2 files changed, 14 insertions, 1 deletions
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 17b14bd2a1b..66b1d180780 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -424,7 +424,11 @@ Parser::ParseRHSOfBinaryExpression(ExprResult LHS, unsigned MinPrec) {
 Parser::ExprResult Parser::ParseCastExpression(bool isUnaryExpression) {
   if (getLang().CPlusPlus) {
     // Annotate typenames and C++ scope specifiers.
-    // Used only in C++; in C let the typedef name be handled as an identifier.
+    // Used only in C++, where the typename can be considered as a functional
+    // style cast ("int(1)").
+    // In C we don't expect identifiers to be treated as typenames; if it's a
+    // typedef name, let it be handled as an identifier and
+    // Actions.ActOnIdentifierExpr will emit the proper diagnostic.
     TryAnnotateTypeOrScopeToken();
   }
 
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index ec07b423193..42d95e7f02e 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -700,6 +700,15 @@ Parser::ExprResult Parser::ParseSimpleAsm() {
 /// This simplifies handling of C++ scope specifiers and allows efficient
 /// backtracking without the need to re-parse and resolve nested-names and
 /// typenames.
+/// It will mainly be called when we expect to treat identifiers as typenames
+/// (if they are typenames). For example, in C we do not expect identifiers
+/// inside expressions to be treated as typenames so it will not be called
+/// for expressions in C.
+/// The benefit for C/ObjC is that a typename will be annotated and
+/// Actions.isTypeName will not be needed to be called again (e.g. isTypeName
+/// will not be called twice, once to check whether we have a declaration
+/// specifier, and another one to get the actual type inside
+/// ParseDeclarationSpecifiers).
 void Parser::TryAnnotateTypeOrScopeToken() {
   if (Tok.is(tok::annot_qualtypename) || Tok.is(tok::annot_cxxscope))
     return;