How to tune gcc for different x86 host and target cpus?

[Michael Roth]

Hello,

as far as I understand, when building gcc, I can use --with-arch=pentium 
to tell configure that the resulting compiler should emit code optimized 
for pentium processors.

But how can I tell the configure script that the compiler itself should 
be optimized for a different cpu architecture?

Example #1: Host and build are athlon-xp, target should be pentium.

Example #2: Build is pentium4, Host should be pentium-mmx, target should 
be 386.

What configure options should I use? (Host, build and target are all 
linux systems, but I think this apply to every system with x86 processor 
variants?)

Michael Roth