Disallow redefinition of variably modified typedefs

[Richard Guenther]

On Sat, Mar 19, 2011 at 12:29 AM, Joseph S. Myers
<joseph@codesourcery.com> wrote:
> This week's London WG14 meeting decided that typedef redefinition
> should not be allowed in the case of variably modified types.  This
> patch implements this, giving an error for such redefinitions.
>
> Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  Applied
> to mainline.  Any comments from other RMs about whether this should go
> in 4.6 as well, to avoid 4.6.0 being more lenient in this area than
> both 4.5 and 4.7?  This is much the same issue as for anonymous
> structs and unions, but for a much more obscure case.
>
> (These two patches cover the only two cases of C1X features that were
> fully implemented for 4.6 according to the pre-London draft, and then
> changed in London.  The post-London document will be going to
> enquiry-stage ITTF/JTC1 ballot so if that passes there should be no
> more technical changes before publication.)

I think it should go into 4.6.0 as well.

Thanks,
Richard.

> 2011-03-18  Joseph Myers  <joseph@codesourcery.com>
>
>        * c-decl.c (diagnose_mismatched_decls): Give an error for
>        redefining a typedef with variably modified type.
>
> testsuite:
> 2011-03-18  Joseph Myers  <joseph@codesourcery.com>
>
>        * gcc.dg/c1x-typedef-1.c: Expect errors for redefinitions of
>        variably modified typedefs.
>        * gcc.dg/c1x-typedef-2.c: Remove.
>
> Index: testsuite/gcc.dg/c1x-typedef-1.c
> ===================================================================
> --- testsuite/gcc.dg/c1x-typedef-1.c    (revision 171110)
> +++ testsuite/gcc.dg/c1x-typedef-1.c    (working copy)
> @@ -3,7 +3,8 @@
>  /* { dg-options "-std=c1x -pedantic-errors" } */
>
>  /* C1X permits typedefs to be redeclared to the same type, but not to
> -   different-but-compatible types.  */
> +   different-but-compatible types, and not when the type is variably
> +   modified.  */
>
>  #include <limits.h>
>
> @@ -60,9 +61,10 @@ f (void)
>   typedef void FN2(int (*p)[*]); /* { dg-message "previous declaration" } */
>   typedef void FN2(int (*p)[]); /* { dg-error "with different type" } */
>   typedef int AV[a]; /* { dg-message "previous declaration" } */
> -  typedef int AV[b-1]; /* { dg-warning "may be a constraint violation at runtime" } */
> -  typedef int AAa[a];
> +  typedef int AV[b-1]; /* { dg-error "redefinition" } */
> +  typedef int AAa[a]; /* { dg-message "previous declaration" } */
>   typedef int AAb[b-1];
>   typedef AAa *VF(void); /* { dg-message "previous declaration" } */
> -  typedef AAb *VF(void); /* { dg-warning "may be a constraint violation at runtime" } */
> +  typedef AAb *VF(void); /* { dg-error "redefinition" } */
> +  typedef AAa AAa; /* { dg-error "redefinition" } */
>  }
> Index: testsuite/gcc.dg/c1x-typedef-2.c
> ===================================================================
> --- testsuite/gcc.dg/c1x-typedef-2.c    (revision 171110)
> +++ testsuite/gcc.dg/c1x-typedef-2.c    (working copy)
> @@ -1,18 +0,0 @@
> -/* Test typedef redeclaration in C1X.  Side effects from duplicate
> -   declarations still apply.  */
> -/* { dg-do run } */
> -/* { dg-options "-std=c1x -pedantic-errors" } */
> -
> -extern void exit (int);
> -extern void abort (void);
> -
> -int
> -main (void)
> -{
> -  int a = 1, b = 1;
> -  typedef int T[++a]; /* { dg-message "previous declaration" } */
> -  typedef int T[++b]; /* { dg-warning "may be a constraint violation at runtime" } */
> -  if (a != 2 || b != 2)
> -    abort ();
> -  exit (0);
> -}
> Index: c-decl.c
> ===================================================================
> --- c-decl.c    (revision 171110)
> +++ c-decl.c    (working copy)
> @@ -1813,20 +1813,16 @@ diagnose_mismatched_decls (tree newdecl,
>          || TREE_NO_WARNING (olddecl))
>        return true;  /* Allow OLDDECL to continue in use.  */
>
> -      if (pedantic && !flag_isoc1x)
> +      if (variably_modified_type_p (newtype, NULL))
>        {
> -         pedwarn (input_location, OPT_pedantic,
> -                  "redefinition of typedef %q+D", newdecl);
> +         error ("redefinition of typedef %q+D with variably modified type",
> +                newdecl);
>          locate_old_decl (olddecl);
>        }
> -      else if (variably_modified_type_p (newtype, NULL))
> +      else if (pedantic && !flag_isoc1x)
>        {
> -         /* Whether there is a constraint violation for the types not
> -            being the same cannot be determined at compile time; a
> -            warning that there may be one at runtime is considered
> -            appropriate (WG14 reflector message 11743, 8 May 2009).  */
> -         warning (0, "redefinition of typedef %q+D may be a constraint "
> -                  "violation at runtime", newdecl);
> +         pedwarn (input_location, OPT_pedantic,
> +                  "redefinition of typedef %q+D", newdecl);
>          locate_old_decl (olddecl);
>        }
>
>
> --
> Joseph S. Myers
> joseph@codesourcery.com
>