Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C

["René Scharfe" <l.s.r@web.de>]

Am 10.02.2017 um 15:20 schrieb Johannes Schindelin:
> It is curious that only MacOSX builds trigger an error about this, both
> GCC and Clang, but not Linux GCC nor Clang (see
> https://travis-ci.org/git/git/jobs/200182819#L1152 for details):
>
> builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used
> 		uninitialized whenever 'if' condition is true
> 		[-Werror,-Wsometimes-uninitialized]
>         if (missing_good && !missing_bad && current_term &&
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> builtin/bisect--helper.c:350:7: note: uninitialized use occurs here
>         if (!good_syn)
>              ^~~~~~~~

The only way that good_syn could be used in the if block is by going to 
the label finish, which does the following before returning:

	if (!bad_ref)
		free(bad_ref);
	if (!good_glob)
		free(good_glob);
	if (!bad_syn)
		free(bad_syn);
	if (!good_syn)
		free(good_syn);

On Linux that code is elided completely -- freeing NULL is a no-op.  I 
guess free(3) has different attributes on OS X and compilers don't dare 
to optimize it away there.

So instead of calling free(3) only in the case when we did not allocate 
memory (which makes no sense and leaks) we should either call it in the 
opposite case, or (preferred) unconditionally, as it can handle the NULL 
case itself.  Once that's fixed initialization will be required even on 
Linux.

René