[FFmpeg-devel] [PATCH] configure: fix linking with MSVC when using --disable-optimizations

[Matt Oliver]

On 16 December 2016 at 11:20, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:

> 2016-12-14 16:47 GMT+01:00 Steve Lhomme <robux4 at gmail.com>:
> > From: Steve Lhomme <robux4 at gmail.com>
> >
> > Without any optimization flags, MSVC does no dead code elimination (DCE)
> at
> > all, even for the most trivial cases. DCE is a prerequisite for building
> ffmpeg
> > correctly, otherwise there are undefined references to functions for
> other
> > architectures and disabled components.
> >
> > -Os -Og is the minimal optimization flags for MSVC that does include DCE.
>
> The patch looks good to me if -Og alone doesn't help,
> thank you for the improved commit message.


Im not sure this is a good idea. It doesnt seem right to me that if the
user selects to disable optimizations that configure still performs some
anyway. As far as I see it if the user selects to have no optimizations
then there should be no optimizations. This seems like a slightly incorrect
hack to get around ffmpeg using DCE as opposed to tackling the broader
issue of DCE breaking builds, and not just with msvc and not just with no
optimizations enabled.

As a slightly more appropriate (although still hacky fix) you can instead
add /FORCE:UNRESOLVED to the linker command which will still result in a
large number off errors being generated however they will be ignored and an
output binary will still be generated. As the errors all relate to
functions that never get called the output binary is still perfectly
functional and i think importantly doesnt contain optimizations just as the
user requested. Also this fixes debug builds aswell.

I still think the best solution would be to apply a broader ranging fix to
the use of DCE but until a consensus is made on that then the above may be
of some help.