0

Permit no simplifying assumptions. Preserve strict IEEE 754 conformance. 

1

Allow conservative simplification. 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:

• IEEE754 default rounding/trapping modes do not change after process initialization.

• Computation producing no visible result other than potential floating-point exceptions can be deleted.

• Computation with infinities or NaNs as operands needs to propagate NaNs to their results; that is, x*0 can 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 when rounding modes are held constant at runtime.

2

Includes all the functionality of -fsimple=1 and also permits aggressive floating-point optimization that can cause many programs to produce different numeric results due to changes in rounding. For example, permit 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.