Re: C++ PATCH for DR 1571 (reference binding)

[Jason Merrill <jason at redhat dot com>]

On 02/25/2014 04:27 PM, Jason Merrill wrote:
> Getting the reference binding rules for C++11 right (in the standard)
> has taken quite a few iterations.  I'm pretty happy with the latest
> wording, which deals with user-defined conversions by recursing on the
> result of the conversion.  This patch implements those rules.

The earlier patch broke Firefox and was reverted; this patch avoids that 
regression.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit 17d24bce33f71316e2b1f0a4a96deb29d09de0be
Author: jason <jason@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Tue Feb 25 21:27:51 2014 +0000

    	DR 1571
    	* call.c (reference_binding): Recurse on user-defined conversion.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index fbd2f83..8c55c32 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -1684,20 +1684,30 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
   if (!conv)
     return NULL;
 
+  if (conv->user_conv_p)
+    {
+      /* If initializing the temporary used a conversion function,
+	 recalculate the second conversion sequence.  */
+      for (conversion *t = conv; t; t = next_conversion (t))
+	if (t->kind == ck_user
+	    && DECL_CONV_FN_P (t->cand->fn))
+	  {
+	    tree ftype = TREE_TYPE (TREE_TYPE (t->cand->fn));
+	    int sflags = (flags|LOOKUP_NO_CONVERSION)&~LOOKUP_NO_TEMP_BIND;
+	    conversion *new_second
+	      = reference_binding (rto, ftype, NULL_TREE, c_cast_p,
+				   sflags, complain);
+	    if (!new_second)
+	      return NULL;
+	    return merge_conversion_sequences (t, new_second);
+	  }
+    }
+
   conv = build_conv (ck_ref_bind, rto, conv);
   /* This reference binding, unlike those above, requires the
      creation of a temporary.  */
   conv->need_temporary_p = true;
-  if (TYPE_REF_IS_RVALUE (rto))
-    {
-      conv->rvaluedness_matches_p = 1;
-      /* In the second case, if the reference is an rvalue reference and
-	 the second standard conversion sequence of the user-defined
-	 conversion sequence includes an lvalue-to-rvalue conversion, the
-	 program is ill-formed.  */
-      if (conv->user_conv_p && next_conversion (conv)->kind == ck_rvalue)
-	conv->bad_p = 1;
-    }
+  conv->rvaluedness_matches_p = TYPE_REF_IS_RVALUE (rto);
 
   return conv;
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/overload3.C b/gcc/testsuite/g++.dg/cpp0x/overload3.C
index 2d95783..0eecabd 100644
--- a/gcc/testsuite/g++.dg/cpp0x/overload3.C
+++ b/gcc/testsuite/g++.dg/cpp0x/overload3.C
@@ -13,5 +13,5 @@ struct wrap
 int main()
 {
   wrap w;
-  f(w);				// { dg-error "lvalue" }
+  f(w);				// { dg-error "" }
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-init1.C b/gcc/testsuite/g++.dg/cpp0x/rv-init1.C
new file mode 100644
index 0000000..2e8d4f7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/rv-init1.C
@@ -0,0 +1,26 @@
+// Core DR 1604/1571/1572
+// { dg-require-effective-target c++11 }
+
+struct Banana { };
+struct Enigma { operator const Banana(); };
+struct Doof { operator Banana&(); };
+void enigmatic() {
+  typedef const Banana ConstBanana;
+  Banana &&banana1 = ConstBanana(); // { dg-error "" }
+  Banana &&banana2 = Enigma();      // { dg-error "" }
+  Banana &&banana3 = Doof();        // { dg-error "" }
+}
+
+class A {
+public:
+  operator volatile int &();
+};
+A a;
+
+const int & ir1a = a.operator volatile int&(); // { dg-error "" }
+const int & ir2a = a;			       // { dg-error "" }
+
+struct X {
+  operator int&();
+} x;
+int&& rri2 = X();		// { dg-error "" }