When either the static type or the target type of a dynamic cast is
marked 'final', and the type marked final is not derived from the other,
then there is no way to declare a class that is derived from both types
(since one of the types is marked final) so there is no way for such a
dynamic cast to possibly succeed.
This patch detects this case and emits a warning accordingly.
Bootstrap + regtest in progress. Is this OK to commit if testing
succeeds?
gcc/cp/ChangeLog:
PR c++/12277
* rtti.c (build_dynamic_cast_1): Warn on dynamic_cast that can
never succeed due to either the target type or the static type
being marked final.
gcc/testsuite/ChangeLog:
PR c++/12277
* g++.dg/rtti/dyncast8.C: New test.
---
gcc/cp/rtti.c | 18 ++++++++++++++
gcc/testsuite/g++.dg/rtti/dyncast8.C | 47 ++++++++++++++++++++++++++++++++++++
2 files changed, 65 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/rtti/dyncast8.C
diff --git a/gcc/cp/rtti.c b/gcc/cp/rtti.c
index be25be4..b823f8b 100644
--- a/gcc/cp/rtti.c
+++ b/gcc/cp/rtti.c
@@ -698,6 +698,24 @@ build_dynamic_cast_1 (tree type, tree expr, tsubst_flags_t
complain)
target_type = TYPE_MAIN_VARIANT (TREE_TYPE (type));
static_type = TYPE_MAIN_VARIANT (TREE_TYPE (exprtype));
+
+ if ((CLASSTYPE_FINAL (static_type)
+ && !DERIVED_FROM_P (target_type, static_type))
+ || (CLASSTYPE_FINAL (target_type)
+ && !DERIVED_FROM_P (static_type, target_type)))
+ {
+ if (complain & tf_warning)
+ {
+ if (VAR_P (old_expr))
+ warning (0, "dynamic_cast of %q#D to %q#T can never
succeed",
+ old_expr, type);
+ else
+ warning (0, "dynamic_cast of %q#E to %q#T can never
succeed",
+ old_expr, type);
+ }
+ return build_zero_cst (type);
+ }
+
td2 = get_tinfo_decl (target_type);
if (!mark_used (td2, complain) && !(complain & tf_error))
return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/rtti/dyncast8.C
b/gcc/testsuite/g++.dg/rtti/dyncast8.C
new file mode 100644
index 0000000..d98878c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/rtti/dyncast8.C
@@ -0,0 +1,47 @@
+// PR c++/12277
+// { dg-do require { target c++11 } }
+
+struct A1 { virtual ~A1 () { } };
+struct A2 { virtual ~A2 () { } };
+
+struct B1 { virtual ~B1 () { } };
+struct B2 final : B1 { virtual ~B2 () { } };
+
+struct C1 { virtual ~C1 () { } };
+struct C2 final { virtual ~C2 () { } };
+
+A1 *a1;
+
+B1 *b1;
+B2 *b2;
+
+C1 *c1;
+C2 *c2;
+
+void
+foo (void)
+{
+ {
+ A2 *x = dynamic_cast<A2 *> (a1); // { dg-bogus "can never succeed" }
+ }
+
+ {
+ B2 *x = dynamic_cast<B2 *> (b1); // { dg-bogus "can never suceed" }
+ B2 &y = dynamic_cast<B2 &> (*b1); // { dg-bogus "can never suceed" }
+ }
+
+ {
+ B1 *x = dynamic_cast<B1 *> (b2); // { dg-bogus "can never suceed" }
+ B1 &y = dynamic_cast<B1 &> (*b2); // { dg-bogus "can never suceed" }
+ }
+
+ {
+ C2 *x = dynamic_cast<C2 *> (c1); // { dg-warning "can never succeed" }
+ C2 &y = dynamic_cast<C2 &> (*c1); // { dg-warning "can never suceed" }
+ }
+
+ {
+ C1 *x = dynamic_cast<C1 *> (c2); // { dg-warning "can never succeed" }
+ C1 &y = dynamic_cast<C1 &> (*c2); // { dg-warning "can never suceed" }
+ }
+}
--
2.6.3.412.gac8e876.dirty
