[FFmpeg-cvslog] r14743 - in trunk/libavcodec: ac3dec.c ac3dec.h dsputil.c dsputil.h i386/dsputil_mmx.c

[Mike Melanson]

Uoti Urpala wrote:
> On Wed, 2008-08-13 at 19:49 -0700, Mike Melanson wrote:
>> lorenm wrote:
>>> Author: lorenm
>>> Date: Thu Aug 14 01:35:40 2008
>>> New Revision: 14743
>>>
>>> Log:
>>> simd int->float
>>> 20% faster ac3 if downmixing, 15% if not
>> This made all of the x86_32 gcc configurations fail to build (but not 
>> icc!). The failure looks like this:
> 
> The issue is that the asm uses the "x" constraint for SSE register, and
> GCC doesn't allow that at all if the current instruction set does not
> support SSE. So the asm will fail to compile if you try to compile the
> file without -msse or a -march= option that implies the processor has
> SSE available. If you configure FFmpeg with some --cpu= option that
> supports SSE then it will compile.
> 
> The most robust option would be to compile SSE-using code for runtime
> CPU detection in a separate file and use -msse when compiling that file,
> but probably this function alone isn't enough motivation to do that.

So should we be prepared for an avalanche of bug reports when people try 
to build FFmpeg with their usual 'configure' commands?

-- 
	-Mike Melanson