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Fix for wrong instcombine on vector insert/extract

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When trying to collapse sequences of insertelement/extractelement
instructions into single shuffle instructions, there is one specific
case where the Instruction Combiner wrongly updates the resulting
Mask of shuffle indexes.

The problem is in function CollectShuffleElments.

If we have a sequence of insert/extract element instructions
like the one below:

  %tmp1 = extractelement <4 x float> %LHS, i32 0
  %tmp2 = insertelement <4 x float> %RHS, float %tmp1, i32 1
  %tmp3 = extractelement <4 x float> %RHS, i32 2
  %tmp4 = insertelement <4 x float> %tmp2, float %tmp3, i32 3

Where:
  . %RHS will have a mask of [4,5,6,7]
  . %LHS will have a mask of [0,1,2,3]

The Mask of shuffle indexes is wrongly computed to [4,1,6,7]
instead of [4,0,6,7].
When analyzing %tmp2 in order to compute the Mask for the
resulting shuffle instruction, the algorithm forgets to update
the mask index at position 1 with the index associated to the
element extracted from %LHS by instruction %tmp1.

Patch by Andrea DiBiagio!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179291 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2013-04-11 15:10:09 +00:00
parent 765afbc4ca
commit c37cb66e6e
2 changed files with 31 additions and 0 deletions
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4
lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -336,6 +336,10 @@ static Value *CollectShuffleElements(Value *V, SmallVectorImpl<Constant*> &Mask,
if (VecOp == RHS) {
Value *V = CollectShuffleElements(EI->getOperand(0), Mask, RHS);
// Update Mask to reflect that `ScalarOp' has been inserted at
// position `InsertedIdx' within the vector returned by IEI.
Mask[InsertedIdx % NumElts] = Mask[ExtractedIdx];
// Everything but the extracted element is replaced with the RHS.
for (unsigned i = 0; i != NumElts; ++i) {
if (i != InsertedIdx)

27
test/Transforms/InstCombine/vec_shuffle.ll
View File

@ -196,3 +196,30 @@ define <4 x i16> @test13e(<4 x i16> %lhs, <4 x i16> %rhs) {
<4 x i16> %lhs, <4 x i16> %rhs
ret <4 x i16> %A
}
; Check that sequences of insert/extract element are
; collapsed into shuffle instruction with correct shuffle indexes.
define <4 x float> @test14a(<4 x float> %LHS, <4 x float> %RHS) {
; CHECK: @test14a
; CHECK-NEXT: shufflevector <4 x float> %LHS, <4 x float> %RHS, <4 x i32> <i32 4, i32 0, i32 6, i32 6>
; CHECK-NEXT: ret <4 x float> %tmp4
%tmp1 = extractelement <4 x float> %LHS, i32 0
%tmp2 = insertelement <4 x float> %RHS, float %tmp1, i32 1
%tmp3 = extractelement <4 x float> %RHS, i32 2
%tmp4 = insertelement <4 x float> %tmp2, float %tmp3, i32 3
ret <4 x float> %tmp4
}
define <4 x float> @test14b(<4 x float> %LHS, <4 x float> %RHS) {
; CHECK: @test14b
; CHECK-NEXT: shufflevector <4 x float> %LHS, <4 x float> %RHS, <4 x i32> <i32 4, i32 3, i32 6, i32 6>
; CHECK-NEXT: ret <4 x float> %tmp5
%tmp0 = extractelement <4 x float> %LHS, i32 3
%tmp1 = insertelement <4 x float> %RHS, float %tmp0, i32 0
%tmp2 = extractelement <4 x float> %tmp1, i32 0
%tmp3 = insertelement <4 x float> %RHS, float %tmp2, i32 1
%tmp4 = extractelement <4 x float> %RHS, i32 2
%tmp5 = insertelement <4 x float> %tmp3, float %tmp4, i32 3
ret <4 x float> %tmp5
}