c++gccoptimizationfloating-pointfast-math

C++ gcc does associative-math flag disable float NAN values?

I'm working with statistic functions with a lot of float data. I want it to run faster but Ofast disable NAN (fno-finite-math-only flag), which is not allowed in my case.

In this case, is it safe to turn on only associative-math ? I think this flag allows things like vectorized sum of vector array, even if the array contains NAN.

Solution

  • From the docs:

    NOTE: re-ordering may change the sign of zero as well as ignore NaNs

    So if you want correct handling of NaNs, you should not use -fassociative-math.