HP C/aC++ for PA-RISC Software manual +O0, +O1, +O2, +O3

tunable will ensure that the compiler does not run out of virtual memory when compiling large files or functions.

In addition, maxssiz_64bit should be set to 128 MB for very large or complex input files. (Normally a maxssiz_64bit setting of 64 MB will be sufficient.)

See the kctune man page for more information on how to change kernel tunable parameters.

-O

-O

The -Ooption invokes the optimizer to perform level 2 optimization. This option is equivalent to +O2 option.

Example:

This command compiles prog.C and optimizes at level 2:

aCC -O prog.C

+O0

+O0

Use +O0 for fastest compile time or with simple programs. No optimizations are performed.

Example:

This command compiles prog.C and optimizes at level 0:

aCC +O0 prog.C

+O1

+O1

The +O1 option performs level 1 optimization only. This includes branch optimization, dead code elimination, faster register allocation, instruction scheduling, peephole optimization, and generation of data prefetch instructions for the benefit of direct (but not indirect) memory accesses. This is the default optimization level.

Example:

This command compiles prog.C and optimizes at level 1:

aCC +O1 prog.C

+O2

+O2

The +O2 option performs level 2 optimization. This includes level 1 optimizations plus optimizations performed over entire functions in a single file.

NOTE: Compiling with this optimization setting may require additional memory resources. Refer to the memory resource discussion above.

Example:

This command compiles prog.C and optimizes at level 2:

aCC +O2 prog.C

+O3

+O3

The +O3 option performs level 3 optimization. This includes level 2 optimizations plus full optimization across all subprograms within a single file.

54 Command-Line Options