HP 3000 Manuals

HP C Programmer's Guide

Enabling Aggressive Optimizations on HP-UX 

To enable aggressive optimizations at the second, third, or fourth
optimization levels, use the +Oaggressive option as follows:

     cc +O2 +Oaggressive sourcefile.c 

or:

     cc +O3 +Oaggressive sourcefile.c 

or:

     cc +O4 +Oaggressive sourcefile.c 

Aggressive optimizations are new optimizations or are optimizations that
can change the behavior of programs.  These optimizations may do any of
the following:

   *   convert certain library calls to millicode and inline instructions
   *   cause the inlined routines strcpy(), sqrt(), fabs(), and alloca()
       to not return the routine's completion status in ERRNO
   *   alter exception handling and asynchronous interrupt handling as a
       result of instruction scheduling optimization
   *   cause less precise floating-point results
   *   cause programs that perform comparisions between pointers to
       shared memory and pointers to private memory to run incorrectly

Use aggressive optimizations with stable, well-structured,
ANSI-conforming code.  These types of optimizations give you faster code,
but are riskier than the default optimizations.

MPE/iX 5.0 Documentation