Re: [PATCH 8/9] Add TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID

[Jeff Law <law at redhat dot com>]

On 10/13/2015 04:13 AM, Richard Biener wrote:
> On Tue, Oct 13, 2015 at 1:27 AM, Richard Henderson <rth@redhat.com> wrote:
> > On 10/12/2015 09:10 PM, Richard Biener wrote:
> > > > > The check_loadstore change should instead have adjusted the
> > > > > flag_delete_null_pointer_checks guard in
> > > > > infer_nonnull_range_by_dereference.
> > > >
> > > >
> > > >
> > > > Nope, that doesn't work.  You have to wait until you see the actual MEM
> > > > being dereferenced before you can look at it's address space.
> > >
> > >
> > > Well, as we are explicitely looking for the pointer 'op' we know the
> > > address-space
> > > beforehand, no?  TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (op)))?
> >
> >
> > No.  We don't even know what type we're looking for; we're merely looking
> > for any use of NULL within any memory reference within STMT.
> >
> > Specifically, when we're not looking for a specific SSA_NAME (which would be
> > properly typed), we always pass in a plain (void *)0:
> >
> >            bool by_dereference
> >              = infer_nonnull_range_by_dereference (stmt, null_pointer_node);
>
> Ick.
It's just looking to see if there's an explicit *0 in stmt.  That can 
occur due to cprop & friends obviously.  It was an easy way to avoid 
having to write a special walker.

The problem here is we don't know what address space the *0 is going to 
hit, right?   Isn't that also an issue for code generation as well?

Jeff