On Tue, Mar 9, 2010 at 9:31 AM, drew stortz <drew.stortz@xxxxxxxxx> wrote: > From the following page > > http://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/Optimize-Options.html#Optimize-Options > > I gather that using GCC 4.2.2 with the -O option is the equivalent of > using all of the following options explicitly: -fdefer-pop > -fdelayed-branch -fguess-branch-probability -fcprop-registers > -fif-conversion -fif-conversion2 -ftree-ccp -ftree-dce > -ftree-dominator-opts -ftree-dse -ftree-ter -ftree-lrs -ftree-sra > -ftree-copyrename -ftree-fre -ftree-ch -funit-at-a-time > -fmerge-constants -fomit-frame-pointer > > However, experiment tells me that this is far from true. When I > compile the same c file both ways, the object file produced with -O is > around 20% smaller than the one produced with all of the individual > optimizations added. Before filing a bug or investigating further, I > wanted to ask the list: is my interpretation of the -O switch > incorrect? Is it more than just the sum of those individual > optimizations? > > I’m using sles9 sp3 on an x86-64 machine, and the observation hold > whether using -m32 or -m64 and also whether I include or exclude > -fomit-frame-pointer > > thanks for your help, > Drew > http://gcc.gnu.org/ml/gcc-help/2009-10/msg00128.html
