[FFmpeg-trac] #265(swscale:new): MMX2 yuv420p10 → yuv444p scaler produces vertical undithered(?) lines with GCC 4.6

[FFmpeg]

#265: MMX2 yuv420p10 → yuv444p scaler produces vertical undithered(?) lines with
GCC 4.6
----------------------+--------------------------------------
  Reporter:  lachs0r  |      Owner:  michael
      Type:  defect   |     Status:  new
  Priority:  normal   |  Component:  swscale
   Version:  git      |   Keywords:  yuv420p10, yuv444p, mmx2
Blocked By:           |   Blocking:
Reproduced:  0        |   Analyzed:  0
----------------------+--------------------------------------
 I know this might be a PITA to reproduce since it only happens with GCC
 4.6, but I’ll report it anyway.

 Background: I’ve been trying to play yuv420p10 video with my patched
 MPlayer2 builds for Windows (http://mplayer2.srsfckn.biz/mplayer2-high-
 bit-depth-latest.7z).
 MPlayer2 apparently chooses the yuv420p10 → yuv444p scaler by default.

 That is probably fine, but there’s a problem: The MMX2 version of that
 scaler seems to break with GCC 4.6.0, causing vertical lines of what seems
 to be undithered luma (can’t tell for sure since I didn’t actually
 investigate that in detail, but I’ll attach a screenshot).
 The C version works fine.

 This can be reproduced with for example:
 ffmpeg -i test10bit.mkv -pix_fmt yuv444p -vcodec ffv1 out.mkv

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/265>
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