Ping.
On Thu, Jan 16, 2014 at 07:52:43PM +0100, Marek Polacek wrote:
> On Wed, Jan 15, 2014 at 09:23:06PM +0000, Joseph S. Myers wrote:
> > On Wed, 15 Jan 2014, Marek Polacek wrote:
> >
> > > +/* Return true if T is a pointer to a zero-sized struct/union. */
> > > +
> > > +bool
> > > +pointer_to_zero_sized_aggr_p (tree t)
> > > +{
> > > + t = strip_pointer_operator (t);
> > > + return ((RECORD_OR_UNION_TYPE_P (t) || TREE_CODE (t) == ARRAY_TYPE)
> > > + && TYPE_SIZE (t)
> > > + && integer_zerop (TYPE_SIZE (t)));
> >
> > Why have the (RECORD_OR_UNION_TYPE_P (t) || TREE_CODE (t) == ARRAY_TYPE)
> > check at all? It may well be the case that those are the only kinds of
> > types that can have zero size here, but the principle of this error
> > applies to anything with zero size so it would seem best not to have that
> > part of the check at all.
>
> Ok, changed.
>
> > strip_pointer_operator seems wrong here. It recursively removes an
> > arbitrary number of pointer type derivations - but where the types are
> > pointer to pointer to zero-size, arithmetic is perfectly valid (so you
> > should have a test that such cases are still accepted, where this patch
> > version would have rejected them). I believe this function should return
> > true if the argument is a pointer (to anything) and after removal of
> > exactly one level of pointer type derivation, the result has zero size
> > (constant zero - also add a test that the array case where the size is a
> > const int initialized to 0 is not, for C, rejected, as those are VLAs in C
> > terms).
>
> Ah, right, sorry about that. Hopefully all done in the following.
> The if (!POINTER_TYPE_P (t)) check in pointer_to_zero_sized_aggr_p
> could perhaps go; I added it mostly for paranoia sake.
>
> 2014-01-16 Marek Polacek <pola...@redhat.com>
>
> PR c/58346
> c-family/
> * c-common.c (pointer_to_zero_sized_aggr_p): New function.
> * c-common.h: Declare it.
> cp/
> * typeck.c (pointer_diff): Give an error on arithmetic on pointer to
> an empty aggregate.
> c/
> * c-typeck.c (pointer_diff): Give an error on arithmetic on pointer to
> an empty aggregate.
> testsuite/
> * c-c++-common/pr58346-1.c: New test.
> * c-c++-common/pr58346-2.c: New test.
> * c-c++-common/pr58346-3.c: New test.
>
> --- gcc/c-family/c-common.h.mp 2014-01-15 11:24:41.438608787 +0100
> +++ gcc/c-family/c-common.h 2014-01-16 16:40:06.105688048 +0100
> @@ -789,6 +789,7 @@ extern bool keyword_is_storage_class_spe
> extern bool keyword_is_type_qualifier (enum rid);
> extern bool keyword_is_decl_specifier (enum rid);
> extern bool cxx_fundamental_alignment_p (unsigned);
> +extern bool pointer_to_zero_sized_aggr_p (tree);
>
> #define c_sizeof(LOC, T) c_sizeof_or_alignof_type (LOC, T, true, false, 1)
> #define c_alignof(LOC, T) c_sizeof_or_alignof_type (LOC, T, false, false, 1)
> --- gcc/c-family/c-common.c.mp 2014-01-16 16:39:17.093487218 +0100
> +++ gcc/c-family/c-common.c 2014-01-16 17:15:37.466403444 +0100
> @@ -11823,4 +11823,15 @@ cxx_fundamental_alignment_p (unsigned a
> TYPE_ALIGN (long_double_type_node)));
> }
>
