[clang] [Clang] Fix potential null pointer dereference in retain cycle detection (PR #95192)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (smanna12)

<details>
<summary>Changes</summary>

This patch resolves a static analyzer bug where `S.getCurMethodDecl()` could return `nullptr` when calling `getSelfDecl(()` and was being dereferenced without a null check. The fix introduces a check for a non-null return value before accessing `getSelfDecl()` to ensure safe dereferencing.

This change prevents undefined behavior in scenarios where the current method declaration is not available, thus enhancing the robustness of the retain cycle detection logic.

---
Full diff: https://github.com/llvm/llvm-project/pull/95192.diff


1 Files Affected:

- (modified) clang/lib/Sema/SemaObjC.cpp (+9-5) 


``````````diff
diff --git a/clang/lib/Sema/SemaObjC.cpp b/clang/lib/Sema/SemaObjC.cpp
index d396258cfc7d1..69c78f034bd43 100644
--- a/clang/lib/Sema/SemaObjC.cpp
+++ b/clang/lib/Sema/SemaObjC.cpp
@@ -848,12 +848,16 @@ static bool findRetainCycleOwner(Sema &S, Expr *e, RetainCycleOwner &owner) {
 
       owner.Indirect = true;
       if (pre->isSuperReceiver()) {
-        owner.Variable = S.getCurMethodDecl()->getSelfDecl();
-        if (!owner.Variable)
+        if (const auto *CurMethodDecl = S.getCurMethodDecl()) {
+          owner.Variable = CurMethodDecl()->getSelfDecl();
+          if (!owner.Variable)
+            return false;
+          owner.Loc = pre->getLocation();
+          owner.Range = pre->getSourceRange();
+          return true;
+        } else {
           return false;
-        owner.Loc = pre->getLocation();
-        owner.Range = pre->getSourceRange();
-        return true;
+        }
       }
       e = const_cast<Expr *>(
           cast<OpaqueValueExpr>(pre->getBase())->getSourceExpr());

``````````

</details>


https://github.com/llvm/llvm-project/pull/95192