[PATCH] s390: Fix C++14 vs. C++17 ABI incompatibility on s390{,x} [PR94704]

[Jakub Jelinek]

Hi!

The following patch fixes the C++14 vs. C++17 ABI passing incompatibility
on s390x-linux.

Bootstrapped/regtested on s390x-linux without and with the patch, the
difference being:
-FAIL: tmpdir-g++.dg-struct-layout-1/t032 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t032 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t032 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t055 cp_compat_x_alt.o-cp_compat_y_alt.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t055 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t055 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t055 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t056 cp_compat_x_alt.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t056 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t056 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t056 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t057 cp_compat_x_alt.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t057 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t057 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t057 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t058 cp_compat_x_alt.o-cp_compat_y_alt.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t058 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t058 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t058 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t059 cp_compat_x_alt.o-cp_compat_y_alt.o execute 
 FAIL: tmpdir-g++.dg-struct-layout-1/t059 cp_compat_x_alt.o-cp_compat_y_tst.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t059 cp_compat_x_tst.o-cp_compat_y_alt.o execute 
-FAIL: tmpdir-g++.dg-struct-layout-1/t059 cp_compat_x_tst.o-cp_compat_y_tst.o execute 
when performing ALT_CXX_UNDER_TEST=g++ testing with a system GCC 10 compiler
from a week ago.  So, the alt vs. alt FAILs are all expected (we know before
this patch there is an ABI incompatibility) and some alt vs. tst (or tst vs.
alt) FAILs too - that depends on if the particular x or y test is compiled
with -std=c++14 or -std=c++17 - if x_tst is compiled with -std=c++14 and
y_alt is compiled with -std=c++17, then it should FAIL, similarly if x_alt
is compiled with -std=c++17 and y_tst is compiled with -std=c++14.

Ok for trunk?  Or do you want -Wpsabi warning too (seems s390 backend
doesn't have any -Wpsabi warnings or informs yet)?

2020-04-22  Jakub Jelinek  <jakub@redhat.com>

	PR target/94704
	* config/s390/s390.c (s390_function_arg_vector,
	s390_function_arg_float): Ignore cxx17_empty_base_field_p fields.

--- gcc/config/s390/s390.c.jj	2020-03-14 08:14:47.097741411 +0100
+++ gcc/config/s390/s390.c	2020-04-22 14:24:17.980091105 +0200
@@ -11917,7 +11917,8 @@ s390_function_arg_vector (machine_mode m
 
       for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
 	{
-	  if (TREE_CODE (field) != FIELD_DECL)
+	  if (TREE_CODE (field) != FIELD_DECL
+	      || cxx17_empty_base_field_p (field))
 	    continue;
 
 	  if (single == NULL_TREE)
@@ -11967,7 +11968,8 @@ s390_function_arg_float (machine_mode mo
 
       for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
 	{
-	  if (TREE_CODE (field) != FIELD_DECL)
+	  if (TREE_CODE (field) != FIELD_DECL
+	      || cxx17_empty_base_field_p (field))
 	    continue;
 
 	  if (single == NULL_TREE)

	Jakub