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

[Jie Zhang <jie at codesourcery dot com>]

On 01/21/2011 06:35 PM, Ramana Radhakrishnan wrote:
> On Fri, 2011-01-21 at 10:28 +0800, Jie Zhang wrote:
> > 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.
>
> Probably - Just noticed that you'd tested only for the basic
> multilibs.It might be worth testing for a vfp variant at v7-a just of
> paranoia since this is a code path that hasn't been exercised for 15
> years though I think it should be safe.
I did a regression testing with "-march=armv7-a -mfloat-abi=softfp 
-mfpu=neon" on qemu for gcc, g++, libstdc++. No regressions are found.


--
Jie Zhang