REG_UNUSED notes problem

[Jeffrey A Law]

  In message < 199812091142.LAA24541@phal.cygnus.co.uk >you write:
  > Huh?  That is wrong.  The compiler has to assume that the register is
  > clobbered.
I went back and double checked, you're right.  The compiler considers the
value live until the point midway between the insn with the REG_UNUSED note
and the immediately following insn (ie, it conflicts with the outputs).

  > So it is a reload bug that reg 0 was used for the reload.
  > I guess that the problem stems from single_set returning the set of reg
  > 42, and the caller then checking only for clobbers, but not for unused
  > sets.
I find myself agreeing.  Thanks for the help.

So we punt this back into reload's court.  It shouldn't be using (reg 0) for
an output reload.

jeff