calls: Remove FIXME for cxx17_empty_base_field_p

This predicate is now used by aarch64 targets.

2020-04-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* calls.h (cxx17_empty_base_field_p): Turn into a function declaration.
	* calls.c (cxx17_empty_base_field_p): New function.  Check
	DECL_ARTIFICIAL and RECORD_OR_UNION_TYPE_P in addition to the
	previous checks.

gcc/ChangeLog

+2020-04-29  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* calls.h (cxx17_empty_base_field_p): Turn into a function declaration.
+	* calls.c (cxx17_empty_base_field_p): New function.  Check
+	DECL_ARTIFICIAL and RECORD_OR_UNION_TYPE_P in addition to the
+	previous checks.
+
 2020-04-29  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/93654

gcc/calls.c

@@ -6261,5 +6261,20 @@ must_pass_va_arg_in_stack (tree type)
   return targetm.calls.must_pass_in_stack (arg);
 }
 
+/* Return true if FIELD is the C++17 empty base field that should
+   be ignored for ABI calling convention decisions in order to
+   maintain ABI compatibility between C++14 and earlier, which doesn't
+   add this FIELD to classes with empty bases, and C++17 and later
+   which does.  */
+
+bool
+cxx17_empty_base_field_p (const_tree field)
+{
+  return (DECL_FIELD_ABI_IGNORED (field)
+	  && DECL_ARTIFICIAL (field)
+	  && RECORD_OR_UNION_TYPE_P (TREE_TYPE (field))
+	  && !lookup_attribute ("no_unique_address", DECL_ATTRIBUTES (field)));
+}
+
 /* Tell the garbage collector about GTY markers in this source file.  */
 #include "gt-calls.h"

gcc/calls.h

@@ -135,9 +135,6 @@ extern tree get_attr_nonstring_decl (tree, tree * = NULL);
 extern void maybe_warn_nonstring_arg (tree, tree);
 extern bool get_size_range (tree, tree[2], bool = false);
 extern rtx rtx_for_static_chain (const_tree, bool);
-/* FIXME: Remove after all backends are converted.  */
-#define cxx17_empty_base_field_p(t) \
-  (DECL_FIELD_ABI_IGNORED (t)						\
-   && !lookup_attribute ("no_unique_address", DECL_ATTRIBUTES (t)))
+extern bool cxx17_empty_base_field_p (const_tree);
 
 #endif // GCC_CALLS_H