From: Bernd Edlinger <bernd.edlinger@hotmail.de>
To: Richard Biener <rguenther@suse.de>
Cc: Jakub Jelinek <jakub@redhat.com>,
Jonathan Wakely <jwakely@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Jason Merrill <jason@redhat.com>, Jeff Law <law@redhat.com>
Subject: Re: [PATCH] Add a new type attribute always_alias (PR79671)
Date: Fri, 07 Apr 2017 15:33:00 -0000 [thread overview]
Message-ID: <AM4PR0701MB2162DF600463D9C655DC8FA4E40C0@AM4PR0701MB2162.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <A970E82F-1A82-43A9-B283-06B71A1CBB7F@suse.de>
[-- Attachment #1: Type: text/plain, Size: 1646 bytes --]
On 04/07/17 17:10, Richard Biener wrote:
> On April 7, 2017 3:37:30 PM GMT+02:00, Bernd Edlinger <bernd.edlinger@hotmail.de> wrote:
>> On 04/07/17 08:54, Richard Biener wrote:
>>> On Thu, 6 Apr 2017, Bernd Edlinger wrote:
>>>> I think get_alias_set(t) will return 0 for typeless_storage
>>>> types, and therefore has_zero_child will be set anyway.
>>>> I think both mean the same thing in the end, but it depends on
>>>> what typeless_storage should actually mean, and we have
>>>> not yet the same idea about it.
>>>
>>> But has_zero_child does not do what we like it to because otherwise
>>> in the PR using the char[] array member would have worked!
>>>
>>> has_zero_child doesn't do that on purpose of course, but this means
>>> returing alias-set zero for the typeless storage _member_ doesn't
>>> suffice.
>>>
>>
>> I see you have a certain idea how to solve the C++17 issue.
>> And yes, I apologize, if I tried to pee on your tree :)
>
> We do have the need to support this part of the C++ standard. For other user code may_alias suffices and I see no reason to haste inventing sth new without a single convincing testcase. GCC/Language extensions should not be added without a good reason.
>
> I didn't propose to expose the type flag to users at all.
>
> Richard.
>
Well, actually you did:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671#c100
But I won't argue if you prefer to do it as you like,
after all TBAA is your area. So that is fine for me.
Attached is the latest version of my patch, I fixed
the issue with the type-flag conversion, and it is
already fully functional.
Bernd.
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gcc
2017-04-05 Bernd Edlinger <bernd.edlinger@hotmail.de>
* doc/extend.texi: Document the typeless_storage type attribute.
* alias.c (get_alias_set): Handle the typeless_storage attribute.
(record_component_aliases): Likewise.
* tree-streamer-in.c (unpack_ts_type_common_value_fields): Likewise.
* tree-streamer-out.c (pack_ts_type_common_value_fields): Likewise.
* tree.h (TYPE_TYPELESS_STORAGE): New access macro.
* tree-core.h: Update comment.
gcc/c-family
2017-04-05 Bernd Edlinger <bernd.edlinger@hotmail.de>
* c-attribs.c (c_common_attribute_tab): Add the typeless_storage
attribute.
(handle_typeless_storage_attribute): New function.
gcc/cp
2017-04-05 Bernd Edlinger <bernd.edlinger@hotmail.de>
* class.c (fixup_attribute_variants): Handle the typeless_storage
attribute.
(finish_struct_1): Set the typeless_storage attribute if required
by C++17.
* decl.c (start_enum): Likewise.
* pt.c (lookup_template_class_1): Handle the typeless_storage
attribute.
* typeck2.c (cxx_type_contains_byte_buffer): New function.
* cp-tree.h (cxx_type_contains_byte_buffer): Declare.
gcc/lto
2017-04-05 Bernd Edlinger <bernd.edlinger@hotmail.de>
* lto.c (compare_tree_sccs_1, hash_tree): Handle the typeless_storage
attribute.
gcc/testsuite
2017-04-05 Bernd Edlinger <bernd.edlinger@hotmail.de>
* c-c++-common/attr-typeless-storage-1.c: New test.
