[FFmpeg-devel] Amazing intrinsics improvments in gcc 4

[Luca Barbato]

Michael Niedermayer wrote:
> I thought some people here would be interrested as there were various claims
> on gccs abilities and improvments posted here lately ...

------- Comment #23 From Uros Bizjak 2008-03-19 10:45 -------

As said in PR 19161:

The LCM infrastructure doesn't support mode switching in the way that 
would be
usable for emms. Additionally, there are MANY problems expected when sharing
x87 and MMX registers (i.e. handling of uninitialized x87 registers at the
beginning of the function - this is the reason we don't implement x87 
register
passing ABI).

Automatic MMX vectorization is not exactly a much usable feature 
nowadays (we
have SSE that works quite well here). Due to recent changes in MMX register
allocation area, excellent code is produced using MMX intrinsics, I'm 
closing
this bug as WONTFIX.

Also, auto-vectorization would produce either MMX or SSE code, but not 
both of
them:

#define UNITS_PER_SIMD_WORD (TARGET_SSE ? 16 : UNITS_PER_WORD)

Seems Uros is fighting your battle and providing some interesting code.

Still, the root of the problem is that x86 sucks.

lu

-- 

Luca Barbato
Gentoo Council Member
Gentoo/linux Gentoo/PPC
http://dev.gentoo.org/~lu_zero