[PATCH] c++: Skip unnamed bit-fields more

[PATCH] c++: Skip unnamed bit-fields more

[Marek Polacek]

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.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

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.
---
 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(-)
 create mode 100644 gcc/testsuite/g++.dg/init/bitfield6.C

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;

base-commit: d626fe77cdc40de0ae1651c8b94090eea73a719f
-- 
2.33.1

Re: [PATCH] c++: Skip unnamed bit-fields more

[Jason Merrill]

On 11/8/21 14:49, Marek Polacek wrote:
> 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.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> 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.
> ---
>   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(-)
>   create mode 100644 gcc/testsuite/g++.dg/init/bitfield6.C
> 
> 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;
> 
> base-commit: d626fe77cdc40de0ae1651c8b94090eea73a719f
>