HP-UX 11i Tuning and Performance

11.2. Optimization Levels

Table 11-1 shows the basic optimization levels that are included in many compilers and indicates how they are invoked:.

Table 11-1. Compiler Optimization Levels

Level	Description	Command Line Option	C Directive	Fortran Directive
0	Very little optimization.	PA-RISC: the default, so no flag needed IPF: +O0	#pragma opt_level 0 #pragma optimize off	$Optimize off
1	Local optimization within block boundaries only.	PA-RISC: +O1 IPF: the default, so no flag needed	#pragma opt_level 1	$Optimize level 1 on
2	Global optimization within procedures only.	-O or +O2	#pragma opt_level 2	$Optimize level 2 on
3	Full optimization across all procedures within a single file.	+O3	#pragma opt_level 3	$Optimize level 3 on
4	Full optimization across the entire application ...