[X86] LowerRotate - manually expand rotate by splat constant patterns.

Fixes issue identified on #63980 where the undef rotate amounts (during widening from v2i32 -> v4i32) were being constant folded to 0 when the shift amounts are created during expansion, losing the splat'd shift amounts.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -32489,8 +32489,18 @@ static SDValue LowerRotate(SDValue Op, const X86Subtarget &Subtarget,
   }
 
   // Rotate by an uniform constant - expand back to shifts.
-  if (IsCstSplat)
-    return SDValue();
+  // TODO: Can't use generic expansion as UNDEF amt elements can be converted
+  // to other values when folded to shift amounts, losing the splat.
+  if (IsCstSplat) {
+    uint64_t RotAmt = CstSplatValue.urem(EltSizeInBits);
+    uint64_t ShlAmt = IsROTL ? RotAmt : (EltSizeInBits - RotAmt);
+    uint64_t SrlAmt = IsROTL ? (EltSizeInBits - RotAmt) : RotAmt;
+    SDValue Shl = DAG.getNode(ISD::SHL, DL, VT, R,
+                              DAG.getShiftAmountConstant(ShlAmt, VT, DL));
+    SDValue Srl = DAG.getNode(ISD::SRL, DL, VT, R,
+                              DAG.getShiftAmountConstant(SrlAmt, VT, DL));
+    return DAG.getNode(ISD::OR, DL, VT, Shl, Srl);
+  }
 
   // Split 512-bit integers on non 512-bit BWI targets.
   if (VT.is512BitVector() && !Subtarget.useBWIRegs())

llvm/test/CodeGen/X86/vector-fshl-rot-sub128.ll

@@ -394,34 +394,29 @@ define <2 x i32> @splatconstant_funnnel_v2i32(<2 x i32> %x) nounwind {
 ; SSE2:       # %bb.0:
 ; SSE2-NEXT:    movdqa %xmm0, %xmm1
 ; SSE2-NEXT:    psrld $28, %xmm1
-; SSE2-NEXT:    movdqa %xmm0, %xmm2
-; SSE2-NEXT:    pslld $4, %xmm2
-; SSE2-NEXT:    por %xmm1, %xmm2
-; SSE2-NEXT:    movsd {{.*#+}} xmm0 = xmm2[0],xmm0[1]
+; SSE2-NEXT:    pslld $4, %xmm0
+; SSE2-NEXT:    por %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: splatconstant_funnnel_v2i32:
 ; SSE41:       # %bb.0:
 ; SSE41-NEXT:    movdqa %xmm0, %xmm1
 ; SSE41-NEXT:    psrld $28, %xmm1
-; SSE41-NEXT:    movdqa %xmm0, %xmm2
-; SSE41-NEXT:    pslld $4, %xmm2
-; SSE41-NEXT:    por %xmm1, %xmm2
-; SSE41-NEXT:    pblendw {{.*#+}} xmm0 = xmm2[0,1,2,3],xmm0[4,5,6,7]
+; SSE41-NEXT:    pslld $4, %xmm0
+; SSE41-NEXT:    por %xmm1, %xmm0
 ; SSE41-NEXT:    retq
 ;
 ; AVX1-LABEL: splatconstant_funnnel_v2i32:
 ; AVX1:       # %bb.0:
 ; AVX1-NEXT:    vpsrld $28, %xmm0, %xmm1
-; AVX1-NEXT:    vpslld $4, %xmm0, %xmm2
-; AVX1-NEXT:    vpor %xmm1, %xmm2, %xmm1
-; AVX1-NEXT:    vpblendw {{.*#+}} xmm0 = xmm1[0,1,2,3],xmm0[4,5,6,7]
+; AVX1-NEXT:    vpslld $4, %xmm0, %xmm0
+; AVX1-NEXT:    vpor %xmm1, %xmm0, %xmm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: splatconstant_funnnel_v2i32:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    vpsrlvd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm1
-; AVX2-NEXT:    vpsllvd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0
+; AVX2-NEXT:    vpsrld $28, %xmm0, %xmm1
+; AVX2-NEXT:    vpslld $4, %xmm0, %xmm0
 ; AVX2-NEXT:    vpor %xmm1, %xmm0, %xmm0
 ; AVX2-NEXT:    retq
 ;
@@ -473,10 +468,8 @@ define <2 x i32> @splatconstant_funnnel_v2i32(<2 x i32> %x) nounwind {
 ; X86-SSE2:       # %bb.0:
 ; X86-SSE2-NEXT:    movdqa %xmm0, %xmm1
 ; X86-SSE2-NEXT:    psrld $28, %xmm1
-; X86-SSE2-NEXT:    movdqa %xmm0, %xmm2
-; X86-SSE2-NEXT:    pslld $4, %xmm2
-; X86-SSE2-NEXT:    por %xmm1, %xmm2
-; X86-SSE2-NEXT:    movsd {{.*#+}} xmm0 = xmm2[0],xmm0[1]
+; X86-SSE2-NEXT:    pslld $4, %xmm0
+; X86-SSE2-NEXT:    por %xmm1, %xmm0
 ; X86-SSE2-NEXT:    retl
   %res = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> %x, <2 x i32> %x, <2 x i32> <i32 4, i32 4>)
   ret <2 x i32> %res

