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Re: Susprising behavior of gcc on x86 (-m32)
- From: Markus Trippelsdorf <markus at trippelsdorf dot de>
- To: Mathieu Malaterre <malat at debian dot org>
- Cc: Jonathan Wakely <jwakely dot gcc at gmail dot com>, gcc-help <gcc-help at gcc dot gnu dot org>
- Date: Tue, 8 Sep 2015 15:16:47 +0200
- Subject: Re: Susprising behavior of gcc on x86 (-m32)
- Authentication-results: sourceware.org; auth=none
- References: <CA+7wUsydzQTunngu5x46MGJm5BqRbysPHL9G1if-Kpf2cAbBDg at mail dot gmail dot com> <55EEAE4A dot 40307 at redhat dot com> <CA+7wUsxqBk0DDVD5zX-c-ngUGMWTLPdr1n5707_G7A+cVhWdwA at mail dot gmail dot com> <CAH6eHdQ2mMTuue=+4OqL_1jpG2ET0EwCGDzhBJtHZDG=iz6F2Q at mail dot gmail dot com> <CA+7wUswSJ1auXVvTUxipske9JTbJbye0P42eyDhLkWh=J7jxEg at mail dot gmail dot com> <CA+7wUszRQuMGDKMx5-PXECHBeWFZfB=3Y2TqBjpFdJ-adi54_g at mail dot gmail dot com>
On 2015.09.08 at 14:40 +0200, Mathieu Malaterre wrote:
> On Tue, Sep 8, 2015 at 2:00 PM, Mathieu Malaterre <malat@debian.org> wrote:
> > FYI,
> >
> > On Tue, Sep 8, 2015 at 12:04 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> > [...]
> >> That's not the only option. You could compile one file with GCC and
> >> all others with Clang and see if you can reproduce it. Repeat for each
> >> file, which will narrow down the file where the problem occurs. Then
> >> you can try splitting that file into smaller pieces, with one function
> >> per file, and repeat the process. That would tell you which function
> >> or functions get miscompiled by GCC.
> >
> > Ok so if I compile eveything with gcc and then only `tcd.c` using
> > clang, then everything works as expected (no symptoms).
> > ref: https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/tcd.c
> >
> > I'll repeat your approach to find the culprit function.
>
> And the culprit function is `opj_tcd_makelayer`:
>
> https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/tcd.c#L218
>
> Other than the `if (dd / dr >= thresh)` I do not see anything
> obviously suspicious.
Looks like a x87 vs. SSE2 issue. You could try adding "-msse2
-mfpmath=sse" for the -m32 case.
--
Markus