The biggest you can go to currently is -O3, I believe. Anything beyond that
turns on the same flags.
>
> And is -fomit-frame-pointer a workaround for a bug in some implimentations
> of -O2 (I compiled X without it and it's working fine. Hasn't crashed) or
> is it something the kernel needs? And, what exactly does this do? I've read
> the manpage but what that has doesn't mean much to me. I wish there was
> info on not just what an optimisation flag does but also how it might effect
> performance and what sideeffects it might have. (this is probably real hard
> to do but it would be way useful. I don't mind long compile times as long
> as runtime performance is imporved)
>From the gcc manual:
`-fomit-frame-pointer'
Don't keep the frame pointer in a register for functions that
don't need one. This avoids the instructions to save, set up and
restore frame pointers; it also makes an extra register available
in many functions. *It also makes debugging impossible on some
machines.*
This option is never turned on by default (on i386), so the kernel Makefile
turns it on.
Obviously, it should improve run-time performance, unless the gcc code
optimizer is so buggy that it generates faster code with less registers
available ;)
-- arvind
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