[PATCH] c++: direct-init of an array of class type [PR59465]

[Marek Polacek <polacek@redhat.com>]

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?  I don't
claim that this has to go to 14 though.

-- >8 --
...from another array in a mem-initializer should not be accepted.

We already reject

  struct string {} a[1];
  string x[1](a);

but

  struct pair {
    string s[1];
    pair() : s(a) {}
  };

is wrongly accepted.

It started to be accepted with r0-110915-ga034826198b771:
<https://gcc.gnu.org/pipermail/gcc-patches/2011-August/320236.html>
which was supposed to be a cleanup, not a deliberate change to start
accepting the code.  The build_vec_init_expr code was added in r165976:
<https://gcc.gnu.org/pipermail/gcc-patches/2010-October/297582.html>.

It appears that we do the magic copy array when we have a defaulted
constructor and we generate code for its mem-initializer which
initializes an array.  I also see that we go that path for compound
literals.  So when initializing an array member, we can limit building
up a VEC_INIT_EXPR to those special cases.

	PR c++/59465

gcc/cp/ChangeLog:

	* init.cc (can_init_array_with_p): New.
	(perform_member_init): Check it.

gcc/testsuite/ChangeLog:

	* g++.dg/init/array62.C: New test.
	* g++.dg/init/array63.C: New test.
	* g++.dg/init/array64.C: New test.
---
 gcc/cp/init.cc                      | 27 ++++++++++++++++++++++++++-
 gcc/testsuite/g++.dg/init/array62.C | 19 +++++++++++++++++++
 gcc/testsuite/g++.dg/init/array63.C | 13 +++++++++++++
 gcc/testsuite/g++.dg/init/array64.C | 22 ++++++++++++++++++++++
 4 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/init/array62.C
 create mode 100644 gcc/testsuite/g++.dg/init/array63.C
 create mode 100644 gcc/testsuite/g++.dg/init/array64.C

diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index d2586fad86b..fb8c0e521fb 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -934,6 +934,31 @@ find_uninit_fields (tree *t, hash_set<tree> *uninitialized, tree member)
     }
 }
 
+/* Return true if it's OK to initialize an array from INIT.  Mere mortals
+   can't copy arrays, but the compiler can do so with a VEC_INIT_EXPR in
+   certain cases.  */
+
+static bool
+can_init_array_with_p (tree init)
+{
+  if (!init)
+    return true;
+
+  /* We're called from synthesize_method, and we're processing the
+     mem-initializers of a constructor.  */
+  if (DECL_DEFAULTED_FN (current_function_decl))
+    return true;
+  /* As an extension, we allow copying from a compound literal.  */
+  else if (TREE_CODE (init) == TARGET_EXPR)
+    {
+      init = TARGET_EXPR_INITIAL (init);
+      if (TREE_CODE (init) == CONSTRUCTOR)
+	return CONSTRUCTOR_C99_COMPOUND_LITERAL (init);
+    }
+
+  return false;
+}
+
 /* Initialize MEMBER, a FIELD_DECL, with INIT, a TREE_LIST of
    arguments.  If TREE_LIST is void_type_node, an empty initializer
    list was given; if NULL_TREE no initializer was given.  UNINITIALIZED
@@ -1085,7 +1110,7 @@ perform_member_init (tree member, tree init, hash_set<tree> &uninitialized)
   else if (type_build_ctor_call (type)
 	   || (init && CLASS_TYPE_P (strip_array_types (type))))
     {
-      if (TREE_CODE (type) == ARRAY_TYPE)
+      if (TREE_CODE (type) == ARRAY_TYPE && can_init_array_with_p (init))
 	{
 	  if (init == NULL_TREE
 	      || same_type_ignoring_top_level_qualifiers_p (type,
diff --git a/gcc/testsuite/g++.dg/init/array62.C b/gcc/testsuite/g++.dg/init/array62.C
new file mode 100644
index 00000000000..6d3935d7a66
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/array62.C
@@ -0,0 +1,19 @@
+// PR c++/59465
+// { dg-do compile }
+
+struct string {} a[1];
+struct pair {
+  string s[1];
+  pair() : s(a) {} // { dg-error "array must be initialized" }
+};
+
+struct S {
+  char s[10];
+  S() : s("aaa") {}
+};
+
+void
+g ()
+{
+  string x[1](a); // { dg-error "array must be initialized" }
+}
diff --git a/gcc/testsuite/g++.dg/init/array63.C b/gcc/testsuite/g++.dg/init/array63.C
new file mode 100644
index 00000000000..96bc9a64b26
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/array63.C
@@ -0,0 +1,13 @@
+// PR c++/59465
+// { dg-do compile }
+
+struct I {
+    const bool b;
+};
+struct O {
+    I a[2];
+    static I const data[2];
+    O() : a(data){}  // { dg-error "array must be initialized" }
+};
+
+I const O::data[2] = {true, false};
diff --git a/gcc/testsuite/g++.dg/init/array64.C b/gcc/testsuite/g++.dg/init/array64.C
new file mode 100644
index 00000000000..bbdd70c6df8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/array64.C
@@ -0,0 +1,22 @@
+// PR c++/59465
+// { dg-do compile }
+
+static const int my_size = 10;
+
+class UserType
+{
+public:
+  UserType(): f_(){}
+private:
+int f_;
+};
+
+typedef UserType Array[my_size];
+
+class Foo
+{
+public:
+  Foo(Array& m) : m_(m) {};  // { dg-error "array must be initialized" }
+private:
+  Array m_;
+};

base-commit: 574fd1f17f100c7c355ad26bc525ab5a3386bb2d
-- 
2.44.0