Constraint modifier for partially overlaping operands

[Ian Lance Taylor]

Andrew Hutchinson <andrewhutchinson@cox.net> writes:

> I can use "=" modifier to make operands use same register and early
> clobber "&" to avoid overlaps.
>
> Is it possible to have or construct a contraint that permits partial
> overlap operands. (which neither = or & would allow)
> The case would be  wide types taking multiple hard registers.
>
> eg Input r20..23 Output r22..25

There is no such constraint today.  I suppose it would be possible to
define such a constraint if it seemed useful.  It would not be a
simple change.  A number of different parts of the compiler know about
register constraints, and some of them would have to change in
relatively substantial ways to track this.

Ian