hard_regno_nregs == 0 ?

[Jim Wilson]

DJ Delorie wrote:
> Are there any ports besides m32c that have registers which can hold HI
> (or SI I suppose) but not QI values?

IA-64 has branch registers that are only allowed to hold DImode values. 
  We use CANNOT_CHANGE_MODE_CLASS to enforce this.

On x86, the vector registers can hold SImode, but do not allow 
HImode/QImode loads, and again CANNOT_CHANGE_MODE_CLASS is used to 
enforce this.

I'm sure that there are other examples out there.
-- 
Jim Wilson, GNU Tools Support, http://www.specifix.com