[llvm] [AMDGPU] Set success flag for weak cmpxchg in LowerBufferFatPointers (PR #203033)

[Arseniy Obolenskiy via llvm-commits]

https://github.com/aobolensk created https://github.com/llvm/llvm-project/pull/203033

The weak cmpxchg lowering never set the success bool leaving it poison and breaking code that reads it

The buffer atomic cmpswap never fails by chance, so the strong path works for weak too

>From 74df75feda70df9b7c55bec1d6cf6ca6022f8f4e Mon Sep 17 00:00:00 2001
From: Arseniy Obolenskiy <arseniy.obolenskiy at amd.com>
Date: Wed, 10 Jun 2026 17:35:07 +0200
Subject: [PATCH] [AMDGPU] Set success flag for weak cmpxchg in
 LowerBufferFatPointers

The weak cmpxchg lowering never set the success bool leaving it poison and breaking code that reads it

The buffer atomic cmpswap never fails by chance, so the strong path works for weak too
---
 llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp     | 6 ++----
 .../test/CodeGen/AMDGPU/lower-buffer-fat-pointers-memops.ll | 4 +++-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
index 679f7d5d8329f..300c2f8782ae1 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
@@ -1880,10 +1880,8 @@ PtrParts SplitPtrStructs::visitAtomicCmpXchgInst(AtomicCmpXchgInst &AI) {
 
   Value *Res = PoisonValue::get(AI.getType());
   Res = IRB.CreateInsertValue(Res, Call, 0);
-  if (!AI.isWeak()) {
-    Value *Succeeded = IRB.CreateICmpEQ(Call, AI.getCompareOperand());
-    Res = IRB.CreateInsertValue(Res, Succeeded, 1);
-  }
+  Value *Succeeded = IRB.CreateICmpEQ(Call, AI.getCompareOperand());
+  Res = IRB.CreateInsertValue(Res, Succeeded, 1);
   SplitUsers.insert(&AI);
   AI.replaceAllUsesWith(Res);
   return {nullptr, nullptr};
diff --git a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-memops.ll b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-memops.ll
index ca51a08920aba..756a6af4ccbcd 100644
--- a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-memops.ll
+++ b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-memops.ll
@@ -175,7 +175,9 @@ define {i32, i1} @cmpxchg_weak(ptr addrspace(8) %buf, i32 %wanted, i32 %new) {
 ; CHECK-NEXT:    [[RET:%.*]] = call i32 @llvm.amdgcn.raw.ptr.buffer.atomic.cmpswap.i32(i32 [[NEW]], i32 [[WANTED]], ptr addrspace(8) align 4 [[BUF]], i32 16, i32 0, i32 0)
 ; CHECK-NEXT:    fence syncscope("wavefront") acquire
 ; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i32, i1 } poison, i32 [[RET]], 0
-; CHECK-NEXT:    ret { i32, i1 } [[TMP1]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i32 [[RET]], [[WANTED]]
+; CHECK-NEXT:    [[TMP3:%.*]] = insertvalue { i32, i1 } [[TMP1]], i1 [[TMP2]], 1
+; CHECK-NEXT:    ret { i32, i1 } [[TMP3]]
 ;
   %base = addrspacecast ptr addrspace(8) %buf to ptr addrspace(7)
   %p = getelementptr i32, ptr addrspace(7) %base, i32 4