On Mon, Jun 06, 2016 at 03:06:18PM +0000, Joseph Myers wrote:
> On Tue, 31 May 2016, Marek Polacek wrote:
>
> > > diff --git gcc/testsuite/c-c++-common/attr-may-alias-1.c
> > > gcc/testsuite/c-c++-common/attr-may-alias-1.c
> > > index e69de29..978b9a5 100644
> > > --- gcc/testsuite/c-c++-common/attr-may-alias-1.c
> > > +++ gcc/testsuite/c-c++-common/attr-may-alias-1.c
> > > @@ -0,0 +1,26 @@
> > > +/* { dg-do compile } */
> > > +/* { dg-options "-O2 -Wall" } */
> > > +
> > > +typedef int T __attribute__((may_alias));
> > > +
> > > +extern T *p;
> > > +extern int *p;
> > > +
> > > +extern int *p2;
> > > +extern T *p2;
> > > +
> > > +void fn1 (T);
> > > +void fn1 (int);
> > > +
> > > +void fn2 (int);
> > > +void fn2 (T);
> > > +
> > > +/* Ensure that the composite types have may_alias. */
> > > +void
> > > +f (long *i)
> > > +{
> > > + *i = *(__typeof (*p) *) &p;
> > > + asm ("" : : "r" (*p));
> > > + *i = *(__typeof (*p2) *) &p2;
> > > + asm ("" : : "r" (*p2));
>
> I don't see how this test is supposed to verify properties of the
> composite type. I'd expect you to need to verify that something does not
> get optimized away, that would get optimized away in the absence of
> may_alias.
Well, were it not for the may_alias attribute, we'd warn about type punning
(hence the -O2), so I thought that this test would be enough.
Marek
