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Remove indirection in structs

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* libguile/gc.c (scm_storage_prehistory): Register struct displacement
  here.
* libguile/goops.c (scm_sys_modify_instance): Fix the format of a
  comment.
* libguile/modules.c (scm_post_boot_init_modules): Update for new format
  of struct vtable references.
* libguile/struct.c (scm_i_alloc_struct): Update to include slots
  directly, instead of being indirected by an embedded pointer.
  (scm_c_make_structv, scm_allocate_struct, scm_i_make_vtable_vtable):
  Adapt to pass vtable bits as argument to scm_i_alloc_struct, not
  vtable data bits.
  (scm_init_struct): Remove two-word displacement from libgc.
* libguile/struct.h: Update comment.
  (SCM_STRUCT_SLOTS, SCM_STRUCT_DATA): Update definitions.
  (SCM_STRUCT_VTABLE_DATA, SCM_STRUCT_VTABLE_SLOTS): Remove.
  (SCM_STRUCT_VTABLE, SCM_STRUCT_LAYOUT, SCM_STRUCT_PRINTER)
  (SCM_STRUCT_FINALIZER, SCM_STRUCT_VTABLE_FLAGS)
  (SCM_STRUCT_VTABLE_FLAG_IS_SET): Simplify definitions.
* module/system/base/types.scm (cell->object, address->inferior-struct):
  Adapt to struct representation change.
This commit is contained in:
Andy Wingo 2017-09-07 16:55:30 +02:00
parent 4898959901
commit 7e91ff651b
6 changed files with 51 additions and 95 deletions
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47
libguile/struct.c
View file

@ -1,5 +1,5 @@
/* Copyright (C) 1996,1997,1998,1999,2000,2001, 2003, 2004, 2006, 2007,
* 2008, 2009, 2010, 2011, 2012, 2013, 2015 Free Software Foundation, Inc.
* 2008, 2009, 2010, 2011, 2012, 2013, 2015, 2017 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
@ -420,30 +420,17 @@ struct_finalizer_trampoline (void *ptr, void *unused_data)
finalize (obj);
}
/* All struct data must be allocated at an address whose bottom three
bits are zero. This is because the tag for a struct lives in the
bottom three bits of the struct's car, and the upper bits point to
the data of its vtable, which is a struct itself. Thus, if the
address of that data doesn't end in three zeros, tagging it will
destroy the pointer.
I suppose we should make it clear here that, the data must be 8-byte aligned,
*within* the struct, and the struct itself should be 8-byte aligned. In
practice we ensure this because the data starts two words into a struct.
This function allocates an 8-byte aligned block of memory, whose first word
points to the given vtable data, then a data pointer, then n_words of data.
*/
SCM
scm_i_alloc_struct (scm_t_bits *vtable_data, int n_words)
/* A struct is a sequence of words preceded by a pointer to the struct's
vtable. The vtable reference is tagged with the struct tc3. */
static SCM
scm_i_alloc_struct (scm_t_bits vtable_bits, int n_words)
{
SCM ret;
ret = scm_words ((scm_t_bits)vtable_data | scm_tc3_struct, n_words + 2);
SCM_SET_CELL_WORD_1 (ret, (scm_t_bits)SCM_CELL_OBJECT_LOC (ret, 2));
ret = scm_words (vtable_bits | scm_tc3_struct, n_words + 1);
/* vtable_data can be null when making a vtable vtable */
if (vtable_data && vtable_data[scm_vtable_index_instance_finalize])
/* vtable_bits can be 0 when making a vtable vtable */
if (vtable_bits && SCM_VTABLE_INSTANCE_FINALIZER (SCM_PACK (vtable_bits)))
/* Register a finalizer for the newly created instance. */
scm_i_set_finalizer (SCM2PTR (ret), struct_finalizer_trampoline, NULL);
@ -481,7 +468,7 @@ scm_c_make_structv (SCM vtable, size_t n_tail, size_t n_init, scm_t_bits *init)
goto bad_tail;
}
obj = scm_i_alloc_struct (SCM_STRUCT_DATA (vtable), basic_size + n_tail);
obj = scm_i_alloc_struct (SCM_UNPACK (vtable), basic_size + n_tail);
scm_struct_init (obj, layout, n_tail, n_init, init);
@ -538,7 +525,7 @@ SCM_DEFINE (scm_allocate_struct, "allocate-struct", 2, 0, 0,
SCM_ASSERT (SCM_STRUCT_DATA_REF (vtable, scm_vtable_index_size) == c_nfields,
nfields, 2, FUNC_NAME);
ret = scm_i_alloc_struct (SCM_STRUCT_DATA (vtable), c_nfields);
ret = scm_i_alloc_struct (SCM_UNPACK (vtable), c_nfields);
if (SCM_LIKELY (SCM_VTABLE_FLAG_IS_SET (vtable, SCM_VTABLE_FLAG_SIMPLE)))
{
@ -612,9 +599,9 @@ scm_i_make_vtable_vtable (SCM fields)
basic_size = scm_i_symbol_length (layout) / 2;
obj = scm_i_alloc_struct (NULL, basic_size);
obj = scm_i_alloc_struct (0, basic_size);
/* Make it so that the vtable of OBJ is itself. */
SCM_SET_CELL_WORD_0 (obj, (scm_t_bits) SCM_STRUCT_DATA (obj) | scm_tc3_struct);
SCM_SET_CELL_WORD_0 (obj, SCM_UNPACK (obj) | scm_tc3_struct);
v = SCM_UNPACK (layout);
scm_struct_init (obj, layout, 0, 1, &v);
@ -980,16 +967,6 @@ scm_init_struct ()
{
SCM name;
/* The first word of a struct is equal to `SCM_STRUCT_DATA (vtable) +
scm_tc3_struct', and `SCM_STRUCT_DATA (vtable)' is 2 words after VTABLE by
default. */
GC_REGISTER_DISPLACEMENT (2 * sizeof (scm_t_bits) + scm_tc3_struct);
/* In the general case, `SCM_STRUCT_DATA (obj)' points 2 words after the
beginning of a GC-allocated region; that region is different from that of
OBJ once OBJ has undergone class redefinition. */
GC_REGISTER_DISPLACEMENT (2 * sizeof (scm_t_bits));
required_vtable_fields = scm_from_latin1_string (SCM_VTABLE_BASE_LAYOUT);
scm_c_define ("standard-vtable-fields", required_vtable_fields);
required_applicable_fields = scm_from_latin1_string (SCM_APPLICABLE_BASE_LAYOUT);