On Fri, Feb 28, 2020 at 04:04:10PM +0100, Jakub Jelinek wrote: > On Fri, Feb 28, 2020 at 08:53:11AM -0600, Segher Boessenkool wrote: > > On Thu, Feb 27, 2020 at 09:25:27PM -0800, Steve Kargl wrote: > > > On Fri, Feb 28, 2020 at 01:02:28PM +0800, Jiufu Guo wrote: > > > > > > > > With -ffast-math -O3, this case `STOP 3` on a few platforms, e.g. > > > > ppc64le/x86. > > > > > > IMHO, using -ffast-math with Fortran code is never correct. > > > With this option, you got exactly what you wanted. > > > > It happens with -O2 already. > > > > The frontend generates a MIN_EXPR (or MAX_EXPR) for this, which is > > undefined for NaNs already. I think the testcase is just invalid? > > Or maybe just the FE shouldn't use MIN_EXPR/MAX_EXPR if NaN is allowed, > but fmax/fmaxf/fmaxl etc. or x < y ? x : y or whatever exactly is expected > instead to yield the right answer for NaN? >
If a Fortran program does not use the IEEE_ARITHMETIC module and specifically handle +-inf and nan and that program generates one of those values, then that program is in "undefined behavior" territory. Replacing MIN_EXPR/MAX_EXPR (everywhere?) would seem to be a pessimization for correctly written code. -- Steve