> +/* Return true if T is a pointer to a zero-sized aggregate. */
> +
> +bool
> +pointer_to_zero_sized_aggr_p (tree t)
> +{
> + if (!POINTER_TYPE_P (t))
> + return false;
> + t = TREE_TYPE (t);
> + return (TYPE_SIZE (t) && integer_zerop (TYPE_SIZE (t)));
> +}
> +
> #include "gt-c-family-c-common.h"
> --- gcc/cp/typeck.c.mp 2014-01-15 11:24:48.940639724 +0100
> +++ gcc/cp/typeck.c 2014-01-16 16:40:06.120688120 +0100
> @@ -5043,6 +5043,14 @@ pointer_diff (tree op0, tree op1, tree p
> return error_mark_node;
> }
>
> + if (pointer_to_zero_sized_aggr_p (TREE_TYPE (op1)))
> + {
> + if (complain & tf_error)
> + error ("arithmetic on pointer to an empty aggregate");
> + else
> + return error_mark_node;
> + }
> +
> op1 = (TYPE_PTROB_P (ptrtype)
> ? size_in_bytes (target_type)
> : integer_one_node);
> --- gcc/c/c-typeck.c.mp 2014-01-15 11:24:53.699659333 +0100
> +++ gcc/c/c-typeck.c 2014-01-16 16:40:06.130688170 +0100
> @@ -3536,6 +3536,9 @@ pointer_diff (location_t loc, tree op0,
> /* This generates an error if op0 is pointer to incomplete type. */
> op1 = c_size_in_bytes (target_type);
>
> + if (pointer_to_zero_sized_aggr_p (TREE_TYPE (orig_op1)))
> + error_at (loc, "arithmetic on pointer to an empty aggregate");
> +
> /* Divide by the size, in easiest possible way. */
> result = fold_build2_loc (loc, EXACT_DIV_EXPR, inttype,
> op0, convert (inttype, op1));
> --- gcc/testsuite/c-c++-common/pr58346-3.c.mp 2014-01-16 17:13:26.184800572
> +0100
> +++ gcc/testsuite/c-c++-common/pr58346-3.c 2014-01-16 17:30:15.503506328
> +0100
> @@ -0,0 +1,16 @@
> +/* PR c/58346 */
> +/* { dg-do compile } */
> +
> +void
> +foo (void)
> +{
> + __PTRDIFF_TYPE__ d;
> + const int i = 0;
> + int a1[2][0], a2[2][0];
> + int b1[3][i], b2[4][i];
> + d = a1 - a2; /* { dg-error "arithmetic on pointer to an empty aggregate" }
> */
> + __asm volatile ("" : "+g" (d));
> + /* No error here for C. */
> + d = b1 - b2; /* { dg-error "arithmetic on pointer to an empty aggregate"
> "" { target c++ } } */
> + __asm volatile ("" : "+g" (d));
> +}
> --- gcc/testsuite/c-c++-common/pr58346-1.c.mp 2014-01-15 14:04:27.159428834
> +0100
> +++ gcc/testsuite/c-c++-common/pr58346-1.c 2014-01-16 16:59:13.428236540
> +0100
> @@ -0,0 +1,24 @@
> +/* PR c/58346 */
> +/* { dg-do compile } */
> +
> +struct U {
> +#ifdef __cplusplus
> + char a[0];
> +#endif
> +};
> +static struct U b[6];
> +static struct U *u1, *u2;
> +
> +int
> +foo (struct U *p, struct U *q)
> +{
> + return q - p; /* { dg-error "arithmetic on pointer to an empty aggregate"
> } */
> +}
> +
> +void
> +bar (void)
> +{
> + __PTRDIFF_TYPE__ d = u1 - u2; /* { dg-error "arithmetic on pointer to an
> empty aggregate" } */
> + __asm volatile ("" : "+g" (d));
> + foo (&b[0], &b[4]);
> +}
> --- gcc/testsuite/c-c++-common/pr58346-2.c.mp 2014-01-13 15:48:20.011420141
> +0100
> +++ gcc/testsuite/c-c++-common/pr58346-2.c 2014-01-15 14:05:57.042817401
> +0100
> @@ -0,0 +1,8 @@
> +/* PR c/58346 */
> +/* { dg-do compile } */
> +
> +__PTRDIFF_TYPE__
> +foo (int p[3][0], int q[3][0])
> +{
> + return p - q; /* { dg-error "arithmetic on pointer to an empty aggregate"
> } */
> +}
>
> Marek
Marek
