re PR c++/54020 ([c++0x] incorrectly accepted constexpr functions)

	PR c++/54020
	* semantics.c (potential_constant_expression_1) [COND_EXPR]: Call
	maybe_constant_value.

From-SVN: r189851

gcc/cp/ChangeLog

 2012-07-25  Jason Merrill  <jason@redhat.com>
 
+	PR c++/54020
+	* semantics.c (potential_constant_expression_1) [COND_EXPR]: Call
+	maybe_constant_value.
+
 	* cp-tree.h (tsubst_flags): Remove tf_no_access_control.
 	* call.c (standard_conversion): Don't set it.
 	* class.c (resolve_address_of_overloaded_function): Don't check it.

gcc/cp/semantics.c

@@ -8497,10 +8497,17 @@ potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
     case TRUTH_ORIF_EXPR:
       tmp = boolean_false_node;
     truth:
-      if (TREE_OPERAND (t, 0) == tmp)
-	return potential_constant_expression_1 (TREE_OPERAND (t, 1), rval, flags);
-      else
-	return potential_constant_expression_1 (TREE_OPERAND (t, 0), rval, flags);
+      {
+	tree op = TREE_OPERAND (t, 0);
+	if (!potential_constant_expression_1 (op, rval, flags))
+	  return false;
+	if (!processing_template_decl)
+	  op = maybe_constant_value (op);
+	if (tree_int_cst_equal (op, tmp))
+	  return potential_constant_expression_1 (TREE_OPERAND (t, 1), rval, flags);
+	else
+	  return true;
+      }
 
     case PLUS_EXPR:
     case MULT_EXPR:
@@ -8556,7 +8563,9 @@ potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
       tmp = TREE_OPERAND (t, 0);
       if (!potential_constant_expression_1 (tmp, rval, flags))
 	return false;
-      else if (integer_zerop (tmp))
+      if (!processing_template_decl)
+	tmp = maybe_constant_value (tmp);
+      if (integer_zerop (tmp))
 	return potential_constant_expression_1 (TREE_OPERAND (t, 2),
 						want_rval, flags);
       else if (TREE_CODE (tmp) == INTEGER_CST)

gcc/testsuite/g++.dg/cpp0x/constexpr-neg2.C

+// PR c++/54020
+// { dg-do compile { target c++11 } }
+
+// Preliminaries.
+extern int nonconst_func(int);
+constexpr int identity(int x) { return x; }
+constexpr int zero() { return identity(0); }
+constexpr int one() { return identity(1); }
+
+// Correctly accepted.
+constexpr int three = one() ? 3 : nonconst_func(0);
+
+// Incorrectly accepted.  See [dcl.constexpr] #5:
+//   For a constexpr function, if no function argument values exist
+//   such that the function invocation sub-stitution would produce a
+//   constant expression (5.19), the program is ill-formed; no diagnostic
+//   required.
+constexpr int bogus() { return zero () ? 3 : nonconst_func(0); } // { dg-error "nonconst_func" }
+
+// Correctly rejected (not sure why).
+constexpr int correct_error() { return nonconst_func(0); } // { dg-error "nonconst_func" }
+
+// Correctly rejected.
+constexpr int z = bogus();	// { dg-error "" }
+
+// This is also correctly rejected.
+constexpr int correct_failure() { return 0 ? 3 : nonconst_func(0); } // { dg-error "nonconst_func" }