[gcc r11-5147] Objective-C++ : Avoid ICE on invalid with empty attributes.

[Iain D Sandoe]

https://gcc.gnu.org/g:08028093211c1b57f33e5669f816157934ab23dd

commit r11-5147-g08028093211c1b57f33e5669f816157934ab23dd
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Tue Nov 17 20:05:22 2020 +0000

    Objective-C++ : Avoid ICE on invalid with empty attributes.
    
    Empty prefix attributes like:
    
    __attribute__ (())
    @interface MyClass
    @end
    
    cause an ICE at present, check for that case and skip them.
    
    gcc/cp/ChangeLog:
    
            * parser.c (cp_parser_objc_valid_prefix_attributes): Check
            for empty attributes.

Diff:
---
 gcc/cp/parser.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index b7ef259b048..cf4e4aa1b75 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -33992,8 +33992,8 @@ cp_parser_objc_valid_prefix_attributes (cp_parser* parser, tree *attrib)
 {
   cp_lexer_save_tokens (parser->lexer);
   tree addon = cp_parser_attributes_opt (parser);
-  gcc_checking_assert (addon);
-  if (OBJC_IS_AT_KEYWORD (cp_lexer_peek_token (parser->lexer)->keyword))
+  if (addon
+      && OBJC_IS_AT_KEYWORD (cp_lexer_peek_token (parser->lexer)->keyword))
     {
       cp_lexer_commit_tokens (parser->lexer);
       if (*attrib)