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C++ PATCH for core issue 253: const objects and explicit initializers
- From: Jason Merrill <jason at redhat dot com>
- To: gcc-patches List <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 23 Sep 2011 18:17:15 -0400
- Subject: C++ PATCH for core issue 253: const objects and explicit initializers
Issue 253 was raised in 2000, but was considered low priority at the
time; it pointed out that classes with no actual data don't really need
an initializer, so we shouldn't require one. This becomes more
important now that we have non-static data member initializers that can
initialize all the members without a user-provided constructor.
Tested x86_64-pc-linux-gnu, applied to trunk. I'm also considering
applying it to 4.6 since we got more strict about the pre-253 rule in 4.6.
commit f8bbf6bb2853ef073807b5e275fa40edae3d8aa0
Author: Jason Merrill <jason@redhat.com>
Date: Thu Sep 15 17:15:34 2011 -0400
Core 253 - allow const objects with no initializer or
user-provided default constructor if the defaulted constructor
initializes all the subobjects.
PR c++/20039
PR c++/42844
* class.c (default_init_uninitialized_part): New.
* cp-tree.h: Declare it.
* decl.c (check_for_uninitialized_const_var): Use it.
* init.c (perform_member_init): Likewise.
(build_new_1): Likewise.
* method.c (walk_field_subobs): Likewise.
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index e398416..1887526 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -4356,6 +4356,40 @@ type_has_user_provided_default_constructor (tree t)
return false;
}
+/* If default-initialization leaves part of TYPE uninitialized, returns
+ a DECL for the field or TYPE itself (DR 253). */
+
+tree
+default_init_uninitialized_part (tree type)
+{
+ tree t, r, binfo;
+ int i;
+
+ type = strip_array_types (type);
+ if (!CLASS_TYPE_P (type))
+ return type;
+ if (type_has_user_provided_default_constructor (type))
+ return NULL_TREE;
+ for (binfo = TYPE_BINFO (type), i = 0;
+ BINFO_BASE_ITERATE (binfo, i, t); ++i)
+ {
+ r = default_init_uninitialized_part (BINFO_TYPE (t));
+ 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))
+ {
+ r = default_init_uninitialized_part (TREE_TYPE (t));
+ if (r)
+ return DECL_P (r) ? r : t;
+ }
+
+ return NULL_TREE;
+}
+
/* Returns true iff for class T, a trivial synthesized default constructor
would be constexpr. */
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index bcfc3b3..573c166 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4838,6 +4838,7 @@ extern tree in_class_defaulted_default_constructor (tree);
extern bool user_provided_p (tree);
extern bool type_has_user_provided_constructor (tree);
extern bool type_has_user_provided_default_constructor (tree);
+extern tree default_init_uninitialized_part (tree);
extern bool trivial_default_constructor_is_constexpr (tree);
extern bool type_has_constexpr_default_constructor (tree);
extern bool type_has_virtual_destructor (tree);
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 709deca..495d8a0 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4899,15 +4899,16 @@ check_for_uninitialized_const_var (tree decl)
if (TREE_CODE (decl) == VAR_DECL
&& TREE_CODE (type) != REFERENCE_TYPE
&& CP_TYPE_CONST_P (type)
- && (!TYPE_NEEDS_CONSTRUCTING (type)
- || !type_has_user_provided_default_constructor (type))
&& !DECL_INITIAL (decl))
{
+ tree field = default_init_uninitialized_part (type);
+ if (!field)
+ return;
+
permerror (DECL_SOURCE_LOCATION (decl),
"uninitialized const %qD", decl);
- if (CLASS_TYPE_P (type)
- && !type_has_user_provided_default_constructor (type))
+ if (CLASS_TYPE_P (type))
{
tree defaulted_ctor;
@@ -4918,6 +4919,8 @@ check_for_uninitialized_const_var (tree decl)
inform (DECL_SOURCE_LOCATION (defaulted_ctor),
"constructor is not user-provided because it is "
"explicitly defaulted in the class body");
+ inform (0, "and the implicitly-defined constructor does not "
+ "initialize %q+#D", field);
}
}
}
diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index ff1884b..68d4e68 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -579,7 +579,7 @@ perform_member_init (tree member, tree init)
flags |= LOOKUP_DEFAULTED;
if (CP_TYPE_CONST_P (type)
&& init == NULL_TREE
- && !type_has_user_provided_default_constructor (type))
+ && default_init_uninitialized_part (type))
/* TYPE_NEEDS_CONSTRUCTING can be set just because we have a
vtable; still give this diagnostic. */
permerror (DECL_SOURCE_LOCATION (current_function_decl),
@@ -2088,7 +2088,7 @@ build_new_1 (VEC(tree,gc) **placement, tree type, tree nelts,
}
if (CP_TYPE_CONST_P (elt_type) && *init == NULL
- && !type_has_user_provided_default_constructor (elt_type))
