[X86] X86ISD::PACKSS/US do not create undef/poison #161534
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@llvm/pr-subscribers-backend-x86 Author: Simon Pilgrim (RKSimon) ChangesFull diff: https://github.com/llvm/llvm-project/pull/161534.diff 2 Files Affected:
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a04c3e8f70c89..34854e4d8b6c0 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -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:
@@ -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:
diff --git a/llvm/test/CodeGen/X86/combine-pack.ll b/llvm/test/CodeGen/X86/combine-pack.ll
index 1e7c700055e3f..2f5454dc2c3ec 100644
--- a/llvm/test/CodeGen/X86/combine-pack.ll
+++ b/llvm/test/CodeGen/X86/combine-pack.ll
@@ -26,14 +26,12 @@ 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:
@@ -41,7 +39,6 @@ define <8 x i16> @combine_packss_v4i32_freeze_signsplat(<4 x i32> %a0, <4 x i32>
; 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>
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/116/builds/19117 Here is the relevant piece of the build log for the reference |
mahesh-attarde
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Oct 3, 2025
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