Sun Studio 12 Update 1: Fortran User's Guide

3.4.71 –O5

Attempt aggressive optimizations.

Suitable only for that small fraction of a program that uses the largest fraction of compute time. -O5’s optimization algorithms take more compilation time, and may also degrade performance when applied to too large a fraction of the source program.

Optimization at this level is more likely to improve performance if done with profile feedback. See -xprofile=p.