What happens if you repeat two optimization parameters in GCC with different values?

Question

C++ / C#

What will happen if my package is built with parameters, for example "-O2 -O3"? Or, for example, "-march=armv8-a -march=x86-64"? Or "-mtune=generic -mtune=native"?

Answer 1

For most options -- will be overwritten with the last value passed. This is particularly true for -march and -mtune on x86.
But in the general case, it can be anything, since gcc can convert one option to another according to its specs before invoking the actual compiler.