On Mon, Dec 17, 2018 at 1:43 PM H.J. Lu <[email protected]> wrote:
>
> On Mon, Dec 17, 2018 at 1:39 AM Richard Biener
> <[email protected]> wrote:
> >
> > On Fri, Dec 14, 2018 at 11:48 PM H.J. Lu <[email protected]> wrote:
> > >
> > > On Fri, Dec 14, 2018 at 2:10 PM Jason Merrill <[email protected]> wrote:
> > > >
> > > > On 12/13/18 6:56 PM, H.J. Lu wrote:
> > > > > On Thu, Dec 13, 2018 at 12:50 PM Jason Merrill <[email protected]>
> > > > > wrote:
> > > > >>
> > > > >> On 9/25/18 11:46 AM, H.J. Lu wrote:
> > > > >>> On Fri, Aug 31, 2018 at 2:04 PM, Jason Merrill <[email protected]>
> > > > >>> wrote:
> > > > >>>> On 07/23/2018 05:24 PM, H.J. Lu wrote:
> > > > >>>>>
> > > > >>>>> On Mon, Jun 18, 2018 at 12:26 PM, Joseph Myers
> > > > >>>>> <[email protected]>
> > > > >>>>> wrote:
> > > > >>>>>>
> > > > >>>>>> On Mon, 18 Jun 2018, Jason Merrill wrote:
> > > > >>>>>>
> > > > >>>>>>> On Mon, Jun 18, 2018 at 11:59 AM, Joseph Myers
> > > > >>>>>>> <[email protected]>
> > > > >>>>>>> wrote:
> > > > >>>>>>>>
> > > > >>>>>>>> On Mon, 18 Jun 2018, Jason Merrill wrote:
> > > > >>>>>>>>
> > > > >>>>>>>>>> + if (TREE_CODE (rhs) == COND_EXPR)
> > > > >>>>>>>>>> + {
> > > > >>>>>>>>>> + /* Check the THEN path first. */
> > > > >>>>>>>>>> + tree op1 = TREE_OPERAND (rhs, 1);
> > > > >>>>>>>>>> + context = check_address_of_packed_member (type, op1);
> > > > >>>>>>>>>
> > > > >>>>>>>>>
> > > > >>>>>>>>> This should handle the GNU extension of re-using operand 0 if
> > > > >>>>>>>>> operand
> > > > >>>>>>>>> 1 is omitted.
> > > > >>>>>>>>
> > > > >>>>>>>>
> > > > >>>>>>>> Doesn't that just use a SAVE_EXPR?
> > > > >>>>>>>
> > > > >>>>>>>
> > > > >>>>>>> Hmm, I suppose it does, but many places in the compiler seem to
> > > > >>>>>>> expect
> > > > >>>>>>> that it produces a COND_EXPR with TREE_OPERAND 1 as NULL_TREE.
> > > > >>>>>>
> > > > >>>>>>
> > > > >>>>>> Maybe that's used somewhere inside the C++ front end. For C a
> > > > >>>>>> SAVE_EXPR
> > > > >>>>>> is produced directly.
> > > > >>>>>
> > > > >>>>>
> > > > >>>>> Here is the updated patch. Changes from the last one:
> > > > >>>>>
> > > > >>>>> 1. Handle COMPOUND_EXPR.
> > > > >>>>> 2. Fixed typos in comments.
> > > > >>>>> 3. Combined warn_for_pointer_of_packed_member and
> > > > >>>>> warn_for_address_of_packed_member into
> > > > >>>>> warn_for_address_or_pointer_of_packed_member.
> > > > >>>>
> > > > >>>>
> > > > >>>>> c.i:4:33: warning: converting a packed ‘struct C *’ pointer
> > > > >>>>> increases the
> > > > >>>>> alignment of ‘long int *’ pointer from 1 to 8
> > > > >>>>> [-Waddress-of-packed-member]
> > > > >>>>
> > > > >>>>
> > > > >>>> I think this would read better as
> > > > >>>>
> > > > >>>> c.i:4:33: warning: converting a packed ‘struct C *’ pointer
> > > > >>>> (alignment 1) to
> > > > >>>> ‘long int *’ (alignment 8) may result in an unaligned pointer value
> > > > >>>> [-Waddress-of-packed-member]
> > > > >>>
> > > > >>> Fixed.
> > > > >>>
> > > > >>>>> + while (TREE_CODE (base) == ARRAY_REF)
> > > > >>>>> + base = TREE_OPERAND (base, 0);
> > > > >>>>> + if (TREE_CODE (base) != COMPONENT_REF)
> > > > >>>>> + return NULL_TREE;
> > > > >>>>
> > > > >>>>
> > > > >>>> Are you deliberately not handling the other handled_component_p
> > > > >>>> cases? If
> > > > >>>> so, there should be a comment.
> > > > >>>
> > > > >>> I changed it to
> > > > >>>
> > > > >>> while (handled_component_p (base))
> > > > >>> {
> > > > >>> enum tree_code code = TREE_CODE (base);
> > > > >>> if (code == COMPONENT_REF)
> > > > >>> break;
> > > > >>> switch (code)
> > > > >>> {
> > > > >>> case ARRAY_REF:
> > > > >>> base = TREE_OPERAND (base, 0);
> > > > >>> break;
> > > > >>> default:
> > > > >>> /* FIXME: Can it ever happen? */
> > > > >>> gcc_unreachable ();
> > > > >>> break;
> > > > >>> }
> > > > >>> }
> > > > >>>
> > > > >>> Is there a testcase to trigger this ICE? I couldn't find one.
> > > > >>
> > > > >> You can take the address of an element of complex:
> > > > >>
> > > > >> __complex int i;
> > > > >> int *p = &__real(i);
> > > > >>
> > > > >> You may get VIEW_CONVERT_EXPR with location wrappers.
> > > > >
> > > > > Fixed. I replaced gcc_unreachable with return NULL_TREE;
> > > >
> > > > Then we're back to my earlier question: are you deliberately not
> > > > handling the other cases? Why not look through them as well? What if
> > > > e.g. the operand of __real is a packed field?
> > > >
> > >
> > > Here is the updated patch with
> > >
> > > diff --git a/gcc/c-family/c-warn.c b/gcc/c-family/c-warn.c
> > > index 615134cfdac..f105742598e 100644
> > > --- a/gcc/c-family/c-warn.c
> > > +++ b/gcc/c-family/c-warn.c
> > > @@ -2669,6 +2669,9 @@ check_address_of_packed_member (tree type, tree rhs)
> > > switch (code)
> > > {
> > > case ARRAY_REF:
> > > + case REALPART_EXPR:
> > > + case IMAGPART_EXPR:
> > > + case VIEW_CONVERT_EXPR:
> > > base = TREE_OPERAND (base, 0);
> > > break;
> > > default:
> >
> > don't we have handled_component_p () for this? (you're still
> > missing BIT_FIELD_REF which might be used for vector
> > element accesses)
> >
>
> Do you have a testcase?
No, I suspect it might need some folding to trigger (IIRC I made the FEs
use ARRAY_REFs but I'm not sure whether fully, esp. in the case of
address-taking). My attempt:
typedef int v4si __attribute__((vector_size(16)));
struct X
{
v4si x;
} __attribute__((packed)) x;
int *foo()
{
return &x.x[1];
}
that shows
return &VIEW_CONVERT_EXPR<int[4]>(x.x)[1];
for both C and C++ (albeit checked GCC 8 here).
Richard.
> --
> H.J.
