-fsimple=0

Permits no simplifying assumptions. Preserve strict IEEE 754 conformance. 

-fsimple=1

Allows 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 as operands need not propagate NaNs to their results; for example, 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 runtime.

-fsimple=2

Includes all the functionality of -fsimple=1 and also enables use of SIMD instructions to compute reductions when -xvector=simd is in effect.

The compiler attempts 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 replace all computations of x/y in a given loop with x*z, where x/y is guaranteed to be evaluated at least once in the loop, z=1/y, and the values of y and z are known to have constant values during execution of the loop.