Simplification of combine patterns with subreg and zero_extract

[Paolo Bonzini]

> I think it is simply because combine.c doesn't have any code to simplify this kind of expression. 
>   
In theory it should have...
>> However, if you add these simplifications to simplify-rtx.c, it will 
>> be picked up by combine.
>>     
> There is a lot of simplification code in combine.c too. Should I try to add these simplifications to both combine.c and simplify-rtx.c?
No, combine.c calls simplify-rtx.c before attempting its own share of 
simplifications.

Paolo