Paolo Bonzini <bonzini@gnu.org> writes:
Here's my take on the part on mems, trying to make the usage in s390
sound less brittle (because cleanups in the area will make it kosher,
not invalid).
TBH, I prefer Kenny's version. I thought Ulrich's point was that,
if combine didn't convert the (sign_extend (mem)) into a (subreg (mem)),
there'd be no need for the s390.md uses of (subreg (mem)). I wouldn't want
the documentation to make it sound like that's not a sensible way to go.
Canonicalising _to_ a subreg from something else seems less than ideal.