RFC/RFA: Fix bug with REE optimization corrupting extended registers

[Jeff Law]

On 11/19/2015 08:34 AM, Nick Clifton wrote:
> Hi Bernd,
>
>> I had a look around. There's code testing HARD_REGNO_NREGS in
>> ree.c:combine_set_extension. It's inside #if 0, and labelled
>> "temporarily disabled". See if enabling that helps you? (Jeff, that #if
>> 0 was added by you).
>
> I suspect that the code was disabled because it prevented too many
> useful optimization opportunities.
>
> The code there would solve this problem, but the approach is is overly
> cautious, since it disables the optimization for all extensions that
> increase the number of hard registers used.  Some of these will be
> viable candidates, provided that the extra hard registers are no used.
> (This is certainly true for the RL78, where the (patched) optimization
> does improve code, even though the widening does use extra registers).
Nick -- can you pass along your testcode?

Jeff