Don't revisit the subexpressions of PseudoObjectExpr when building a ParentMap

[ahatanak]

Summary

The assertion that is removed in this patch was failing when ObjC dot notation expressions appear in both sides of an assignment (see the test case in arc-repeated-weak.mm). Visit the PseudoObjectExpr once when the syntactic expression is visited and return without visiting the subexpressions when it's visited again when the semantic expressions are visited.

[rjmccall]

LGTM

clang/lib/AST/ParentMap.cpp

 
 static void BuildParentMap(MapTy& M, Stmt* S,
                            OpaqueValueMode OVMode = OV_Transparent) {
   if (!S)
     return;
 
   switch (S->getStmtClass()) {
   case Stmt::PseudoObjectExprClass: {
-    assert(OVMode == OV_Transparent && "Should not appear alongside OVEs");
     PseudoObjectExpr *POE = cast<PseudoObjectExpr>(S);
 
+    if (OVMode == OV_Opaque && M[POE->getSyntacticForm()])
+      break;
+
     // If we are rebuilding the map, clear out any existing state.
     if (M[POE->getSyntacticForm()])
       for (Stmt *SubStmt : S->children())
         M[SubStmt] = nullptr;
 
     M[POE->getSyntacticForm()] = S;
     BuildParentMap(M, POE->getSyntacticForm(), OV_Transparent);
 

clang/test/SemaObjC/arc-repeated-weak.mm

 }
 
 void doWhileLoop(Test *a) {
   do {
     use(a.weakProp); // no-warning
   } while(0);
 }
 
+struct S {
+  int a;
+  id b;
+};
+
+@interface C
+@property S p;
+@end
+
+void test_list_init(C *c) {
+  c.p = {0, c.p.b};
+}
 
 @interface Test (Methods)
 @end
 
 @implementation Test (Methods)
 - (void)basicCorrectnessTest {
   use(self.weakProp); // expected-warning{{weak property 'weakProp' is accessed multiple times in this method but may be unpredictably set to nil; assign to a strong variable to keep the object alive}}
   use(self.weakProp); // expected-note{{also accessed here}}