[X86] canCreateUndefOrPoisonForTargetNode - SSE vector shifts handle out of bounds shift amounts

SHL/SRL are guaranteed to fold to zero, SRA is guaranteed to fold to 'all sign bits'

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -42930,7 +42930,6 @@ bool X86TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
     bool PoisonOnly, unsigned Depth) const {
   unsigned NumElts = DemandedElts.getBitWidth();
 
-  // TODO: Add more target shuffles.
   switch (Op.getOpcode()) {
   case X86ISD::PSHUFD:
   case X86ISD::VPERMILPI: {
@@ -42966,8 +42965,12 @@ bool X86TargetLowering::canCreateUndefOrPoisonForTargetNode(
     SDValue Op, const APInt &DemandedElts, const SelectionDAG &DAG,
     bool PoisonOnly, bool ConsiderFlags, unsigned Depth) const {
 
-  // TODO: Add more target shuffles.
   switch (Op.getOpcode()) {
+  // SSE vector shifts handle out of bounds shift amounts.
+  case X86ISD::VSHLI:
+  case X86ISD::VSRLI:
+  case X86ISD::VSRAI:
+    return false;
   case X86ISD::PSHUFD:
   case X86ISD::VPERMILPI:
   case X86ISD::UNPCKH:

llvm/test/CodeGen/X86/freeze-binary.ll

@@ -546,9 +546,8 @@ define <8 x i16> @freeze_ashr_vec(<8 x i16> %a0) nounwind {
 define <4 x i32> @freeze_ashr_vec_outofrange(<4 x i32> %a0) nounwind {
 ; X86-LABEL: freeze_ashr_vec_outofrange:
 ; X86:       # %bb.0:
-; X86-NEXT:    psrad $1, %xmm0
 ; X86-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[0,3,2,3]
-; X86-NEXT:    psrad $2, %xmm0
+; X86-NEXT:    psrad $3, %xmm0
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: freeze_ashr_vec_outofrange:
@@ -660,9 +659,8 @@ define <8 x i16> @freeze_lshr_vec(<8 x i16> %a0) nounwind {
 define <4 x i32> @freeze_lshr_vec_outofrange(<4 x i32> %a0) nounwind {
 ; X86-LABEL: freeze_lshr_vec_outofrange:
 ; X86:       # %bb.0:
-; X86-NEXT:    psrld $1, %xmm0
 ; X86-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[0,3,2,3]
-; X86-NEXT:    psrld $2, %xmm0
+; X86-NEXT:    psrld $3, %xmm0
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: freeze_lshr_vec_outofrange: