HP Fortran Programmer's Guide (March 2010)

Compiling and linking
Compiling with the f90 command
Chapter 268
direct—enable generation of data prefetch instructions for the benefit of
direct memory accesses, but not indirect memory accesses.
indirect—enable 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—disable generation of data prefetch instructions. This is the default at
optimization levels +O1 and below.
+O[no]dynopt
Enable [disable] dynamic optimization for the output file, if the run-time
environment supports this feature. Both forms of this option change the
default setting, which allows the run-time environment to enable or disable
dynamic optimization according to a system-wide default. This option
applies only to executable files and shared libraries. chatr(1) can be used
to change this setting, including restoration of the default setting, after the
output file has been created.
+O[no]entrysched
+Oentrysched allows the optimizer to perform instruction scheduling on a
subprogram’s entry and exit code sequences. This option is only effective at
optimization level 1 or higher.
The option can change the behavior of programs that perform
exception-handling or that handle asynchronous interrupts.
The default is +Onoentrysched.
+O[no]failsafe
Enable [disable] failsafe optimization. When a compilation fails at the
current optimization level, +Ofailsafe will automatically restart the
compilation at +O2 (for specific high level optimizer errors +O3/+O4) or +O1
for Itanium processor family architecture and +O0 for PA-RISC
architecture.
The default is +Ofailsafe.
+Ofast
Select a combination of compilation options for optimum execution speed of
the compiled program. Those options include: +O2, +Olibcalls,
+Onolimit, +Ofltacc=relaxed, and +FPD. +Ofast also causes the +pi4M,
+pd4M options to be passed to the linker. In addition to these options, on the
Itanium processor family architecture, +DSnative instruction scheduling
is selected and +mergeseg is also passed to the linker.