PR c++/89836 - bool constant expression and explicit conversions.

* call.c (build_converted_constant_expr_internal): New function,
	renamed from...
	(build_converted_constant_expr): ...this.  New.
	(build_converted_constant_bool_expr): New.
	* cp-tree.h (build_converted_constant_bool_expr): Declare.
	* decl.c (build_explicit_specifier): Call
	build_converted_constant_bool_expr.

	* g++.dg/cpp2a/explicit15.C: New test.

From-SVN: r270002

gcc/cp/ChangeLog

@@ -1,3 +1,14 @@
+2019-03-28  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/89836 - bool constant expression and explicit conversions.
+	* call.c (build_converted_constant_expr_internal): New function,
+	renamed from...
+	(build_converted_constant_expr): ...this.  New.
+	(build_converted_constant_bool_expr): New.
+	* cp-tree.h (build_converted_constant_bool_expr): Declare.
+	* decl.c (build_explicit_specifier): Call
+	build_converted_constant_bool_expr.
+
 2019-03-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/89785

gcc/cp/call.c

@@ -4175,18 +4175,11 @@ build_user_type_conversion (tree totype, tree expr, int flags,
   return ret;
 }
 
-/* Subroutine of convert_nontype_argument.
+/* Worker for build_converted_constant_expr.  */
 
-   EXPR is an expression used in a context that requires a converted
-   constant-expression, such as a template non-type parameter.  Do any
-   necessary conversions (that are permitted for converted
-   constant-expressions) to convert it to the desired type.
-
-   If conversion is successful, returns the converted expression;
-   otherwise, returns error_mark_node.  */
-
-tree
-build_converted_constant_expr (tree type, tree expr, tsubst_flags_t complain)
+static tree
+build_converted_constant_expr_internal (tree type, tree expr,
+					int flags, tsubst_flags_t complain)
 {
   conversion *conv;
   void *p;
@@ -4200,8 +4193,7 @@ build_converted_constant_expr (tree type, tree expr, tsubst_flags_t complain)
   p = conversion_obstack_alloc (0);
 
   conv = implicit_conversion (type, TREE_TYPE (expr), expr,
-			      /*c_cast_p=*/false,
-			      LOOKUP_IMPLICIT, complain);
+			      /*c_cast_p=*/false, flags, complain);
 
   /* A converted constant expression of type T is an expression, implicitly
      converted to type T, where the converted expression is a constant
@@ -4304,6 +4296,38 @@ build_converted_constant_expr (tree type, tree expr, tsubst_flags_t complain)
   return expr;
 }
 
+/* Subroutine of convert_nontype_argument.
+
+   EXPR is an expression used in a context that requires a converted
+   constant-expression, such as a template non-type parameter.  Do any
+   necessary conversions (that are permitted for converted
+   constant-expressions) to convert it to the desired type.
+
+   This function doesn't consider explicit conversion functions.  If
+   you mean to use "a contextually converted constant expression of type
+   bool", use build_converted_constant_bool_expr.
+
+   If conversion is successful, returns the converted expression;
+   otherwise, returns error_mark_node.  */
+
+tree
+build_converted_constant_expr (tree type, tree expr, tsubst_flags_t complain)
+{
+  return build_converted_constant_expr_internal (type, expr, LOOKUP_IMPLICIT,
+						 complain);
+}
+
+/* Used to create "a contextually converted constant expression of type
+   bool".  This differs from build_converted_constant_expr in that it
+   also considers explicit conversion functions.  */
+
+tree
+build_converted_constant_bool_expr (tree expr, tsubst_flags_t complain)
+{
+  return build_converted_constant_expr_internal (boolean_type_node, expr,
+						 LOOKUP_NORMAL, complain);
+}
+
 /* Do any initial processing on the arguments to a function call.  */
 
 static vec<tree, va_gc> *

gcc/cp/cp-tree.h

@@ -6233,6 +6233,7 @@ extern int remaining_arguments			(tree);
 extern tree perform_implicit_conversion		(tree, tree, tsubst_flags_t);
 extern tree perform_implicit_conversion_flags	(tree, tree, tsubst_flags_t, int);
 extern tree build_converted_constant_expr	(tree, tree, tsubst_flags_t);
+extern tree build_converted_constant_bool_expr	(tree, tsubst_flags_t);
 extern tree perform_direct_initialization_if_possible (tree, tree, bool,
                                                        tsubst_flags_t);
 extern tree in_charge_arg_for_name		(tree);

gcc/cp/decl.c

@@ -16700,7 +16700,7 @@ build_explicit_specifier (tree expr, tsubst_flags_t complain)
   expr = instantiate_non_dependent_expr_sfinae (expr, complain);
   /* Don't let convert_like_real create more template codes.  */
   processing_template_decl_sentinel s;
-  expr = build_converted_constant_expr (boolean_type_node, expr, complain);
+  expr = build_converted_constant_bool_expr (expr, complain);
   expr = cxx_constant_value (expr);
   return expr;
 }

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2019-03-28  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/89836 - bool constant expression and explicit conversions.
+	* g++.dg/cpp2a/explicit15.C: New test.
+
 2019-03-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/89812

gcc/testsuite/g++.dg/cpp2a/explicit15.C

@@ -0,0 +1,10 @@
+// PR c++/89836
+// { dg-do compile { target c++2a } }
+
+struct W { 
+  constexpr explicit operator bool() { return true; };
+};
+
+struct U {
+  explicit(W()) U(int);
+};