[FFmpeg-devel] [PATCH 2/4] cbs: Remove useless initializations

Andreas Rheinhardt andreas.rheinhardt at gmail.com
Mon Jun 3 15:07:00 EEST 2019

Reimar Döffinger:
> On 03.06.2019, at 00:37, Andreas Rheinhardt <andreas.rheinhardt at gmail.com> wrote:
>> Up until now, a temporary variable was used and initialized every time a
>> value was read in CBS; if reading turned out to be successfull, this
>> value was overwritten (without having ever been looked at) with the
>> value read if reading was successfull; on failure the variable wasn't
>> touched either. Therefore these initializations can be and have been
>> removed.
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>> And? What did the ancient compilers say?
> Not sure how to read that, but some compilers probably produce "may be used uninitialized" warnings after this change.
> IMHO it would be better to need evidence of an advantage to remove variable initialization for non-trivial code, even if they are unnecessary. Your commit message doesn't seem to mention one at least.
> But I am happy to let some maintainer have the last word.
This comment refers to what Mark said in his review [1] of an earlier
version of this patchset. He explicitly mentioned that (if his memory
is right) an older compiler warned without the initializations.
And I actually thought that there is no need for a further reason to
remove unnecessary initializations despite the usual ones: Speed and
code size. E.g. the size of my cbs_mpeg2.o went down from 30421 B to
29445 B after this patch; for  cbs_h2645.o the numbers are 249605 B
and 242245 B. These macros are used a lot (mostly indirectly via other
macros); see the various cbs_*_syntax_template.c files for that.

- Andreas

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