[X86] Fold scalar_to_vector(funnel(x,y,imm)) -> funnel(scalar_to_vector(x),scalar_to_vector(y),imm)

Limit this to cases where x, y are known to be extracted from a vector.

Addresses poor x86 codegen on #107289

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -57500,6 +57500,24 @@ static SDValue combineScalarToVector(SDNode *N, SelectionDAG &DAG,
       }
     }
     break;
+  case ISD::FSHL:
+  case ISD::FSHR:
+    if (auto *Amt = dyn_cast<ConstantSDNode>(Src.getOperand(2))) {
+      if (supportedVectorShiftWithImm(VT, Subtarget, ISD::SHL) &&
+          Src.getOperand(0).getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
+          Src.getOperand(1).getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
+          Src.hasOneUse()) {
+        uint64_t AmtVal =
+            Amt->getAPIntValue().urem(Src.getScalarValueSizeInBits());
+        SDValue SrcVec0 =
+            DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, VT, Src.getOperand(0));
+        SDValue SrcVec1 =
+            DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, VT, Src.getOperand(1));
+        return DAG.getNode(Src.getOpcode(), DL, VT, SrcVec0, SrcVec1,
+                           DAG.getConstant(AmtVal, DL, VT));
+      }
+    }
+    break;
   }
 
   return SDValue();

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

@@ -3534,46 +3534,14 @@ define <4 x i32> @PR63700(i128 %0) {
 }
 
 define <16 x i8> @PR107289(<16 x i8> %0) {
-; SSE2-LABEL: PR107289:
-; SSE2:       # %bb.0:
-; SSE2-NEXT:    movq %xmm0, %rax
-; SSE2-NEXT:    pshufd {{.*#+}} xmm1 = xmm0[2,3,2,3]
-; SSE2-NEXT:    movq %xmm1, %rcx
-; SSE2-NEXT:    shldq $8, %rax, %rcx
-; SSE2-NEXT:    movq %rcx, %xmm1
-; SSE2-NEXT:    psllq $8, %xmm0
-; SSE2-NEXT:    punpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
-; SSE2-NEXT:    retq
-;
-; SSSE3-LABEL: PR107289:
-; SSSE3:       # %bb.0:
-; SSSE3-NEXT:    movq %xmm0, %rax
-; SSSE3-NEXT:    pshufd {{.*#+}} xmm1 = xmm0[2,3,2,3]
-; SSSE3-NEXT:    movq %xmm1, %rcx
-; SSSE3-NEXT:    shldq $8, %rax, %rcx
-; SSSE3-NEXT:    movq %rcx, %xmm1
-; SSSE3-NEXT:    psllq $8, %xmm0
-; SSSE3-NEXT:    punpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
-; SSSE3-NEXT:    retq
-;
-; SSE41-LABEL: PR107289:
-; SSE41:       # %bb.0:
-; SSE41-NEXT:    movq %xmm0, %rax
-; SSE41-NEXT:    pextrq $1, %xmm0, %rcx
-; SSE41-NEXT:    shldq $8, %rax, %rcx
-; SSE41-NEXT:    movq %rcx, %xmm1
-; SSE41-NEXT:    psllq $8, %xmm0
-; SSE41-NEXT:    punpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
-; SSE41-NEXT:    retq
+; SSE-LABEL: PR107289:
+; SSE:       # %bb.0:
+; SSE-NEXT:    pslldq {{.*#+}} xmm0 = zero,xmm0[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14]
+; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: PR107289:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vmovq %xmm0, %rax
-; AVX-NEXT:    vpextrq $1, %xmm0, %rcx
-; AVX-NEXT:    shldq $8, %rax, %rcx
-; AVX-NEXT:    vmovq %rcx, %xmm1
-; AVX-NEXT:    vpsllq $8, %xmm0, %xmm0
-; AVX-NEXT:    vpunpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
+; AVX-NEXT:    vpslldq {{.*#+}} xmm0 = zero,xmm0[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14]
 ; AVX-NEXT:    retq
   %src = bitcast <16 x i8> %0 to i128
   %shl = shl i128 %src, 8