Is (set (subreg:SI (reg:HI) 0) (const_int)) valid rtx?

[Kazu Hirata]

Hi,

Is the following valid rtx?

  (set (subreg:SI (reg:HI ...) 0)
       (const_int ...))

Here (reg:HI ...) is a pseudo register.  If this is valid, is the
register allocator supposed to allocate an SImode hard register for
(subreg:SI (reg:HI) 0)?  Or should this be canonicalized to the
following?

  (set (reg:HI ...)
       (const_int ...))

Thanks,

Kazu Hirata