Re: Question about movM insn restrictions

[DJ Delorie <dj at redhat dot com>]

> But I can't find this restriction in the manual - does it still
> exist?

Yes.  In the overview, "For the generate pass, only the names of the
insns matter, . . . without regard for the RTL template or operand
constraints. Note that the names the compiler looks for are hard-coded
in the compiler . . ."

In the movM description, it says that these patterns will be used for
many things.  Since it's invoked by name, there's no opportunity for
predicates or constraints to even apply until later.

> I ask because in the AVR port, there are so many alternatives to
> handle and it would be easier to read if the move insns were split
> into a few smaller unnamed insns, each handling only some of the
> possible operands.

Use a define_expand for movM and have it expand into the appropriate
specific pattern(s).  Once it's expanded by name, you can use as few
or as many patterns as you like, as long as they're unambiguously
matchable.  Note that you must use predicates to do matching -
constraints will *not* cause a mismatch.  You must have a constraint
for every type of operand the predicate allows.