This chapter discusses the following:
When and how to use the optimizer.
The four levels of optimization.
Profile-based optimization.
Advanced optimization options and pragmas
Improving compile and link time
The HP C optimizer transforms programs so machine resources
are used more efficiently. The optimizer can dramatically improve
application run-time speed. HP C performs only minimal optimizations
unless you specify otherwise. You activate additional optimizations
using HP C command-line options and pragmas.
There are four major levels of optimization: levels 1, 2,
3, and 4. Level 4 optimization can produce the fastest executable
code. Level 4 is a superset of the other levels.
Additional parameters enable you to control the size of the
executable program, compile time, and aggressiveness of the optimizations
performed.
Compile time memory and CPU usage increase with each higher
level of optimization due to the increasingly complex analysis that
must be performed. You can control the trade-offs between compile-time
penalties and code performance by choosing the level of optimization
you desire.
Generally, the optimizer is not used during code development.
It is used when compiling production-level code for benchmarking
and general use.
