re PR c++/83692 (Rejects valid constexpr with unrelated code fixing problem)

PR c++/83692
	* constexpr.c (maybe_constant_init_1): New function.
	(maybe_constant_init): Make it a wrapper around maybe_constant_init_1.
	(cxx_constant_init): New function.
	* cp-tree.h (cxx_constant_init): Declare.
	* typeck2.c (store_init_value): Call cxx_constant_init instead of
	cxx_constant_value.  Move the maybe_constant_init call under an 'else'.

	* g++.dg/cpp1z/constexpr-83692.C: New test.

From-SVN: r257961

gcc/cp/ChangeLog

@@ -1,3 +1,13 @@
+2018-02-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/83692
+	* constexpr.c (maybe_constant_init_1): New function.
+	(maybe_constant_init): Make it a wrapper around maybe_constant_init_1.
+	(cxx_constant_init): New function.
+	* cp-tree.h (cxx_constant_init): Declare.
+	* typeck2.c (store_init_value): Call cxx_constant_init instead of
+	cxx_constant_value.  Move the maybe_constant_init call under an 'else'.
+
 2018-02-22  Jason Merrill  <jason@redhat.com>
 
 	PR c++/70468 - ICE with constructor delegation via typedef.

gcc/cp/constexpr.c

@@ -5123,8 +5123,8 @@ fold_non_dependent_expr (tree t)
 /* Like maybe_constant_value, but returns a CONSTRUCTOR directly, rather
    than wrapped in a TARGET_EXPR.  */
 
-tree
-maybe_constant_init (tree t, tree decl)
+static tree
+maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant)
 {
   if (!t)
     return t;
@@ -5139,10 +5139,10 @@ maybe_constant_init (tree t, tree decl)
     t = TARGET_EXPR_INITIAL (t);
   if (!is_nondependent_static_init_expression (t))
     /* Don't try to evaluate it.  */;
-  else if (CONSTANT_CLASS_P (t))
+  else if (CONSTANT_CLASS_P (t) && allow_non_constant)
     /* No evaluation needed.  */;
   else
-    t = cxx_eval_outermost_constant_expr (t, true, false, decl);
+    t = cxx_eval_outermost_constant_expr (t, allow_non_constant, false, decl);
   if (TREE_CODE (t) == TARGET_EXPR)
     {
       tree init = TARGET_EXPR_INITIAL (t);
@@ -5152,6 +5152,22 @@ maybe_constant_init (tree t, tree decl)
   return t;
 }
 
+/* Wrapper for maybe_constant_init_1 which permits non constants.  */
+
+tree
+maybe_constant_init (tree t, tree decl)
+{
+  return maybe_constant_init_1 (t, decl, true);
+}
+
+/* Wrapper for maybe_constant_init_1 which does not permit non constants.  */
+
+tree
+cxx_constant_init (tree t, tree decl)
+{
+  return maybe_constant_init_1 (t, decl, false);
+}
+
 #if 0
 /* FIXME see ADDR_EXPR section in potential_constant_expression_1.  */
 /* Return true if the object referred to by REF has automatic or thread

gcc/cp/cp-tree.h

@@ -7411,6 +7411,7 @@ extern bool require_potential_constant_expression (tree);
 extern bool require_constant_expression (tree);
 extern bool require_potential_rvalue_constant_expression (tree);
 extern tree cxx_constant_value			(tree, tree = NULL_TREE);
+extern tree cxx_constant_init			(tree, tree = NULL_TREE);
 extern tree maybe_constant_value		(tree, tree = NULL_TREE);
 extern tree maybe_constant_init			(tree, tree = NULL_TREE);
 extern tree fold_non_dependent_expr		(tree);

gcc/cp/typeck2.c

@@ -830,9 +830,10 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
 	  if (!require_constant_expression (value))
 	    value = error_mark_node;
 	  else
-	    value = cxx_constant_value (value, decl);
+	    value = cxx_constant_init (value, decl);
 	}
-      value = maybe_constant_init (value, decl);
+      else
+	value = maybe_constant_init (value, decl);
       if (TREE_CODE (value) == CONSTRUCTOR && cp_has_mutable_p (type))
 	/* Poison this CONSTRUCTOR so it can't be copied to another
 	   constexpr variable.  */

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2018-02-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/83692
+	* g++.dg/cpp1z/constexpr-83692.C: New test.
+
 2018-02-23  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/84346

gcc/testsuite/g++.dg/cpp1z/constexpr-83692.C

@@ -0,0 +1,21 @@
+// PR c++/83692
+// { dg-options -std=c++17 }
+
+struct integer {
+  constexpr int value() const { return m_value;	}
+  int m_value;
+};
+
+struct outer {
+  integer m_x{0};
+  constexpr outer()
+    {
+      if (m_x.value() != 0)
+	throw 0;
+      m_x.m_value = integer{1}.value();
+      if (m_x.value() != 1)
+	throw 0;
+    }
+};
+
+constexpr outer o{};