gcc partial optimization

I missed that and so far thought this is hardly possible, but, for your note, 

you can set per-function optimization levels with Function Specific Option Pragmas: 

For example:

#pragma GCC push_options
#pragma GCC optimize ("O2") 

   code
#pragma GCC pop_options

OTOH, of course, you can split the source code into several files and compile 

each with specific optimization options. Anyway.