media-video/ffmpeg: can be built w/ LTO

[pchome]

No description provided.

[InBetweenNames]

Hi @pchome , I'm actually getting some ODR violations when I try to build it with LTO. What are your CFLAGS/CXXFLAGS for this one?

[pchome]

CFLAGS/CXXFLAGS same as yours (from make.conf.lto)

Version: 3.4(0/55.57.57)
USE flags set: X alsa bzip2 encode gpl hardcoded-tables iconv jack ladspa mp3 network openal opengl openssl postproc pulseaudio sdl svg threads truetype vdpau vorbis x264 xcb xvid zlib 
ABI_X86="64 -32 -x32"
CPU_FLAGS_X86="3dnow 3dnowext mmx mmxext sse sse2 sse3 -aes -avx -avx2 -fma3 -fma4 -sse4_1 -sse4_2 -ssse3 -xop"
FFTOOLS="aviocat cws2fws ffescape ffeval ffhash fourcc2pixfmt graph2dot ismindex pktdumper qt-faststart sidxindex trasher"

[0xBRM]

@InBetweenNames I can confirm. I actually tried to build ffmpeg with -flto yesterday or two days ago and it failed spectacularly.
@pchome any ffmpeg benchmarks?

[pchome]

Maybe it builds for me because I have every dependency LTOed or have no problematic USE flag set?
Better if someone show build error or attach build.log there ⬇️ in comment block .

@CrisBRM no, nothing to compare with and I don't want to play with it for now.

[InBetweenNames]

I actually just did an emerge -1e ffmpeg just to see if that was the case, and I still get an error:

error: `asm` operand has impossible constraints

My USE: X encode mp3 sdl threads truetype vaapi vdpau x264

[0xBRM]

@pchome if you have mpv you can easily benchmark it. Add this to mpv.conf

[bench]
audio=no
untimed=yes
video-sync=display-desync
vulkan-swap-mode=immediate
opengl-swapinterval=0
osd-msg1="FPS: ${estimated-display-fps}"

... and then, mpv --no-config --scale=ewa_lanczossharp --cscale=ewa_lanczossharp --profile=bench /path/to/video. You'd just have to reemerge ffmpeg without lto...

[InBetweenNames]

I'm actually wondering if it is from the CPU_FLAGS_X86, since @pchome has a more restricted set than I do. I could see that resulting in a codegen error with asm usages.

[InBetweenNames]

Upon further investigation it looks like this is actually related to SSE. I'll make a small note in the workarounds file to reflect this, as we can't toggle LTO based on USE flags yet. Although, I think such a thing would be possible with the right patches.