[C++ PATCH] Fix xvalue COND_EXPR handling (PR c++/88103)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

On the following testcase, build_conditional_expr_1 tries hard to make sure
that if both arguments are xvalue_p (or one is and the other throw) the
result is still xvalue_p.  But, later on we call unary_complex_lvalue,
which does rationalize_conditional_expr which changes it from
cond ? x : y to *(cond ? &x : &y) and that change turns something formerly
xvalue_p into newly lvalue_p.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
ok for trunk?

2018-11-29  Jakub Jelinek  <jakub@redhat.com>

	PR c++/88103
	* typeck.c (unary_complex_lvalue): If a COND_EXPR is xvalue_p, make
	sure the result is as well.

	* g++.dg/cpp0x/rv-cond3.C: New test.

--- gcc/cp/typeck.c.jj	2018-11-27 09:48:58.506103668 +0100
+++ gcc/cp/typeck.c	2018-11-29 21:00:33.900636750 +0100
@@ -6503,7 +6503,16 @@ unary_complex_lvalue (enum tree_code cod
   /* Handle (a ? b : c) used as an "lvalue".  */
   if (TREE_CODE (arg) == COND_EXPR
       || TREE_CODE (arg) == MIN_EXPR || TREE_CODE (arg) == MAX_EXPR)
-    return rationalize_conditional_expr (code, arg, tf_warning_or_error);
+    {
+      tree ret = rationalize_conditional_expr (code, arg, tf_warning_or_error);
+      /* Preserve xvalue kind.  */
+      if (xvalue_p (arg))
+	{
+	  tree reftype = cp_build_reference_type (TREE_TYPE (arg), true);
+	  ret = cp_convert (reftype, ret, tf_warning_or_error);
+	}
+      return ret;
+    }
 
   /* Handle (a = b), (++a), and (--a) used as an "lvalue".  */
   if (TREE_CODE (arg) == MODIFY_EXPR
--- gcc/testsuite/g++.dg/cpp0x/rv-cond3.C.jj	2018-11-29 21:04:48.228440774 +0100
+++ gcc/testsuite/g++.dg/cpp0x/rv-cond3.C	2018-11-29 21:06:22.315888491 +0100
@@ -0,0 +1,22 @@
+// PR c++/88103
+// { dg-do compile { target c++11 } }
+
+struct A {
+  A (int);
+  A&& foo () &&;
+  int i;
+};
+void free (A&&);
+
+void test_xvalue (A a){
+  A&& ref = true ? static_cast<A&&> (a) : static_cast<A&&> (a); 
+  free (true ? static_cast<A&&> (a) : static_cast<A&&> (a));
+  (true ? static_cast<A&&> (a) : static_cast<A&&> (a)).foo ();
+  int&& k = (true ? static_cast<A&&> (a) : static_cast<A&&> (a)).i;
+}
+void test_prvalue (A a){
+  A&& ref = true ? static_cast<A&&> (a) : 1; 
+  free (true ? static_cast<A&&> (a) : 1);
+  (true ? static_cast<A&&> (a) : 1).foo ();
+  int&& k = (true ? static_cast<A&&> (a) : 1).i;
+}

	Jakub