On 04/06/17 09:47, Richard Biener wrote:
> On Wed, 5 Apr 2017, 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.
>>
>> I have changed the documentation as Richi suggested, but
>> I am not too sure what to say here.
>
> The alias.c changes are not sufficient. I think what you want is
> sth like
>
> Index: gcc/alias.c
> ===================================================================
> --- gcc/alias.c (revision 246678)
> +++ gcc/alias.c (working copy)
> @@ -136,6 +136,9 @@ struct GTY(()) alias_set_entry {
> bool is_pointer;
> /* Nonzero if is_pointer or if one of childs have has_pointer set. */
> bool has_pointer;
> + /* Nonzero if we have a child serving as typeless storage (or are
> + such storage ourselves). */
> + bool has_typeless_storage;
>
> /* The children of the alias set. These are not just the immediate
> children, but, in fact, all descendants. So, if we have:
> @@ -419,7 +422,8 @@ alias_set_subset_of (alias_set_type set1
> /* Check if set1 is a subset of set2. */
> ase2 = get_alias_set_entry (set2);
> if (ase2 != 0
> - && (ase2->has_zero_child
> + && (ase2->has_typeless_storage
> + || ase2->has_zero_child
> || (ase2->children && ase2->children->get (set1))))
> return true;
>
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.
> @@ -825,6 +829,7 @@ init_alias_set_entry (alias_set_type set
> ase->has_zero_child = false;
> ase->is_pointer = false;
> ase->has_pointer = false;
> + ase->has_typeless_storage = false;
> gcc_checking_assert (!get_alias_set_entry (set));
> (*alias_sets)[set] = ase;
> return ase;
> @@ -955,6 +960,7 @@ get_alias_set (tree t)
> Just be pragmatic here and make sure the array and its element
> type get the same alias set assigned. */
> else if (TREE_CODE (t) == ARRAY_TYPE
> + && ! TYPE_TYPELESS_STORAGE (t)
> && (!TYPE_NONALIASED_COMPONENT (t)
> || TYPE_STRUCTURAL_EQUALITY_P (t)))
> set = get_alias_set (TREE_TYPE (t));
> @@ -1094,6 +1100,15 @@ get_alias_set (tree t)
>
> TYPE_ALIAS_SET (t) = set;
>
> + if (TREE_CODE (t) == ARRAY_TYPE
> + && TYPE_TYPELESS_STORAGE (t))
> + {
> + alias_set_entry *ase = get_alias_set_entry (set);
> + if (!ase)
> + ase = init_alias_set_entry (set);
> + ase->has_typeless_storage = true;
> + }
> +
> /* If this is an aggregate type or a complex type, we must record any
> component aliasing information. */
> if (AGGREGATE_TYPE_P (t) || TREE_CODE (t) == COMPLEX_TYPE)
> @@ -1173,6 +1188,8 @@ record_alias_subset (alias_set_type supe
> superset_entry->has_zero_child = true;
> if (subset_entry->has_pointer)
> superset_entry->has_pointer = true;
> + if (subset_entry->has_typeless_storage)
> + superset_entry->has_typeless_storage = true;
>
> if (subset_entry->children)
> {
>
>
> please also restrict TYPE_TYPELESS_STORAGE to ARRAY_TYPEs (otherwise
> more complications will arise).
>
> Index: gcc/cp/class.c
> ===================================================================
> --- gcc/cp/class.c (revision 246678)
> +++ gcc/cp/class.c (working copy)
> @@ -2083,7 +2083,8 @@ 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 = TYPE_TYPELESS_STORAGE (t)
> + || lookup_attribute ("may_alias", attrs);
>
> if (may_alias)
> fixup_may_alias (t);
> @@ -7345,6 +7348,12 @@ 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);
> ...
>
> I don't think you need all this given alias.c only looks at
> TYPE_MAIN_VARIANTs.
I wanted to be able to declare a int __attribute__((typeless_storage))
as in the test case, and the sample in the spec. And that
information is not in the TYPE_MAIN_VARIANT. Therefore I look for
typeless_storage before "t = TYPE_MAIN_VARIANT (t)".
>
> 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
>
> not needed (but also not sufficient - you need to handle arrays of
> byte somewhere).
See cxx_type_contains_byte_buffer: this function looks recursively into
structures and unions, and returns the information if the beast
contains an array of unsigned char or std::byte.
>
> @@ -1491,6 +1491,7 @@ struct GTY(()) tree_type_common {
> unsigned needs_constructing_flag : 1;
> unsigned transparent_aggr_flag : 1;
> unsigned restrict_flag : 1;
> + unsigned typeless_storage_flag : 1;
> unsigned contains_placeholder_bits : 2;
>
> ENUM_BITFIELD(machine_mode) mode : 8;
>
> bits are grouped in groups of 8 bits, this breaks it.
>
Oh..., does this explain the problems that I had with this version???
> @@ -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 (TYPE_TYPELESS_STORAGE (to_type)
> + || lookup_attribute ("may_alias", 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 (TYPE_TYPELESS_STORAGE (to_type)
> + || lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type)))
> can_alias_all = true;
>
> /* In some cases, languages will have things that aren't a
>
> not needed.
>
You mean, because the get_alias_set (to_type) will be 0 anyways,
and can_alias_all wont change the semantic?
Bernd.
> +/* Nonzero if the type should behave like a character type
> + with respect to aliasing sementics. */
> +#define TYPE_TYPELESS_STORAGE(NODE) \
> + (TYPE_CHECK (NODE)->type_common.typeless_storage_flag)
>
> ARRAY_TYPE_CHECK (NODE)->
>
> Richard.
>
