Combiner fix for PR79910

[Jeff Law]

On 03/17/2017 04:16 PM, Segher Boessenkool wrote:
> On Wed, Mar 15, 2017 at 12:09:18AM +0100, Bernd Schmidt wrote:
>> I suppose at the moment we don't do 2->2 combinations, so we could
>> conditionalize this on having an i1.
>
> You suppose wrong.  If one of the resulting insns is set_noop_p then
> 2->2 is allowed, for example.  Also in the hopefully not so far future
> we will allow 2->2 in general.
But in a 2->2 where one is a nop we're not going to run into problems.

jeff