On 3/13/25 11:27 AM, Jakub Jelinek wrote:
Hi!Apparently some programs in the wild use #if __has_attribute(musttail) __attribute__((musttail)) return foo (); #else return foo (); #endif clang supports musttail both as a standard attribute ([[clang::musttail]] which we also support for compatibility) and the above worked just fine with GCC 14 which had __has_attribute(musttail) 0. Now that it is 0, this doesn't compile anymore. So, either we need to ensure that __has_attribute(musttail) is 0 and just __has_c{,pp}_attribute({gnu,clang}::musttail) are non-zero, or IMHO better we just make it work in the attribute form, especially for C < C23 I can see why some projects would prefer that form. While [[gnu::musttail]] is rejected as an error in C11 etc. before GCC 15, rather than just handled as an unknown attribute. I view this as both a regression and compatibility issue. The patch handles it in similar spots to fallthrough/assume attributes inside of __attribute__. While working on it, I've noticed we weren't diagnosing arguments to the clang::musttail attribute (fixed by the c-attribs.cc hunk) and newly on the __attribute__ form attribute (in that case the arguments aren't just skipped, they are always parsed and because we don't call decl_attributes etc., it wouldn't be diagnosed without a manual check). Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2025-03-13 Jakub Jelinek <[email protected]> PR c/116545 gcc/ * doc/extend.texi (musttail statement attribute): Document that musttail GNU attribute can be used as well. gcc/c-family/ * c-attribs.cc (c_common_clang_attributes): Add musttail. gcc/c/ * c-parser.cc (c_parser_declaration_or_fndef): Parse __attribute__((musttail)) return. (c_parser_handle_musttail): Diagnose attribute arguments. (c_parser_statement_after_labels): Parse __attribute__((musttail)) return. gcc/cp/ * parser.cc (cp_parser_expression_statement): Parse __attribute__((musttail)) return.
Parsing a jump-statement under cp_parser_expression_statement just because it happens to start with __attribute is pretty strange.
How about changing cp_parser_std_attribute_spec_seq in cp_parser_statement to cp_parser_attributes_opt?
Jason
