matchThreeWayIntCompare() looks for
select i1 (a == b), i32 Equal, i32 (select i1 (a < b), i32 Less, i32 Greater)
but both of these selects/compares can be in it's commuted form,
so out of 8 variants, only the two most basic ones is handled.
This fixes regression being introduced in D66232.
I had not seen this API before. The header comment doesn't make sense:
(what does zero constant have to do with this?)
...and I don't like the name either, but that's independent of this patch. :)