[llvm] AMDGPU: Replace unused permlane inputs with poison instead of undef (PR #131288)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/131288

>From f44ea0eab2528a59221b6311eb84ef200465bde2 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 14 Mar 2025 14:12:08 +0700
Subject: [PATCH] AMDGPU: Replace unused permlane inputs with poison instead of
 undef

---
 llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp     | 4 ++--
 .../Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll    | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
index 26c48c19ebfd8..7cd97e95b0189 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
@@ -1115,7 +1115,7 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
   case Intrinsic::amdgcn_permlanex16_var: {
     // Discard vdst_in if it's not going to be read.
     Value *VDstIn = II.getArgOperand(0);
-    if (isa<UndefValue>(VDstIn))
+    if (isa<PoisonValue>(VDstIn))
       break;
 
     // FetchInvalid operand idx.
@@ -1134,7 +1134,7 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
     if (!FetchInvalid->getZExtValue() && !BoundCtrl->getZExtValue())
       break;
 
-    return IC.replaceOperand(II, 0, UndefValue::get(VDstIn->getType()));
+    return IC.replaceOperand(II, 0, PoisonValue::get(VDstIn->getType()));
   }
   case Intrinsic::amdgcn_permlane64:
   case Intrinsic::amdgcn_readfirstlane:
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll b/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
index 3e30b2a5b0911..99e6fc98588ae 100644
--- a/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
@@ -3272,7 +3272,7 @@ define amdgpu_kernel void @permlane16(ptr addrspace(1) %out, i32 %src0, i32 %src
 
 define amdgpu_kernel void @permlane16_bound_ctrl(ptr addrspace(1) %out, i32 %src0, i32 %src1, i32 %src2) {
 ; CHECK-LABEL: @permlane16_bound_ctrl(
-; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlane16.i32(i32 undef, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 false, i1 true)
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlane16.i32(i32 poison, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 false, i1 true)
 ; CHECK-NEXT:    store i32 [[RES]], ptr addrspace(1) [[OUT:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
@@ -3283,7 +3283,7 @@ define amdgpu_kernel void @permlane16_bound_ctrl(ptr addrspace(1) %out, i32 %src
 
 define amdgpu_kernel void @permlane16_fetch_invalid_bound_ctrl(ptr addrspace(1) %out, i32 %src0, i32 %src1, i32 %src2) {
 ; CHECK-LABEL: @permlane16_fetch_invalid_bound_ctrl(
-; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlane16.i32(i32 undef, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 true, i1 true)
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlane16.i32(i32 poison, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 true, i1 true)
 ; CHECK-NEXT:    store i32 [[RES]], ptr addrspace(1) [[OUT:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
@@ -3311,7 +3311,7 @@ define amdgpu_kernel void @permlanex16(ptr addrspace(1) %out, i32 %src0, i32 %sr
 
 define amdgpu_kernel void @permlanex16_bound_ctrl(ptr addrspace(1) %out, i32 %src0, i32 %src1, i32 %src2) {
 ; CHECK-LABEL: @permlanex16_bound_ctrl(
-; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlanex16.i32(i32 undef, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 false, i1 true)
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlanex16.i32(i32 poison, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 false, i1 true)
 ; CHECK-NEXT:    store i32 [[RES]], ptr addrspace(1) [[OUT:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
@@ -3322,7 +3322,7 @@ define amdgpu_kernel void @permlanex16_bound_ctrl(ptr addrspace(1) %out, i32 %sr
 
 define amdgpu_kernel void @permlanex16_fetch_invalid_bound_ctrl(ptr addrspace(1) %out, i32 %src0, i32 %src1, i32 %src2) {
 ; CHECK-LABEL: @permlanex16_fetch_invalid_bound_ctrl(
-; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlanex16.i32(i32 undef, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 true, i1 true)
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.amdgcn.permlanex16.i32(i32 poison, i32 [[SRC0:%.*]], i32 [[SRC1:%.*]], i32 [[SRC2:%.*]], i1 true, i1 true)
 ; CHECK-NEXT:    store i32 [[RES]], ptr addrspace(1) [[OUT:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;