On Sun, Mar 8, 2009 at 11:26 PM, Sylvain Pion <sylvain.p...@sophia.inria.fr> wrote: > Joseph S. Myers a écrit : >> >> On Sun, 8 Mar 2009, Sylvain Pion wrote: >> >>> http://gcc.gnu.org/ml/gcc-patches/2003-09/msg00104.html >>> introduced the -frounding-math option, and changed >>> the default behavior of GCC to optimize "unsafely". >> >> That is a misleading description. The cautionary text added by that patch >> is still present: >> >> This option is experimental and does not currently guarantee to >> disable all GCC optimizations that are affected by rounding mode. >> >> This is still true. GCC did not before the patch, did not after the patch >> and does not now fully support disabling optimizations that are unsafe in >> the presence of rounding mode changes; a few affected optimizations are >> disabled, but noone has seriously attempted to cover them all. GCC was >> "unsafe" before the patch and remains so whether or not you use the option. > > You are playing with words. Please step back and look at the facts > for a moment. > > The fact is that Roger's patch introduced a regression (this word > should be clear enough here), in that some users now have their old > code broken, and they are forced to add the -frounding-math option > (after having lost some time finding about this non trivial issue). > This is a long term hindrance. > > Even if -frounding-math is not 100% correct, it makes things work > (more precisely, lack of it breaks code), and this is the only > thing that matters here.
Your position is clear. There is others complaining about the exact opposite of course - those that see -ffast-math "violating IEEE" and that want "fast math", but IEEE by default. Whatever that means to them, of course. We try to have a sensible default setting that doesn't prevent constant folding (which -frounding-math does). I don't have a solution for you unfortunately, other than finally trying to implement FENV access. But that requires a considerable amount of ressources that I cannot see being spent at any point in time. Thanks, Richard.
