This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: [ tree-ssa] PRE problem
- From: Diego Novillo <dnovillo at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: Daniel Berlin <dberlin at dberlin dot org>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Fri, 20 Feb 2004 15:03:14 -0500
- Subject: Re: [ tree-ssa] PRE problem
- Organization: Red Hat Canada
- References: <200402201956.i1KJuuL4002739@speedy.slc.redhat.com>
On Fri, 2004-02-20 at 14:56, law@redhat.com wrote:
> p = x;
> y = p;
> *y;
>
> "y" will have a tag, but by no means does that mean p or x will have a
> tag.
>
We are talking past each other again. When I say it's impossible for
them to have different tags, I am talking about *non-NULL* tags. It's
perfectly OK for a pointer to *not* have a tag. Only dereferenced
pointers need tags.
To summarize:
p = PHI <q, r>
If all three pointers 'p', 'q' and 'r' have been dereferenced, then they
must have the same tag.
Diego.