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[VectorCombine] make helper function for shift-shuffle; NFC 

This will probably be useful for other extract patterns.
This commit is contained in:
Sanjay Patel 2020-06-22 12:22:45 -04:00
parent 328c8642e2
commit 9934cc544c
1 changed files with 20 additions and 15 deletions
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35
llvm/lib/Transforms/Vectorize/VectorCombine.cpp
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@ -65,8 +65,6 @@ private:
unsigned Opcode,
ExtractElementInst *&ConvertToShuffle,
unsigned PreferredExtractIndex);
ExtractElementInst *translateExtract(ExtractElementInst *ExtElt,
unsigned NewIndex);
void foldExtExtCmp(ExtractElementInst *Ext0, ExtractElementInst *Ext1,
Instruction &I);
void foldExtExtBinop(ExtractElementInst *Ext0, ExtractElementInst *Ext1,
@ -190,12 +188,27 @@ bool VectorCombine::isExtractExtractCheap(ExtractElementInst *Ext0,
return OldCost < NewCost;
}
/// Create a shuffle that translates (shifts) 1 element from the input vector
/// to a new element location.
static Value *createShiftShuffle(Value *Vec, unsigned OldIndex,
unsigned NewIndex, IRBuilder<> &Builder) {
// The shuffle mask is undefined except for 1 lane that is being translated
// to the new element index. Example for OldIndex == 2 and NewIndex == 0:
// ShufMask = { 2, undef, undef, undef }
auto *VecTy = cast<FixedVectorType>(Vec->getType());
SmallVector<int, 32> ShufMask(VecTy->getNumElements(), -1);
ShufMask[NewIndex] = OldIndex;
Value *Undef = UndefValue::get(VecTy);
return Builder.CreateShuffleVector(Vec, Undef, ShufMask, "shift");
}
/// Given an extract element instruction with constant index operand, shuffle
/// the source vector (shift the scalar element) to a NewIndex for extraction.
/// Return null if the input can be constant folded, so that we are not creating
/// unnecessary instructions.
ExtractElementInst *VectorCombine::translateExtract(ExtractElementInst *ExtElt,
unsigned NewIndex) {
static ExtractElementInst *translateExtract(ExtractElementInst *ExtElt,
unsigned NewIndex,
IRBuilder<> &Builder) {
// If the extract can be constant-folded, this code is unsimplified. Defer
// to other passes to handle that.
Value *X = ExtElt->getVectorOperand();
@ -204,16 +217,8 @@ ExtractElementInst *VectorCombine::translateExtract(ExtractElementInst *ExtElt,
if (isa<Constant>(X))
return nullptr;
// The shuffle mask is undefined except for 1 lane that is being translated
// to the cheap extraction lane. Example:
// ShufMask = { 2, undef, undef, undef }
auto *VecTy = cast<FixedVectorType>(X->getType());
SmallVector<int, 32> Mask(VecTy->getNumElements(), -1);
Mask[NewIndex] = cast<ConstantInt>(C)->getZExtValue();
// extelt X, C --> extelt (shuffle X), NewIndex
Value *Shuf =
Builder.CreateShuffleVector(X, UndefValue::get(VecTy), Mask, "shift");
Value *Shuf = createShiftShuffle(X, cast<ConstantInt>(C)->getZExtValue(),
NewIndex, Builder);
return cast<ExtractElementInst>(Builder.CreateExtractElement(Shuf, NewIndex));
}
@ -301,7 +306,7 @@ bool VectorCombine::foldExtractExtract(Instruction &I) {
if (ExtractToChange) {
unsigned CheapExtractIdx = ExtractToChange == Ext0 ? C1 : C0;
ExtractElementInst *NewExtract =
translateExtract(ExtractToChange, CheapExtractIdx);
translateExtract(ExtractToChange, CheapExtractIdx, Builder);
if (!NewExtract)
return false;
if (ExtractToChange == Ext0)