https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66588
--- Comment #5 from ktkachov at gcc dot gnu.org --- (In reply to Segher Boessenkool from comment #4) > combine should not in general try multiple ways to write the same > thing; this will not scale. In this case, I don't see that some > backends would really like to write it one way and some the other, > so we should just use one way. > > There are no defined canonicalization rules for this, but there > are for the similar cases involving MULT, where the extends are > moved inwards as well. This is most in line with how other extends > are treated as well. > > We probably should document the canonicalization rules better; > current practice for backends is to just look at what combine does > and use that; not a great idea in my opinion. Ok, thanks. I've opened PR 66776 for the aarch64 MD changes. Would you like to keep this open to track any documentation changes? Or shall we close this off?
