HP Fortran Programmer's Guide (B3908-90031; September 2011)

Compiling and linking

Compiling with the f90 command

Chapter 248

+Ooptlevel=name1 [,name2...]

2 Optimizations performed at level 1, plus the following:

• Coloring register allocation

• Induction variables and strength reduction

• Common subexpression elimination

• Loop invariant code motion

• Store/copy optimization

• Unused definition elimination

• Dataflow analysis

• Software pipelining

• Scalar replacement

• Sum reduction optimization

3 Optimizations performed at levels 1 and 2, plus the following:

• Interprocedural optimizations, including cloning and inlining

• Loop transformations to improve memory performance,

including fusion and interchange

Level 4 optimizations are not currently supported by the PA-RISC

compiler. If +O4 is specified, the compiler will issue a warning

message and compile at optimization level 3.

For Itanium applications, performs level 3 as well as doing

interprocedural optimizations across translation units (link time

optimizations). Object files generated at this level contain an

intermediate representation of the user code and are intended to be

temporary files. These intermediate object files are not guaranteed to

be compatible from one version of the compiler to the next. This

requires concurrent use of the +Oprofile=use option.

Table 2-6 Levels of optimization (Continued)

Level Optimizations