HP C Programmer's Guide (92434-90009)

64 Chapter4

Optimizing HP C Programs

Changing the Aggressiveness of Optimizations

At each level of optimization, you can control the aggressiveness of the optimizations

performed.

Use the +Oconservative option at optimization level 2, 3, or 4 if you are not sure if your

code conforms to standards. This option provides more safety.

Use the +Oaggressive option at optimization level 2, 3, or 4 for best performance when

you are willing to risk changes to the behavior of your programs. Using the +Oaggressive

option can cause your program to have compilation or run-time problems that require

troubleshooting.

Enabling Only Conservative Optimizations

You can enable conservative optimizations at the second, third, or fourth optimization

levels by using the +Oconservative option, as follows:

cc +O2 +Oconservative

sourcefile

or:

cc +O3 +Oconservative

sourcefile

or:

cc +O4 +Oconservative

sourcefile

Conservative optimizations are optimizations that do not change the behavior of code, in

most cases, even if the code does not conform to standards.

Use the conservative optimizations provided with level 2, 3, and 4 when your code is

non-ANSI.

Enabling Aggressive Optimizations

To enable aggressive optimizations at the second, third, or fourth optimization levels,

use the +Oaggressive option as follows:

cc +O2 +Oaggressive

sourcefile

or:

cc +O3 +Oaggressive

sourcefile

or:

cc +O4 +Oaggressive

sourcefile