HP aC++/HP C A.06.28 Programmer's Guide Integrity servers (769150-001, March 2014)

+Olevel

+Olevel=name1[,name2,...,nameN]

The +Olevel option lowers optimization to the specified level for one or more named functions.

level can be 0, 1, 2, 3, or 4.

The name parameters are names of functions in the module being compiled. Use this option when

one or more functions do not optimize well or properly. This option must be used with a basic

+Olevel or -O option. Note that currently only the C++ mangled name of the function is allowed

for name.

This option works like the OPT_LEVEL pragma. The option overrides the pragma for the specified

functions. As with the pragma, you can only lower the level of optimization; you cannot raise it

above the level specified by a basic +Olevel or -O option. To avoid confusion, it is best to use

either this option or the OPT_LEVEL pragma rather than both.

You can use this option at optimization levels 1, 2, 3, and 4. The default is to optimize all functions

at the level specified by the basic +Olevel or -O option.

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]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 is 4, that is, four

copies of the loop body. The unroll_factor controls code expansion. Note that

+Onoloop_unroll has no effect on loop unroll-and-jam.

+O[no]openmp

The +Oopenmp option causes the OpenMP directives to be honored. This option is effective at any

optimization level. Non OpenMP parallelization directives are ignored with warnings. +Onoopenmp

requests that OpenMP directives be silently ignored. If neither +Oopenmp nor +Onoopenmp is

specified, OpenMP directives will be ignored with warnings.

The OpenMP specification is available at http://www.openmp.org/specs. OpenMP programs

require the libomp and libcps runtime support libraries to be present on both the compilation

and runtime systems. The compiler driver automatically includes them when linking.

If you use +Oopenmp in an application, you must use -mt with any files that are not compiled

with +Oopenmp. For additional information and restrictions, See “-mt” (page 66).

Code Optimizing Options 61