On Tue, 2010-02-02 at 17:34 -0800, Jeremy Huddleston wrote: > On Feb 2, 2010, at 17:11, Gaetan Nadon wrote: > > > On Tue, 2010-02-02 at 14:00 -0800, Jeremy Huddleston wrote: > > > >> On Feb 2, 2010, at 13:18, Gaetan Nadon wrote: > >> > >>> I have not seen any compelling reasons to turn off this optimization. > >>> Maybe 10 years ago when it was first introduced. I have seen reports of > >>> large number of warnings, but from older gcc versions. As it is today, > >>> we are losing some optimization that could be beneficial. > >>> > >>> This option has been there for so long (most likely copied along), I > >>> doubt you will will get a clear answer for each of the 240 xorg modules. > >>> It would take a few modules to try it out first. > >> > >> I see it in libX11 has historically used -fno-strict-aliasing: > >> http://cgit.freedesktop.org/xorg/lib/libX11/commit/?id=db7c6fdeeaef9475458498e4cf09d6b1329e9aa3 > >> > >> but adding XORG_CWARNFLAGS to XORG_DEFAULT_OPTIONS has caused this to > >> change for other modules. > >> > >> Looking at historic versions of modules, I see it present in: > >> > >> libICE > >> libSM > >> libX11 > >> libXau > >> libXfont > >> libXft > >> libXpm > >> libXres > >> xorg-server > >> > >> of course most of these seem to have just copied the entire GCC_WARNINGS > >> block and probably didn't actually need -fno-strict-aliasing > > > > Of course. Whatever the reasons were, if anyone remembers, may not apply > > anymore. Devising a plan for it's removal will not be an easy task. I > > see 3 options: > > > > 1) take it out of macros, 1 patch > > I sent that patch already. > > > 2) transfer it to all makefiles and then removing it gradually, that's > > 2*240 +1 patches > > I don't think that's wise. If anything, you should just put it in the ones > where it was prior to XORG_CWARNFLAGS (the 9 mentioned above). > > That being said, I also enabled the warning which should mention when it > discovers code sensitive to the -fstrict-aliasing optimization, and none of > the libs in the list above spewed such a warning. > > > 3) override in 'n' makefiles until proven safe. Then take it out macros. > > That's 2*n +1 patches. > > We could do that for the 9 modules above. I'm fairly confident that the libs > don't need it, but I haven't rebuilt all of the server to be confident it > doesn't spew any warnings about strict-aliasing.
Oh, just 9. It thought these were just examples and that there were many more. I noticed the patch later, sorry. I had a quick look in xserver and I saw some warnings, as expected.
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