On 04/05/17 23:02, Bernd Edlinger wrote:
> On 04/05/17 19:22, Bernd Edlinger wrote:
>> On 04/05/17 18:08, Jakub Jelinek wrote:
>>
>> Yes, exactly. I really want to reach the deadline for gcc-7.
>> Fixing the name is certainly the most important first step,
>> and if everybody agrees on "typeless_storage", for the name
>> I can start with adjusting the name, and look into how
>> to use a spare type-flag that should be a mechanical change.
>>
>
> Jakub, I just renamed the attribute and reworked the patch
> as you suggested, reg-testing is not yet completed, but
> it looks good so far. I also added a few more tests.
>
Aehm, sorry, actually I ran into a problem with the latest
patch version, where I tried to convert the TYPE_ATTRIBUTE
into a TYPE_FLAG here:
https://gcc.gnu.org/ml/gcc-patches/2017-04/msg00254.html
That is for instance with g++.dg/cpp1z/init-statement6.C an
internal error: "same canonical type node for different types"
happened, and I was not able to fix it immediately.
Although I would have liked it better this way, I think this
can be fixed separately, unless someone sees an obvious thinko
in the previous version.
So in the moment I restored the typeless_storage as an
ordinary TYPE_ATTRIBUTE, but at least it bootstraps and
causes no test regressions, as always with
languages=all,ada,go,obj-c++
Thanks
Bernd.
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 (lookup_attribute ("typeless_storage", TYPE_ATTRIBUTES (t)))
+ return 0;
+
/* Variant qualifiers don't affect the alias set, so get the main
variant. */
t = TYPE_MAIN_VARIANT (t);
@@ -1234,7 +1238,9 @@ 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)
+ && !lookup_attribute ("typeless_storage",
+ TYPE_ATTRIBUTES (t)))
{
gcc_checking_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
t = TREE_TYPE (t);
Index: gcc/tree.c
===================================================================
--- gcc/tree.c (revision 246678)
+++ gcc/tree.c (working copy)
@@ -8041,7 +8041,8 @@ build_pointer_type_for_mode (tree to_type, machine
/* If the pointed-to type has the may_alias attribute set, force
a TYPE_REF_CAN_ALIAS_ALL pointer to be generated. */
- if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type)))
+ if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type))
+ || lookup_attribute ("typeless_storage", TYPE_ATTRIBUTES (to_type)))
can_alias_all = true;
/* In some cases, languages will have things that aren't a POINTER_TYPE
@@ -8110,7 +8111,8 @@ build_reference_type_for_mode (tree to_type, machi
/* If the pointed-to type has the may_alias attribute set, force
a TYPE_REF_CAN_ALIAS_ALL pointer to be generated. */
- if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type)))
+ if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type))
+ || lookup_attribute ("typeless_storage", TYPE_ATTRIBUTES (to_type)))
can_alias_all = true;
/* In some cases, languages will have things that aren't a REFERENCE_TYPE
Index: gcc/c-family/c-attribs.c
===================================================================
--- gcc/c-family/c-attribs.c (revision 246678)
+++ gcc/c-family/c-attribs.c (working copy)
@@ -265,6 +265,7 @@ 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, NULL, false },
{ "cleanup", 1, 1, true, false, false,
handle_cleanup_attribute, false },
{ "warn_unused_result", 0, 0, false, true, true,
Index: gcc/cp/class.c
===================================================================
--- gcc/cp/class.c (revision 246678)
+++ gcc/cp/class.c (working copy)
@@ -2083,7 +2082,8 @@ fixup_attribute_variants (tree t)
tree attrs = TYPE_ATTRIBUTES (t);
unsigned align = TYPE_ALIGN (t);
bool user_align = TYPE_USER_ALIGN (t);
- bool may_alias = lookup_attribute ("may_alias", attrs);
+ bool may_alias = lookup_attribute ("may_alias", attrs)
+ || lookup_attribute ("typeless_storage", attrs);
if (may_alias)
fixup_may_alias (t);
@@ -7345,6 +7346,15 @@ 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)
+ && !lookup_attribute ("typeless_storage", TYPE_ATTRIBUTES (t)))
+ {
+ TYPE_ATTRIBUTES (t)
+ = tree_cons (get_identifier ("typeless_storage"),
+ NULL_TREE, TYPE_ATTRIBUTES (t));
+ 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 +14081,15 @@ 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;
+ && !strcmp ("byte", TYPE_NAME_STRING (enumtype))
+ && !lookup_attribute ("typeless_storage",
+ TYPE_ATTRIBUTES (enumtype)))
+ TYPE_ATTRIBUTES (enumtype)
+ = tree_cons (get_identifier ("typeless_storage"),
+ NULL_TREE, TYPE_ATTRIBUTES (enumtype));
}
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)
@@ -8851,9 +8851,10 @@ lookup_template_class_1 (tree d1, tree arglist, tr
if (OVERLOAD_TYPE_P (t)
&& !DECL_ALIAS_TEMPLATE_P (gen_tmpl))
{
- static const char *tags[] = {"abi_tag", "may_alias"};
+ static const char *tags[] = {"abi_tag", "may_alias",
+ "typeless_storage"};
- for (unsigned ix = 0; ix != 2; ix++)
+ 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;
+}
+
#include "gt-cp-typeck2.h"
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);
+}
