[FFmpeg-devel] Inline ASM vs. Intrinsics

Michael Niedermayer michaelni
Fri May 11 21:20:04 CEST 2007


On Fri, May 11, 2007 at 07:44:53PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > Hi
> >
> > On Fri, May 11, 2007 at 10:22:32AM -0400, Dave Dodge wrote:
> >> On Fri, May 11, 2007 at 02:06:11PM +0200, Guillaume POIRIER wrote:
> >> > Exactly. I wrongfully assumed that "register" keywork was honnored
> >> > with xmm/mm intrinsics, but I was wrong. It's simply ignored by ICC. I
> >> > don't know about GCC.
> >> 
> >> According to its documentation gcc also ignores the "register" storage
> >> class specifier, except in a few special cases:
> >> 
> >>   - when using asm in a declaration to explicitly specify which register.
> >>   - when using -O0.
> >>   - when using setjmp on certain rare target platforms.
> >> 
> >> Aside: on IA64 icc supports only intrinsics -- no inline assembly.  On
> >> the one hand IA64 assembly is so painful that you'd rarely want to
> >> write it manually anyway; but the downside is that the intrinsics
> >
> > IA64 is a complete failure with and without intrinsics
> IA64 is a complete commercial failure.  Its performance is far better
> than any x86-based CPU of the same time period.  The main reason it
> failed was lack of good x86 emulation, and people insisting on
> continuing to run the same old rubbish non-portable software.

can you point to some benchmarks? (not from intel of course)
i thought it was significantly slower than compareable CPUs (same time period
and same price range) even when both run natively compiled code
(with similarly good compilers of course)

and even if it was faster its was conceptually flawed (=missdesigned)
it tried to move things from runtime to compiletime which are not
"constant" but change depending on the data the code works on
and from what i remember its a nightmare for a compiler to generate
good code for it ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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