s390: -Wpsabi diagnostics for C++14 vs. C++17 ABI incompatibility on s390{,x} [PR94704]

> We probably have to look into providing a -Wpsabi warning as well.

So like this?

2020-04-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/94704
	* config/s390/s390.c (s390_function_arg_vector,
	s390_function_arg_float): Emit -Wpsabi diagnostics if the ABI changed.

gcc/ChangeLog

+2020-04-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/94704
+	* config/s390/s390.c (s390_function_arg_vector,
+	s390_function_arg_float): Emit -Wpsabi diagnostics if the ABI changed.
+
 2020-04-28  Richard Sandiford  <richard.sandiford@arm.com>
 
 	PR tree-optimization/94727

gcc/config/s390/s390.c

@@ -11911,16 +11911,22 @@ s390_function_arg_vector (machine_mode mode, const_tree type)
 
   /* The ABI says that record types with a single member are treated
      just like that member would be.  */
+  bool cxx17_empty_base_seen = false;
   while (TREE_CODE (type) == RECORD_TYPE)
     {
       tree field, single = NULL_TREE;
 
       for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
 	{
-	  if (TREE_CODE (field) != FIELD_DECL
-	      || cxx17_empty_base_field_p (field))
+	  if (TREE_CODE (field) != FIELD_DECL)
 	    continue;
 
+	  if (cxx17_empty_base_field_p (field))
+	    {
+	      cxx17_empty_base_seen = true;
+	      continue;
+	    }
+
 	  if (single == NULL_TREE)
 	    single = TREE_TYPE (field);
 	  else
@@ -11940,7 +11946,22 @@ s390_function_arg_vector (machine_mode mode, const_tree type)
 	}
     }
 
-  return VECTOR_TYPE_P (type);
+  if (!VECTOR_TYPE_P (type))
+    return false;
+
+  if (warn_psabi && cxx17_empty_base_seen)
+    {
+      static unsigned last_reported_type_uid;
+      unsigned uid = TYPE_UID (TYPE_MAIN_VARIANT (type));
+      if (uid != last_reported_type_uid)
+	{
+	  last_reported_type_uid = 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);
+	}
+    }
+  return true;
 }
 
 /* Return true if a function argument of type TYPE and mode MODE
@@ -11962,15 +11983,20 @@ s390_function_arg_float (machine_mode mode, const_tree type)
 
   /* The ABI says that record types with a single member are treated
      just like that member would be.  */
+  bool cxx17_empty_base_seen = false;
   while (TREE_CODE (type) == RECORD_TYPE)
     {
       tree field, single = NULL_TREE;
 
       for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
 	{
-	  if (TREE_CODE (field) != FIELD_DECL
-	      || cxx17_empty_base_field_p (field))
+	  if (TREE_CODE (field) != FIELD_DECL)
 	    continue;
+	  if (cxx17_empty_base_field_p (field))
+	    {
+	      cxx17_empty_base_seen = true;
+	      continue;
+	    }
 
 	  if (single == NULL_TREE)
 	    single = TREE_TYPE (field);
@@ -11984,7 +12010,23 @@ s390_function_arg_float (machine_mode mode, const_tree type)
 	type = single;
     }
 
-  return TREE_CODE (type) == REAL_TYPE;
+  if (TREE_CODE (type) != REAL_TYPE)
+    return false;
+
+  if (warn_psabi && cxx17_empty_base_seen)
+    {
+      static unsigned last_reported_type_uid;
+      unsigned uid = TYPE_UID (TYPE_MAIN_VARIANT (type));
+      if (uid != last_reported_type_uid)
+	{
+	  last_reported_type_uid = 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);
+	}
+    }
+
+  return true;
 }
 
 /* Return true if a function argument of type TYPE and mode MODE