* c-c++-common/attr-typeless-storage-2.c: New test.
* gcc.c-torture/execute/typeless-storage-1.c: New test.
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[-- Attachment #3: patch-typeless-storage.diff --]
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Index: gcc/doc/extend.texi
===================================================================
--- gcc/doc/extend.texi (revision 246678)
+++ gcc/doc/extend.texi (working copy)
@@ -6656,6 +6656,36 @@
@option{-fstrict-aliasing}, which is on by default at @option{-O2} or
above.
+@item typeless_storage
+@cindex @code{typeless_storage} type attribute
+In the context of section 6.5 paragraph 6 of the C11 standard,
+an object of this type behaves as if it has no declared type.
+In the context of section 6.5 paragraph 7 of the C11 standard,
+an object or a pointer if this type behaves as if it were a
+character type.
+This attribute is similar to the @code{may_alias} attribute,
+except that it is not restricted to pointers.
+
+Example of use:
+
+@smallexample
+typedef int __attribute__((__typeless_storage__)) int_a;
+
+int
+main (void)
+@{
+ int_a a = 0x12345678;
+ short *b = (short *) &a;
+
+ b[1] = 0;
+
+ if (a == 0x12345678)
+ abort();
+
+ exit(0);
+@}
+@end smallexample
+
@item packed
@cindex @code{packed} type attribute
This attribute, attached to @code{struct} or @code{union} type
Index: gcc/alias.c
===================================================================
--- gcc/alias.c (revision 246678)
+++ gcc/alias.c (working copy)
@@ -879,6 +879,10 @@ get_alias_set (tree t)
t = TREE_TYPE (t);
}
+ /* Honor the typeless_storage type attribute. */
+ if (TYPE_TYPELESS_STORAGE (t))
+ return 0;
+
/* Variant qualifiers don't affect the alias set, so get the main
variant. */
t = TYPE_MAIN_VARIANT (t);
@@ -1234,7 +1238,8 @@ record_component_aliases (tree type)
/* VECTOR_TYPE and ARRAY_TYPE share the alias set with their
element type and that type has to be normalized to void *,
too, in the case it is a pointer. */
- while (!canonical_type_used_p (t) && !POINTER_TYPE_P (t))
+ while (!canonical_type_used_p (t) && !POINTER_TYPE_P (t)
+ && !TYPE_TYPELESS_STORAGE (t))
{
gcc_checking_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
t = TREE_TYPE (t);
Index: gcc/c-family/c-attribs.c
===================================================================
--- gcc/c-family/c-attribs.c (revision 246678)
+++ gcc/c-family/c-attribs.c (working copy)
@@ -113,6 +113,7 @@ static tree handle_vector_size_attribute (tree *,
bool *);
static tree handle_nonnull_attribute (tree *, tree, tree, int, bool *);
static tree handle_nothrow_attribute (tree *, tree, tree, int, bool *);
+static tree handle_typeless_storage_attribute (tree *, tree, tree, int, bool *);
static tree handle_cleanup_attribute (tree *, tree, tree, int, bool *);
static tree handle_warn_unused_result_attribute (tree *, tree, tree, int,
bool *);
@@ -265,6 +266,8 @@ const struct attribute_spec c_common_attribute_tab
{ "nothrow", 0, 0, true, false, false,
handle_nothrow_attribute, false },
