Re: POINTER_PLUS branch status?

[Jeffrey Law <law at redhat dot com>]

On Tue, 2007-05-29 at 16:13 -0700, Andrew Pinski wrote:
> On 5/29/07, Jeffrey Law <law@redhat.com> wrote:
> > I haven't followed PTR_PLUS development at all -- what specifically
> > spurred you to hack on this Andrew?
> 

>   Since we lose a
> lot of alignment in 4.0 after
> http://gcc.gnu.org/ml/gcc-patches/2004-06/msg00020.html
Ah.  OK.  There were easier things you could have done rather
than make PTR_PLUS work.  Obviously I'm happy that you've taken
the harder path as it's clearly more correct than some of the
other hacks that could have been done.

> Which actually mention you were working on this before (but it looks
> it was dropped by you).
Correct.  It was going to be a mess and other things became a
priority.

> 
> The next step is to see if that patch is no longer needed for hppa
> (well and fixing the hppa back-end).
I would expect you can kill that patch; I don't think you can "fix"
the PA backend because RTL passes can muck this stuff up pretty
badly (even if you have a solid definition of what REG_POINTER
really means -- see the archives from the late 1990s and early 2000s)

*If* you're going to twiddle the PA backend, then I would strongly
suggest some checking code to verify that REG_POINTER is never set
on both register operands in a reg+reg or reg + scale * index
address.

One of the things you might also want to look at is RTL propagation of
REG_POINTER -- I'm pretty sure it's not all that good and with the
lowering and mucking addresses that happens in RTL I'd be surprised
if we're not missing any registers that can/should be marked with
REG_POINTER.

Jeff