[X86] combinePMULH - we can treat constant vectors as freely truncatable.

Fixes #109790

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -53022,9 +53022,10 @@ static SDValue combinePMULH(SDValue Src, EVT VT, const SDLoc &DL,
 
   // Check if both inputs are extensions, which will be removed by truncation.
   auto isOpTruncateFree = [](SDValue Op) {
-    return (Op.getOpcode() == ISD::SIGN_EXTEND ||
-            Op.getOpcode() == ISD::ZERO_EXTEND) &&
-           Op.getOperand(0).getScalarValueSizeInBits() <= 16;
+    if (Op.getOpcode() == ISD::SIGN_EXTEND ||
+        Op.getOpcode() == ISD::ZERO_EXTEND)
+      return Op.getOperand(0).getScalarValueSizeInBits() <= 16;
+    return ISD::isBuildVectorOfConstantSDNodes(Op.getNode());
   };
   bool IsTruncateFree = isOpTruncateFree(LHS) && isOpTruncateFree(RHS);
 

llvm/test/CodeGen/X86/pmulh.ll

@@ -974,32 +974,11 @@ define <16 x i16> @zext_mulhuw_v16i16_positive_constant(<16 x i16> %a) {
 ; SSE-NEXT:    pmulhw %xmm2, %xmm1
 ; SSE-NEXT:    retq
 ;
-; AVX2-LABEL: zext_mulhuw_v16i16_positive_constant:
-; AVX2:       # %bb.0:
-; AVX2-NEXT:    vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
-; AVX2-NEXT:    vpmovzxwd {{.*#+}} ymm1 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero
-; AVX2-NEXT:    vextracti128 $1, %ymm0, %xmm0
-; AVX2-NEXT:    vpmovzxwd {{.*#+}} ymm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero
-; AVX2-NEXT:    vpbroadcastd {{.*#+}} ymm2 = [1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0]
-; AVX2-NEXT:    vpmulhuw %ymm2, %ymm0, %ymm0
-; AVX2-NEXT:    vpmulhuw %ymm2, %ymm1, %ymm1
-; AVX2-NEXT:    vpackusdw %ymm0, %ymm1, %ymm0
-; AVX2-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
-; AVX2-NEXT:    retq
-;
-; AVX512F-LABEL: zext_mulhuw_v16i16_positive_constant:
-; AVX512F:       # %bb.0:
-; AVX512F-NEXT:    vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
-; AVX512F-NEXT:    vpmulhw {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0 # [1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000]
-; AVX512F-NEXT:    retq
-;
-; AVX512BW-LABEL: zext_mulhuw_v16i16_positive_constant:
-; AVX512BW:       # %bb.0:
-; AVX512BW-NEXT:    vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
-; AVX512BW-NEXT:    vpmovzxwd {{.*#+}} zmm0 = ymm0[0],zero,ymm0[1],zero,ymm0[2],zero,ymm0[3],zero,ymm0[4],zero,ymm0[5],zero,ymm0[6],zero,ymm0[7],zero,ymm0[8],zero,ymm0[9],zero,ymm0[10],zero,ymm0[11],zero,ymm0[12],zero,ymm0[13],zero,ymm0[14],zero,ymm0[15],zero
-; AVX512BW-NEXT:    vpmulhuw {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %zmm0, %zmm0 # [1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0,1000,0]
-; AVX512BW-NEXT:    vpmovdw %zmm0, %ymm0
-; AVX512BW-NEXT:    retq
+; AVX-LABEL: zext_mulhuw_v16i16_positive_constant:
+; AVX:       # %bb.0:
+; AVX-NEXT:    vpand {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
+; AVX-NEXT:    vpmulhw {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0 # [1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000,1000]
+; AVX-NEXT:    retq
   %k = and <16 x i16> %a, <i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767, i16 32767>
   %x = zext nneg <16 x i16> %k to <16 x i32>
   %m = mul nuw nsw <16 x i32> %x, <i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000, i32 1000>