dmd-x64

[Leandro Lucarella]

bearophile, el 23 de diciembre a las 12:02 me escribiste:
> Leandro Lucarella:
> 
> > bearophile, el 23 de diciembre a las 00:13 me escribiste:
> > > Compared to GCC LLVM lacks vectorization (this can be important for
> > > certain heavy numerical computing code), profile-guided optimization
> > > (this is usually less important, it's uncommon that it gives more than
> > > 5-25% performance improvement)
> > 
> > I don't know if that are accurate numbers, but 5-25% looks like a *lot* to
> > me.
> 
> Vectorization can improve 2X or 3X+ the performance of certain code
> (typical example: matrix multiplication done right).
> 
> Performance differences start to matter in practice when they are 2X or
> more. In most situations users aren't able to appreciate a 20%
> performance improvement of an application. (But small improvements are
> important for the compiler devs because they are cumulative, so many
> small improvements may eventually lead some a significant difference).

Well, you are talking about a single user, but for servers, if you have to
provide a minimum quality of service, a 20% difference means you can serve
20% more people, for example (not that people would have to wait 0.2 secs
more, because that is not an option).

> > > but it has a link-time optimizations that gcc lacks (about as important
> > > as profile-guided optimization or a little more).
> > 
> > And GCC have LTO too, see:
> > http://gcc.gnu.org/wiki/LinkTimeOptimization
> 
> Oh, nice, I have not tried this yet. Is this going in Gcc 4.5?
> LTO of LLVM is pretty good, I don't know if GCC implements it equally
> well (I fear that the answer is negative.

I think it will be in GCC 4.5 but I don't know the details.

-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
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