mov arguments are the same

mov arguments are the same

[Paulo J. Matos]

Hello,

In a rule like
 (set (match_operand 0 ...)
        (match_operand 1 ...))

I sometimes have operand0 equal to operand1, as in
rtx_equal_p(operand[0], operand[1]) == 1.
This generates a move between the same location (same as a nop).

Is there a reason for getting this and is it up to me to handle it or
this is just the result of some problem with my md file? I am in
gcc4.4.4.

Cheers,
-- 
PMatos

Re: mov arguments are the same

[Ian Lance Taylor]

"Paulo J. Matos" <pocmatos@gmail.com> writes:

> In a rule like
>  (set (match_operand 0 ...)
>         (match_operand 1 ...))
>
> I sometimes have operand0 equal to operand1, as in
> rtx_equal_p(operand[0], operand[1]) == 1.
> This generates a move between the same location (same as a nop).
>
> Is there a reason for getting this and is it up to me to handle it or
> this is just the result of some problem with my md file? I am in
> gcc4.4.4.

Moves between the same register are normally eliminated by a loop at the
end of reload().  Does your processor support memory-to-memory moves?  I
don't think anything will explicitly eliminate those, though I'm also
not sure why they would be created in the first place.

I'm surprised that it happens, but I don't know what would cause it.  In
particular I don't know that it is a problem in your MD file.  You'll
have to find out where they are coming from.

Ian

Re: mov arguments are the same

[Paulo J. Matos]

On Tue, Aug 24, 2010 at 3:10 PM, Ian Lance Taylor <iant@google.com> wrote:
> "Paulo J. Matos" <pocmatos@gmail.com> writes:
>
> Moves between the same register are normally eliminated by a loop at the
> end of reload().  Does your processor support memory-to-memory moves?

Nope, not really.

> I
> don't think anything will explicitly eliminate those, though I'm also
> not sure why they would be created in the first place.
>
> I'm surprised that it happens, but I don't know what would cause it.  In
> particular I don't know that it is a problem in your MD file.  You'll
> have to find out where they are coming from.
>

Thanks for the comments. I was wondering if gcc was generating them
for some purpose I was not aware of.
From your comments I deduce that this is not the case.

Cheers,

-- 
PMatos