Re: [gentoo-dev] Should this be considered a gcc bug?

[Andrew Savchenko]

Hi,

On Tue, 21 Apr 2015 09:57:16 +0600 (NOVT) grozin@g.o wrote:
> Hello *,
>
> There was a bug #526194 - dev-lisp/sbcl does not respect CFLAGS. It was
> "fixed" by Mark Wright <gienah@g.o> on Jan 31 - Feb 1. However,
> after this fix the upstream CFLAGS were appended to the user-supplyed
> ${CFLAGS}. And the upstream CFLAGS contain -O3. So, is a user has, e.g.,
> -O2 in his/her ${CFLAGS}, it was silently replaced by -O3. For some time,
> nobody noticed this: gcc-4.8 happily compiled the C stuff in sbcl with
> -O3.
>
> However, after the upgrade to gcc-4.9 problems began (bug #544070). On
> amd64, gcc is still happy co compile sbcl with -O3. However, on x86 this
> leads to a crash of a freshly compiled sbcl runtime. Namely, the
> combinations
>
> -O2 -march=<something>
> -O3
>
> behave correctly, and produce a working sbcl; but
>
> -O3 -march=<something>
>
> lead to the crush. I have changed the above "fix" in sbcl-1.2.10 in such a
> way that now it appends only -g -Wall -Wsign-compare to ${CFLAGS}, but
> not -O3. This resolves the bug #544070, unless a user has -O3
> -march=<something> in his/her ${CFLAGS}.
>
> Shouldn't gcc-4.9 on x86 produce with -O3 something functionally
> equivalent to the -O2 case, only more optimized? Should this be considered
> a gcc-4.9 bug?

Please look at gcc-4.9 manual for the list of -O3 expansion and
find what flag exactly causes this issue. There may be two reasons:
gcc bug and sbcl bug. While you have correctly pointed out that
this may be a problem in gcc, another possibility is that extra
optimization triggers some problem in the code itself, which causes
a segfault.

Best regards,
Andrew Savchenko