SH: may miscompile zero extension and test

[kaz Kojima]

Jim Wilson <wilson@tuliptree.org> wrote:
> Subregs act much like regs when recognizing operands.  So if  (REG:SI 
> ...) is a valid operand, then so is (subreg:SI ...).
>
> The SH port defines WORD_REGISTER_OPERATIONS, which means if you put a 
> QImode value in a register, then you can interchangable use either 
> (reg:SI) or (reg:qi) because moving a QImode value sets the entire register.
>
> You do have to get the signedness right though.  There is some 
> interaction with LOAD_EXTEND_OP here to only generate the paradoxical 
> subreg when the signedness is OK.  There are occasional problems with 
> this code.

Thanks for the explanation. I'm slowly understanding about such
subregs.

> It isn't obvious what is wrong from your assembly language fragment.

I'll look the another RTL dumps again to see why zero extension is
removed from the resulting code.

Regards,
	kaz