PR c++/91844 - Implement CWG 2352, Similar types and reference binding.

	* call.c (reference_related_p): Use similar_type_p instead of
	same_type_p.
	(reference_compatible_p): Update implementation to match CWG 2352.
	* cp-tree.h (similar_type_p): Declare.
	* typeck.c (similar_type_p): New.

	* g++.dg/cpp0x/pr33930.C: Add dg-error.
	* g++.dg/cpp0x/ref-bind1.C: New test.
	* g++.dg/cpp0x/ref-bind2.C: New test.
	* g++.dg/cpp0x/ref-bind3.C: New test.
	* g++.old-deja/g++.pt/spec35.C: Remove dg-error.

From-SVN: r276058

4 files changed, 48 insertions, 11 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 4420d8f..7ccc7cd 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,12 @@
+2019-09-23  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+	* call.c (reference_related_p): Use similar_type_p instead of
+	same_type_p.
+	(reference_compatible_p): Update implementation to match CWG 2352.
+	* cp-tree.h (similar_type_p): Declare.
+	* typeck.c (similar_type_p): New.
+
 2019-09-22  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/91819 - ICE with operator++ and enum.
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 2dad699..28b3f33 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -1530,9 +1530,8 @@ reference_related_p (tree t1, tree t2)
   /* [dcl.init.ref]
 
      Given types "cv1 T1" and "cv2 T2," "cv1 T1" is reference-related
-     to "cv2 T2" if T1 is the same type as T2, or T1 is a base class
-     of T2.  */
-  return (same_type_p (t1, t2)
+     to "cv2 T2" if T1 is similar to T2, or T1 is a base class of T2.  */
+  return (similar_type_p (t1, t2)
 	  || (CLASS_TYPE_P (t1) && CLASS_TYPE_P (t2)
 	      && DERIVED_FROM_P (t1, t2)));
 }
@@ -1545,14 +1544,15 @@ reference_compatible_p (tree t1, tree t2)
   /* [dcl.init.ref]
 
      "cv1 T1" is reference compatible with "cv2 T2" if
-       * T1 is reference-related to T2 or
-       * T2 is "noexcept function" and T1 is "function", where the
-         function types are otherwise the same,
-     and cv1 is the same cv-qualification as, or greater cv-qualification
-     than, cv2.  */
-  return ((reference_related_p (t1, t2)
-	   || fnptr_conv_p (t1, t2))
-	  && at_least_as_qualified_p (t1, t2));
+     a prvalue of type "pointer to cv2 T2" can be converted to the type
+     "pointer to cv1 T1" via a standard conversion sequence.  */
+  tree ptype1 = build_pointer_type (t1);
+  tree ptype2 = build_pointer_type (t2);
+  conversion *conv = standard_conversion (ptype1, ptype2, NULL_TREE,
+					  /*c_cast_p=*/false, 0, tf_none);
+  if (!conv || conv->bad_p)
+    return false;
+  return true;
 }
 
 /* A reference of the indicated TYPE is being bound directly to the
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 6d217fc..9c0f394 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7361,6 +7361,7 @@ enum { ce_derived, ce_type, ce_normal, ce_exact };
 extern bool comp_except_specs			(const_tree, const_tree, int);
 extern bool comptypes				(tree, tree, int);
 extern bool same_type_ignoring_top_level_qualifiers_p (tree, tree);
+extern bool similar_type_p			(tree, tree);
 extern bool compparms				(const_tree, const_tree);
 extern int comp_cv_qualification		(const_tree, const_tree);
 extern int comp_cv_qualification		(int, int);
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index d85e547..f427c4f 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1530,6 +1530,33 @@ same_type_ignoring_top_level_qualifiers_p (tree type1, tree type2)
   return same_type_p (type1, type2);
 }
 
+/* Returns nonzero iff TYPE1 and TYPE2 are similar, as per [conv.qual].  */
+
+bool
+similar_type_p (tree type1, tree type2)
+{
+  if (type1 == error_mark_node || type2 == error_mark_node)
+    return false;
+
+  /* Informally, two types are similar if, ignoring top-level cv-qualification:
+     * they are the same type; or
+     * they are both pointers, and the pointed-to types are similar; or
+     * they are both pointers to member of the same class, and the types of
+       the pointed-to members are similar; or
+     * they are both arrays of the same size or both arrays of unknown bound,
+       and the array element types are similar.  */
+
+  if (same_type_ignoring_top_level_qualifiers_p (type1, type2))
+    return true;
+
+  /* FIXME This ought to handle ARRAY_TYPEs too.  */
+  if ((TYPE_PTR_P (type1) && TYPE_PTR_P (type2))
+      || (TYPE_PTRDATAMEM_P (type1) && TYPE_PTRDATAMEM_P (type2)))
+    return comp_ptr_ttypes_const (type1, type2);
+
+  return false;
+}
+
 /* Returns 1 if TYPE1 is at least as qualified as TYPE2.  */
 
 bool