Re: [Emacs-diffs] master 6cd5678: Clarify compiler-pacifier in frame.c

[Eli Zaretskii <eliz@gnu.org>]

> Cc: emacs-devel@gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Tue, 27 Aug 2019 02:28:42 -0700
> 
> There are two reasons that omitting UNINIT causes GCC to warn about 
> Fx_parse_geometry but not image_create_bitmap_from_file. First, under MS-Windows 
> GCC has access to the source code of the initialization function XParseGeometry 
> that Fx_parse_geometry calls, whereas under X Windows GCC lacks access to the 
> source code of the initialization function XReadBitmapFile that 
> image_create_bitmap_from_file calls (I am assuming typical builds without fancy 
> link-time optimization). Second, GCC does not fully grok the source code of 
> MS-Windows XParseGeometry; GCC gets lost and thinks that there's a path through 
> Fx_parse_geometry + XParseGeometry that will use Fx_parse_geometry's x without 
> initializing it, even though there is no such path.

Do you have a guess why GCC might get lost in that code?

> > And how should GCC know that?
> 
> GCC could use the same sort of reasoning I used.

Which reasoning is that?  You haven't presented your reasoning for
XParseGeometry, AFAICT.  You presented reasoning for some other code,
which you consider similar.

> And perhaps some future version of GCC will do that. But in the
> meantime GCC gives a false alarm, so UNINIT is warranted here.
> 
> UNINIT is precisely for this sort of situation: the programmer knows that a 
> variable need not be initialized, but GCC falsely warns about the lack of 
> initialization.

No, UNINIT is for you to be able to use your tools of choice, and
perhaps also to cater to your personal stylistic preferences.  I
consider an initialization with a comment explaining why to be a
better alternative, whether the warning is real or a false alarm.