https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93341
--- Comment #6 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> --- (In reply to Richard Earnshaw from comment #5) > (In reply to Andrew Pinski from comment #3) > > /* We should be able to reverse all conditions. */ > > gcc_assert (inv_cond_code != UNKNOWN); > > > > Obvious this code is broken because The quiet UN* was converted into the an > > unordered-signalling comparison which was bad. > > > > Quote from the recent change: > > And it would do the same in reverse: convert a quiet UN* into an > > unordered-signalling comparison. > > > > So obvious this code in aarch64_do_track_speculation was broken when it was > > added, just the aarch64 back-end was broken to do the wrong thing in the > > first place so we never able to hit the assert before hand. > > At least as far as Arm hardware is concerned, there is no such thing as an > unreversible comparison. The Arm condition codes (except AL, which isn't > really a condition) are all 100% reversisble. > > The problem here is GCC's insane convolution of the comparison phase with > the final condition and hence its insistance that reversing, say LT to UNGE > is not possible because the associated comparison must change. This is > frankly bonkers. If we want to force the choice of a trapping/non-trapping > comparison, it really, Really, REALLY should be described independently of > the condition under which the branch is taken. Agreed. Like I said in the commit message, I think we should just add an rtx comparison code for each IEEE comparison predicate, rather than leave some cases with no direct representation.
