Hi! On Tue, Feb 11, 2020 at 07:43:31PM +0100, Ulrich Weigand wrote: > 1. If a component flag of -ffast-math (or -funsafe-math-optimizations) > is explicitly set (or reset) on the command line, this should override > any implicit change due to -f(no-)fast-math, no matter in which order > the flags come on the command line. This change affects all flags.
Ack. > 2. Any component flag modified from its default by -ffast-math should > be reset to the default by -fno-fast-math. This was previously > not done for the following flags: > -fcx-limited-range > -fexcess-precision= Ack. > 3. Once -ffinite-math-only is true, the -f(no-)signaling-nans flag has > no meaning (if we have no NaNs at all, it does not matter whether > there is a difference between quiet and signaling NaNs). Therefore, > it does not make sense for -ffast-math to imply -fno-signaling-nans. > This is also a documentation change. Ack. > 4. -ffast-math is documented to imply -fno-rounding-math, however the > latter setting is the default anyway; therefore it does not make > sense to try to modify it from its default setting. Ack. It might be more robust to *do* set it, so that it still works if the default ever changes. > 5. The __FAST_MATH__ preprocessor macro should be defined if and only > if all the component flags of -ffast-math are set to the value that > is documented as the effect of -ffast-math. The following flags > were currently *not* so tested: > -fcx-limited-range > -fassociative-math > -freciprocal-math > -frounding-math > (Note that we should still *test* for -fno-rounding-math here even > though it is not set as per 4. -ffast-math -frounding-math should > not set the __FAST_MATH__ macro.) > This is also a documentation change. Ack. All looks good to me, but I'm not maintainer of this. This should be mentioned in the release notes I think, it does change behaviour (for the better, but any change is a change). Thanks, Segher
