Towards GNU11

[Jeff Law]

On 10/07/14 15:07, 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?
>
> 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.
I like it.  And one could reasonably argue that now is the time to 
change since that maximizes the time for folks to find broken code.

I'd go so far as to conditionally approve -- if other maintainers don't 
shout out in the next week or so against, then I feel this should go 
forward.

I know it's really early, but a "porting to ..." document ought to be 
started and have something in it about these changes.  Both how to fix 
the broken code or how to go back to c89.

Jeff