Simplify code, add an assertion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157111 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index d760e6d..49f76fe 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -1721,15 +1721,12 @@
   /// interface, or null if non exists.
   const ObjCMethodDecl *getObjCMethodRedeclaration(
                                                const ObjCMethodDecl *MD) const {
-    llvm::DenseMap<const ObjCMethodDecl*, const ObjCMethodDecl*>::const_iterator
-      I = ObjCMethodRedecls.find(MD);
-    if (I == ObjCMethodRedecls.end())
-      return 0;
-    return I->second;
+    return ObjCMethodRedecls.lookup(MD);
   }
 
   void setObjCMethodRedeclaration(const ObjCMethodDecl *MD,
                                   const ObjCMethodDecl *Redecl) {
+    assert(!getObjCMethodRedeclaration(MD) && "MD already has a redeclaration");
     ObjCMethodRedecls[MD] = Redecl;
   }