[llvm-branch-commits] [llvm] Attributor: Propagate align to cmpxchg instructions (PR #134838)

[Matt Arsenault via llvm-branch-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/134838

Fixes #134480

>From e945a79a89839db98c4d43c1825b07cb1bda4a98 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 8 Apr 2025 17:31:24 +0700
Subject: [PATCH] Attributor: Propagate align to cmpxchg instructions

Fixes #134480
---
 llvm/lib/Transforms/IPO/AttributorAttributes.cpp | 9 +++++++++
 llvm/test/Transforms/Attributor/align-atomic.ll  | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index 717ba7f688548..cc6e846f4f211 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -5317,6 +5317,15 @@ struct AAAlignImpl : AAAlign {
             InstrChanged = ChangeStatus::CHANGED;
           }
         }
+      } else if (auto *CAS = dyn_cast<AtomicCmpXchgInst>(U.getUser())) {
+        if (CAS->getPointerOperand() == &AssociatedValue) {
+          if (CAS->getAlign() < getAssumedAlign()) {
+            STATS_DECLTRACK(AAAlign, AtomicCmpXchg,
+                            "Number of times alignment added to cmpxchg");
+            CAS->setAlignment(getAssumedAlign());
+            InstrChanged = ChangeStatus::CHANGED;
+          }
+        }
       }
     }
 
diff --git a/llvm/test/Transforms/Attributor/align-atomic.ll b/llvm/test/Transforms/Attributor/align-atomic.ll
index 0931c14685a87..0b363741cc168 100644
--- a/llvm/test/Transforms/Attributor/align-atomic.ll
+++ b/llvm/test/Transforms/Attributor/align-atomic.ll
@@ -37,7 +37,7 @@ define ptr @atomicrmw_non_ptr_op_no_propagate(ptr %ptr, ptr align 16 %val) {
 define i32 @cmpxchg_propagate(ptr align 8 %ptr, i32 %cmp, i32 %val) {
 ; CHECK-LABEL: define i32 @cmpxchg_propagate(
 ; CHECK-SAME: ptr nofree noundef nonnull align 8 captures(none) dereferenceable(4) [[PTR:%.*]], i32 [[CMP:%.*]], i32 [[VAL:%.*]]) #[[ATTR0]] {
-; CHECK-NEXT:    [[PAIR:%.*]] = cmpxchg ptr [[PTR]], i32 [[CMP]], i32 [[VAL]] seq_cst monotonic, align 2
+; CHECK-NEXT:    [[PAIR:%.*]] = cmpxchg ptr [[PTR]], i32 [[CMP]], i32 [[VAL]] seq_cst monotonic, align 8
 ; CHECK-NEXT:    [[RESULT:%.*]] = extractvalue { i32, i1 } [[PAIR]], 0
 ; CHECK-NEXT:    ret i32 [[RESULT]]
 ;