> On Jan 9, 2023, at 11:27 AM, Stefan Kanthak <stefan.kant...@nexgo.de> wrote:
>
> "Paul Koning" <paulkon...@comcast.net> wrote:
>
>>> ...
>
>> Yes, I was thinking the same. But I spent a while on that pattern -- I
>> wanted to support div/mod as a single operation because the machine has
>> that primitive. And I'm pretty sure I saw it work before I committed
>> that change. That's why I'm wondering if something changed.
>
> I can't tell from the past how GCC once worked, but today it can't
> (or doesn't) use such patterns, at least not on i386/AMD64 processors.
It turns out I was confused by the RTL generated by my pattern. That pattern
is for divmodhi, so it works as desired given same-size inputs.
I'm wondering if the case of longer dividend -- which is a common thing for
several machines -- could be handled by a define_peephole2 that matches the
sign-extend of the divisor followed by the (longer) divide. I made a stab at
that but what I wrote wasn't valid.
So, question to the list: suppose I want to write RTL that matches what Stefan
is talking about, with a div or mod or divmod that has si results and a di
dividend (or hi results and an si dividend), how would you do that? Can a
define_peephole2 do it, and if so, what would it look like?
paul
