[FFmpeg-trac] #11420(ffmpeg:new): macos clang -O3 produce buggy ffmpeg: output is rotated 90 degree.

[FFmpeg]

#11420: macos clang -O3 produce buggy ffmpeg: output is rotated 90 degree.
---------------------------------------+----------------------------------
             Reporter:  ffmpeg-fixes   |                    Owner:  (none)
                 Type:  defect         |                   Status:  new
             Priority:  important      |                Component:  ffmpeg
              Version:  unspecified    |               Resolution:
             Keywords:  clang rotated  |               Blocked By:
             Blocking:                 |  Reproduced by developer:  0
Analyzed by developer:  0              |
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Description changed by ffmpeg-fixes:

Old description:

> Summary of the bug:
>
> compile with clang, CFLAGS=" -O3" ./configure, ffmpeg output is rotated
> 90 degree by default, tested on ffmpeg 6.1.2, 7.1 and latest git, all the
> same. work around is rolling back to ffmpeg 5.1.5, or drop the '-O3'
> flag.
>
> could be some 'volatile' keyword missing, to prevent the compiler from
> optimizing away some variables.
>
> How to reproduce:
>
> CC=/usr/bin/clang \
> CXX=/usr/bin/clang++ \
> LDFLAGS=" -O3 ....._some_other_flags" \
> CFLAGS="  -O3 ....._some_other_flags" \
> CXXFLAGS="-O3 ....._some_other_flags" \
> CPPFLAGS="-O3 ....._some_other_flags" \
> ./configure
>
> make -j8
>
> {{{
>
> % ffmpeg -i in.mp4 out.mp4 -y
>
> ffmpeg 6.1.2, 7.1 and latest git
>
> built on Apple clang version 15.0.0 (clang-1500.3.9.4)
> Target: x86_64-apple-darwin23.5.0
>
> }}}

New description:

 Summary of the bug:

 compile with clang, CFLAGS=" -O3" ./configure, ffmpeg output is rotated 90
 degree by default, tested on ffmpeg 6.1.2, 7.1 and latest git, all the
 same. work around is rolling back to ffmpeg 5.1.5, or drop the '-O3' flag.

 could be some 'volatile' keyword missing, to prevent the compiler from
 optimizing away some variables.

 How to reproduce:

 CC=/usr/bin/clang \
 CXX=/usr/bin/clang++ \
 LDFLAGS=" -O3 ....._some_other_flags" \
 CFLAGS="  -O3 ....._some_other_flags" \
 CXXFLAGS="-O3 ....._some_other_flags" \
 CPPFLAGS="-O3 ....._some_other_flags" \
 ./configure

 make -j8

 {{{

 % ffmpeg -i in.mp4 out.mp4 -y

 input:  1920x1080 [SAR 1:1 DAR 16:9]
 output: 1080x1920 [SAR 1:1 DAR 9:16]

 ffmpeg 6.1.2, 7.1 and latest git

 built on Apple clang version 15.0.0 (clang-1500.3.9.4)
 Target: x86_64-apple-darwin23.5.0

 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/11420#comment:1>
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