUsesWith(
IRB.CreateShuffleVector(LHS, RHS, ConstantVector::get(Mask)));
// The chain of now-dead insertelement / extractelement
// instructions can be deleted.
Kill.push_back(&IE);
return true;
}
}
}
return false;
}
