[SCM] libav/experimental: doc: mention xmm clobber macros usage

[siretart at users.alioth.debian.org]

The following commit has been merged in the experimental branch:
commit 2344dc6bb6e3a14a1752f1774fd98eaca6568d86
Author: Ramiro Polla <ramiro.polla at gmail.com>
Date:   Wed Oct 6 02:46:22 2010 +0000

    doc: mention xmm clobber macros usage
    
    Originally committed as revision 25364 to svn://svn.ffmpeg.org/ffmpeg/trunk

diff --git a/doc/optimization.txt b/doc/optimization.txt
index 3a5d85e..5d51235 100644
--- a/doc/optimization.txt
+++ b/doc/optimization.txt
@@ -172,6 +172,12 @@ yasm), you do this by using:
 cglobal functon_name, num_args, num_regs, num_xmm_regs
 In inline asm, you specify clobbered registers at the end of your asm:
 __asm__(".." ::: "%eax").
+If gcc is not set to support sse (-msse) it will not accept xmm registers
+in the clobber list. For that we use two macros to declare the clobbers.
+XMM_CLOBBERS should be used when there are other clobbers, for example:
+__asm__(".." ::: XMM_CLOBBERS("xmm0",) "eax");
+and XMM_CLOBBERS_ONLY should be used when the only clobbers are xmm registers:
+__asm__(".." :: XMM_CLOBBERS_ONLY("xmm0"));
 
 Do not expect a compiler to maintain values in your registers between separate
 (inline) asm code blocks. It is not required to. For example, this is bad:

-- 
Libav/FFmpeg packaging