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

cycles must be in the range of 0 to 10000. A value of 0 instructs the compiler to use

the default value, which is 480 cycles for loops containing floating-point accesses and

150 cycles for loops that do not contain any floating-point accesses.

For tuning purposes, it is recommended that users measure their application’s

performance using a few different prefetch latency settings to determine the optimal

value. Some floating-point codes may benefit by increasing the distance to 960. Parallel

applications frequently benefit from a shorter prefetch distance of 150.

+O[no]preserved_fpregs

The +O[no]preserved_fprefs option specifies whether the compiler is allowed

[not allowed] to make use of the preserved subset of the floating-point register file as

defined by the Itanium runtime architecture.

The default is +Opreserved_fpregs.

+O[no]rotating_fpregs

The +O[no]rotating_fpregs option specifies whether the compiler is allowed [not

allowed] to make use of the rotating subset of the floating-point register file.

The default is +Orotating_fpregs.

+O[no]sumreduction

This option enables [disables] sum reduction optimization. It allows the compiler to

compute partial sums to allow faster computations. It is not technically legal to do this

in C or C++ because of floating-point accuracy issues. This option is useful if an

application cannot use the +Onofltacc option but wants sum reduction to be

performed.

When sum reduction optimization is enabled, the compiler may evaluate intermediate

partial sums of float or double precision terms using (wider) extended precision, which

reduces variation in the result caused by different optimization strategies and generally

produces a more accurate result.

Header File Options

Following are the command-line options you can use for header files:

-H

cc -H file

54 Command-Line Options