gcc 3.4.1 and CPU optimization

[Zbigniew Łuszpiński]

Helo!

I compile many programs from sources. A lot of them have optimizations like 
-m386, -mcpu=486, -mtune=i686, -march=i686 or other.
I use AMD AthlonXP 2500+. Everytime I compile program first do ./configure 
CFLAGS="-march=athlon-xp". Could you tell me which one optimization will be 
used? These hardcoded into configure script or this one provided by me with 
CFLAGS parameter ?

What will happen when gcc will get -march=i586 from script and 
-march=athlon-xp from me?

Which optimization will be used when some of them are placed together? e.g. 
-mtune=pentium -march=athlon-xp.

greetings,
Zbigniew