CWG2084 clarifies that a variant member with a non-trivial constructor does
not make the union's defaulted default constructor deleted if another
variant member has a default member initializer.
Tested x86_64-pc-linux-gnu, applying to trunk.
DR 2084
PR c++/94823
gcc/cp/ChangeLog:
* method.cc (walk_field_subobs): Fix DMI in union case.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/nsdmi-union7.C: New test.
---
gcc/cp/method.cc | 35 ++++++++++++++++++++---
gcc/testsuite/g++.dg/cpp0x/nsdmi-union7.C | 13 +++++++++
2 files changed, 44 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-union7.C
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index f2050f6e970..573ef016f82 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2315,8 +2315,19 @@ walk_field_subobs (tree fields, special_function_kind
sfk, tree fnname,
bool diag, int flags, tsubst_flags_t complain,
bool dtor_from_ctor)
{
- tree field;
- for (field = fields; field; field = DECL_CHAIN (field))
+ if (!fields)
+ return;
+
+ tree ctx = DECL_CONTEXT (fields);
+
+ /* CWG2084: A defaulted default ctor for a union with a DMI only initializes
+ that member, so don't check other members. */
+ enum { unknown, no, yes }
+ only_dmi_mem = (sfk == sfk_constructor && TREE_CODE (ctx) == UNION_TYPE
+ ? unknown : no);
+
+ again:
+ for (tree field = fields; field; field = DECL_CHAIN (field))
{
tree mem_type, argtype, rval;
@@ -2331,9 +2342,18 @@ walk_field_subobs (tree fields, special_function_kind
sfk, tree fnname,
asking if this is deleted, don't even look up the function; we don't
want an error about a deleted function we aren't actually calling. */
if (sfk == sfk_destructor && deleted_p == NULL
- && TREE_CODE (DECL_CONTEXT (field)) == UNION_TYPE)
+ && TREE_CODE (ctx) == UNION_TYPE)
break;
+ if (only_dmi_mem != no)
+ {
+ if (DECL_INITIAL (field))
+ only_dmi_mem = yes;
+ else
+ /* Don't check this until we know there's no DMI. */
+ continue;
+ }
+
mem_type = strip_array_types (TREE_TYPE (field));
if (SFK_ASSIGN_P (sfk))
{
@@ -2416,7 +2436,7 @@ walk_field_subobs (tree fields, special_function_kind
sfk, tree fnname,
if (constexpr_p
&& cxx_dialect < cxx20
&& !CLASS_TYPE_P (mem_type)
- && TREE_CODE (DECL_CONTEXT (field)) != UNION_TYPE)
+ && TREE_CODE (ctx) != UNION_TYPE)
{
*constexpr_p = false;
if (diag)
@@ -2465,6 +2485,13 @@ walk_field_subobs (tree fields, special_function_kind
sfk, tree fnname,
process_subob_fn (rval, sfk, spec_p, trivial_p, deleted_p,
constexpr_p, diag, field, dtor_from_ctor);
}
+
+ /* We didn't find a DMI in this union, now check all the members. */
+ if (only_dmi_mem == unknown)
+ {
+ only_dmi_mem = no;
+ goto again;
+ }
}
/* Base walker helper for synthesized_method_walk. Inspect a direct
diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-union7.C
b/gcc/testsuite/g++.dg/cpp0x/nsdmi-union7.C
new file mode 100644
index 00000000000..c840ddf5fbc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-union7.C
@@ -0,0 +1,13 @@
+// PR c++/94823
+// { dg-do compile { target c++11 } }
+
+struct A{
+ A(){}
+};
+union C{
+ A a;
+ int b = 0;
+};
+int main(){
+ C c;
+}
base-commit: f4ed610d02aaf8cfcdcb5cf03e0cde65f1f5f890
--
2.31.1
