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[X86] X86ISD::PACKSS/US do not create undef/poison #161534

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Merged
merged 1 commit into from
Oct 1, 2025
+16 −3
Merged

[X86] X86ISD::PACKSS/US do not create undef/poison #161534

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16 changes: 16 additions & 0 deletions llvm/lib/Target/X86/X86ISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -45172,6 +45172,18 @@ bool X86TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode(
case X86ISD::Wrapper:
case X86ISD::WrapperRIP:
return true;
case X86ISD::PACKSS:
case X86ISD::PACKUS: {
APInt DemandedLHS, DemandedRHS;
getPackDemandedElts(Op.getSimpleValueType(), DemandedElts, DemandedLHS,
DemandedRHS);
return (!DemandedLHS ||
DAG.isGuaranteedNotToBeUndefOrPoison(Op.getOperand(0), DemandedLHS,
PoisonOnly, Depth + 1)) &&
(!DemandedRHS ||
DAG.isGuaranteedNotToBeUndefOrPoison(Op.getOperand(1), DemandedRHS,
PoisonOnly, Depth + 1));
}
case X86ISD::INSERTPS:
case X86ISD::BLENDI:
case X86ISD::PSHUFB:
Expand Down Expand Up @@ -45242,6 +45254,10 @@ bool X86TargetLowering::canCreateUndefOrPoisonForTargetNode(
case X86ISD::BLENDI:
case X86ISD::BLENDV:
return false;
// SSE packs.
case X86ISD::PACKSS:
case X86ISD::PACKUS:
return false;
// SSE target shuffles.
case X86ISD::INSERTPS:
case X86ISD::PSHUFB:
Expand Down
3 changes: 0 additions & 3 deletions llvm/test/CodeGen/X86/combine-pack.ll
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Expand Up @@ -26,22 +26,19 @@ define <8 x i16> @combine_packss_v4i32_signsplat(<4 x i32> %a0, <4 x i32> %a1) {
ret <8 x i16> %signsplat
}

; TODO: Failure to remove unnecessary signsplat through freeze
define <8 x i16> @combine_packss_v4i32_freeze_signsplat(<4 x i32> %a0, <4 x i32> %a1) {
; SSE-LABEL: combine_packss_v4i32_freeze_signsplat:
; SSE: # %bb.0:
; SSE-NEXT: pcmpgtd %xmm1, %xmm0
; SSE-NEXT: pcmpeqd %xmm1, %xmm1
; SSE-NEXT: packssdw %xmm1, %xmm0
; SSE-NEXT: psraw $15, %xmm0
; SSE-NEXT: retq
;
; AVX-LABEL: combine_packss_v4i32_freeze_signsplat:
; AVX: # %bb.0:
; AVX-NEXT: vpcmpgtd %xmm1, %xmm0, %xmm0
; AVX-NEXT: vpcmpeqd %xmm1, %xmm1, %xmm1
; AVX-NEXT: vpackssdw %xmm1, %xmm0, %xmm0
; AVX-NEXT: vpsraw $15, %xmm0, %xmm0
; AVX-NEXT: retq
%cmp = icmp sgt <4 x i32> %a0, %a1
%ext = sext <4 x i1> %cmp to <4 x i32>
Expand Down
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