[llvm] r229301 - [x86] Stop shuffling zero vectors. =]

[Chandler Carruth]

Author: chandlerc
Date: Sun Feb 15 04:34:52 2015
New Revision: 229301

URL: http://llvm.org/viewvc/llvm-project?rev=229301&view=rev
Log:
[x86] Stop shuffling zero vectors. =]

I was somewhat surprised this pattern really came up, but it does. It
seems better to just directly handle it than try to special case every
place where we end up forming a shuffle that devolves to a shuffle of
a zero vector.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll
    llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=229301&r1=229300&r2=229301&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Feb 15 04:34:52 2015
@@ -11285,6 +11285,13 @@ static SDValue lowerVectorShuffle(SDValu
         return DAG.getVectorShuffle(VT, dl, V1, V2, NewMask);
       }
 
+  // We actually see shuffles that are entirely re-arrangements of a set of
+  // zero inputs. This mostly happens while decomposing complex shuffles into
+  // simple ones. Directly lower these as a buildvector of zeros.
+  SmallBitVector Zeroable = computeZeroableShuffleElements(Mask, V1, V2);
+  if (Zeroable.all())
+    return getZeroVector(VT, Subtarget, DAG, dl);
+
   // Try to collapse shuffles into using a vector type with fewer elements but
   // wider element types. We cap this to not form integers or floating point
   // elements wider than 64 bits, but it might be interesting to form i128

Modified: llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll?rev=229301&r1=229300&r2=229301&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll (original)
+++ llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v16.ll Sun Feb 15 04:34:52 2015
@@ -1457,10 +1457,9 @@ define <16 x i16> @shuffle_v16i16_16_zz_
 define <16 x i16> @shuffle_v16i16_16_zz_17_zz_18_zz_19_zz_20_zz_21_zz_22_zz_22_zz(<16 x i16> %a) {
 ; AVX1-LABEL: shuffle_v16i16_16_zz_17_zz_18_zz_19_zz_20_zz_21_zz_22_zz_22_zz:
 ; AVX1:       # BB#0:
-; AVX1-NEXT:    vpxor %xmm1, %xmm1, %xmm1
-; AVX1-NEXT:    vpmovzxwq {{.*#+}} xmm1 = xmm1[0],zero,zero,zero,xmm1[1],zero,zero,zero
-; AVX1-NEXT:    vpshufd {{.*#+}} xmm2 = xmm0[2,3,0,1]
-; AVX1-NEXT:    vpunpcklwd {{.*#+}} xmm1 = xmm2[0],xmm1[0],xmm2[1],xmm1[1],xmm2[2],xmm1[2],xmm2[3],xmm1[3]
+; AVX1-NEXT:    vpshufd {{.*#+}} xmm1 = xmm0[2,3,0,1]
+; AVX1-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; AVX1-NEXT:    vpunpcklwd {{.*#+}} xmm1 = xmm1[0],xmm2[0],xmm1[1],xmm2[1],xmm1[2],xmm2[2],xmm1[3],xmm2[3]
 ; AVX1-NEXT:    vpmovzxwd {{.*#+}} xmm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero
 ; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
 ; AVX1-NEXT:    retq

Modified: llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll?rev=229301&r1=229300&r2=229301&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll (original)
+++ llvm/trunk/test/CodeGen/X86/vector-shuffle-256-v32.ll Sun Feb 15 04:34:52 2015
@@ -1802,10 +1802,9 @@ define <32 x i8> @shuffle_v32i8_32_zz_zz
 define <32 x i8> @shuffle_v32i8_32_zz_33_zz_34_zz_35_zz_36_zz_37_zz_38_zz_39_zz_40_zz_41_zz_42_zz_43_zz_44_zz_45_zz_46_zz_47_zz(<32 x i8> %a) {
 ; AVX1-LABEL: shuffle_v32i8_32_zz_33_zz_34_zz_35_zz_36_zz_37_zz_38_zz_39_zz_40_zz_41_zz_42_zz_43_zz_44_zz_45_zz_46_zz_47_zz:
 ; AVX1:       # BB#0:
-; AVX1-NEXT:    vpxor %xmm1, %xmm1, %xmm1
-; AVX1-NEXT:    vpsllq $56, %xmm1, %xmm1
-; AVX1-NEXT:    vpshufd {{.*#+}} xmm2 = xmm0[2,3,0,1]
-; AVX1-NEXT:    vpunpcklbw {{.*#+}} xmm1 = xmm2[0],xmm1[0],xmm2[1],xmm1[1],xmm2[2],xmm1[2],xmm2[3],xmm1[3],xmm2[4],xmm1[4],xmm2[5],xmm1[5],xmm2[6],xmm1[6],xmm2[7],xmm1[7]
+; AVX1-NEXT:    vpshufd {{.*#+}} xmm1 = xmm0[2,3,0,1]
+; AVX1-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; AVX1-NEXT:    vpunpcklbw {{.*#+}} xmm1 = xmm1[0],xmm2[0],xmm1[1],xmm2[1],xmm1[2],xmm2[2],xmm1[3],xmm2[3],xmm1[4],xmm2[4],xmm1[5],xmm2[5],xmm1[6],xmm2[6],xmm1[7],xmm2[7]
 ; AVX1-NEXT:    vpmovzxbw {{.*#+}} xmm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero
 ; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
 ; AVX1-NEXT:    retq