Re: core2 flag for arch on gcc 4.3.2

[Tim Prince <TimothyPrince@sbcglobal.net>]

tom gogh wrote:
> 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?
> 
You're still being unclear.  If you mean rebuilding an entire distro with
an up to date compiler, there may be reasons why it hasn't been done
already.  If you don't have any idea what kernel or glibc operations you
want to speed up, and how to measure it, and can't define what you mean by
worth while, I have no qualification to make that determination for you.
You give the impression that you haven't even compared the performance of
the compilers on applications which matter to you, or haven't even thought
about which applications matter.  gcc has made great advances since 4.1,
not only in optimizing for current CPU types, but in supporting OpenMP,
auto-vectorization, and current language standards.
Some of the more critical glibc operations are hand coded with inline asm,
so as to prevent gcc optimization from helping out.  If you choose not to
use an up to date memcpy(), for example, you can make it perform much
better by discarding the old glibc source and compiling C source with an
up to date gcc.  I don't know whether your gentoo uses up to date glibc,
but I would doubt it, if the recommended gcc is so old.