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

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.

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

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);

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

gcc/testsuite/ChangeLog

@@ -1,3 +1,12 @@
+2019-09-23  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+	* 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.
+
 2019-09-23  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* gcc.dg/ucnid-5-utf8.c: Skip unless ucn is supported.

gcc/testsuite/g++.dg/cpp0x/pr33930.C

@@ -6,5 +6,5 @@ int& foo( type&& ggg );
 
 void bar( int* someptr )
 {
-  int& x = foo( someptr );
+  int& x = foo( someptr ); // { dg-error "cannot bind non-const lvalue reference" }
 }

gcc/testsuite/g++.dg/cpp0x/ref-bind1.C

@@ -0,0 +1,44 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+// These should bind directly to ptr, so no -Wreturn-local-addr warnings.
+int *ptr;
+
+const int *const &
+fn1 ()
+{
+  return ptr;
+}
+
+int **const ptr2 = nullptr;
+const int *const *const &
+fn2 ()
+{
+  return ptr2;
+}
+
+int (*ptr3)[10];
+using T = const int (*const)[10];
+
+T&
+fn3 ()
+{
+  return ptr3;
+}
+
+int (**ptr4)[5] = nullptr;
+using T2 = const int (*const *const)[5];
+
+T2&
+fn4 ()
+{
+  return ptr4;
+}
+
+const int **ptr5 = nullptr;
+
+const int *const *const &
+fn5 ()
+{
+  return ptr5;
+}

gcc/testsuite/g++.dg/cpp0x/ref-bind2.C

@@ -0,0 +1,15 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+// "const int *" and "int *" are reference-related, and 5.4.4.
+// says that in that case, if the reference is an rvalue reference,
+// the initializer expression shall not be an lvalue.
+
+int &f (const int *&&);
+
+void
+fn (int *p)
+{
+  const int *&&r = p; // { dg-error "cannot bind rvalue reference" }
+  f (p); // { dg-error "cannot bind rvalue reference" }
+}

gcc/testsuite/g++.dg/cpp0x/ref-bind3.C

@@ -0,0 +1,22 @@
+// PR c++/91844 - Implement CWG 2352, Similar types and reference binding.
+// { dg-do compile { target c++11 } }
+
+template<typename T> int f (const T *const &); // (1)
+template<typename T> int f (T *const &); // (2)
+template<typename T> int f (T *); // (3)
+
+/* Before CWG 2352, (2) was a better match than (1), but (2) and (3) were
+   equally good, so there was an ambiguity.  (2) was better than (1) because
+   (1) required a qualification conversion whereas (2) didn't.  But with this
+   CWG, (1) no longer requires a qualification conversion, because the types
+   "const int* const" and "int *" are now considered reference-related and we
+   bind directly, and (1) is more specialized than (2).  And (1) is also a
+   better match than (3).  */
+
+void
+g (int *p, const int *q, const int *const r)
+{
+  f (p); // calls (1)
+  f (q); // calls (1)
+  f (r); // calls (1)
+}

gcc/testsuite/g++.old-deja/g++.pt/spec35.C

@@ -14,9 +14,9 @@ template <typename T> int Foo (T &);  // { dg-message "note" } candidate
 template <typename T> int Qux (T);    // { dg-message "note" } 
 template <typename T> int Qux (T const &);  // { dg-message "note" } candidate
 
-template <typename T> int Bar (T const *const &); // { dg-message "note" } 
-template <typename T> int Bar (T *const &);       // { dg-message "note" } candidate
-template <typename T> int Bar (T *);              // { dg-message "note" } candidate
+template <typename T> int Bar (T const *const &);
+template <typename T> int Bar (T *const &);
+template <typename T> int Bar (T *);
 
 template <typename T> int Baz (T *const &);       // { dg-message "note" } 
 template <typename T> int Baz (T *);              // { dg-message "note" } candidate
@@ -24,7 +24,7 @@ template <typename T> int Baz (T *);              // { dg-message "note" } candi
 int Baz (int const *ptr, int *ptr2)
 {
   Baz (ptr2);   // { dg-error "ambiguous" } 
-  Bar (ptr2);   // { dg-error "ambiguous" } 
+  Bar (ptr2);
   Foo (ptr2);   // { dg-error "ambiguous" } 
   Qux (ptr2);   // { dg-error "ambiguous" } 
   return 0;