Re: PING [ARM, RFC] Fix strange code in arm_legitimize_address

[Jie Zhang <jie at codesourcery dot com>]

On 01/21/2011 02:58 AM, Ramana Radhakrishnan wrote:
> On Mon, Jan 17, 2011 at 2:12 AM, Jie Zhang<jie@codesourcery.com>  wrote:
> > PING.
> >
> > On 12/31/2010 10:26 PM, Jie Zhang wrote:
> > > Hi,
> > >
> > > I found this while looking at something else. The following code in
> > > arm_legitimize_address is confusing for me:
> > >
> > > if (GET_CODE (x) == PLUS)
> > > {
> > > rtx xop0 = XEXP (x, 0);
> > > rtx xop1 = XEXP (x, 1);
> > >
> > > if (CONSTANT_P (xop0)&&  !symbol_mentioned_p (xop0))
> > > xop0 = force_reg (SImode, xop0);
> > >
> > > if (CONSTANT_P (xop1)&&  !symbol_mentioned_p (xop1))
> > > xop1 = force_reg (SImode, xop1);<== code A
> > >
> > > if (ARM_BASE_REGISTER_RTX_P (xop0)
> > > &&  GET_CODE (xop1) == CONST_INT)
> > > {
> > > ...<== code B
> > > }
> > > ...
> > > }
> > >
> > > The code B will never be executed since xop1 will never be a CONST_INT.
> > > If it were, it would have already been put into a reg by code A.
>
> Yeah I went through this and couldn't make out why this is the way it
> is. Looks good to me though I can't approve or reject your patch.
Thanks for taking a look! That piece of code can be traced back to more 
than 15 years ago. Maybe only Richard still remembers the original 
reason behind it.


Regards,
--
Jie Zhang