[gcc r12-5064] c++: Skip unnamed bit-fields more

[gcc r12-5064] c++: Skip unnamed bit-fields more

[Marek Polacek]

https://gcc.gnu.org/g:a648acc3b4ce528464ca23ee233de8f320542195

commit r12-5064-ga648acc3b4ce528464ca23ee233de8f320542195
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Nov 8 12:55:52 2021 -0500

    c++: Skip unnamed bit-fields more
    
    As Jason noticed in
    <https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583592.html>,
    we shouldn't require an initializer for an unnamed bit-field, because,
    as [class.bit] says, they cannot be initialized.
    
    gcc/cp/ChangeLog:
    
            * class.c (default_init_uninitialized_part): Use
            next_initializable_field.
            * method.c (walk_field_subobs): Skip unnamed bit-fields.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/init/bitfield6.C: New test.

Diff:
---
 gcc/cp/class.c                        |  7 +++----
 gcc/cp/method.c                       |  4 +++-
 gcc/testsuite/g++.dg/init/bitfield6.C | 20 ++++++++++++++++++++
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index f16e50b9de9..bf92300a178 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -5455,10 +5455,9 @@ default_init_uninitialized_part (tree type)
       if (r)
 	return r;
     }
-  for (t = TYPE_FIELDS (type); t; t = DECL_CHAIN (t))
-    if (TREE_CODE (t) == FIELD_DECL
-	&& !DECL_ARTIFICIAL (t)
-	&& !DECL_INITIAL (t))
+  for (t = next_initializable_field (TYPE_FIELDS (type)); t;
+       t = next_initializable_field (DECL_CHAIN (t)))
+    if (!DECL_INITIAL (t) && !DECL_ARTIFICIAL (t))
       {
 	r = default_init_uninitialized_part (TREE_TYPE (t));
 	if (r)
diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 1023aefc575..935946f5eef 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -2295,7 +2295,9 @@ walk_field_subobs (tree fields, special_function_kind sfk, tree fnname,
     {
       tree mem_type, argtype, rval;
 
-      if (TREE_CODE (field) != FIELD_DECL || DECL_ARTIFICIAL (field))
+      if (TREE_CODE (field) != FIELD_DECL
+	  || DECL_ARTIFICIAL (field)
+	  || DECL_UNNAMED_BIT_FIELD (field))
 	continue;
 
       /* Variant members only affect deletedness.  In particular, they don't
diff --git a/gcc/testsuite/g++.dg/init/bitfield6.C b/gcc/testsuite/g++.dg/init/bitfield6.C
new file mode 100644
index 00000000000..70854ee9588
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/bitfield6.C
@@ -0,0 +1,20 @@
+// { dg-do compile { target c++11 } }
+
+struct A
+{
+  int : 8;
+  int i = 42;
+};
+
+constexpr A a;
+
+struct B : A {
+};
+
+constexpr B b;
+
+struct C {
+  int : 0;
+};
+
+constexpr C c;