Attributor: Propagate align to atomicrmw instructions (#134837)

Partially fixes #134480

Author: arsenm

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -5283,7 +5283,7 @@ struct AAAlignImpl : AAAlign {
 
   /// See AbstractAttribute::manifest(...).
   ChangeStatus manifest(Attributor &A) override {
-    ChangeStatus LoadStoreChanged = ChangeStatus::UNCHANGED;
+    ChangeStatus InstrChanged = ChangeStatus::UNCHANGED;
 
     // Check for users that allow alignment annotations.
     Value &AssociatedValue = getAssociatedValue();
@@ -5297,16 +5297,26 @@ struct AAAlignImpl : AAAlign {
             STATS_DECLTRACK(AAAlign, Store,
                             "Number of times alignment added to a store");
             SI->setAlignment(getAssumedAlign());
-            LoadStoreChanged = ChangeStatus::CHANGED;
+            InstrChanged = ChangeStatus::CHANGED;
           }
       } else if (auto *LI = dyn_cast<LoadInst>(U.getUser())) {
         if (LI->getPointerOperand() == &AssociatedValue)
           if (LI->getAlign() < getAssumedAlign()) {
             LI->setAlignment(getAssumedAlign());
             STATS_DECLTRACK(AAAlign, Load,
                             "Number of times alignment added to a load");
-            LoadStoreChanged = ChangeStatus::CHANGED;
+            InstrChanged = ChangeStatus::CHANGED;
           }
+      } else if (auto *RMW = dyn_cast<AtomicRMWInst>(U.getUser())) {
+        if (RMW->getPointerOperand() == &AssociatedValue) {
+          if (RMW->getAlign() < getAssumedAlign()) {
+            STATS_DECLTRACK(AAAlign, AtomicRMW,
+                            "Number of times alignment added to atomicrmw");
+
+            RMW->setAlignment(getAssumedAlign());
+            InstrChanged = ChangeStatus::CHANGED;
+          }
+        }
       }
     }
 
@@ -5315,8 +5325,8 @@ struct AAAlignImpl : AAAlign {
     Align InheritAlign =
         getAssociatedValue().getPointerAlignment(A.getDataLayout());
     if (InheritAlign >= getAssumedAlign())
-      return LoadStoreChanged;
-    return Changed | LoadStoreChanged;
+      return InstrChanged;
+    return Changed | InstrChanged;
   }
 
   // TODO: Provide a helper to determine the implied ABI alignment and check in

llvm/test/Transforms/Attributor/align-atomic.ll

@@ -16,7 +16,7 @@ define i32 @atomicrmw_add_no_op(ptr align 4 %ptr, i32 %val) {
 define i32 @atomicrmw_add_propagate(ptr align 8 %ptr, i32 %val) {
 ; CHECK-LABEL: define i32 @atomicrmw_add_propagate(
 ; CHECK-SAME: ptr nofree noundef nonnull align 8 captures(none) dereferenceable(4) [[PTR:%.*]], i32 [[VAL:%.*]]) #[[ATTR0]] {
-; CHECK-NEXT:    [[RESULT:%.*]] = atomicrmw add ptr [[PTR]], i32 [[VAL]] seq_cst, align 2
+; CHECK-NEXT:    [[RESULT:%.*]] = atomicrmw add ptr [[PTR]], i32 [[VAL]] seq_cst, align 8
 ; CHECK-NEXT:    ret i32 [[RESULT]]
 ;
   %result = atomicrmw add ptr %ptr, i32 %val seq_cst, align 2