HP Fortran Programmer's Guide (March 2010)

Compiling and linking
Compiling with the f90 command
Chapter 2 69
+Ofaster
Selects the +Ofast option at optimization level +O3 for PA-RISC based
architectures. For Itanium processor family architectures, +Ofaster runs
at +O4 and implies -ipo.
+O[no]fenvaccess
Inform the compiler that the program accesses [does not access] the floating
point environment to test flags or run under non-default modes. If it knows
that a program does not access the floating point environment, the compiler
is allowed to perform certain optimizations that it otherwise may not
perform, such as global common subexpression elimination, code motion, or
constant folding.
The default is +Onofenvaccess.
+O[no]fastaccess
+Ofastaccess improves execution time by speeding up access to global data
items. You can use this option at optimization level 1 or higher..
Note that the +Ofastaccess option may increase link time.
The default is +Onofastaccess at optimization levels 1, 2, and 3; and
+Ofastaccess at optimization level 4.
+O[no]fltacc
+Onofltacc enables optimizations that follow the rules of algebra but may
change the order of expression evaluation. For example, if a, b, and c are
floating-point variables, the expressions (a + b) + c and a + (b + c) may
give slightly different results due to roundoff.
The +Onofltacc option also enables the fusion of adjacent multiply and add
operations—resulting in Fused Multiply-Add (FMA). (At optimization level
2 or higher, FMA occurs by default.) FMA improves performance but
occasionally produces results that may differ in accuracy from results
produced by code where fusion has not occurred. In general, the differences
are slight.
+Ofltacc disables optimizations that change the order of expression
evaluation and therefore may affect the accuracy of the result. The
+Ofltacc option also disables fusing.
NOTE +Ofltacc is the same as +Ofltacc=strict. +Onofltacc is
the same as +Ofltacc=relaxed.