Re: [gentoo-user] CFLAGS for both AMD64 and Intel?

["Walter Dnes" <waltdnes@waltdnes.org>]

On Sat, Dec 02, 2017 at 11:23:10PM -0800, Manuel McLure wrote
> Here's the situation. I have a system that's been running for many years
> with an Athlon 5050e processor. The system is built with
> 
> CFLAGS="-march=k8-sse3 -O2 -pipe -msse3"
> CPU_FLAGS_X86="3dnow 3dnowext mmx mmxext sse sse2 sse3"
> 
> I have the possibility of upgrading the system to a first-generation
> Intel Core i5 which should give a nice speed boost, but of course the
> Intel chip doesn't understand 3dnow or 3dnowext, so I'll have to do
> a system rebuild before I switch out the motherboard/processor. It
> seems pretty obvious that I have to take "3dnow 3dnowext" out of
> CPU_FLAGS_X86, but what CFLAGS would be recommended for a system
> that will still run with the AMD processor but won't fall over when
> I switch to the Intel processor? Once I have the Intel in place I
> can rebuild with options more suited for that chip, but I want to
> make sure I don't end up in a catch-22 situation.

https://gcc.gnu.org/onlinedocs/gcc-6.4.0/gcc/x86-Options.html#x86-Options
lists what instruction sets gcc expects for any "-march=<whatever>"

  I would suggest rebuilding with...

CFLAGS="-march=nocona -O2 -pipe"
CPU_FLAGS_X86="mmx sse sse2 sse3"

  nocona was the first Intel cpu to support AMD64 instructions, and it's
the newest Intel that does not exceed your AMD.  The next Intel cpu, the
"core2" supports ssse3 which your AMD does not (count the "s"'s... very
carefully; sse3 != ssse3).

-- 
Walter Dnes <waltdnes@waltdnes.org>
I don't run "desktop environments"; I run useful applications