Re: core2 flag for arch on gcc 4.3.2

[tom gogh <tomgogh20 at yahoo dot com>]

Hi Tim,
      sorry for not making it clear.
I am building Gentoo 2008.0 and gcc supported is 4.1.2 which only
supports -mnocona for core 2 duo processor.
By migrating to gcc 4.3.2 I will get tunning for core 2 with flag
-mcore2 but, it involves going to unsupported gcc for Gentoo.
So, I want to know what is the difference between -mnocona flag of gcc
versus -mcore2 flag of gcc 4.3.2. Is it worth in terms of speed
optimization?



--- On Sun, 12/28/08, Tim Prince <TimothyPrince@sbcglobal.net> wrote:

> From: Tim Prince <TimothyPrince@sbcglobal.net>
> Subject: Re: core2 flag for arch on gcc 4.3.2
> To: "tom gogh" <tomgogh20@yahoo.com>
> Cc: gcc-help@gcc.gnu.org
> Date: Sunday, December 28, 2008, 12:22 AM
> tom gogh wrote:
> 
> >    I am planning to migrate my linux to 4.3.2 but,
> current flag for core 2 duo is nocona.
> > I couldn't find elaborate explanation of core2
> flag compare to nocona.
> > What is difference between core2 and nocona flags?
> > Do they behave identical or core2 offers better
> performance/tunning?
> 
> Not knowing where you're trying to go with this,
> default for 64-bit gcc is
>  good for Core 2, from no difference up to 50% better
> throughput than
> nocona in my tests.  -msse3 is available for either Nocona
> or Core 2 CPUs.
>  You probably wouldn't want the nocona option even for
> the older CPU.  I
> can't imagine why you don't simply try the options
> you have in mind, nor
> do I understand what you mean by nocona being a current
> flag.  Maybe you
> mean the best option for some old version of gcc which
> predates Core 2.
> I don't think -mtune=barcelona is available until more
> recent versions of
> gcc; it may often give better vectorization even on Core 2,
> particularly
> for Fortran, maybe for C, not so much for C++.