看不见的GCC优化标志？

Question

I'm building some large project using GCC 4.4.2 . Since I want to build it for release, I use -O1 GCC optimization flag, but unluckily it messes somehow with my code, and the final binaries do not work as expected, when building with -O0 flag (or no optimization) everything works fine. I had a similar problem with my project before, in that time it was the -fstrict-aliasing flag that caused troubles on -O2 optimization level, I managed to find that it was caused by that specific flag by making a search on all flags that are mentioned in this documentation, regarding the -O2 optimization level:

http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Optimize-Options.html

Now I tried to do the same with the list they mention regarding the -O1 flag, but unfortunately it seems that not all the flags mentioned, or there are some hidden flags being enabled, because when I compile with just -O1 flag or with just a list of the provided flags (without putting -O1 itself) I get different compilation results, and my binaries refuse to work only with the specific -O1 flag, so I can't find the exact troublemaking option.

Is it possible to know what hidden options the -O1 option includes, and how can I disable some of them?

Answer 1

You can run gcc -Q -v on a small C file to have GCC dump the options being used. Run it with and without the -O1 option to get the difference between the enabled options.