Re: stddef.h: Add C2x unreachable macro

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Sep 8, 2022 at 9:32 PM Joseph Myers <joseph@codesourcery.com> wrote:
>
> C2x adds a macro unreachable to stddef.h, with the same semantics as
> __builtin_unreachable.  Define this macro accordingly.
>
> Bootstrapped with no regressions for x86_64-pc-linux-gnu.  OK to commit?

OK.

> gcc/
>         * ginclude/stddef.h [__STDC_VERSION__ > 201710L] (unreachable):
>         New macro.
>
> gcc/testsuite/
>         * gcc.dg/c11-unreachable-1.c, gcc.dg/c2x-unreachable-1.c: New
>         tests.
>
> diff --git a/gcc/ginclude/stddef.h b/gcc/ginclude/stddef.h
> index 315ff786694..3d29213e8f1 100644
> --- a/gcc/ginclude/stddef.h
> +++ b/gcc/ginclude/stddef.h
> @@ -451,6 +451,10 @@ typedef struct {
>  #endif
>  #endif /* C23.  */
>
> +#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
> +#define unreachable() (__builtin_unreachable ())
> +#endif
> +
>  #endif /* _STDDEF_H was defined this time */
>
>  #endif /* !_STDDEF_H && !_STDDEF_H_ && !_ANSI_STDDEF_H && !__STDDEF_H__
> diff --git a/gcc/testsuite/gcc.dg/c11-unreachable-1.c b/gcc/testsuite/gcc.dg/c11-unreachable-1.c
> new file mode 100644
> index 00000000000..28e48392ed1
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/c11-unreachable-1.c
> @@ -0,0 +1,9 @@
> +/* Test unreachable not defined in <stddef.h> for C11.  */
> +/* { dg-do preprocess } */
> +/* { dg-options "-std=c11 -pedantic-errors" } */
> +
> +#include <stddef.h>
> +
> +#ifdef unreachable
> +#error "unreachable defined"
> +#endif
> diff --git a/gcc/testsuite/gcc.dg/c2x-unreachable-1.c b/gcc/testsuite/gcc.dg/c2x-unreachable-1.c
> new file mode 100644
> index 00000000000..468f1f87ebb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/c2x-unreachable-1.c
> @@ -0,0 +1,29 @@
> +/* Test unreachable in <stddef.h> for C2x.  */
> +/* { dg-do run } */
> +/* { dg-options "-std=c2x -pedantic-errors -O2" } */
> +
> +#include <stddef.h>
> +
> +#ifndef unreachable
> +#error "unreachable not defined"
> +#endif
> +
> +extern void *p;
> +extern __typeof__ (unreachable ()) *p;
> +
> +volatile int x = 1;
> +
> +extern void not_defined (void);
> +
> +extern void exit (int);
> +
> +int
> +main ()
> +{
> +  if (x == 2)
> +    {
> +      unreachable ();
> +      not_defined ();
> +    }
> +  exit (0);
> +}
>
> --
> Joseph S. Myers
> joseph@codesourcery.com