HP Fortran Programmer's Guide (March 2010)

Compiling and linking
Compiling with the f90 command
Chapter 266
The default is +Oloop_transform.
+O[no]size
+Osize suppresses optimizations that significantly increase code size. This
option is only effective at optimization level 2 or higher.
The +Onosize option permits optimizations that can increase code size.
The default is +Onosize.
Fine-tuning optimization options
The following options allow you to fine-tune the optimization process by providing control over
the specific techniques that the optimizer applies to your program. The syntax for using these
options is
+O[no]optimization
where optimization is a parameter that specifies an optimization
technique to apply to your program. The different parameters are described
below. The prefix no negates the effect of optimization.
The options do not override a specified level of optimization, nor do they imply a particular
level. To use any of these options you must also include the +On option on the same command
line, where n specifies the level at which the type of optimization can be performed.
For example, if you find that the optimizer is causing your program to produce different
floating-point results from those produced by the unoptimized program, you could use the
following command line to suppress optimizations that affect floating-point calculations:
f90 +O3 +Onomoveflops +Ofltacc my_prog.f90
If an option is mistakenly used at a level for which the corresponding optimization is not
performed, the compiler will issue a warning message.
The defaults given in the following descriptions are in effect only at the specified optimization
levels, unless stated otherwise.
+O[no]cache_pad_common
+Ocache_pad_common can improve program performance by padding
common blocks to avoid cache collisions. Cache-line collisions occur when
the difference between the addresses of two data points is a multiple of the
cache size. By inserting empty space between large variables (for example,
arrays), the optimizer ensures that they do not start at nearby addresses,
where the possibility of a cache collision is greater. This option is only
effective at optimization level 3 or higher.