Date: Wed, 21 Nov 2007 00:19:38 +0100 From: Erik Trulsson <ertr1013@student.uu.se> To: John Birrell <jb@what-creek.com> Cc: ????????? Bill Hacker <askbill@conducive.net>, freebsd-current@freebsd.org Subject: Re: Tinderbox Message-ID: <20071120231938.GA13120@owl.midgard.homeip.net> In-Reply-To: <20071120224337.GB12810@what-creek.com> References: <543425.44000.qm@web50704.mail.re2.yahoo.com> <20071120224337.GB12810@what-creek.com>
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On Tue, Nov 20, 2007 at 10:43:37PM +0000, John Birrell wrote:
> On Tue, Nov 20, 2007 at 07:35:42AM -0800, John Merryweather Cooper wrote:
> > Could not -fno-strict-aliasing be considered as just another WARN level?
> > At least then, there might be some pressure to eliminate strict aliasing
> > warnings as a necessary component to moving to a higher WARN level.
> >
>
> This is something I'd like to do right now as "a step in the right
> direction".
>
> RCS file: /u/freebsd/cvsup/src/src/share/mk/bsd.sys.mk,v
> retrieving revision 1.43
> diff -r1.43 bsd.sys.mk
> 11,12d10
> < NO_WERROR=
> <
> 78a77,80
> > .if defined(NO_WARNS) || (defined(WARNS) && ${WARNS} == 0)
> > CFLAGS += -fno-strict-aliasing
> > .endif
> >
>
>
> and remove it from the default CFLAGS in sys.mk
>
You seem to misunderstand what -fno-strict-aliasing does.
Its purpose is not to disable some warnings, but to disable
certain optimizations which can easily cause not-quite-correct code
to behave differently than the programmer intended.
Such incorrect code is unfortunately fairly common, which is why
-fno-strict-aliasing is often needed.
Which optimizations are enabled or disabled should not depend
on which WARN level is used.
If gcc gives a warning about strict aliasing this means that there is
almost certainly a bug in the code which need to be fixed, to make it safe
to compile with the extra optimizations that an assumption of strict
aliasing enables.
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
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