Patch: Fix match_dup handling in web.c

[Steven Bosscher]

On Wed, Mar 24, 2010 at 11:25 PM, Bernd Schmidt <bernds@codesourcery.com> wrote:
> I found a number of bugs while testing an ARM patch that rewrites the
> ldm/stm peepholes.
>
> In web.c, there is code that tries to detect match_dups by comparing
> operands for equality; this is neither a necessary nor a sufficient
> condition.  In particular, web.c cannot detect an input operand that
> match_dups an in-out output operand; this can result in web.c breaking
> match_dups and replacing only the inputs of an insn.

Hmm, this has always worked ever since web.c was contributed years
ago, you'd think that such a deficiency would have been a problem for
someone by now.

FWIW:

+	  || DF_REF_REGNO (*dupref) < FIRST_PSEUDO_REGISTER)

can also be written as:

+	  || HARD_REGISTER_NUM_P (DF_REF_REGNO (*dupref))

I'm also a bit worried that we still *also* have to union all uses of
the same operand for DEBUG_INSNs, to avoid compare-debug failures.
Jakub, what do you think?

Ciao!
Steven