c++: Tweak PR969626 patch

It occurred to me that other types of conversions use rvaluedness_matches_p,
but those uses don't affect overload resolution, so we shouldn't look at the
flag for them.  Fixing that made decltype64.C compile successfully, because
the non-template candidate was a perfect match, so we now wouldn't consider
the broken template.  Changing the argument to const& makes it no longer a
perfect match (because of the added const), so we again get the infinite
recursion.

This illustrates the limited nature of this optimization/recursion break; it
works for most copy/move constructors because the constructor we're looking
for is almost always a perfect match.  If it happens to help improve compile
time for other calls, that's just a bonus.

gcc/cp/ChangeLog:

	PR c++/96926
	* call.c (perfect_conversion_p): Limit rvalueness
	test to reference bindings.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/decltype64.C: Change argument to const&.

2 files changed, 9 insertions, 7 deletions

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index bc369c6..0ba0e19 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -5864,12 +5864,14 @@ perfect_conversion_p (conversion *conv)
 {
   if (CONVERSION_RANK (conv) != cr_identity)
     return false;
-  if (!conv->rvaluedness_matches_p)
-    return false;
-  if (conv->kind == ck_ref_bind
-      && !same_type_p (TREE_TYPE (conv->type),
-		       next_conversion (conv)->type))
-    return false;
+  if (conv->kind == ck_ref_bind)
+    {
+      if (!conv->rvaluedness_matches_p)
+	return false;
+      if (!same_type_p (TREE_TYPE (conv->type),
+			next_conversion (conv)->type))
+	return false;
+    }
   return true;
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype64.C b/gcc/testsuite/g++.dg/cpp0x/decltype64.C
index 46d1859..0cd614c 100644
--- a/gcc/testsuite/g++.dg/cpp0x/decltype64.C
+++ b/gcc/testsuite/g++.dg/cpp0x/decltype64.C
@@ -5,7 +5,7 @@ template<int I>
 struct index
 {};
 
-constexpr int recursive_impl(index<0u>)
+constexpr int recursive_impl(const index<0u>&)
 {
   return 0;
 }