Thread Safety Analysis: Handle parenthesis

When the variable guared by a lock was enclosed in parenthesis, access
violation warnings were not emitted. This patch fixes it and adds a
regression test.

Author: Prabhuk

clang/lib/Analysis/ThreadSafety.cpp

@@ -1671,7 +1671,7 @@ void ThreadSafetyAnalyzer::checkAccess(const FactSet &FSet, const Expr *Exp,
         // Guard against self-initialization. e.g., int &i = i;
         if (E == Exp)
           break;
-        Exp = E;
+        Exp = E->IgnoreImplicit()->IgnoreParenCasts();
         continue;
       }
     }

clang/test/Analysis/thread-safety-handle-parenthesis.cpp

@@ -0,0 +1,20 @@
+
+// RUN: %clang_cc1 -verify -fsyntax-only -std=c++20 -Wthread-safety %s
+
+class __attribute__((lockable)) Lock {};
+
+void sink_protected(int) {}
+
+class Baz {
+public:
+    Lock lock_;
+    int protected_num_ __attribute__((guarded_by(lock_))) = 1;
+};
+
+void baz_paran_test() {
+    Baz baz;     
+    int& n = baz.protected_num_;
+    sink_protected(n); // expected-warning{{reading variable 'protected_num_' requires holding mutex 'baz.lock_'}}
+    int& n2 = (baz.protected_num_);
+    sink_protected(n2); // expected-warning{{reading variable 'protected_num_' requires holding mutex 'baz.lock_'}}
+}