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

The default, in the absence of +Oprofile=use, is +Onodatalayout.
+O[no]dataprefetch
+O[no]dataprefetch
When +Odataprefetch is enabled, the optimizer inserts instructions within innermost
loops to explicitly prefetch data from memory into the data cache. Data prefetch
instructions are inserted only for data structures referenced within innermost loops
using simple loop varying addresses (that is, in a simple arithmetic progression).
Use this option for applications that have high data cache miss overhead. The default
is +Onodataprefetch.
+Odataprefetch is equivalent to +Odataprefetch=indirect.
+Onodataprefetch is equivalent to +Odataprefetch=none.
Usage:
+Odataprefetch=kind
The defined values for kind are:
direct
Enable generation of data prefetch instructions for the benefit of direct
memory accesses, but not indirect memory accesses.
indirect
Enables the generation of data prefetch instructions for the benefit of
both direct and indirect memory accesses. This is the default at
optimization levels +O2 and above.
none
Disables the generation of data prefetch instructions. This is the default
at optimization levels +O1 and below.
+O[no]extern
+O[no]extern
Use the +O[no]extern option at optimization levels 0, 1, 2, 3, or 4. The default is
+Oextern with no name list.
+Oextern is equivalent to -Bextern.
+Onoextern is equivalent to -Bprotected.
NOTE: This option is deprecated and may not be supported in the future releases.
+O[no]fltacc
+O[no]fltacc=level
The +O[no]fltacc option disables [enables] floating-point optimizations that can
result in numerical differences. Any option other than +Ofltacc=strict also
generates Fused Multiply-Add (FMA) instructions. FMA instructions can improve
performance of floating-point applications.
74 Command-Line Options