9.1.1.7 -fsimple=2

Unless directed to, the compiler does not attempt to simplify floating-point computations (the default is -fsimple=0). -fsimple=2 enables the optimizer to make aggressive simplifications with the understanding that this might cause some programs to produce slightly different results due to rounding effects. If -fsimple level 1 or 2 is used, all program units should be similarly compiled to ensure consistent numerical accuracy. See the Fortran User’s Guide for important information about this option.