Determine optimization level in preprocessor?

Question

-Og is a relatively new optimization option that is intended to improve the debugging experience while apply optimizations. If a user selects -Og,

Answer 1

I don't know if this is clever hack, but it is a hack.

$ gcc -Xpreprocessor -dM -E - < /dev/null > 1
$ gcc -Xpreprocessor -dM -O -E - < /dev/null > 2
$ diff 1 2
53a54
> #define __OPTIMIZE__ 1
68a70
> #define _FORTIFY_SOURCE 2
154d155
< #define __NO_INLINE__ 1

clang didn't produce the FORTIFY one.