{ "may_alias", 0, 0, false, true, false, NULL, false },
+ { "typeless_storage", 0, 0, false, true, false,
+ handle_typeless_storage_attribute, false },
{ "cleanup", 1, 1, true, false, false,
handle_cleanup_attribute, false },
{ "warn_unused_result", 0, 0, false, true, true,
@@ -2879,6 +2882,24 @@ handle_nothrow_attribute (tree *node, tree name, t
return NULL_TREE;
}
+/* Handle a "typeless_storage" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+static tree
+handle_typeless_storage_attribute (tree *node, tree name, tree ARG_UNUSED (args),
+ int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+ if (TYPE_P (*node))
+ TYPE_TYPELESS_STORAGE (*node) = 1;
+ else
+ {
+ warning (OPT_Wattributes, "%qE attribute ignored", name);
+ *no_add_attrs = true;
+ }
+
+ return NULL_TREE;
+}
+
/* Handle a "cleanup" attribute; arguments as in
struct attribute_spec.handler. */
Index: gcc/cp/class.c
===================================================================
--- gcc/cp/class.c (revision 246678)
+++ gcc/cp/class.c (working copy)
@@ -2097,6 +2097,7 @@ fixup_attribute_variants (tree t)
/* These are the two fields that check_qualified_type looks at and
are affected by attributes. */
TYPE_ATTRIBUTES (variants) = attrs;
+ TYPE_TYPELESS_STORAGE (variants) = TYPE_TYPELESS_STORAGE (t);
unsigned valign = align;
if (TYPE_USER_ALIGN (variants))
valign = MAX (valign, TYPE_ALIGN (variants));
@@ -7345,6 +7346,12 @@ finish_struct_1 (tree t)
the class or perform any other required target modifications. */
targetm.cxx.adjust_class_at_definition (t);
+ if (cxx_dialect >= cxx1z && cxx_type_contains_byte_buffer (t))
+ {
+ TYPE_TYPELESS_STORAGE (t) = 1;
+ fixup_attribute_variants (t);
+ }
+
maybe_suppress_debug_info (t);
if (flag_vtable_verify)
Index: gcc/cp/cp-tree.h
===================================================================
--- gcc/cp/cp-tree.h (revision 246678)
+++ gcc/cp/cp-tree.h (working copy)
@@ -6858,6 +6858,7 @@ extern tree finish_binary_fold_expr (tree
extern void require_complete_eh_spec_types (tree, tree);
extern void cxx_incomplete_type_diagnostic (location_t, const_tree,
const_tree, diagnostic_t);
+extern bool cxx_type_contains_byte_buffer (tree);
inline void
cxx_incomplete_type_diagnostic (const_tree value, const_tree type,
diagnostic_t diag_kind)
Index: gcc/cp/decl.c
===================================================================
--- gcc/cp/decl.c (revision 246678)
+++ gcc/cp/decl.c (working copy)
@@ -14081,10 +14081,11 @@ start_enum (tree name, tree enumtype, tree underly
enumtype = pushtag (name, enumtype, /*tag_scope=*/ts_current);
/* std::byte aliases anything. */
- if (enumtype != error_mark_node
+ if (cxx_dialect >= cxx1z
+ && enumtype != error_mark_node
&& TYPE_CONTEXT (enumtype) == std_node
&& !strcmp ("byte", TYPE_NAME_STRING (enumtype)))
- TYPE_ALIAS_SET (enumtype) = 0;
+ TYPE_TYPELESS_STORAGE (enumtype) = 1;
}
else
enumtype = xref_tag (enum_type, name, /*tag_scope=*/ts_current,
Index: gcc/cp/pt.c
===================================================================
