Matthew Fortune <matthew.fort...@imgtec.com> writes: > Sandra Loosemore <san...@codesourcery.com> writes: >> On 12/21/2016 11:54 AM, Yunqiang Su wrote: >> > By this patch, I add a build-time option ` --with-unfused-madd4=yes/no', >> > and runtime option -m(no-)unfused-madd4, >> > to disable generate madd.fmt instructions. >> >> Your patch also needs a documentation change so that the new >> command-line option is listed in the GCC manual with other MIPS target >> options. > > Any opinions on option names to control this? Is it best to target the > specific > feature that is non-compliant on loongson or apply a general -mfix-loongson > type option? > > I'm not sure I have a strong opinion either way but there do seem to be > multiple possible variants.
Wasn't sure from this thread whether Loongson simply had a fused implementation (without intermediate rounding) or whether the instructions gave numerically incorrect results for some inputs. It sounds from a later thread like it's generating incorrect results, is that right? If so, then FWIW I agree an -mfix option would be more consistent. E.g. one of the -mfix-vr4120 errata was an incorrect integer division result and one of the -mfix-sb1 errata was an incorrect single-precision float division result. The latter case could have been handled by an option to disable DIV.S and DIV.PS, but the -mfix option gave more control. If instead the problem is that the instructions are fused then that's also what the original MIPS 4 parts did, so maybe an option to control fusedness would make sense. Thanks, Richard
