[WebKit Checkers] Treat offsetof as a trivial expression. (#126996)

Author: rniwa

clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp

@@ -503,6 +503,11 @@ class TrivialFunctionAnalysisVisitor
     return true;
   }
 
+  bool VisitOffsetOfExpr(const OffsetOfExpr *OE) {
+    // offsetof(T, D) is considered trivial.
+    return true;
+  }
+
   bool VisitCXXMemberCallExpr(const CXXMemberCallExpr *MCE) {
     if (!checkArguments(MCE))
       return false;

clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp

@@ -77,6 +77,8 @@ T&& forward(T& arg);
 template<typename T>
 T&& move( T&& t );
 
+#define offsetof(t, d) __builtin_offsetof(t, d)
+
 } // namespace std
 
 bool isMainThread();
@@ -373,6 +375,7 @@ class RefCounted {
     double y;
   };
   void trivial68() { point pt = { 1.0 }; }
+  unsigned trivial69() { return offsetof(RefCounted, children); }
 
   static RefCounted& singleton() {
     static RefCounted s_RefCounted;
@@ -560,6 +563,7 @@ class UnrelatedClass {
     getFieldTrivial().trivial66()->trivial6(); // no-warning
     getFieldTrivial().trivial67()->trivial6(); // no-warning
     getFieldTrivial().trivial68(); // no-warning
+    getFieldTrivial().trivial69(); // no-warning
 
     RefCounted::singleton().trivial18(); // no-warning
     RefCounted::singleton().someFunction(); // no-warning