--- gcc/cp/pt.c (revision 246678)
+++ gcc/cp/pt.c (working copy)
@@ -8853,7 +8853,8 @@ lookup_template_class_1 (tree d1, tree arglist, tr
{
static const char *tags[] = {"abi_tag", "may_alias"};
- for (unsigned ix = 0; ix != 2; ix++)
+ TYPE_TYPELESS_STORAGE (t) |= TYPE_TYPELESS_STORAGE (template_type);
+ for (unsigned ix = 0; ix < sizeof (tags) / sizeof (tags[0]); ix++)
{
tree attributes
= lookup_attribute (tags[ix], TYPE_ATTRIBUTES (template_type));
Index: gcc/cp/typeck2.c
===================================================================
--- gcc/cp/typeck2.c (revision 246678)
+++ gcc/cp/typeck2.c (working copy)
@@ -2234,5 +2234,29 @@ require_complete_eh_spec_types (tree fntype, tree
}
}
+/* True iff type either is or contains a byte buffer (which can be used for
+ storing any trivially copyable type). */
+
+bool
+cxx_type_contains_byte_buffer (tree type)
+{
+ if (TREE_CODE (type) == ARRAY_TYPE
+ && (cxx_type_contains_byte_buffer (TREE_TYPE (type))
+ || TREE_TYPE (type) == unsigned_char_type_node
+ || (TREE_CODE (TREE_TYPE (type)) == ENUMERAL_TYPE
+ && TYPE_CONTEXT (TREE_TYPE (type)) == std_node
+ && !strcmp ("byte", TYPE_NAME_STRING (TREE_TYPE (type))))))
+ return true;
+
+ if (CLASS_TYPE_P (type))
+ for (tree field = next_initializable_field (TYPE_FIELDS (type));
+ field;
+ field = next_initializable_field (DECL_CHAIN (field)))
+ if (cxx_type_contains_byte_buffer (TREE_TYPE (field)))
+ return true;
+
+ return false;
+}
+
\f
#include "gt-cp-typeck2.h"
Index: gcc/lto/lto.c
===================================================================
--- gcc/lto/lto.c (revision 246678)
+++ gcc/lto/lto.c (working copy)
@@ -1164,6 +1164,7 @@ compare_tree_sccs_1 (tree t1, tree t2, tree **map)
compare_values (TYPE_NONALIASED_COMPONENT);
compare_values (TYPE_PACKED);
compare_values (TYPE_RESTRICT);
+ compare_values (TYPE_TYPELESS_STORAGE);
compare_values (TYPE_USER_ALIGN);
compare_values (TYPE_READONLY);
compare_values (TYPE_PRECISION);
Index: gcc/lto-streamer-out.c
===================================================================
--- gcc/lto-streamer-out.c (revision 246678)
+++ gcc/lto-streamer-out.c (working copy)
@@ -1134,6 +1134,7 @@ hash_tree (struct streamer_tree_cache_d *cache, ha
hstate.add_flag (TYPE_NEEDS_CONSTRUCTING (t));
hstate.add_flag (TYPE_PACKED (t));
hstate.add_flag (TYPE_RESTRICT (t));
+ hstate.add_flag (TYPE_TYPELESS_STORAGE (t));
hstate.add_flag (TYPE_USER_ALIGN (t));
hstate.add_flag (TYPE_READONLY (t));
if (RECORD_OR_UNION_TYPE_P (t))
Index: gcc/tree-core.h
===================================================================
--- gcc/tree-core.h (revision 246678)
+++ gcc/tree-core.h (working copy)
@@ -1216,6 +1216,9 @@ struct GTY(()) tree_base {
DECL_NONALIASED in
VAR_DECL
+ TYPE_TYPELESS_STORAGE in
+ all types
+
deprecated_flag:
TREE_DEPRECATED in
Index: gcc/tree-streamer-in.c
===================================================================
--- gcc/tree-streamer-in.c (revision 246678)
+++ gcc/tree-streamer-in.c (working copy)
