[Sema][ObjC] Complete merging ObjC methods before checking their

overriding methods.

This should fix test case Analysis/retain-release.m that was failing on
the reverse iteration bot:

http://lab.llvm.org:8011/builders/reverse-iteration

The test used to fail because the loop in CheckObjCMethodOverrides would
merge attribute ns_returns_retained on methods while checking whether
the overriding methods were compatible. Since OverrideSearch::Overridden
is a SmallPtrSet and the order in which the elements of the set are
visited is non-deterministic, the test would fail when method 'clone' of
the protocol 'F18P' was visited before F18(Cat)'s method 'clone' was
visited.

llvm-svn: 315639

clang/lib/Sema/SemaDecl.cpp

@@ -3580,8 +3580,6 @@ void Sema::mergeObjCMethodDecls(ObjCMethodDecl *newMethod,
          ni = newMethod->param_begin(), ne = newMethod->param_end();
        ni != ne && oi != oe; ++ni, ++oi)
     mergeParamDeclAttributes(*ni, *oi, *this);
-
-  CheckObjCMethodOverride(newMethod, oldMethod);
 }
 
 static void diagnoseVarDeclTypeMismatch(Sema &S, VarDecl *New, VarDecl* Old) {

clang/lib/Sema/SemaDeclObjC.cpp

@@ -4223,6 +4223,10 @@ void Sema::CheckObjCMethodOverrides(ObjCMethodDecl *ObjCMethod,
 
     // Then merge the declarations.
     mergeObjCMethodDecls(ObjCMethod, overridden);
+  }
+
+  for (ObjCMethodDecl *overridden : overrides) {
+    CheckObjCMethodOverride(ObjCMethod, overridden);
 
     if (ObjCMethod->isImplicit() && overridden->isImplicit())
       continue; // Conflicting properties are detected elsewhere.