c++: wrong error with constexpr COMPOUND_EXPR [PR105321]

Here we issue a bogus error for the first assert in the test.  Therein
we have

<retval> = (void) (VIEW_CONVERT_EXPR<bool>(yes) || handle_error ());, VIEW_CONVERT_EXPR<int>(value);

which has a COMPOUND_EXPR, so we get to cxx_eval_constant_expression
<case COMPOUND_EXPR>.  The problem here is that we call

7044             /* Check that the LHS is constant and then discard it.  */
7045             cxx_eval_constant_expression (ctx, op0,
7046                                           true, non_constant_p, overflow_p,
7047                                           jump_target);

where lval is always true, so the PARM_DECL 'yes' is not evaluated into
its value.

Fixed by always passing false for 'lval' in cxx_eval_logical_expression;
there's no case where we actually expect an lvalue from a TRUTH_*.

	PR c++/105321

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_logical_expression): Always pass false for lval
	to cxx_eval_constant_expression.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-105321.C: New test.

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index e89440e..fa65290 100644 (file)
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -4566,19 +4566,18 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool *non_constant_p,
 static tree
 cxx_eval_logical_expression (const constexpr_ctx *ctx, tree t,
                              tree bailout_value, tree continue_value,
-                            bool lval,
-                            bool *non_constant_p, bool *overflow_p)
+                            bool, bool *non_constant_p, bool *overflow_p)
 {
   tree r;
   tree lhs = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
-                                          lval,
-                                          non_constant_p, overflow_p);
+                                          /*lval*/false, non_constant_p,
+                                          overflow_p);
   VERIFY_CONSTANT (lhs);
   if (tree_int_cst_equal (lhs, bailout_value))
     return lhs;
   gcc_assert (tree_int_cst_equal (lhs, continue_value));
   r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
-                                   lval, non_constant_p,
+                                   /*lval*/false, non_constant_p,
                                    overflow_p);
   VERIFY_CONSTANT (r);
   return r;

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
new file mode 100644 (file)
index 0000000..adb6830
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
@@ -0,0 +1,18 @@
+// PR c++/105321
+// { dg-do compile { target c++11 } }
+
+bool handle_error();
+
+constexpr int echo(int value, bool yes = true) noexcept
+{
+    return (yes || handle_error()), value;
+}
+
+static_assert(echo(10) == 10, "");
+
+constexpr int echo2(int value, bool no = false) noexcept
+{
+    return (!no || handle_error()), value;
+}
+
+static_assert(echo2(10) == 10, "");