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?
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