+ && default_init_uninitialized_part (elt_type))
{
if (complain & tf_error)
error ("uninitialized const in %<new%> of %q#T", elt_type);
diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 5b24f8f..757e711 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -1015,8 +1015,7 @@ walk_field_subobs (tree fields, tree fnname, special_function_kind sfk,
{
bool bad = true;
if (CP_TYPE_CONST_P (mem_type)
- && (!CLASS_TYPE_P (mem_type)
- || !type_has_user_provided_default_constructor (mem_type)))
+ && default_init_uninitialized_part (mem_type))
{
if (msg)
error ("uninitialized non-static const member %q#D",
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
index 3af8509..4ff398b 100644
--- a/gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
@@ -7,7 +7,7 @@
// p 1 constexpr specifier
// objects, static const data
-struct A1 { }; // { dg-message "no user-provided default constructor" }
+struct A1 { int i; }; // { dg-message "no user-provided default constructor" }
constexpr int i1 = 1024;
constexpr A1 a1 = A1();
diff --git a/gcc/testsuite/g++.dg/cpp0x/defaulted2.C b/gcc/testsuite/g++.dg/cpp0x/defaulted2.C
index 1f400f4..e3aac8f 100644
--- a/gcc/testsuite/g++.dg/cpp0x/defaulted2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/defaulted2.C
@@ -17,7 +17,8 @@ void g() = delete; // { dg-error "redefinition" }
struct B // { dg-message "user-provided default constructor" }
{
- B() = default; // { dg-message "not user-provided" }
+ int i;
+ B() = default; // { dg-message "not user-provided" }
};
const B b; // { dg-error "uninitialized const" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr42844-2.C b/gcc/testsuite/g++.dg/cpp0x/pr42844-2.C
index 5af4ff2..4425aac 100644
--- a/gcc/testsuite/g++.dg/cpp0x/pr42844-2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/pr42844-2.C
@@ -4,6 +4,7 @@
struct A // { dg-message "user-provided default constructor" }
{
+ int i;
A() = default; // { dg-message "not user-provided" }
};
@@ -14,17 +15,20 @@ struct Base
struct Derived : Base // { dg-message "user-provided default constructor" }
{
+ int i;
Derived() = default; // { dg-message "not user-provided" }
};
struct Derived2 : Base // { dg-message "user-provided default constructor" }
{
+ int i;
Derived2() = default; // { dg-message "not user-provided" }
Derived2( Derived2 const& ) = default;
};
struct Derived3 : Base // { dg-message "user-provided default constructor" }
{
+ int i;
Derived3( Derived3 const& ) = default;
Derived3() = default; // { dg-message "not user-provided" }
};
diff --git a/gcc/testsuite/g++.dg/init/const8.C b/gcc/testsuite/g++.dg/init/const8.C
new file mode 100644
index 0000000..4eb293d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/const8.C
@@ -0,0 +1,11 @@
+// DR 234 - it should be OK to leave off the initializer of a const
+// variable if the default constructor fully initializes the object.
+
+struct A { };
+const A a;
+
+struct B { A a; };
+const B b;
+
+struct C { virtual void f(); };
+const C c;
diff --git a/gcc/testsuite/g++.dg/init/pr20039.C b/gcc/testsuite/g++.dg/init/pr20039.C
index 9b0c12d..aaac8bd 100644
--- a/gcc/testsuite/g++.dg/init/pr20039.C
+++ b/gcc/testsuite/g++.dg/init/pr20039.C
@@ -10,6 +10,7 @@ struct M
struct X
{
M m;
+ int i;
};
int mymain()
diff --git a/gcc/testsuite/g++.dg/init/pr42844.C b/gcc/testsuite/g++.dg/init/pr42844.C
index 7b423cc..299a30a 100644
--- a/gcc/testsuite/g++.dg/init/pr42844.C
+++ b/gcc/testsuite/g++.dg/init/pr42844.C
@@ -6,19 +6,19 @@ struct A
A(){}
};
-struct B : A {}; // { dg-message "user-provided default constructor" }
+struct B : A { int i; }; // { dg-message "user-provided default constructor" }
-struct C : A {}; // { dg-message "user-provided default constructor" }
+struct C : A { int i; }; // { dg-message "user-provided default constructor" }
struct D : B { D() {} };
-struct E {}; // { dg-message "user-provided default constructor" }
+struct E { int i; }; // { dg-message "user-provided default constructor" }
template <class T>
-struct F : A {}; // { dg-message "user-provided default constructor" }
+struct F : A { T t; }; // { dg-message "user-provided default constructor" }
template <class T>
-struct G {}; // { dg-message "user-provided default constructor" }
+struct G { T t; }; // { dg-message "user-provided default constructor" }
void f ()
{
@@ -41,9 +41,9 @@ void f ()
extern G<int> const gext;
}
-struct H {}; // { dg-message "user-provided default constructor" }
+struct H { int i; }; // { dg-message "user-provided default constructor" }
-struct I : A {}; // { dg-message "user-provided default constructor" }
+struct I : A { int i; }; // { dg-message "user-provided default constructor" }
template <class T>
void g ()