On Wed, Jan 31, 2018 at 11:02:36AM -0500, Jason Merrill wrote:
> > In this case I was just extending existing warning and wanted
> > consistency with that. Both can be changed in a GCC9 follow-up,
> > or if Jason/Nathan want it now, even for GCC8, sure.
So, do you want %qE as in the patch or %E? Note, sidx might
actually not be a INTEGER_CST (as we only verify_constant it which
allows all kinds of expressions), though usually it will be.
E.g. the
if (!tree_fits_shwi_p (index)
|| (i = tree_to_shwi (index)) < 0)
{
diag_array_subscript (ctx, ary, index);
case will call it if index is some reduced_constant_expression_p
which is not INTEGER_CST, initializer_constant_valid_p* has lots
of cases, sure not all apply to integral types.
> > Well, even zero subscript is wrong if lval is false, i.e. a[0] + 1
> > rather than e.g. &a[0]. So we'd need to have another wordings
> > for the case when the index is zero.
>
> But if lval is false we want the value of the array, and if we know
> the value we know the bounds, so that shouldn't be needed.
You're right, when dereferencing it we'll error already earlier,
because the array of unknown bounds can't be constexpr.
I think the " with unknown bounds" part still might be useful to users,
it can be seen in the type as [], but it might take some time to the users
to figure out that is the reason why we disallow it.
So like this?
2018-01-31 Jakub Jelinek <ja...@redhat.com>
PR c++/83993
* constexpr.c (diag_array_subscript): Emit different diagnostics
if TYPE_DOMAIN (arraytype) is NULL.
(cxx_eval_array_reference, cxx_eval_store_expression): For arrays
with NULL TYPE_DOMAIN use size_zero_node as nelts.
* g++.dg/init/pr83993-1.C: New test.
* g++.dg/cpp0x/pr83993.C: New test.
--- gcc/cp/constexpr.c.jj 2018-01-19 23:34:04.897278768 +0100
+++ gcc/cp/constexpr.c 2018-01-24 13:38:40.572913190 +0100
@@ -2270,13 +2270,20 @@ diag_array_subscript (const constexpr_ct
tree sidx = fold_convert (ssizetype, index);
if (DECL_P (array))
{
- error ("array subscript value %qE is outside the bounds "
- "of array %qD of type %qT", sidx, array, arraytype);
+ if (TYPE_DOMAIN (arraytype))
+ error ("array subscript value %qE is outside the bounds "
+ "of array %qD of type %qT", sidx, array, arraytype);
+ else
+ error ("non-zero array subscript %qE is used with array %qD of "
+ "type %qT with unknown bounds", sidx, array, arraytype);
inform (DECL_SOURCE_LOCATION (array), "declared here");
}
- else
+ else if (TYPE_DOMAIN (arraytype))
error ("array subscript value %qE is outside the bounds "
"of array type %qT", sidx, arraytype);
+ else
+ error ("non-zero array subscript %qE is used with array of type %qT "
+ "with unknown bounds", sidx, arraytype);
}
}
@@ -2361,7 +2368,12 @@ cxx_eval_array_reference (const constexp
tree nelts;
if (TREE_CODE (TREE_TYPE (ary)) == ARRAY_TYPE)
- nelts = array_type_nelts_top (TREE_TYPE (ary));
+ {
+ if (TYPE_DOMAIN (TREE_TYPE (ary)))
+ nelts = array_type_nelts_top (TREE_TYPE (ary));
+ else
+ nelts = size_zero_node;
+ }
else if (VECTOR_TYPE_P (TREE_TYPE (ary)))
nelts = size_int (TYPE_VECTOR_SUBPARTS (TREE_TYPE (ary)));
else
@@ -3439,7 +3451,12 @@ cxx_eval_store_expression (const constex
tree nelts, ary;
ary = TREE_OPERAND (probe, 0);
if (TREE_CODE (TREE_TYPE (ary)) == ARRAY_TYPE)
- nelts = array_type_nelts_top (TREE_TYPE (ary));
+ {
+ if (TYPE_DOMAIN (TREE_TYPE (ary)))
+ nelts = array_type_nelts_top (TREE_TYPE (ary));
+ else
+ nelts = size_zero_node;
+ }
else if (VECTOR_TYPE_P (TREE_TYPE (ary)))
nelts = size_int (TYPE_VECTOR_SUBPARTS (TREE_TYPE (ary)));
else
--- gcc/testsuite/g++.dg/init/pr83993-1.C.jj 2018-01-24 13:45:43.430864528
+0100
+++ gcc/testsuite/g++.dg/init/pr83993-1.C 2018-01-24 13:44:59.352869530
+0100
@@ -0,0 +1,11 @@
+// PR c++/83993
+// { dg-do compile }
+
+extern const int a[];
+const int *const b = &a[0];
+
+int
+foo ()
+{
+ return b[0];
+}
--- gcc/testsuite/g++.dg/cpp0x/pr83993.C.jj 2018-01-24 14:09:01.846716177
+0100
+++ gcc/testsuite/g++.dg/cpp0x/pr83993.C 2018-01-24 14:08:41.246718212
+0100
@@ -0,0 +1,49 @@
+// PR c++/83993
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+extern const int a[];
+const int b[5] = { 1, 2, 3, 4, 5 };
+extern const int c[4];
+constexpr const int *d = &a[0];
+constexpr const int *d2 = a;
+constexpr const int *e = &a[1]; // { dg-error "non-zero array
subscript '1' is used with array 'a' of type 'const int \\\[\\\]' with unknown
bounds" }
+constexpr const int *f = &b[0];
+constexpr const int *f2 = b;
+constexpr const int *g = &b[5];
+constexpr const int *h = &b[6]; // { dg-error "array subscript
value '6' is outside the bounds of array 'b' of type 'const int \\\[5\\\]'" }
+constexpr const int *i = &c[0];
+constexpr const int *i2 = c;
+constexpr const int *j = &c[4];
+constexpr const int *k = &c[5]; // { dg-error "array subscript
value '5' is outside the bounds of array 'c' of type 'const int \\\[4\\\]'" }
+extern const int l[];
+
+void
+foo ()
+{
+ extern const int l[3];
+ constexpr const int *m = &l[0];
+ constexpr const int *m2 = l;
+ constexpr const int *n = &l[1];
+ static_assert (m == m2, "");
+}
+
+constexpr const int *m = &l[0];
+constexpr const int *m2 = l;
+constexpr const int *n = &l[1]; // { dg-error "non-zero array
subscript '1' is used with array 'l' of type 'const int \\\[\\\]' with unknown
bounds" }
+static_assert (d == d2 && f == f2 && i == i2 && m == m2, "");
+const int o[] = { 1, 2 };
+constexpr const int *p = &o[0];
+constexpr const int *p2 = o;
+constexpr const int *q = &o[2];
+constexpr const int *r = &o[3]; // { dg-error "array subscript
value '3' is outside the bounds of array 'o' of type 'const int \\\[2\\\]'" }
+struct S { char a; char b[]; } s;
+constexpr const char *t = &s.b[0];
+constexpr const char *t2 = s.b;
+constexpr const char *u = &s.b[1]; // { dg-error "non-zero array subscript
'1' is used with array of type 'char \\\[\\\]' with unknown bounds" }
+struct V { int a; };
+extern V v[];
+constexpr V *w = &v[0];
+constexpr V *w2 = v;
+constexpr int *x = &v[0].a;
+constexpr int y = a[0]; // { dg-error "the value of 'a'
is not usable in a constant expression" }
Jakub
