gcc with O2 and O3

If I would compile with O2 and O3; I would get the O3 one right? They haven't done such a bad thing as checking the flags and choosing the only of of them?

and if i use cpu type flags? will the highest cpu get precedence? Meaning if I have two flags one saying pentium3 the other saying 386 or something would the pentium3 flags get compiled?

i think you would be better off just not confusing the compiler by giving it conflicting arguments.

Well, the later it comes in the gcc argument list, the more it takes precedence. For example:

gcc -O2 -O3 foo.c

would generate -O3 optimized binaries, while

gcc -O3 -O2 foo.c

would generate -O2 optimized binaries.

I do not recommend O3 anyways, as it's almost always a speed DROP from -O2 due to missing L1/L2 cache limitations and generating substantially larger binaries.

Thank you jdong:D

I do not recommend O3 anyways, as it's almost always a speed DROP from -O2 due to missing L1/L2 cache limitations and generating substantially larger binaries.

If you wanted to do some benchmarks (I don't have anything to benchmark with) you could try "-O3 -fno-inline-functions", as I believe that its the function inlining that dramatically increases size, but there are some other optimizations in there (although depending on your version, it may varry.)