llvm/test/CodeGen/X86/vector-fshr-rot-sub128.ll

@@ -408,34 +408,29 @@ define <2 x i32> @splatconstant_funnnel_v2i32(<2 x i32> %x) nounwind {
 ; SSE2:       # %bb.0:
 ; SSE2-NEXT:    movdqa %xmm0, %xmm1
 ; SSE2-NEXT:    psrld $4, %xmm1
-; SSE2-NEXT:    movdqa %xmm0, %xmm2
-; SSE2-NEXT:    pslld $28, %xmm2
-; SSE2-NEXT:    por %xmm1, %xmm2
-; SSE2-NEXT:    movsd {{.*#+}} xmm0 = xmm2[0],xmm0[1]
+; SSE2-NEXT:    pslld $28, %xmm0
+; SSE2-NEXT:    por %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: splatconstant_funnnel_v2i32:
 ; SSE41:       # %bb.0:
 ; SSE41-NEXT:    movdqa %xmm0, %xmm1
 ; SSE41-NEXT:    psrld $4, %xmm1
-; SSE41-NEXT:    movdqa %xmm0, %xmm2
-; SSE41-NEXT:    pslld $28, %xmm2
-; SSE41-NEXT:    por %xmm1, %xmm2
-; SSE41-NEXT:    pblendw {{.*#+}} xmm0 = xmm2[0,1,2,3],xmm0[4,5,6,7]
+; SSE41-NEXT:    pslld $28, %xmm0
+; SSE41-NEXT:    por %xmm1, %xmm0
 ; SSE41-NEXT:    retq
 ;
 ; AVX1-LABEL: splatconstant_funnnel_v2i32:
 ; AVX1:       # %bb.0:
 ; AVX1-NEXT:    vpsrld $4, %xmm0, %xmm1
-; AVX1-NEXT:    vpslld $28, %xmm0, %xmm2
-; AVX1-NEXT:    vpor %xmm1, %xmm2, %xmm1
-; AVX1-NEXT:    vpblendw {{.*#+}} xmm0 = xmm1[0,1,2,3],xmm0[4,5,6,7]
+; AVX1-NEXT:    vpslld $28, %xmm0, %xmm0
+; AVX1-NEXT:    vpor %xmm1, %xmm0, %xmm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: splatconstant_funnnel_v2i32:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    vpsrlvd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm1
-; AVX2-NEXT:    vpsllvd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0
+; AVX2-NEXT:    vpsrld $4, %xmm0, %xmm1
+; AVX2-NEXT:    vpslld $28, %xmm0, %xmm0
 ; AVX2-NEXT:    vpor %xmm1, %xmm0, %xmm0
 ; AVX2-NEXT:    retq
 ;
@@ -487,10 +482,8 @@ define <2 x i32> @splatconstant_funnnel_v2i32(<2 x i32> %x) nounwind {
 ; X86-SSE2:       # %bb.0:
 ; X86-SSE2-NEXT:    movdqa %xmm0, %xmm1
 ; X86-SSE2-NEXT:    psrld $4, %xmm1
-; X86-SSE2-NEXT:    movdqa %xmm0, %xmm2
-; X86-SSE2-NEXT:    pslld $28, %xmm2
-; X86-SSE2-NEXT:    por %xmm1, %xmm2
-; X86-SSE2-NEXT:    movsd {{.*#+}} xmm0 = xmm2[0],xmm0[1]
+; X86-SSE2-NEXT:    pslld $28, %xmm0
+; X86-SSE2-NEXT:    por %xmm1, %xmm0
 ; X86-SSE2-NEXT:    retl
   %res = call <2 x i32> @llvm.fshr.v2i32(<2 x i32> %x, <2 x i32> %x, <2 x i32> <i32 4, i32 4>)
   ret <2 x i32> %res