>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
