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

+Ofltacc disables optimizations that change the
order of expression evaluation and therefore may affect
the accuracy of the result. The +Ofltaccoption also
disables fusing.
NOTE: +Ofltacc is the same as
+Ofltacc=strict. +Onofltacc is the same as
+Ofltacc=relaxed.
Table 2-9 identifies the different actions taken by the
optimizer, according to whether you specify
+Ofltacc, +Onofltacc, or neither option. In all
cases, the table assumes that you are compiling at
optimization level 2 (+O2) or higher.
Table 18 Optimizations performed by +O[no]fltacc
FMA?Expression reordering?+O[no]fltacc
YesNo
NoNo+Ofltacc
YesYes+Onofltacc
Control the level of floating point
optimizations that the compiler may
+O[no]fltacc=[strict|default|limited|relaxed]
perform. The defined values for optlevel
are:
strict—disallow any floating point
optimization that can result in numerical
differences. This is the same as
+Ofltacc.
default—allow contractions, such as
fused multiply-add (FMA), but disallows
any other floating point optimization that
can result in numerical differences.
limited—like default, but also allows
floating point optimizations which may
affect the generation and propogation of
infinities, NaNs, and the sign of zero.
Also implies +Ocxlimitedrange.
relaxed—in addition to the
optimizations allowed by limited, permits
optimizations, such as reordering of
expressions, even if parenthesized, that
may affect a rounding error. This is the
same as +Onofltacc. Also implies
+Ocxlimitedrange.
The named functions are assumed to be
frequently called. This option overrides
any information in a profile database.
+Ofrequently_called=function1[,function2...]
The file indicated by filename contains a
list of function names, separated by
+Ofrequently_called:filename
spaces or newlines. These functions are
assumed to be frequently called. This
option overrides any information in a
profile database.
+Oinfo causes the compiler to display
informational messages about the
+O[no]info
optimization process. The +Oinfo option
provides feedback that can help you to
Fine-tuning optimization options 43