-fsimple[=n]

Select floating-point optimization preferences.

SPARC: 77/90 x86:77

Allow the optimizer to make simplifying assumptions concerning floating-point arithmetic. (See the Floating-Point Arithmetic chapter of the Fortran Programming Guide.)

For consistent results, compile all units of a program with the same -fsimple option.

If n is present, it must be 0, 1, or 2. The defaults are:

• Without the -fsimple flag, the compiler defaults to -fsimple=0

• With -fsimple alone, the compiler defaults to -fsimple=1

The different floating-point simplification levels are:

-fsimple=0

Permit no simplifying assumptions. Preserve strict IEEE 754 conformance.

-fsimple=1

Allow conservative simplifications. The resulting code does not strictly conform to IEEE 754, but numeric results of most programs are unchanged.

With -fsimple=1, the optimizer can assume the following:

• IEEE 754 default rounding/trapping modes do not change after process initialization.

• Computations producing no visible result other than potential floating point exceptions may be deleted.

• Computations with Infinity or NaNs ("Not a Number") as operands need not propagate NaNs to their results; e.g., x*0 may be replaced by 0.

• Computations do not depend on sign of zero.

  With -fsimple=1, the optimizer is not allowed to optimize completely without regard to roundoff or exceptions. In particular, a floating-point computation cannot be replaced by one that produces different results with rounding modes held constant at run time. -fast includes -fsimple=1.

  -fsimple=2

  Permit aggressive floating point optimizations that may cause many programs to produce different numeric results due to changes in rounding.

  For example, -fsimple=2 permits the optimizer to attempt to replace repeated computations of x/y with x*z, where z=1/y is computed once and saved in a temporary, eliminating the costly divide operation.

  Even with -fsimple=2, the optimizer still is not permitted to introduce a floating point exception in a program that otherwise produces none.