On Sat, 2005-01-22 at 19:54 -0600, Andrew Gaffney wrote: > Nick Smith wrote: > >>-O3 is more optimized than -O2, but those optimizations usually make the > >>binaries larger which causes other slowdowns. The ideal system-wide > >>optimization > >>level is -O2 or -Os (-O2 with additional flags for small binaries). > >> > > > > could you go a little further on this? whats the difference between -O2 > > and -Os? which is better for overal and what additional flags for small > > binaries are you talking about? > > From 'man gcc': > > -O2 Optimize even more. GCC performs nearly all supported optimiza- > tions that do not involve a space-speed tradeoff. The compiler > does not perform loop unrolling or function inlining when you > spec- > ify -O2. As compared to -O, this option increases both > compilation > time and the performance of the generated code. > > -O2 turns on all optimization flags specified by -O. It also > turns > on the following optimization flags: -fforce-mem -foptimize-sib- > ling-calls -fstrength-reduce -fcse-follow-jumps -fcse-skip-blocks > -frerun-cse-after-loop -frerun-loop-opt -fgcse -fgcse-lm > -fgcse-sm -fgcse-las -fdelete-null-pointer-checks -fexpen- > sive-optimizations -fregmove -fschedule-insns -fschedule-insns2 > -fsched-interblock -fsched-spec -fcaller-saves -fpeephole2 -fre- > order-blocks -freorder-functions -fstrict-aliasing > -funit-at-a-time -falign-functions -falign-jumps -falign-loops > -falign-labels -fcrossjumping > <snip> > -Os Optimize for size. -Os enables all -O2 optimizations that do not > typically increase code size. It also performs further optimiza- > tions designed to reduce code size. > > -Os disables the following optimization flags: -falign-functions > -falign-jumps -falign-loops -falign-labels -freorder-blocks > -fprefetch-loop-arrays > > -- > Andrew Gaffney > Gentoo Linux Developer > Installer Project > http://dev.gentoo.org/~agaffney/ > so in your guys experience/opinion what would you use?
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