[X86] lowerShuffleAsDecomposedShuffleMerge - prefer permute+unpck patterns vs blend+permute on pre-SSE41 targets (llvm#160301)

Pre-SSE41 we don't have BLENDI so blend patterns tend to get expanded to
more complex shuffles

Fixes 128-bit case from llvm#159670

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -11721,10 +11721,19 @@ static SDValue lowerShuffleAsDecomposedShuffleMerge(
   // we'll have to do 2x as many shuffles in order to achieve this, a 2-input
   // pre-shuffle first is a better strategy.
   if (!isNoopShuffleMask(V1Mask) && !isNoopShuffleMask(V2Mask)) {
+    // If we don't have blends, see if we can create a cheap unpack.
+    if (!Subtarget.hasSSE41() && VT.is128BitVector() &&
+        (is128BitUnpackShuffleMask(V1Mask, DAG) ||
+         is128BitUnpackShuffleMask(V2Mask, DAG)))
+      if (SDValue PermUnpack = lowerShuffleAsPermuteAndUnpack(
+              DL, VT, V1, V2, Mask, Subtarget, DAG))
+        return PermUnpack;
+
     // Only prefer immediate blends to unpack/rotate.
-    if (SDValue BlendPerm = lowerShuffleAsBlendAndPermute(DL, VT, V1, V2, Mask,
-                                                          DAG, true))
+    if (SDValue BlendPerm =
+            lowerShuffleAsBlendAndPermute(DL, VT, V1, V2, Mask, DAG, true))
       return BlendPerm;
+
     // If either input vector provides only a single element which is repeated
     // multiple times, unpacking from both input vectors would generate worse
     // code. e.g. for
@@ -11736,13 +11745,16 @@ static SDValue lowerShuffleAsDecomposedShuffleMerge(
       if (SDValue UnpackPerm =
               lowerShuffleAsUNPCKAndPermute(DL, VT, V1, V2, Mask, DAG))
         return UnpackPerm;
+
     if (SDValue RotatePerm = lowerShuffleAsByteRotateAndPermute(
             DL, VT, V1, V2, Mask, Subtarget, DAG))
       return RotatePerm;
+
     // Unpack/rotate failed - try again with variable blends.
     if (SDValue BlendPerm = lowerShuffleAsBlendAndPermute(DL, VT, V1, V2, Mask,
                                                           DAG))
       return BlendPerm;
+
     if (VT.getScalarSizeInBits() >= 32)
       if (SDValue PermUnpack = lowerShuffleAsPermuteAndUnpack(
               DL, VT, V1, V2, Mask, Subtarget, DAG))

llvm/test/CodeGen/X86/vector-shuffle-128-v16.ll

@@ -1051,28 +1051,11 @@ define <16 x i8> @shuffle_v16i8_01_03_05_07_09_11_13_15_17_19_21_23_25_27_29_31(
 
 ; PR159670
 define <16 x i8> @shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31(<16 x i8> %a, <16 x i8> %b) {
-; SSE2-LABEL: shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31:
-; SSE2:       # %bb.0:
-; SSE2-NEXT:    pxor %xmm2, %xmm2
-; SSE2-NEXT:    punpckhbw {{.*#+}} xmm1 = xmm1[8],xmm2[8],xmm1[9],xmm2[9],xmm1[10],xmm2[10],xmm1[11],xmm2[11],xmm1[12],xmm2[12],xmm1[13],xmm2[13],xmm1[14],xmm2[14],xmm1[15],xmm2[15]
-; SSE2-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0],xmm2[0],xmm0[1],xmm2[1],xmm0[2],xmm2[2],xmm0[3],xmm2[3],xmm0[4],xmm2[4],xmm0[5],xmm2[5],xmm0[6],xmm2[6],xmm0[7],xmm2[7]
-; SSE2-NEXT:    movdqa %xmm0, %xmm2
-; SSE2-NEXT:    punpckhwd {{.*#+}} xmm2 = xmm2[4],xmm1[4],xmm2[5],xmm1[5],xmm2[6],xmm1[6],xmm2[7],xmm1[7]
-; SSE2-NEXT:    punpcklwd {{.*#+}} xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1],xmm0[2],xmm1[2],xmm0[3],xmm1[3]
-; SSE2-NEXT:    packuswb %xmm2, %xmm0
-; SSE2-NEXT:    retq
-;
-; SSSE3-LABEL: shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31:
-; SSSE3:       # %bb.0:
-; SSSE3-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]
-; SSSE3-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1],xmm0[2],xmm1[2],xmm0[3],xmm1[3],xmm0[4],xmm1[4],xmm0[5],xmm1[5],xmm0[6],xmm1[6],xmm0[7],xmm1[7]
-; SSSE3-NEXT:    retq
-;
-; SSE41-LABEL: shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31:
-; SSE41:       # %bb.0:
-; SSE41-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]
-; SSE41-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1],xmm0[2],xmm1[2],xmm0[3],xmm1[3],xmm0[4],xmm1[4],xmm0[5],xmm1[5],xmm0[6],xmm1[6],xmm0[7],xmm1[7]
-; SSE41-NEXT:    retq
+; SSE-LABEL: shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31:
+; SSE:       # %bb.0:
+; SSE-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]
+; SSE-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1],xmm0[2],xmm1[2],xmm0[3],xmm1[3],xmm0[4],xmm1[4],xmm0[5],xmm1[5],xmm0[6],xmm1[6],xmm0[7],xmm1[7]
+; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: shuffle_v16i8_00_24_01_25_02_26_03_27_04_28_05_29_06_30_07_31:
 ; AVX:       # %bb.0:

llvm/test/CodeGen/X86/vector-shuffle-sse4a.ll

@@ -362,11 +362,9 @@ define <8 x i16> @shuf_089uuuuu(<8 x i16> %a0, <8 x i16> %a1) {
 define <16 x i8> @shuffle_8_18_uuuuuuuuuuuuuu(<16 x i8> %a, <16 x i8> %b) {
 ; AMD10H-LABEL: shuffle_8_18_uuuuuuuuuuuuuu:
 ; AMD10H:       # %bb.0:
-; AMD10H-NEXT:    movsd {{.*#+}} xmm0 = xmm1[0],xmm0[1]
-; AMD10H-NEXT:    shufps {{.*#+}} xmm0 = xmm0[0,2,2,3]
-; AMD10H-NEXT:    andps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
-; AMD10H-NEXT:    pshuflw {{.*#+}} xmm0 = xmm0[2,1,2,3,4,5,6,7]
-; AMD10H-NEXT:    packuswb %xmm0, %xmm0
+; AMD10H-NEXT:    psrld $16, %xmm1
+; AMD10H-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[2,3,2,3]
+; AMD10H-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1],xmm0[2],xmm1[2],xmm0[3],xmm1[3],xmm0[4],xmm1[4],xmm0[5],xmm1[5],xmm0[6],xmm1[6],xmm0[7],xmm1[7]
 ; AMD10H-NEXT:    retq
 ;
 ; BTVER1-LABEL: shuffle_8_18_uuuuuuuuuuuuuu: