Re: free is a killer

[Jeff Law <law at redhat dot com>]

On 10/29/13 00:38, Marc Glisse wrote:
> On Mon, 28 Oct 2013, Jeff Law wrote:
>
> > On 10/28/13 16:05, Marc Glisse wrote:
> > > I checked and it does the wrong thing (I don't have the testcase handy
> > > anymore, but it shouldn't be hard to recreate one), I even wrote a patch
> > > (attached) but it is related to:
> > > http://gcc.gnu.org/ml/gcc-patches/2013-10/msg02238.html
> > > so it can't go in. A more limited fix (still missing many cases) would
> > > be possible. I didn't test VA_END, but it doesn't look as bad (it is the
> > > SSA_NAME case that is wrong for memcpy
> > Actually, it's fairly easy to see with memset.  Something like this:
> >
> > /* { dg-do compile } */
> > /* { dg-options "-O1 -fdump-tree-optimized" } */
> >
> > void f (long *p) {
> >  *p = 42;
> >  p[4] = 42;
> >  __builtin_memset (p, 0, 100);
> > }
> >
> > /* { dg-final { scan-tree-dump-not "= 42" "optimized" } } */
> > /* { dg-final { cleanup-tree-dump "optimized" } } */
>
> Indeed. Do you want to commit it xfailed or put it in bugzilla so we
> don't lose it? (it becomes harder if you replace p with p-1 in the
> memset arguments).
BTW, you can get a VAR_DECL (and presumably a PARM_DECL) from 
ao_ref_base.  Some of the ssa-dse tests show this.

Jeff