[Bug] subword handling for DI modes

[Ben Elliston]

I wrote:

   Here is a minimal test case that reproduces the problem.  Does anyone
   have any ideas?  Thanks,

        (set reg (subword SI reg 0))

FYI, I was able to work around this by using:

	(subword SI (reg h-reg) 0)

So it seems something is amiss in the determination of the operand's mode.

Ben