In in gcc-4.4.4 (and likely in many other versions), the "man gcc" paragraph about -O3 is:
Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions, -funswitch-loops, -fpredictive-commoning, -fgcse-after-reload and -ftree-vectorize options. The above list of optimizations, as well as http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html, don't mention -fipa-cp-clone, although -O3 turns enables it: $ gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts $ gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts $ diff /tmp/O2-opts /tmp/O3-opts ⎪ grep enabled > -fgcse-after-reload [enabled] > -finline-functions [enabled] > -fipa-cp-clone [enabled] > -fpredictive-commoning [enabled] > -ftree-vectorize [enabled] > -funswitch-loops [enabled] -- Summary: GCC documentation for -O3 flag doesn't mention -fipa-cp- clone Product: gcc Version: 4.4.4 Status: UNCONFIRMED Severity: trivial Priority: P3 Component: spam AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: ristioja at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45443
