HP aC++/HP C A.06.20 Programmer's Guide

Examples:

• The following command optimizes all functions at level 3, except for the functions

myfunc1 and myfunc2, which it optimizes at level 1.

aCC +O3 +O1=myfunc1,myfunc2 funcs.c main.c

• The following command optimizes all functions at level 2, except for the functions

myfunc1 and myfunc2, which it optimizes at level 0.

aCC -O +O0=myfunc1,myfunc2 funcs.c main.c

+O[no]libcalls

The +O[no]libcalls option is deprecated and may not be supported in future

releases. On Itanium®-based systems, including a system header file will cause the

functions declared therein to be eligible for libcalls transformations, regardless of

the state of +O[no]libcalls.

The default is +Onolibcalls. Use +O[no]libcalls at any optimization level.

See also +Onolibcalls=.

+O[no]loop_block

Loop blocking is a combination of strip mining and interchange that improves data

cache locality. It is provided primarily to deal with nested loops that manipulate arrays

that are too large to fit into the data cache. Under certain circumstances, loop blocking

allows reuse of these arrays by transforming the loops that manipulate them so that

they manipulate strips of the arrays that fit into the cache.

At optimization levels 3 and 4, using +Oloop_block (the default) allows automatic

loop blocking. Specifying +Onoloop_block disables loop blocking.

+O[no]loop_transform

This option transforms [does not transform] eligible loops for improved cache and

other performance. This option can be used at optimization levels 2, 3 and 4.

The default is +Oloop_transform.

+O[no]loop_unroll

+O[no]loop_unroll [=unroll_factor]

The +O[no]loop_unroll option enables [disables] loop unrolling. This optimization

can occur at optimization levels 2, 3, and 4. The default is +Oloop_unroll. The default

Code Optimizing Options 79