https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111770
--- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> --- (In reply to Richard Biener from comment #3) > As said X + 0. -> X is an invalid transform with FP unless there are no > signed zeros (maybe also problematic with sign-dependent rounding). Yeah, I was thinking about the integer case above. > > I think we agree to define .MASK_LOAD to zero masked elements. When we need > something else we need to add an explicit ELSE value. That needs documenting > of course and also possibly testsuite coverage - I _think_ you should be able > to do a GIMPLE frontend testcase for this. Sounds good, thanks. > > Note this behavior would extend to .MASK_GATHER_LOAD as well as > the load-lanes and -len variants. > > Unfortunately we do not have _any_ internals manual documentation for > internal functions - but you can backtrack to the optabs documentation > where this would need documenting. > > Now, if-conversion could indeed elide the .COND_ADD for integers. It's > problematic there only because of signed overflow undefinedness, so > you shouldn't see it for 'unsigned' already, and adding zero is safe. Can you elaborate on this a bit? Do you mean to say that the .COND_ADD is only there to avoid if-conversion introducing UB due to signed overflow? ISTM it's needed for correctness even without that, as the addend needn't be guaranteed to be zero in the general case. > if-conversion would need to have an idea of all the ranges involved here > so it might be a bit sophisticated to get it right. Does what I suggested above make any sense, or do you have in mind a different way of handling this in if-conversion? I'm wondering how ifcvt should determine that the addend is zero in the case where the predicate is false. Thanks
