HP UX Fortran Software manual Optimizations performed by +Onofltacc

+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

+O[no]fltacc	Expression reordering?	FMA?
	No	Yes
+Ofltacc	No	No
+Onofltacc	Yes	Yes
+O[no]fltacc=[strictdefaultlimitedrelaxed]		Control the level of floating point
		optimizations that the compiler may
		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.
+Ofrequently_called=function1[,function2...]		The named functions are assumed to be
		frequently called. This option overrides
		any information in a profile database.
+Ofrequently_called:filename		The file indicated by filename contains a
		list of function names, separated by
		spaces or newlines. These functions are
		assumed to be frequently called. This
		option overrides any information in a
		profile database.
+O[no]info		+Oinfo causes the compiler to display
		informational messages about the
		optimization process. The +Oinfo option
		provides feedback that can help you to

Fine-tuning optimization options 43