HP-UX Floating-Point Guide

174 Chapter 7
Performance Tuning
Inefficient Code
+Odataprefetch in conjunction
with+Ovectorize. The math library
contains special prefetching versions
of the vector routines, which are
called if you specify both options.
+O[no]fltacc +Ofltacc, which is the default at
levels 2, 3, and 4, disables
optimizations that are algebraically
correct but that may result in
numerical differences. (Usually these
differences are insignificant.) To
enable these optimizations, use
+Onofltacc.
On PA2.0 systems at level 2 and
higher, if you specify neither
+Ofltacc nor +Onofltacc, or if you
specify +Onofltacc, the compiler
generates FMA (fused multiply-add)
instructions (see “Architecture Type
of Run-Time System” on page 80 for
details). Specify +Ofltacc to
suppress the generation of these
instructions.
The +Onofltacc option is invoked
by default when you specify the
optimization type +Oaggressive;
use +Oaggressive +Ofltacc if you
want aggressive optimization without
sacrificing floating-point accuracy.
+O[no]inline,
+Oinline_budget=n +Oinline, which is available at
levels 3 and 4 and is the default at
those levels, enables inlining of
function calls. Inlining can improve
performance significantly if your
application makes many math library
calls. It is especially effective on
PA2.0 systems. The
+Oinline_budget option, also
available at levels 3 and 4, can be