| Message ID | 20131016113405.GC10967@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Wed, 16 Oct 2013, Marek Polacek wrote: > This PR is about _Alignas in contexts like > char x[_Alignas (int) 20]; > C grammar does not allow _Alignas to be in an array declarator, yet we > don't issue any warning or an error. This patch implements a pedwarn > for this. I'm however highly unsure whether we want pedwarn, error, or > normal warning for this - currently we just DTRT and ignore the > _Alignas altogether. I think this should be an error. I see this as a problem with how the parsing of array declarators uses c_parser_declspecs to parse a sequence of qualifiers and attributes, with scspec_ok=false and typespec_ok=false to ensure those kinds of specifiers can't occur in the list, but without any measure to exclude alignment specifiers. That is, I think c_parser_declspecs should gain an argument specifying whether alignment specifiers are OK, and the relevant calls from c_parser_direct_declarator_inner would pass false for that argument, and uses of alignment specifiers here would result in parse errors. (Incidentally, the comments in c-parser.c that are supposed to give the grammar accepted are missing the syntax of array-declarator.) > --- gcc/testsuite/gcc.dg/c1x-align-5.c.mp 2013-10-16 11:11:16.432690963 +0200 > +++ gcc/testsuite/gcc.dg/c1x-align-5.c 2013-10-16 11:15:09.269514593 +0200 > @@ -0,0 +1,17 @@ > +/* Test C1X alignment support. Test invalid code. */ > +/* { dg-do compile } */ > +/* { dg-options "-std=c1x -pedantic-errors" } */ > + > +static int > +foo (int a[_Alignas (0) 10]) /* { dg-error "meaningless in array declarator" } */ > +{ > + return a[0]; > +} > + > +int > +main () > +{ > + int a[_Alignas (int) 10]; /* { dg-error "meaningless in array declarator" } */ > + foo (a); > + return 0; > +} I think this should also be tested after "static" (given that there are two separate calls to c_parser_declspecs involved), as well as in an abstract declarator.
--- gcc/c/c-tree.h.mp 2013-10-15 19:36:09.548670833 +0200 +++ gcc/c/c-tree.h 2013-10-15 19:36:25.003727398 +0200 @@ -480,8 +480,8 @@ extern void c_init_decl_processing (void extern void c_print_identifier (FILE *, tree, int); extern int quals_from_declspecs (const struct c_declspecs *); extern struct c_declarator *build_array_declarator (location_t, tree, - struct c_declspecs *, - bool, bool); + struct c_declspecs *, + bool, bool, bool); extern tree build_enumerator (location_t, location_t, struct c_enum_contents *, tree, tree); extern tree check_for_loop_decls (location_t, bool); --- gcc/c/c-parser.c.mp 2013-10-15 19:33:47.706150200 +0200 +++ gcc/c/c-parser.c 2013-10-15 19:35:57.557627164 +0200 @@ -3096,8 +3096,10 @@ c_parser_direct_declarator_inner (c_pars struct c_declspecs *quals_attrs = build_null_declspecs (); bool static_seen; bool star_seen; + bool alignas_seen; tree dimen; c_parser_consume_token (parser); + alignas_seen = c_parser_next_token_is_keyword (parser, RID_ALIGNAS); c_parser_declspecs (parser, quals_attrs, false, false, true, cla_prefer_id); static_seen = c_parser_next_token_is_keyword (parser, RID_STATIC); if (static_seen) @@ -3169,7 +3171,8 @@ c_parser_direct_declarator_inner (c_pars if (dimen) mark_exp_read (dimen); declarator = build_array_declarator (brace_loc, dimen, quals_attrs, - static_seen, star_seen); + static_seen, star_seen, + alignas_seen); if (declarator == NULL) return NULL; inner = set_array_declarator_inner (declarator, inner); --- gcc/c/c-decl.c.mp 2013-10-15 19:35:30.172525717 +0200 +++ gcc/c/c-decl.c 2013-10-16 11:05:06.046383071 +0200 @@ -3866,7 +3866,7 @@ quals_from_declspecs (const struct c_dec struct c_declarator * build_array_declarator (location_t loc, tree expr, struct c_declspecs *quals, bool static_p, - bool vla_unspec_p) + bool vla_unspec_p, bool alignas_p) { struct c_declarator *declarator = XOBNEW (&parser_obstack, struct c_declarator); @@ -3908,6 +3908,9 @@ build_array_declarator (location_t loc, } current_scope->had_vla_unspec = true; } + if (alignas_p) + pedwarn (loc, OPT_Wpedantic, "%<_Alignas%> meaningless in array " + "declarator"); return declarator; } --- gcc/testsuite/gcc.dg/c1x-align-5.c.mp 2013-10-16 11:11:16.432690963 +0200 +++ gcc/testsuite/gcc.dg/c1x-align-5.c 2013-10-16 11:15:09.269514593 +0200 @@ -0,0 +1,17 @@ +/* Test C1X alignment support. Test invalid code. */ +/* { dg-do compile } */ +/* { dg-options "-std=c1x -pedantic-errors" } */ + +static int +foo (int a[_Alignas (0) 10]) /* { dg-error "meaningless in array declarator" } */ +{ + return a[0]; +} + +int +main () +{ + int a[_Alignas (int) 10]; /* { dg-error "meaningless in array declarator" } */ + foo (a); + return 0; +}