rs6000: Fix C++14 vs. C++17 ABI bug on powerpc64le [PR94707]

As mentioned in the PR and on IRC, the recently added struct-layout-1.exp
new tests FAIL on powerpc64le-linux (among other targets).
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/t058 cp_compat_x_tst.o-cp_compat_y_tst.o execute
FAIL: tmpdir-g++.dg-struct-layout-1/t059 cp_compat_x_tst.o-cp_compat_y_tst.o execute
in particular.  The problem is that the presence or absence of the C++17
artificial empty base fields, which have non-zero TYPE_SIZE, but zero
DECL_SIZE, change the ABI decisions, if it is present (-std=c++17), the type
might not be considered homogeneous, while if it is absent (-std=c++14), it
can be.

The following patch fixes that and emits a -Wpsabi inform; perhaps more
often than it could, because the fact that rs6000_discover_homogeneous_aggregate
returns true when it didn't in in GCC 7/8/9 with -std=c++17 doesn't still
mean it will make a different ABI decision, but the warning triggered only
on the test I've changed (the struct-layout-1.exp tests use -w -Wno-psabi
already).

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

	PR target/94707
	* config/rs6000/rs6000-call.c (rs6000_aggregate_candidate): Add
	cxx17_empty_base_seen argument.  Pass it to recursive calls.
	Ignore cxx17_empty_base_field_p fields after setting
	*cxx17_empty_base_seen to true.
	(rs6000_discover_homogeneous_aggregate): Adjust
	rs6000_aggregate_candidate caller.  With -Wpsabi, diagnose homogeneous
	aggregates with C++17 empty base fields.

	* g++.dg/tree-ssa/pr27830.C: Use -Wpsabi -w for -std=c++17 and higher.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 06f7eda00339cc8950fedffa21b11b2f8d500ac6..93c3076eb86e3d3f0fa81cdc3c18eec4b96b1d08 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,18 @@
 2020-04-23  Jakub Jelinek  <jakub@redhat.com>
 
+       PR target/94707
+       * config/rs6000/rs6000-call.c (rs6000_aggregate_candidate): Add
+       cxx17_empty_base_seen argument.  Pass it to recursive calls.
+       Ignore cxx17_empty_base_field_p fields after setting
+       *cxx17_empty_base_seen to true.
+       (rs6000_discover_homogeneous_aggregate): Adjust
+       rs6000_aggregate_candidate caller.  With -Wpsabi, diagnose homogeneous
+       aggregates with C++17 empty base fields.
+
+       PR c/94705
+       * attribs.c (decl_attribute): Don't diagnose attribute exclusions
+       if last_decl is error_mark_node or has such a TREE_TYPE.
+
        PR c/94705
        * attribs.c (decl_attribute): Don't diagnose attribute exclusions
        if last_decl is error_mark_node or has such a TREE_TYPE.

diff --git a/gcc/config/rs6000/rs6000-call.c b/gcc/config/rs6000/rs6000-call.c
index e08621ace27eb22958481516786778328d404d5d..a9ae7ab70ca3235651aaeaf8631f2ebdf832b490 100644 (file)
--- a/gcc/config/rs6000/rs6000-call.c
+++ b/gcc/config/rs6000/rs6000-call.c
@@ -5528,7 +5528,8 @@ const struct altivec_builtin_types altivec_overloaded_builtins[] = {
    sub-tree.  */
 
 static int
-rs6000_aggregate_candidate (const_tree type, machine_mode *modep)
+rs6000_aggregate_candidate (const_tree type, machine_mode *modep,
+                           bool *cxx17_empty_base_seen)
 {
   machine_mode mode;
   HOST_WIDE_INT size;
@@ -5598,7 +5599,8 @@ rs6000_aggregate_candidate (const_tree type, machine_mode *modep)
            || TREE_CODE (TYPE_SIZE (type)) != INTEGER_CST)
          return -1;
 
-       count = rs6000_aggregate_candidate (TREE_TYPE (type), modep);
+       count = rs6000_aggregate_candidate (TREE_TYPE (type), modep,
+                                           cxx17_empty_base_seen);
        if (count == -1
            || !index
            || !TYPE_MAX_VALUE (index)
@@ -5636,7 +5638,14 @@ rs6000_aggregate_candidate (const_tree type, machine_mode *modep)
            if (TREE_CODE (field) != FIELD_DECL)
              continue;
 
-           sub_count = rs6000_aggregate_candidate (TREE_TYPE (field), modep);
+           if (cxx17_empty_base_field_p (field))
+             {
+               *cxx17_empty_base_seen = true;
+               continue;
+             }
+
+           sub_count = rs6000_aggregate_candidate (TREE_TYPE (field), modep,
+                                                   cxx17_empty_base_seen);
            if (sub_count < 0)
              return -1;
            count += sub_count;
@@ -5669,7 +5678,8 @@ rs6000_aggregate_candidate (const_tree type, machine_mode *modep)
            if (TREE_CODE (field) != FIELD_DECL)
              continue;
 
-           sub_count = rs6000_aggregate_candidate (TREE_TYPE (field), modep);
+           sub_count = rs6000_aggregate_candidate (TREE_TYPE (field), modep,
+                                                   cxx17_empty_base_seen);
            if (sub_count < 0)
              return -1;
            count = count > sub_count ? count : sub_count;
@@ -5710,7 +5720,9 @@ rs6000_discover_homogeneous_aggregate (machine_mode mode, const_tree type,
       && AGGREGATE_TYPE_P (type))
     {
       machine_mode field_mode = VOIDmode;
-      int field_count = rs6000_aggregate_candidate (type, &field_mode);
+      bool cxx17_empty_base_seen = false;
+      int field_count = rs6000_aggregate_candidate (type, &field_mode,
+                                                   &cxx17_empty_base_seen);
 
       if (field_count > 0)
        {
@@ -5725,6 +5737,18 @@ rs6000_discover_homogeneous_aggregate (machine_mode mode, const_tree type,
                *elt_mode = field_mode;
              if (n_elts)
                *n_elts = field_count;
+             if (cxx17_empty_base_seen && warn_psabi)
+               {
+                 static const_tree last_reported_type;
+                 if (type != last_reported_type)
+                   {
+                     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;
+                   }
+               }
              return true;
            }
        }

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 684e408c1a55a53b6fc9aea3c00b7851faf8ee46..245c1512c76f260d380dec7f4f1a548f9269a216 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2020-04-23  Jakub Jelinek  <jakub@redhat.com>
 
+       PR target/94707
+       * g++.dg/tree-ssa/pr27830.C: Use -Wpsabi -w for -std=c++17 and higher.
+
        PR c/94705
        * gcc.dg/pr94705.c: New test.
 

diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr27830.C b/gcc/testsuite/g++.dg/tree-ssa/pr27830.C
index 01c7fc1878395ca4b409bc3dcfb90158f2b6b733..551ebc428cd71c01ad4caaec4b15fa66273d7708 100644 (file)
--- a/gcc/testsuite/g++.dg/tree-ssa/pr27830.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr27830.C
@@ -1,5 +1,7 @@
 /* { dg-do compile } */
 /* { dg-options "-O" } */
+/* Ignore ABI warnings for C++17 and later.  */
+/* { dg-additional-options "-Wno-psabi -w" { target c++17 } } */
 
 struct gc{};
 struct transform:public gc