[dataflow] partial register handling

[Richard Sandiford]

Paolo Bonzini <bonzini@gnu.org> writes:
> My opinion:
>>> (set (subreg:HI (reg:SI) 2) ...
>>> DF_REF_READ_WRITE?
>
> yep, only case without PARTIAL

Sorry if this is a daft question, but why would it be treated as a read?
I thought that without strict_lowpart, this sort of subreg assignment
was morally equivalent to a normal REG definition in which the upper
bits are "don't care".

Richard