[vlc-devel] [vlc-commits] configure.ac: fix use of *FLAGS_save and VLC_{SAVE, RESTORE}_FLAGS

[Felix Paul Kühne]

On 19.11.2011, at 13:36, Rémi Denis-Courmont wrote:

> Le samedi 19 novembre 2011 14:28:48 Felix Paul Kühne, vous avez écrit :
>> Hello,
>> 
>> On 19.11.2011, at 12:46, Rafaël Carré wrote:
>>> vlc | branch: master | Rafaël Carré <funman at videolan.org> | Sat Nov 19
>>> 06:41:57 2011 -0500| [49125107995744edb8ca6b6fa154f69c68e28262] |
>>> committer: Rafaël Carré
>>> 
>>> configure.ac: fix use of *FLAGS_save and VLC_{SAVE,RESTORE}_FLAGS
>>> 
>>> Other changes:
>>> - remove -O4 optimization, undocumented for gcc
>> 
>> Could you retain this in future optimizations of this commit, please? -O4
>> is supported in clang / LLVM-based compilers and leads to noticeable speed
>> increases while taking the same compilation time as gcc with -O3.
>> Therefore, it definitely makes sense to keep it in VLC's configure since I
>> intend to use clang for the compilation of production releases of VLC
>> (64bit, 10.6 & later).
> 
> One tangential problem is, are those optimizations even safe? In particular, 
> do they not often trigger compiler bugs? automake defaults to -O2...

Good point. I didn't sneak around in the resulting intermediate asm code to be honest. However, I've been using clang for compilation of VLC (just VLC, not its contribs) since the early pre-releases of clang 2.0 (aka full c++ support) and didn't notice any drawbacks in terms of crashes or bugs which didn't occur with gcc or vice versa. In case we do a clang-based 64bit release, this is definitely worth testing.

Best regards,
Felix