@@ -367,6 +367,7 @@ unpack_ts_type_common_value_fields (struct bitpack
TYPE_NEEDS_CONSTRUCTING (expr) = (unsigned) bp_unpack_value (bp, 1);
TYPE_PACKED (expr) = (unsigned) bp_unpack_value (bp, 1);
TYPE_RESTRICT (expr) = (unsigned) bp_unpack_value (bp, 1);
+ TYPE_TYPELESS_STORAGE (expr) = (unsigned) bp_unpack_value (bp, 1);
TYPE_USER_ALIGN (expr) = (unsigned) bp_unpack_value (bp, 1);
TYPE_READONLY (expr) = (unsigned) bp_unpack_value (bp, 1);
if (RECORD_OR_UNION_TYPE_P (expr))
Index: gcc/tree-streamer-out.c
===================================================================
--- gcc/tree-streamer-out.c (revision 246678)
+++ gcc/tree-streamer-out.c (working copy)
@@ -316,6 +316,7 @@ pack_ts_type_common_value_fields (struct bitpack_d
bp_pack_value (bp, TYPE_NEEDS_CONSTRUCTING (expr), 1);
bp_pack_value (bp, TYPE_PACKED (expr), 1);
bp_pack_value (bp, TYPE_RESTRICT (expr), 1);
+ bp_pack_value (bp, TYPE_TYPELESS_STORAGE (expr), 1);
bp_pack_value (bp, TYPE_USER_ALIGN (expr), 1);
bp_pack_value (bp, TYPE_READONLY (expr), 1);
/* We used to stream TYPE_ALIAS_SET == 0 information to let frontends mark
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 246678)
+++ gcc/tree.h (working copy)
@@ -1944,6 +1944,11 @@ extern machine_mode element_mode (const_tree t);
the term. */
#define TYPE_RESTRICT(NODE) (TYPE_CHECK (NODE)->type_common.restrict_flag)
+/* Nonzero if the type should behave like a character type
+ with respect to aliasing sementics. */
+#define TYPE_TYPELESS_STORAGE(NODE) \
+ (TYPE_CHECK (NODE)->base.nothrow_flag)
+
/* If nonzero, type's name shouldn't be emitted into debug info. */
#define TYPE_NAMELESS(NODE) (TYPE_CHECK (NODE)->base.u.bits.nameless_flag)
Index: gcc/testsuite/c-c++-common/attr-typeless-storage-1.c
===================================================================
--- gcc/testsuite/c-c++-common/attr-typeless-storage-1.c (revision 0)
+++ gcc/testsuite/c-c++-common/attr-typeless-storage-1.c (working copy)
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+typedef int T __attribute__((typeless_storage));
+
+extern T t, v;
+extern T *p;
+extern int *p;
+
+extern int *p2;
+extern T *p2;
+
+void fn1 (T);
+void fn1 (int);
+
+void fn2 (int);
+void fn2 (T);
+
+/* Ensure that the composite types have typeless_storage. */
+void
+f (long *i)
+{
+ *i = *(__typeof (*p) *) &p;
+ asm ("" : : "r" (*p));
+ *i = *(__typeof (*p2) *) &p2;
+ asm ("" : : "r" (*p2));
+ t = v;
+ asm ("" : : "r" (t));
+}
Index: gcc/testsuite/c-c++-common/attr-typeless-storage-2.c
===================================================================
--- gcc/testsuite/c-c++-common/attr-typeless-storage-2.c (revision 0)
+++ gcc/testsuite/c-c++-common/attr-typeless-storage-2.c (working copy)
@@ -0,0 +1,17 @@
+/* We used to reject this because types differentiating only in
+ TYPE_REF_CAN_ALIAS_ALL were deemed incompatible. */
+/* { dg-do compile } */
+
+struct sockaddr;
+struct sockaddr *f (void);
+
+struct __attribute__((typeless_storage)) sockaddr { int j; };
+struct sockaddr *
+f (void)
+{
+ return
