On Mon, Jun 9, 2025 at 7:28 PM Jakub Jelinek <ja...@redhat.com> wrote:
>
> Hi!
>
> For C++26 P2786R13 I'm afraid I'll need 4 new flags on class types
> in struct lang_type (1 bit for trivially_relocatable_if_eligible,
> 1 for replaceable_if_eligible, 1 for not_trivially_relocatable and
> 1 for not_replaceable) and there are just 2 bits left.
>
> The following patch is an attempt to save 8 bytes of memory
> in those structures when not compiling ObjC or ObjC++ (I think those
> are used fairly rarely and the patch keeps the sizes unmodified for
> those 2). The old allocations were 32 bytes for C and 120 bytes
> for C++. The patch moves the objc_info member last in the C++ case
> (it was already last in the C case), arranges for GC to skip it
> for C and C++ but walk for ObjC and ObjC++ and allocates or
> copies over just offsetof bytes instead of sizeof.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Just as reminder, not necessarily to make use of them, there are
10 spare bits in tree_base::u.bits, we could add lang_flag_{7,8,...}
Richard.
> 2025-06-09 Jakub Jelinek <ja...@redhat.com>
>
> gcc/c/
> * c-lang.h (union lang_type::maybe_objc_info): New type.
> (struct lang_type): Use union maybe_objc_info info member
> instead of tree objc_info.
> * c-decl.cc (finish_struct): Allocate struct lang_type using
> ggc_internal_cleared_alloc instead of ggc_cleared_alloc,
> and use sizeof (struct lang_type) for ObjC and otherwise
> offsetof (struct lang_type, info) as size.
> (finish_enum): Likewise.
> gcc/cp/
> * cp-tree.h (union lang_type::maybe_objc_info): New type.
> (struct lang_type): Use union maybe_objc_info info member
> instead of tree objc_info.
> * lex.cc (copy_lang_type): Use sizeof (struct lang_type)
> just for ObjC++ and otherwise offsetof (struct lang_type, info).
> (maybe_add_lang_type_raw): Likewise.
> (cxx_make_type): Formatting fix.
> gcc/objc/
> * objc-act.h (TYPE_OBJC_INFO): Define to info.objc_info
> instead of objc_info.
> gcc/objcp/
> * objcp-decl.h (TYPE_OBJC_INFO): Define to info.objc_info
> instead of objc_info.
>
> --- gcc/c/c-lang.h.jj 2025-04-08 14:08:48.398321583 +0200
> +++ gcc/c/c-lang.h 2025-06-09 12:50:21.631284689 +0200
> @@ -35,10 +35,14 @@ struct GTY(()) lang_type {
> /* In an ENUMERAL_TYPE, the min and max values. */
> tree enum_min;
> tree enum_max;
> - /* In a RECORD_TYPE, information specific to Objective-C, such
> - as a list of adopted protocols or a pointer to a corresponding
> - @interface. See objc/objc-act.h for details. */
> - tree objc_info;
> + union maybe_objc_info {
> + /* If not c_dialect_objc, this part is not even allocated. */
> + char GTY((tag ("0"))) non_objc;
> + /* In a RECORD_TYPE, information specific to Objective-C, such
> + as a list of adopted protocols or a pointer to a corresponding
> + @interface. See objc/objc-act.h for details. */
> + tree GTY((tag ("1"))) objc_info;
> + } GTY ((desc ("c_dialect_objc ()"))) info;
> };
>
> struct GTY(()) lang_decl {
> --- gcc/c/c-decl.cc.jj 2025-06-04 17:21:01.111783263 +0200
> +++ gcc/c/c-decl.cc 2025-06-09 13:10:56.724561444 +0200
> @@ -9790,12 +9790,17 @@ finish_struct (location_t loc, tree t, t
> len += list_length (x);
>
> /* Use the same allocation policy here that make_node uses, to
> - ensure that this lives as long as the rest of the struct decl.
> - All decls in an inline function need to be saved. */
> + ensure that this lives as long as the rest of the struct decl.
