Re: Towards GNU11

[Richard Biener <rguenther at suse dot de>]

On Tue, 7 Oct 2014, Marek Polacek wrote:

> Hi!
> 
> I'd like to kick off a discussion about moving the default standard
> for C from gnu89 to gnu11.
> 
> This really shouldn't be much of a surprise: the docs mention that
> gnu11 is intended future default for a year now.  I would presume now
> is a good time to make this move: together with the new naming scheme
> this should make GCC more modern (C89 really is as old as the hills).
> And we're still in stage1.
> 
> Prerequisites should be largely complete at this point:
> - we have -Wc90-c99-compat option that warns about features not present
>   in ISO C90, but present in ISO C99,
> - we have -Wc99-c11-compat option that warns about features not present
>   in ISO C99, but present in ISO C11,
> - the testsuite has been adjusted so all the test that pass with gnu89
>   default should pass with gnu11 default as well (see my recent batch
>   of cleanup patches).  This unfortunately isn't correct for all archs,
>   I just don't have enough resources to test everything.  But generally
>   the fallout from moving to gnu11 is easy to fix: just add proper decls
>   and return types (to fix defaulting to int), or for inline stuff use
>   -fgnu89-inline/gnu_inline attribute.  I'd appreciate testing on other
>   architectures than x86_64/ppc64.
> 
> The things I had to fix in the testsuite nicely reflect what we can expect
> in the real life: mostly bunch of new warnings about missing declarations
> and defaulting to int (this is probably going to be a pain with -Werror,
> but I feel that people really should write proper declarations), different
> inline semantics (in C99 semantics, the TU has to have the body of the inline
> function etc.), new "return with no value, in function returning non-void"
> warnings.  Different rules for constant expressions, the fact that in C90
> non-lvalue arrays do not decay to pointers, slightly different rules for
> compatible types (?) might come in game as well.
> 
> In turn, you can use all C99 and C11 features even with -pedantic.
> 
> Comments?

I think it makes sense to do this (and I expect C++ will follow
with defaulting to -std=c++11 once the ABI stuff has settled).

Of course it would be nice to look at the actual fallout in
a whole-distribution rebuild...

Thanks,
Richard.

> Regtested/bootstrapped on powerpc64-linux and x86_64-linux.
> 
> 2014-10-07  Marek Polacek  <polacek@redhat.com>
> 
> 	* doc/invoke.texi: Update to reflect that GNU11 is the default
> 	mode for C.
> 	* c-common.h (c_language_kind): Update comment.
> c-family/
> 	* c-opts.c (c_common_init_options): Make -std=gnu11 the default for C.
> 
> diff --git gcc/c-family/c-common.h gcc/c-family/c-common.h
> index 1e3477f..a895084 100644
> --- gcc/c-family/c-common.h
> +++ gcc/c-family/c-common.h
> @@ -445,7 +445,7 @@ struct GTY(()) sorted_fields_type {
>  
>  typedef enum c_language_kind
>  {
> -  clk_c		= 0,		/* C90, C94 or C99 */
> +  clk_c		= 0,		/* C90, C94, C99 or C11 */
>    clk_objc	= 1,		/* clk_c with ObjC features.  */
>    clk_cxx	= 2,		/* ANSI/ISO C++ */
>    clk_objcxx	= 3		/* clk_cxx with ObjC features.  */
> diff --git gcc/c-family/c-opts.c gcc/c-family/c-opts.c
> index 3f295d8..eb078e3 100644
> --- gcc/c-family/c-opts.c
> +++ gcc/c-family/c-opts.c
> @@ -250,6 +250,9 @@ c_common_init_options (unsigned int decoded_options_count,
>  
>    if (c_language == clk_c)
>      {
> +      /* The default for C is gnu11.  */
> +      set_std_c11 (false /* ISO */);
> +
>        /* If preprocessing assembly language, accept any of the C-family
>  	 front end options since the driver may pass them through.  */
>        for (i = 1; i < decoded_options_count; i++)
> diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
> index 5fe7e15..fa84ed4 100644
> --- gcc/doc/invoke.texi
> +++ gcc/doc/invoke.texi
> @@ -1692,8 +1692,7 @@ interfaces) and L (Analyzability).  The name @samp{c1x} is deprecated.
>  
>  @item gnu90
>  @itemx gnu89
> -GNU dialect of ISO C90 (including some C99 features). This
> -is the default for C code.
> +GNU dialect of ISO C90 (including some C99 features).
>  
>  @item gnu99
>  @itemx gnu9x
> @@ -1701,8 +1700,8 @@ GNU dialect of ISO C99.  The name @samp{gnu9x} is deprecated.
>  
>  @item gnu11
>  @itemx gnu1x
> -GNU dialect of ISO C11.  This is intended to become the default in a
> -future release of GCC.  The name @samp{gnu1x} is deprecated.
> +GNU dialect of ISO C11.  This is the default for C code.
> +The name @samp{gnu1x} is deprecated.
>  
>  @item c++98
>  @itemx c++03
> 
> 	Marek
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
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