+#ifndef __cplusplus
+ (void *)
+#endif
+ 0;
+}
Index: gcc/testsuite/gcc.c-torture/execute/typeless-storage-1.c
===================================================================
--- gcc/testsuite/gcc.c-torture/execute/typeless-storage-1.c (revision 0)
+++ gcc/testsuite/gcc.c-torture/execute/typeless-storage-1.c (working copy)
@@ -0,0 +1,20 @@
+/* Tests that the typeless_storage attribute works as expected. */
+
+extern void abort(void);
+extern void exit(int);
+
+typedef int __attribute__((__typeless_storage__)) int_a;
+
+int
+main (void)
+{
+ int_a a = 0x12345678;
+ short *b = (short*) &a;
+
+ b[1] = 0;
+
+ if (a == 0x12345678)
+ abort();
+
+ exit(0);
+}
next prev parent reply other threads:[~2017-04-07 15:33 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 9:46 Bernd Edlinger
2017-04-05 13:28 ` Jakub Jelinek
2017-04-05 15:20 ` Richard Biener
2017-04-05 17:41 ` Bernd Edlinger
2017-04-05 20:18 ` Jason Merrill
2017-04-05 20:46 ` Bernd Edlinger
2017-04-05 22:54 ` Pedro Alves
2017-04-06 10:08 ` Jonathan Wakely
2017-04-06 7:23 ` Richard Biener
2017-04-05 15:27 ` Bernd Edlinger
2017-04-05 15:29 ` Jakub Jelinek
2017-04-05 14:50 ` Florian Weimer
2017-04-05 15:23 ` Richard Biener
2017-04-05 15:38 ` Bernd Edlinger
2017-04-05 16:03 ` Jonathan Wakely
2017-04-05 16:08 ` Jakub Jelinek
2017-04-05 17:23 ` Bernd Edlinger
2017-04-05 21:02 ` Bernd Edlinger
2017-04-05 23:17 ` Sandra Loosemore
2017-04-06 5:40 ` Jakub Jelinek
2017-04-06 7:47 ` Richard Biener
2017-04-06 7:51 ` Jakub Jelinek
2017-04-06 7:55 ` Richard Biener
2017-04-06 14:11 ` Bernd Edlinger
2017-04-06 14:17 ` Florian Weimer
2017-04-06 14:23 ` Richard Biener
2017-04-06 14:43 ` Jonathan Wakely
2017-04-06 14:51 ` Florian Weimer
2017-04-06 15:05 ` Jakub Jelinek
2017-04-06 15:10 ` Florian Weimer
2017-04-06 19:13 ` Richard Biener
2017-04-11 10:43 ` Florian Weimer
2017-04-11 10:48 ` Richard Biener
2017-04-06 17:39 ` Bernd Edlinger
2017-04-06 17:48 ` Florian Weimer
2017-04-06 18:12 ` Bernd Edlinger
2017-04-06 18:19 ` Florian Weimer
2017-04-06 18:49 ` Bernd Edlinger
2017-04-06 19:05 ` Florian Weimer
2017-04-06 19:20 ` Bernd Edlinger
2017-04-07 6:47 ` Richard Biener
2017-04-07 12:58 ` Bernd Edlinger
2017-04-06 19:16 ` Richard Biener
2017-04-07 6:56 ` Florian Weimer
2017-04-07 8:01 ` Richard Biener
2017-04-06 19:14 ` Richard Biener
2017-04-06 19:51 ` Bernd Edlinger
2017-04-06 14:22 ` Richard Biener
2017-04-06 21:00 ` Bernd Edlinger
2017-04-07 6:54 ` Richard Biener
2017-04-07 13:37 ` Bernd Edlinger
2017-04-07 15:10 ` Richard Biener
2017-04-07 15:33 ` Bernd Edlinger [this message]
2017-04-07 20:22 ` Jason Merrill
2017-04-10 12:50 ` Richard Biener
2017-04-10 14:41 ` Jason Merrill
2017-04-10 15:31 ` Richard Biener
2017-04-10 16:35 ` Jason Merrill
2017-04-11 10:32 ` Richard Biener
2017-04-11 11:53 ` Richard Biener
2017-04-11 13:35 ` Richard Biener
2017-04-11 18:47 ` Jason Merrill
2017-04-10 21:40 ` Pedro Alves
2017-04-11 7:37 ` Richard Biener
2017-04-06 20:20 ` Bernd Edlinger
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