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[InstCombine] remove shuffle mask canonicalization that creates undef elements

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This is NFC-intended because SimplifyDemandedVectorElts() does the same
transform later. As discussed in D70641, we may want to change that
behavior, so we need to isolate where it happens.
This commit is contained in:
Sanjay Patel
2019-11-25 13:30:45 -05:00
parent 872a53ef94
commit 35827164c4
1 changed files with 10 additions and 10 deletions
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20
llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
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@@ -1886,24 +1886,18 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
LHS, RHS, SVI.getMask(), SVI.getType(), SQ.getWithInstruction(&SVI)))
return replaceInstUsesWith(SVI, V);
// Canonicalize shuffle(x ,x,mask) -> shuffle(x, undef,mask')
// Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
// shuffle x, x, mask --> shuffle x, undef, mask'
unsigned VWidth = SVI.getType()->getVectorNumElements();
unsigned LHSWidth = LHS->getType()->getVectorNumElements();
SmallVector<int, 16> Mask = SVI.getShuffleMask();
Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
if (LHS == RHS || isa<UndefValue>(LHS)) {
if (LHS == RHS) {
assert(!isa<UndefValue>(RHS) && "Shuffle with 2 undef ops not simplified?");
// Remap any references to RHS to use LHS.
SmallVector<Constant*, 16> Elts;
for (unsigned i = 0; i != VWidth; ++i) {
if (Mask[i] < 0) {
Elts.push_back(UndefValue::get(Int32Ty));
continue;
}
// Change select of undef to undef mask element or force to LHS.
if (Mask[i] < (int)LHSWidth && isa<UndefValue>(LHS))
// Propagate undef elements or force mask to LHS.
if (Mask[i] < 0)
Elts.push_back(UndefValue::get(Int32Ty));
else
Elts.push_back(ConstantInt::get(Int32Ty, Mask[i] % LHSWidth));
@@ -1914,6 +1908,12 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
return &SVI;
}
// shuffle undef, x, mask --> shuffle x, undef, mask'
if (isa<UndefValue>(LHS)) {
SVI.commute();
return &SVI;
}
if (Instruction *I = canonicalizeInsertSplat(SVI, Builder))
return I;