Optimizing at level 5

Benefits at level 5

• Makes most aggressive optimizations available

As the highest optimization level, -O5 includes all -O4 optimizations and deepens whole program analysis by increasing the -qipa level to 2. Compiling with -O5 also increases how aggressively the optimizer pursues aliasing improvements. Additionally, if your application contains a mix of C/C++ and Fortran code that you compile using the XL compilers, you can increase performance by compiling and linking your code with the -O5 option.

Potential trade-offs at level 5

Compiling at -O5 requires more compilation time and machine resources than any other optimization levels, particularly if you include -O5 on the IPA link step. Compile at -O5 as the final phase in your optimization process after successfully compiling and executing your application at -O4.