https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83240
--- Comment #2 from Andreas Gustafsson <gson at gson dot org> --- Re "simply don't use -ffast-math if you are dealing with stuff like denormals", the documentation for -ffinite-math-only (which is implied by -ffast-math) says "Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs". It does not mention denormals, which to me suggests that optimizations that assume arguments are not denormals are *not* allowed. Also, since we are discussing the case where DAZ is 0, it is likely that FTZ (Flush To Zero) is also 0. This means that even if all the inputs to the computation compiled with -ffast-math are guaranteed not to be denormals, denormals can arise within the computation itself, for example any time two inputs are added, subtracted, multiplied, or divided. In other words, if you can't use -ffast-math "when dealing with denormals", you can't use it for any code that does arithmetic on its inputs, which is pretty much the same thing as saying you can't use it ever.
