rs6000: Small improvement to the C++17 ABI fix [PR94707]

Anyway, based on IRC discussion with Richard Sandiford on IRC, we should
probably test type uids instead of type pointers because type uids aren't
reused, but type pointers in a very bad luck case could be, and having the
static var at filescope and GTY((deletable)) is an overkill (and with costs
during GC time).

2020-04-23  Jakub Jelinek  <jakub@redhat.com>

	PR target/94707
	* config/rs6000/rs6000-call.c (rs6000_discover_homogeneous_aggregate):
	Use TYPE_UID (TYPE_MAIN_VARIANT (type)) instead of type to check
	if the same type has been diagnosed most recently already.

gcc/ChangeLog

+2020-04-23  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/94707
+	* config/rs6000/rs6000-call.c (rs6000_discover_homogeneous_aggregate):
+	Use TYPE_UID (TYPE_MAIN_VARIANT (type)) instead of type to check
+	if the same type has been diagnosed most recently already.
+
 2020-04-23  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>
 
 	* config/arm/arm_mve.h (__arm_vbicq_n_u16): Modify function parameter's

gcc/config/rs6000/rs6000-call.c

@@ -5739,14 +5739,15 @@ rs6000_discover_homogeneous_aggregate (machine_mode mode, const_tree type,
 		*n_elts = field_count;
 	      if (cxx17_empty_base_seen && warn_psabi)
 		{
-		  static const_tree last_reported_type;
-		  if (type != last_reported_type)
+		  static unsigned last_reported_type_uid;
+		  unsigned uid = TYPE_UID (TYPE_MAIN_VARIANT (type));
+		  if (uid != last_reported_type_uid)
 		    {
 		      inform (input_location,
 			      "parameter passing for argument of type %qT "
 			      "when C++17 is enabled changed to match C++14 "
 			      "in GCC 10.1", type);
-		      last_reported_type = type;
+		      last_reported_type_uid = uid;
 		    }
 		}
 	      return true;