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From: Mathieu Malaterre <malat@debian.org>
Date: Tue, 08 Sep 2015 12:40:00 -0000
Message-ID: <CA+7wUszRQuMGDKMx5-PXECHBeWFZfB=3Y2TqBjpFdJ-adi54_g@mail.gmail.com>
Subject: Re: Susprising behavior of gcc on x86 (-m32)
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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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.