Hi all, The Gcc Compiler online document(http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html) specifies that "Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed. " Does this mean that for O1/O2/O3/Os optimization levels, the compiler does some optimizations of which only some of them have flags listed ??? For example O1 consists of not just these optimizations -fdefer-pop -fmerge-constants -fthread-jumps -floop-optimize -fif-conversion -fif-conversion2 -fdelayed-branch __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - 100MB free storage! http://promotions.yahoo.com/new_mail