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

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

Fixes #<!-- -->134480

---
Full diff: https://github.com/llvm/llvm-project/pull/134838.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/AttributorAttributes.cpp (+9) 
- (modified) llvm/test/Transforms/Attributor/align-atomic.ll (+1-1) 


``````````diff
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]]
 ;

``````````

</details>


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