Messages in this thread | | | Date | Wed, 6 Oct 1999 09:43:40 -0400 | From | Michael Meissner <> | Subject | Re: [offtopic] gcc optimisation flags documentation |
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On Wed, Oct 06, 1999 at 03:24:37PM +0200, Peter Hanecak wrote: > On Wed, 6 Oct 1999, Marc Duponcheel wrote: > > > I (admit I) grew the habit of adding '-mcpu=i686 -O6' to gcc wherever possible, > > so in /usr/src/linux I do: > > i was wondering now for about few months about gcc/egcs optimisation > flags. i was looking at documentation (in /usr/doc/egcs, etc.) but found > nothing about switches you mentioned. is there any documentation about > such switches (and possibly some more info about optimisation itself - > i.e. risk and advantages of optimising for particular CPU, ...) on the > net?
Whomever packaged up your gcc release obviously didn't put the documentation into /usr/doc/egcs-*. You might want to complain to them about this. To figure out the options GCC supports, use the info command, and then do:
mgcc mInvoking GCC 1
for a summary. Needless to say, GCC supports very many options. For straight GCC, any -O level above -O3 is the same as -O3, but the pgcc varient added more layers. As long as you don't use -march=i686, the compiler won't generate the cmov and fcmov instructions that the Pentium and K6 don't support (the compiler doesn't generate the bswap or 8 byte locking instructions in any case).
-- Michael Meissner, Cygnus Solutions PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886 email: meissner@cygnus.com phone: 978-486-9304 fax: 978-692-4482
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