[llvm-branch-commits] [llvm] AMDGPU: Make fmul_legacy intrinsic propagate poison (PR #131062)

[Matt Arsenault via llvm-branch-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/131062

None

>From 5f4a37dcdb2d6bf9e503bab459d92067e2d885e9 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 13 Mar 2025 10:46:42 +0700
Subject: [PATCH] AMDGPU: Make fmul_legacy intrinsic propagate poison

---
 .../Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp |  5 +++++
 .../Transforms/InstCombine/AMDGPU/fmul_legacy.ll | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
index 083fa2a730fff..ba4e6e530fe56 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp
@@ -1255,6 +1255,11 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
     Value *Op0 = II.getArgOperand(0);
     Value *Op1 = II.getArgOperand(1);
 
+    for (Value *Src : {Op0, Op1}) {
+      if (isa<PoisonValue>(Src))
+        return IC.replaceInstUsesWith(II, Src);
+    }
+
     // The legacy behaviour is that multiplying +/-0.0 by anything, even NaN or
     // infinity, gives +0.0.
     // TODO: Move to InstSimplify?
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/fmul_legacy.ll b/llvm/test/Transforms/InstCombine/AMDGPU/fmul_legacy.ll
index d58470d6b12ad..899b611b929d1 100644
--- a/llvm/test/Transforms/InstCombine/AMDGPU/fmul_legacy.ll
+++ b/llvm/test/Transforms/InstCombine/AMDGPU/fmul_legacy.ll
@@ -75,6 +75,22 @@ define float @test_finite_assumed(float %x, float %y) {
   ret float %call
 }
 
+define float @test_poison_var(float %x) {
+; CHECK-LABEL: @test_poison_var(
+; CHECK-NEXT:    ret float poison
+;
+  %call = call float @llvm.amdgcn.fmul.legacy(float poison, float %x)
+  ret float %call
+}
+
+define float @test_var_poison(float %x) {
+; CHECK-LABEL: @test_var_poison(
+; CHECK-NEXT:    ret float poison
+;
+  %call = call float @llvm.amdgcn.fmul.legacy(float %x, float poison)
+  ret float %call
+}
+
 declare float @llvm.amdgcn.fmul.legacy(float, float)
 declare float @llvm.fabs.f32(float)
 declare void @llvm.assume(i1 noundef)