On Fri, 21 Jul 2023, Xi Ruoyao via Gcc-patches wrote:
> Perhaps -ffp-contract=on (not off) is enough to fix the issue (if you > are building GCC 14 snapshot). The default is "fast" (if no -std= > option is used), which allows some contractions disallowed by the > standard. Not fully, see below. > But GCC is in C++ and I'm not sure if the C++ standard has the same > definition for allowed contractions as C. It doesn't, but in GCC we should aim to provide the same semantics in C++ as in C. > > (Or is the severity of lack of support sufficiently different in the two > > cases that this is fine -- i.e. not compile vs may trigger floating > > point rounding inaccuracies?) > > It's possible that the test itself is flaky. Can you provide some > detail about how it fails? See also PR 99903 for an earlier known issue which appears due to x87 excess precision and so tweaking -ffp-contract wouldn't help: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99903 Now that multiple platforms are hitting this, can we _please_ get rid of the questionable attempt to compute time in a floating-point variable and just use an uint64_t storing nanoseconds? Alexander
