c++: add ref checks in conversion code

While looking at another patch I noticed that on a few tests we were doing
nonsensical things like building a reference to a reference.  Make sure we
catch that sooner.  But let's be friendly in can_convert, since it doesn't
return a conversion that could be wrongly applied to a reference.

gcc/cp/ChangeLog:

	* call.cc (implicit_conversion): Check that FROM isn't a reference
	if we also got an EXPR argument.
	(convert_like_internal): Check that EXPR isn't a reference.
	(can_convert_arg): convert_from_reference if needed.

1 files changed, 13 insertions, 0 deletions

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 47a1251..5dbaec9 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -2116,6 +2116,9 @@ implicit_conversion (tree to, tree from, tree expr, bool c_cast_p,
 	}
     }
 
+  /* An argument should have gone through convert_from_reference.  */
+  gcc_checking_assert (!expr || !TYPE_REF_P (from));
+
   if (TYPE_REF_P (to))
     conv = reference_binding (to, from, expr, c_cast_p, flags, complain);
   else
@@ -8506,6 +8509,8 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
   if (convs->bad_p && !(complain & tf_error))
     return error_mark_node;
 
+  gcc_checking_assert (!TYPE_REF_P (TREE_TYPE (expr)));
+
   if (convs->bad_p
       && convs->kind != ck_user
       && convs->kind != ck_list
@@ -13694,6 +13699,14 @@ can_convert_arg (tree to, tree from, tree arg, int flags,
      conversion.  */
   push_deferring_access_checks (dk_deferred);
 
+  /* Handle callers like check_local_shadow forgetting to
+     convert_from_reference.  */
+  if (TYPE_REF_P (from) && arg)
+    {
+      arg = convert_from_reference (arg);
+      from = TREE_TYPE (arg);
+    }
+
   t  = implicit_conversion (to, from, arg, /*c_cast_p=*/false,
 			    flags, complain);
   ok_p = (t && !t->bad_p);