[llvm] AMDGPU: Make rcp intrinsic propagate poison (PR #130913)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/130913

None

>From 8fd7cd3b57f6392ce4ba46db7d165254b5824252 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Wed, 12 Mar 2025 14:05:47 +0700
Subject: [PATCH] AMDGPU: Make rcp intrinsic propagate poison

---
 llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp     | 2 ++
 .../Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll    | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
index ef076814ffdab..6f6556365ebf6 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
@@ -487,6 +487,8 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
   switch (IID) {
   case Intrinsic::amdgcn_rcp: {
     Value *Src = II.getArgOperand(0);
+    if (isa<PoisonValue>(Src))
+      return IC.replaceInstUsesWith(II, Src);
 
     // TODO: Move to ConstantFolding/InstSimplify?
     if (isa<UndefValue>(Src)) {
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll b/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
index 3c190efca7acf..42ddc71dab848 100644
--- a/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll
@@ -8,6 +8,14 @@
 declare float @llvm.amdgcn.rcp.f32(float) nounwind readnone
 declare double @llvm.amdgcn.rcp.f64(double) nounwind readnone
 
+define float @test_constant_fold_rcp_f32_poison() nounwind {
+; CHECK-LABEL: @test_constant_fold_rcp_f32_poison(
+; CHECK-NEXT:    ret float poison
+;
+  %val = call float @llvm.amdgcn.rcp.f32(float poison) nounwind readnone
+  ret float %val
+}
+
 define float @test_constant_fold_rcp_f32_undef() nounwind {
 ; CHECK-LABEL: @test_constant_fold_rcp_f32_undef(
 ; CHECK-NEXT:    ret float 0x7FF8000000000000