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X86: When combining shuffles just remove shuffles that are completely redundant.

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CombineTo doesn't allow replacing a node with itself so this would crash if the
combined shuffle is the same as the input shuffle.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212181 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2014-07-02 15:09:44 +00:00
parent a3af27aa0b
commit 11be760757
2 changed files with 17 additions and 0 deletions
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7
lib/Target/X86/X86ISelLowering.cpp
View File

@ -18442,6 +18442,13 @@ static bool combineRedundantDWordShuffle(SDValue N, MutableArrayRef<int> Mask,
V = DAG.getNode(X86ISD::PSHUFD, DL, MVT::v4i32, V.getOperand(0),
getV4X86ShuffleImm8ForMask(Mask, DAG));
// It is possible that one of the combinable shuffles was completely absorbed
// by the other, just replace it and revisit all users in that case.
if (Old.getNode() == V.getNode()) {
DCI.CombineTo(N.getNode(), N.getOperand(0), /*AddTo=*/true);
return true;
}
// Replace N with its operand as we're going to combine that shuffle away.
DAG.ReplaceAllUsesWith(N, N.getOperand(0));

10
test/CodeGen/X86/vector-shuffle-combining.ll
View File

@ -66,6 +66,16 @@ define <4 x i32> @combine_pshufd5(<4 x i32> %a) {
ret <4 x i32> %d
}
define <4 x i32> @combine_pshufd6(<4 x i32> %a) {
; CHECK-SSE2-LABEL: @combine_pshufd6
; CHECK-SSE2: # BB#0:
; CHECK-SSE2-NEXT: pshufd $0
; CHECK-SSE2-NEXT: retq
%b = call <4 x i32> @llvm.x86.sse2.pshuf.d(<4 x i32> %a, i8 0)
%c = call <4 x i32> @llvm.x86.sse2.pshuf.d(<4 x i32> %b, i8 8)
ret <4 x i32> %c
}
define <8 x i16> @combine_pshuflw1(<8 x i16> %a) {
; CHECK-SSE2-LABEL: @combine_pshuflw1
; CHECK-SSE2: # BB#0: