PR c++/68206 - Fix constexpr diagnostics with loops.

	PR c++/68530
	* constexpr.c (potential_constant_expression_1): Handle LOOP_EXPR
	and GOTO_EXPR.

From-SVN: r235217

gcc/cp/ChangeLog

 2016-04-19  Jason Merrill  <jason@redhat.com>
 
+	PR c++/68206
+	PR c++/68530
+	* constexpr.c (potential_constant_expression_1): Handle LOOP_EXPR
+	and GOTO_EXPR.
+
 	* pt.c (tsubst_expr): Remove shadowing declaration.
 	(tsubst_pack_expansion): Add assert.
 

gcc/cp/constexpr.c

@@ -4924,6 +4924,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     case NON_DEPENDENT_EXPR:
       /* For convenience.  */
     case RETURN_EXPR:
+    case LOOP_EXPR:
+    case EXIT_EXPR:
       return RECUR (TREE_OPERAND (t, 0), want_rval);
 
     case TRY_FINALLY_EXPR:
@@ -5135,6 +5137,15 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     case EMPTY_CLASS_EXPR:
       return false;
 
+    case GOTO_EXPR:
+      {
+	tree *target = &TREE_OPERAND (t, 0);
+	/* Gotos representing break and continue are OK; we should have
+	   rejected other gotos in parsing.  */
+	gcc_assert (breaks (target) || continues (target));
+	return true;
+      }
+
     default:
       if (objc_is_property_ref (t))
 	return false;

gcc/testsuite/g++.dg/cpp1y/constexpr-loop5.C

+// PR c++/68530
+// { dg-do compile { target c++14 } }
+
+struct thing {
+    void foo() {}
+};
+
+template<typename>
+constexpr int count()
+{
+    auto item = thing {};
+    for(; (item.foo(), false);); // { dg-error "foo" }
+    return 0;
+}
+
+int main()
+{
+    static_assert( count<int>() == 0, "" ); // { dg-error "" }
+}