HP aC++/HP C Programmer's Guide (B3901-90036; A.06.26; September 2011)

Usage:
+Odataprefetch=kind
The defined values for kind are:
direct Enable generation of data prefetch instructions for the benefit of direct
memory accesses, but not indirect memory accesses. This is the default at
optimization level +O1.
indirect Enables the 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. It is treated the same as direct at optimization
level +O1.
none Disables the generation of data prefetch instructions. This is the default at
optimization level +O0.
+O[no]fltacc
+O[no]fltacc=level
The +O[no]fltacc option disables [enables] floating-point optimizations that can result
in numerical differences. Any option other than +Ofltacc=strict also generates
Fused Multiply-Add (FMA) instructions. FMA instructions can improve performance of
floating-point applications.
If you specify neither +Ofltacc nor +Onofltacc, less optimization is performed than
for +Onofltacc. If you specify neither option, the optimizer generates FMA instructions
but does not perform any expression-reordering optimizations.
Specifying +Ofltacc insures the same result as in unoptimized code (+O0).
Usage:
+Ofltacc=level
The defined values for level are:
default Allows 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 propagation of infinities, NaNs, and the sign of zero.
relaxed In addition to the optimizations allowed by limited, permits optimizations,
such as reordering of expressions, even if parenthesized, that may affect
rounding error. This is the same as +Onofltacc.
strict Disallows any floating-point optimization that can result in numerical
differences. This is the same as +Ofltacc.
All options except +Ofltacc=strict option allow the compiler to make transformations
which are algebraically correct, but which may slightly affect the result of computations
due to the inherent imperfection of computer floating-point arithmetic. For many programs,
70 Command-Line Options