HP Fortran Programmer Guide (766160-001, March 2014)

The +Onoconservative option relaxes the optimizer’s
assumptions about the target program.
The +Onoconservative option relaxes the optimizer’s
assumptions about the target program.
The default is +Onoconservative. This option has been
deprecated starting with HP-UX version 11i and later.
+Olimit suppresses optimizations that significantly
increase compilation time or that can consume large
+O[no]limit
amounts of memory at compile time. This option is only
effective at optimization level 2 or higher.
The +Onolimit option allows optimizations to be
performed regardless of their effect on compilation time or
memory usage. The default is +Olimit.
Enables [disables] the following transformations: loop unroll
and jam, loop distribution, loop interchange, loop blocking,
+O[no]loop_transform
loop fusion, and loop unroll. The default is
+Oloop_transform.
+Osize suppresses optimizations that significantly increase
code size. This option is only effective at optimization level
+O[no]size
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
where optimization is a parameter that specifies an
optimization technique to apply to your program. The
+O[no]optimization
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.
+Ocache_pad_common can improve program
performance by padding common blocks to avoid
+O[no]cache_pad_common
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.
40 Compiling and linking