[patch] Fix PR rtl-optimization/78437

[Paolo Bonzini]

On 23/11/2016 10:35, Eric Botcazou wrote:
> I now wonder 
> whether this also matters for !WORD_REGISTER_OPERATIONS targets, e.g. x86:
> 
>          (set (reg1:DI) ...
>          ...
> 	 (set (reg1:QI) (expression:QI))
> 	 ...
> 	 (set (reg2:DI) (any_extend:DI (reg1:QI)))
>          ...
>          (use (reg1:DI))
> 
> where the use reads well-defined upper bits from the very first set.

Does it really do that with a (set (reg1:QI)), as opposed to a
(set (strict_low_part (subreg:QI (reg1:DI)))?

Paolo