HP Fortran Programmer's Guide (September 2007)

Compiling and linking
Compiling with the f90 command
Chapter 244
-O[ n ]
-O invokes the optimizer, where n is the level of optimization, 0 - 4. (+O4 is
recognized but not supported.) The default is optimization level 2.
This option is provided for compatibility and is functionally the same as the
+O n option. The only difference between the two is that the level number is
optional for the -O option. For more information about the levels of
optimization, see the +O n option.
+O n
+O invokes the optimizer, where n is the level of optimization, 0 - 4. +O4 is
recognized but not supported and is provided for compatibility with the f77
option, +O4. The -g option is compatible with the +O0, +O1, and +O2 options.
Table 2-6 lists and describes the different levels of optimization.
NOTE See the Parallel Programming Guide for HP-UX Systems for a
detailed description of optimization levels and methods.
+O[no] optimization
+O[no] options enable or disable specific optimizations or classes of
optimizations (for example, optimizations that affect compilation time). For
detailed information about +O[no] optimization , see “Using optimization
options” on page 58.
Table 2-6 Levels of optimization
Level Optimizations
0 Local optimizations, including constant folding and partial
evaluation of test conditions.
1 Peephole optimizations, including:
• Basic block optimizations
• Branch optimizations
• Instruction scheduling