User's Guide 6.2 says:

"So, when we want very fast code, we use: -O -fvia-C."

but I've seen programs which use the (apparently undocumented) -O2-for-C flag too.

-O2-for-C was removed (from the docs at least) for three reasons: - it is equivalent to -optc-O2 - GCC has a recent history of bugs in -O2, and we didn't want to encourage people to use known-broken compiler options. - it makes very little difference anyway. Cheers, Simon