> + All decls in an inline function need to be saved. */
>
> - space = ggc_cleared_alloc<struct lang_type> ();
> - space2 = (sorted_fields_type *) ggc_internal_alloc
> - (sizeof (struct sorted_fields_type) + len * sizeof (tree));
> + space = ((struct lang_type *)
> + ggc_internal_cleared_alloc (c_dialect_objc ()
> + ? sizeof (struct lang_type)
> + : offsetof (struct lang_type,
> + info)));
> + space2 = ((sorted_fields_type *)
> + ggc_internal_alloc (sizeof (struct sorted_fields_type)
> + + len * sizeof (tree)));
>
> len = 0;
> space->s = space2;
> @@ -10269,7 +10274,10 @@ finish_enum (tree enumtype, tree values,
>
> /* Record the min/max values so that we can warn about bit-field
> enumerations that are too small for the values. */
> - lt = ggc_cleared_alloc<struct lang_type> ();
> + lt = ((struct lang_type *)
> + ggc_internal_cleared_alloc (c_dialect_objc ()
> + ? sizeof (struct lang_type)
> + : offsetof (struct lang_type, info)));
> lt->enum_min = minnode;
> lt->enum_max = maxnode;
> TYPE_LANG_SPECIFIC (enumtype) = lt;
> --- gcc/cp/cp-tree.h.jj 2025-06-07 09:46:31.602393864 +0200
> +++ gcc/cp/cp-tree.h 2025-06-09 12:51:02.905724560 +0200
> @@ -2514,12 +2514,16 @@ struct GTY(()) lang_type {
> tree key_method;
> tree decl_list;
> tree befriending_classes;
> - /* In a RECORD_TYPE, information specific to Objective-C++, such
> - as a list of adopted protocols or a pointer to a corresponding
> - @interface. See objc/objc-act.h for details. */
> - tree objc_info;
> /* FIXME reuse another field? */
> tree lambda_expr;
> + union maybe_objc_info {
> + /* If not c_dialect_objc, this part is not even allocated. */
> + char GTY((tag ("0"))) non_objc;
> + /* In a RECORD_TYPE, information specific to Objective-C, such
> + as a list of adopted protocols or a pointer to a corresponding
> + @interface. See objc/objc-act.h for details. */
> + tree GTY((tag ("1"))) objc_info;
> + } GTY ((desc ("c_dialect_objc ()"))) info;
> };
>
> /* We used to have a variant type for lang_type. Keep the name of the
> --- gcc/cp/lex.cc.jj 2025-04-18 11:23:53.809175088 +0200
> +++ gcc/cp/lex.cc 2025-06-09 13:05:32.117951517 +0200
> @@ -1082,15 +1082,17 @@ copy_lang_type (tree node)
> if (! TYPE_LANG_SPECIFIC (node))
> return;
>
> - auto *lt = (struct lang_type *) ggc_internal_alloc (sizeof (struct
> lang_type));
> + size_t sz = (c_dialect_objc () ? sizeof (struct lang_type)
> + : offsetof (struct lang_type, info));
> + auto *lt = (struct lang_type *) ggc_internal_alloc (sz);
>
> - memcpy (lt, TYPE_LANG_SPECIFIC (node), (sizeof (struct lang_type)));
> + memcpy (lt, TYPE_LANG_SPECIFIC (node), sz);
> TYPE_LANG_SPECIFIC (node) = lt;
>
> if (GATHER_STATISTICS)
> {
> tree_node_counts[(int)lang_type] += 1;
> - tree_node_sizes[(int)lang_type] += sizeof (struct lang_type);
> + tree_node_sizes[(int)lang_type] += sz;
> }
> }
>
> @@ -1114,14 +1116,15 @@ maybe_add_lang_type_raw (tree t)
> if (!RECORD_OR_UNION_CODE_P (TREE_CODE (t)))
> return false;
>
> - auto *lt = (struct lang_type *) (ggc_internal_cleared_alloc
> - (sizeof (struct lang_type)));
> + size_t sz = (c_dialect_objc () ? sizeof (struct lang_type)
> + : offsetof (struct lang_type, info));
> + auto *lt = (struct lang_type *) (ggc_internal_cleared_alloc (sz));
> TYPE_LANG_SPECIFIC (t) = lt;
>
> if (GATHER_STATISTICS)
> {
> tree_node_counts[(int)lang_type] += 1;
> - tree_node_sizes[(int)lang_type] += sizeof (struct lang_type);
> + tree_node_sizes[(int)lang_type] += sz;
> }
>
> return true;
> @@ -1135,8 +1138,8 @@ cxx_make_type (enum tree_code code MEM_S
> if (maybe_add_lang_type_raw (t))
> {
> /* Set up some flags that give proper default behavior. */
> - struct c_fileinfo *finfo =
> - get_fileinfo (LOCATION_FILE (input_location));
> + struct c_fileinfo *finfo
> + = get_fileinfo (LOCATION_FILE (input_location));
> SET_CLASSTYPE_INTERFACE_UNKNOWN_X (t, finfo->interface_unknown);
> CLASSTYPE_INTERFACE_ONLY (t) = finfo->interface_only;
> }
> --- gcc/objc/objc-act.h.jj 2025-04-08 14:08:54.870231485 +0200
> +++ gcc/objc/objc-act.h 2025-06-09 12:54:46.780686364 +0200
> @@ -228,7 +228,7 @@ enum objc_property_nullability {
>
> /* The following three macros must be overridden (in objcp/objcp-decl.h)
> for Objective-C++. */
> -#define TYPE_OBJC_INFO(TYPE) TYPE_LANG_SPECIFIC (TYPE)->objc_info
> +#define TYPE_OBJC_INFO(TYPE) TYPE_LANG_SPECIFIC (TYPE)->info.objc_info
> #define SIZEOF_OBJC_TYPE_LANG_SPECIFIC sizeof (struct lang_type)
> #define ALLOC_OBJC_TYPE_LANG_SPECIFIC(NODE) \
> do { \
> --- gcc/objcp/objcp-decl.h.jj 2025-04-08 14:08:54.874231429 +0200
> +++ gcc/objcp/objcp-decl.h 2025-06-09 12:52:36.351456410 +0200
> @@ -60,7 +60,7 @@ extern tree objcp_end_compound_stmt (tre
> #define OBJC_SET_TYPE_NAME(type, name) (TYPE_IDENTIFIER (type) = (name))
>
> #undef TYPE_OBJC_INFO
> -#define TYPE_OBJC_INFO(TYPE) LANG_TYPE_CLASS_CHECK (TYPE)->objc_info
> +#define TYPE_OBJC_INFO(TYPE) LANG_TYPE_CLASS_CHECK (TYPE)->info.objc_info
> #undef SIZEOF_OBJC_TYPE_LANG_SPECIFIC
> #define SIZEOF_OBJC_TYPE_LANG_SPECIFIC sizeof (struct lang_type)
> #undef ALLOC_OBJC_TYPE_LANG_SPECIFIC
>
> Jakub
>
