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Make instcombine a little more aggressive in combining vector shuffles.

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Allow splats even if they don't match either of the original shuffles,
possibly due to undef entries in the shuffles masks.  Radar 8597790.
Also fix some 80-column violations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117719 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2010-10-29 22:02:50 +00:00
parent 3df518e67e
commit 4cac5facc3
2 changed files with 32 additions and 15 deletions
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37
lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -515,37 +515,44 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// we are absolutely afraid of producing a shuffle mask not in the input
// program, because the code gen may not be smart enough to turn a merged
// shuffle into two specific shuffles: it may produce worse code. As such,
// we only merge two shuffles if the result is one of the two input shuffle
// masks. In this case, merging the shuffles just removes one instruction,
// which we know is safe. This is good for things like turning:
// (splat(splat)) -> splat.
// we only merge two shuffles if the result is either a splat or one of the
// two input shuffle masks. In this case, merging the shuffles just removes
// one instruction, which we know is safe. This is good for things like
// turning: (splat(splat)) -> splat.
if (ShuffleVectorInst *LHSSVI = dyn_cast<ShuffleVectorInst>(LHS)) {
if (isa<UndefValue>(RHS)) {
std::vector<unsigned> LHSMask = getShuffleMask(LHSSVI);
if (LHSMask.size() == Mask.size()) {
std::vector<unsigned> NewMask;
for (unsigned i = 0, e = Mask.size(); i != e; ++i)
if (Mask[i] >= e)
NewMask.push_back(2*e);
else
NewMask.push_back(LHSMask[Mask[i]]);
bool isSplat = true;
unsigned SplatElt = 2 * Mask.size(); // undef
for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
unsigned MaskElt = 2 * e; // undef
if (Mask[i] < e)
MaskElt = LHSMask[Mask[i]];
// Check if this could still be a splat.
if (MaskElt < 2*e) {
if (SplatElt < 2*e && SplatElt != MaskElt)
isSplat = false;
SplatElt = MaskElt;
}
NewMask.push_back(MaskElt);
}
// If the result mask is equal to the src shuffle or this
// shuffle mask, do the replacement.
if (NewMask == LHSMask || NewMask == Mask) {
if (isSplat || NewMask == LHSMask || NewMask == Mask) {
unsigned LHSInNElts =
cast<VectorType>(LHSSVI->getOperand(0)->getType())->
getNumElements();
std::vector<Constant*> Elts;
const Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
for (unsigned i = 0, e = NewMask.size(); i != e; ++i) {
if (NewMask[i] >= LHSInNElts*2) {
Elts.push_back(UndefValue::get(
Type::getInt32Ty(SVI.getContext())));
Elts.push_back(UndefValue::get(Int32Ty));
} else {
Elts.push_back(ConstantInt::get(
Type::getInt32Ty(SVI.getContext()),
NewMask[i]));
Elts.push_back(ConstantInt::get(Int32Ty, NewMask[i]));
}
}
return new ShuffleVectorInst(LHSSVI->getOperand(0),

10
test/Transforms/InstCombine/vec_shuffle.ll
View File

@ -87,3 +87,13 @@ define <4 x i8> @test9(<16 x i8> %tmp6) nounwind {
%tmp9 = shufflevector <4 x i8> %tmp7, <4 x i8> undef, <4 x i32> < i32 3, i32 1, i32 2, i32 0 > ; <<4 x i8>> [#uses=1]
ret <4 x i8> %tmp9
}
; Redundant vector splats should be removed. Radar 8597790.
define <4 x i32> @test10(<4 x i32> %tmp5) nounwind {
; CHECK: @test10
; CHECK-NEXT: shufflevector
; CHECK-NEXT: ret
%tmp6 = shufflevector <4 x i32> %tmp5, <4 x i32> undef, <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
%tmp7 = shufflevector <4 x i32> %tmp6, <4 x i32> undef, <4 x i32> zeroinitializer
ret <4 x i32> %tmp7
}