Jason,
this fixes 65936, where we have two identical types with mismatching
TYPE_CANONICAL. The problem comes from template decl creation vs template
instantiation.
At the point we create 'const C<int>' in the operator function we have not
applied the 'may_alias' attribute to 'const C<int>'. This means that the
following snippet in tree.c:7729 build_pointer_type_for_mode
if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type)))
can_alias_all = true;
doesn't set 'can_alias_all'.
Later we complete C<int> and parse the static_cast in the operator function.
Completing C<int> will have applied the may_alias attribute. So this time
can_alias_all gets set on pointers to C<int> variants. This leads to two
different pointer types differing by TYPE_REF_CAN_ALIAS_ALL, each having
different CANONICAL_TYPEs. However as TYPE_STRUCTURAL_EQUALITY_P is false, we
have a problem. We blow up in comptypes verifying the canonical type machinery.
This patch applies the may_alias attribute to the instantiated decl.
built & tested on x86_64-linux, ok?
nathan
2015-05-21 Nathan Sidwell <nat...@acm.org>
cp/
PR c++/65936
pt.c (lookup_template_class_1): Apply may_alias attribute here.
testsuite/
* g++.dg/template/pr65936.C: New.
Index: cp/pt.c
===================================================================
--- cp/pt.c (revision 223503)
+++ cp/pt.c (working copy)
@@ -7856,6 +7856,10 @@ lookup_template_class_1 (tree d1, tree a
= CLASSTYPE_DECLARED_CLASS (template_type);
SET_CLASSTYPE_IMPLICIT_INSTANTIATION (t);
TYPE_FOR_JAVA (t) = TYPE_FOR_JAVA (template_type);
+ if (lookup_attribute ("may_alias",
+ TYPE_ATTRIBUTES (template_type)))
+ TYPE_ATTRIBUTES (t) = tree_cons (get_identifier ("may_alias"),
+ NULL_TREE, NULL_TREE);
/* A local class. Make sure the decl gets registered properly. */
if (context == current_function_decl)
Index: testsuite/g++.dg/template/pr65936.C
===================================================================
--- testsuite/g++.dg/template/pr65936.C (revision 0)
+++ testsuite/g++.dg/template/pr65936.C (working copy)
@@ -0,0 +1,21 @@
+// checking ICE in canonical typing
+
+class A;
+
+template <typename> struct B
+{
+ typedef A type;
+};
+
+template <class T> class C
+ : public B<T>::type
+{
+} __attribute__ ((__may_alias__));
+
+class A
+{
+ operator const C<int> &()
+ {
+ return *static_cast<const C<int> *> (this);
+ }
+};
