HP 3000 Manuals

HP C Programmer's Guide

Enabling Basic Optimization 

To enable basic optimizations, use the -O option (equivalent to +O2), as
follows:

     cc -O sourcefile.c 

Basic optimizations do not change the behavior of ANSI C
standard-conforming code.  They improve run-time execution time but only
increase compile time and link time by a moderate amount.

MPE/iX 5.0 Documentation