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

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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.
This commit is contained in:
Jakub Jelinek 2020-04-23 09:59:57 +02:00
parent e2a71816b4
commit a39ed81b8a
4 changed files with 47 additions and 5 deletions
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13
gcc/ChangeLog
View file

@ -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.

34
gcc/config/rs6000/rs6000-call.c
View file

@ -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;
}
}

3
gcc/testsuite/ChangeLog
View file

@ -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.

2
gcc/testsuite/g++.dg/tree-ssa/pr27830.C
View file

@ -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