-fno-strict-aliasing in CWARNFLAGS?

Gaetan Nadon memsize at videotron.ca
Tue Feb 2 17:11:59 PST 2010

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
2) transfer it to all makefiles and then removing it gradually, that's
2*240 +1 patches
3) override in 'n' makefiles until proven safe. Then take it out macros.
That's 2*n +1 patches.

I am curious how you can about this. 

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