Revert "[DAGCombine] A shuffle of a splat is always the splat itself"

This reverts commit r299047 which is incorrect because the
simplification may result in incorrect propogation of undefs to users of
the folded shuffle.

Thanks to Andrea Di Biagio for pointing this out.

llvm-svn: 299368

2 files changed, 10 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 82c61faaa54..779a0b5c8bd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -14633,12 +14633,6 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
       return DAG.getVectorShuffle(VT, SDLoc(N), N0, N1, NewMask);
   }
 
-  // A shuffle of a splat is always the splat itself:
-  // shuffle (splat-shuffle), undef, M --> splat-shuffle
-  if (auto *N0Shuf = dyn_cast<ShuffleVectorSDNode>(N0))
-    if (N1.isUndef() && N0Shuf->isSplat())
-      return N0;
-
   // If it is a splat, check if the argument vector is another splat or a
   // build_vector.
   if (SVN->isSplat() && SVN->getSplatIndex() < (int)NumElts) {
diff --git a/llvm/test/CodeGen/X86/shuffle-of-splat-multiuses.ll b/llvm/test/CodeGen/X86/shuffle-of-splat-multiuses.ll
index e7011df8362..38d45ca99eb 100644
--- a/llvm/test/CodeGen/X86/shuffle-of-splat-multiuses.ll
+++ b/llvm/test/CodeGen/X86/shuffle-of-splat-multiuses.ll
@@ -5,8 +5,9 @@
 define <2 x double> @foo2(<2 x double> %v, <2 x double> *%p) nounwind {
 ; AVX2-LABEL: foo2:
 ; AVX2:       # BB#0:
-; AVX2-NEXT:    vpermilpd {{.*#+}} xmm0 = xmm0[1,1]
-; AVX2-NEXT:    vmovapd %xmm0, (%rdi)
+; AVX2-NEXT:    vpermilpd {{.*#+}} xmm1 = xmm0[1,1]
+; AVX2-NEXT:    vpermilpd {{.*#+}} xmm0 = xmm1[1,0]
+; AVX2-NEXT:    vmovapd %xmm1, (%rdi)
 ; AVX2-NEXT:    retq
   %res = shufflevector <2 x double> %v, <2 x double> undef, <2 x i32> <i32 1, i32 1>
   %res1 = shufflevector<2 x double> %res, <2 x double> undef, <2 x i32> <i32 1, i32 undef>
@@ -17,8 +18,9 @@ define <2 x double> @foo2(<2 x double> %v, <2 x double> *%p) nounwind {
 define <4 x double> @foo4(<4 x double> %v, <4 x double> *%p) nounwind {
 ; AVX2-LABEL: foo4:
 ; AVX2:       # BB#0:
-; AVX2-NEXT:    vpermpd {{.*#+}} ymm0 = ymm0[2,2,2,2]
-; AVX2-NEXT:    vmovapd %ymm0, (%rdi)
+; AVX2-NEXT:    vpermpd {{.*#+}} ymm1 = ymm0[2,2,2,2]
+; AVX2-NEXT:    vpermpd {{.*#+}} ymm0 = ymm1[2,0,2,3]
+; AVX2-NEXT:    vmovapd %ymm1, (%rdi)
 ; AVX2-NEXT:    retq
   %res = shufflevector <4 x double> %v, <4 x double> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
   %res1 = shufflevector<4 x double> %res, <4 x double> undef, <4 x i32> <i32 2, i32 0, i32 undef, i32 undef>
@@ -30,8 +32,10 @@ define <8 x float> @foo8(<8 x float> %v, <8 x float> *%p) nounwind {
 ; AVX2-LABEL: foo8:
 ; AVX2:       # BB#0:
 ; AVX2-NEXT:    vmovshdup {{.*#+}} ymm0 = ymm0[1,1,3,3,5,5,7,7]
-; AVX2-NEXT:    vpermpd {{.*#+}} ymm0 = ymm0[2,2,2,2]
-; AVX2-NEXT:    vmovapd %ymm0, (%rdi)
+; AVX2-NEXT:    vpermpd {{.*#+}} ymm1 = ymm0[2,2,2,2]
+; AVX2-NEXT:    vmovaps {{.*#+}} ymm0 = <2,0,u,u,5,1,3,7>
+; AVX2-NEXT:    vpermps %ymm1, %ymm0, %ymm0
+; AVX2-NEXT:    vmovapd %ymm1, (%rdi)
 ; AVX2-NEXT:    retq
   %res = shufflevector <8 x float> %v, <8 x float> undef, <8 x i32> <i32 5, i32 5, i32 5, i32 5, i32 5, i32 5, i32 5, i32 5>
   %res1 = shufflevector<8 x float> %res, <8 x float> undef, <8 x i32> <i32 2, i32 0, i32 undef, i32 undef, i32 5, i32 1, i32 3, i32 7>