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Re: GCC 4.4.1 bug? need help isolating problem


Ryan Hill wrote:
> On Mon, 28 Sep 2009 16:41:57 -0700
> Corey Hickey <bugfood-ml@fatooh.org> wrote:
> 
>> Hello,
>>
>> I'm running into a segfault with MPlayer on MKV files. I think it might
>> be a bug in some aspect of GCC 4.4's optimization, but I'm having
>> trouble narrowing it down. All I know for sure is:
>>
>> Works:
>> * compiled by gcc 4.4 with -O2
>> * compiled by gcc 3.3, 3.4, 4.0, 4.1, 4.2, 4.3 (any optimization level)
>> * compiled by gcc svn trunk (any optimization level)
>>
>> Crashes:
>> * compiled by gcc 4.4 with -O3
>
> We've seen the same problem and I think it was narrowed down to
> -finline-functions.  See http://bugs.gentoo.org/269975.  Unfortunately the
> rest of the bug report is just noise.  Good luck!

Thanks. I ran across that bug report several days ago but hadn't seen
the note about -finline-functions.

Yet, I think my report has a bit more information, at least as it
pertains to the behavior I'm seeing: removing -finline-functions indeed
makes the segfault go away, but so does removing any one of these flags:

-O1
-fgcse
-finline-small-functions
-fschedule-insns2
-fstrict-aliasing
-finline-functions

All of the above have to be present to cause the crash to occur.

Also of interest is that I can compile the rest of MPlayer without any
optimization (except for libswscale/swcale.c, which needs -O1 to
compile). I can then compile demux_mkv.c with the set of flags above to
cause the crash to occur. From within mplayer source tree:

gcc-4.4 -g  -I. -c -o libmpdemux/demux_mkv.o libmpdemux/demux_mkv.c -O1
-fgcse -finline-small-functions -fschedule-insns2 -fstrict-aliasing
-finline-functions && make

Thanks,
Corey


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