auto

auto: one of the following is chosen automatically
idea: straightforward code, assuming 53-bit fp
sparc: idea plus instruction scheduling
x86-idea: straightforward code, using 64-bit x86 fp
pentium-idea: x86-idea plus register assignment and instruction scheduling
pentium: pentium-idea rewritten in asm
ppro: better than pentium for the PPro, PII, PIII
