[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-      |                     Type:  defect
  fixes                              |
               Status:  new          |                 Priority:  important
            Component:  ffmpeg       |                  Version:
             Keywords:  clang        |  unspecified
  rotated                            |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 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

 }}}
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11420>
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