[llvm] [GlobalsAA] Handle self-referencing stores in `AnalyzeUsesOfPointer` (PR #213631)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Antonio Frighetto (antoniofrighetto)

<details>
<summary>Changes</summary>

Correctly recognize that a global address does escape when it is stored into itself. Such globals were previously incorrectly marked as non-address-taken.

Fixes: https://github.com/llvm/llvm-project/issues/213232.

---
Full diff: https://github.com/llvm/llvm-project/pull/213631.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/GlobalsModRef.cpp (+2-1) 
- (added) llvm/test/Analysis/GlobalsModRef/self-addresstaken.ll (+16) 


``````````diff
diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
index 1a0ae25b2b6b3..6471cc0d52cbd 100644
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -328,7 +328,8 @@ bool GlobalsAAResult::AnalyzeUsesOfPointer(Value *V,
       if (Readers)
         Readers->insert(LI->getParent()->getParent());
     } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
-      if (V == SI->getOperand(1)) {
+      // Check the pointer operand use of the store.
+      if (&U == &SI->getOperandUse(1)) {
         if (Writers)
           Writers->insert(SI->getParent()->getParent());
       } else if (SI->getOperand(1) != OkayStoreDest) {
diff --git a/llvm/test/Analysis/GlobalsModRef/self-addresstaken.ll b/llvm/test/Analysis/GlobalsModRef/self-addresstaken.ll
new file mode 100644
index 0000000000000..57fd8259f6790
--- /dev/null
+++ b/llvm/test/Analysis/GlobalsModRef/self-addresstaken.ll
@@ -0,0 +1,16 @@
+; RUN: opt < %s -passes='require<globals-aa>,aa-eval' -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+
+; Ensure @g is correctly marked as address taken when it is stored into itself.
+
+ at g = internal global ptr null
+
+; CHECK-LABEL: self_addresstaken
+; CHECK:       MayAlias:	ptr* %p, ptr* @g
+
+define ptr @self_addresstaken() {
+  store ptr @g, ptr @g, align 8
+  %p = load ptr, ptr @g, align 8
+  store ptr null, ptr %p, align 8
+  %q = load ptr, ptr @g, align 8
+  ret ptr %q
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/213631