Commit e3fb2efb authored by Paul Eggert's avatar Paul Eggert
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Avoid unnecessary pointer scanning in garbage collection (Bug#10780).

* alloc.c (POINTERS_MIGHT_HIDE_IN_OBJECTS): New macro.
(mark_memory): Mark Lisp_Objects only if pointers might hide in
objects, as mark_maybe_pointer will catch them otherwise.
(GC_LISP_OBJECT_ALIGNMENT): Remove; no longer needed.
* s/gnu-linux.h (GC_LISP_OBJECT_ALIGNMENT) [__mc68000__]: Likewise.
parent b5385551
2012-04-07 Paul Eggert <eggert@cs.ucla.edu>
Avoid unnecessary pointer scanning in garbage collection (Bug#10780).
* alloc.c (POINTERS_MIGHT_HIDE_IN_OBJECTS): New macro.
(mark_memory): Mark Lisp_Objects only if pointers might hide in
objects, as mark_maybe_pointer will catch them otherwise.
(GC_LISP_OBJECT_ALIGNMENT): Remove; no longer needed.
* s/gnu-linux.h (GC_LISP_OBJECT_ALIGNMENT) [__mc68000__]: Likewise.
2012-04-07 Paul Eggert <eggert@cs.ucla.edu>
Fix typo that broke non-Windows builds.
......
......@@ -4251,23 +4251,38 @@ mark_maybe_pointer (void *p)
}
/* Alignment of Lisp_Object and pointer values. Use offsetof, as it
sometimes returns a smaller alignment than GCC's __alignof__ and
mark_memory might miss objects if __alignof__ were used. For
example, on x86 with WIDE_EMACS_INT, __alignof__ (Lisp_Object) is 8
but GC_LISP_OBJECT_ALIGNMENT should be 4. */
#ifndef GC_LISP_OBJECT_ALIGNMENT
# define GC_LISP_OBJECT_ALIGNMENT offsetof (struct {char a; Lisp_Object b;}, b)
#endif
/* Alignment of pointer values. Use offsetof, as it sometimes returns
a smaller alignment than GCC's __alignof__ and mark_memory might
miss objects if __alignof__ were used. */
#define GC_POINTER_ALIGNMENT offsetof (struct {char a; void *b;}, b)
/* Define POINTERS_MIGHT_HIDE_IN_OBJECTS to 1 if marking via C pointers does
not suffice, which is the typical case. A host where a Lisp_Object is
wider than a pointer might allocate a Lisp_Object in non-adjacent halves.
If USE_LSB_TAG, the bottom half is not a valid pointer, but it should
suffice to widen it to to a Lisp_Object and check it that way. */
#if defined USE_LSB_TAG || UINTPTR_MAX >> VALBITS != 0
# if !defined USE_LSB_TAG && UINTPTR_MAX >> VALBITS >> GCTYPEBITS != 0
/* If tag bits straddle pointer-word boundaries, neither mark_maybe_pointer
nor mark_maybe_object can follow the pointers. This should not occur on
any practical porting target. */
# error "MSB type bits straddle pointer-word boundaries"
# endif
/* Marking via C pointers does not suffice, because Lisp_Objects contain
pointer words that hold pointers ORed with type bits. */
# define POINTERS_MIGHT_HIDE_IN_OBJECTS 1
#else
/* Marking via C pointers suffices, because Lisp_Objects contain pointer
words that hold unmodified pointers. */
# define POINTERS_MIGHT_HIDE_IN_OBJECTS 0
#endif
/* Mark Lisp objects referenced from the address range START+OFFSET..END
or END+OFFSET..START. */
static void
mark_memory (void *start, void *end)
{
Lisp_Object *p;
void **pp;
int i;
......@@ -4284,11 +4299,6 @@ mark_memory (void *start, void *end)
end = tem;
}
/* Mark Lisp_Objects. */
for (p = start; (void *) p < end; p++)
for (i = 0; i < sizeof *p; i += GC_LISP_OBJECT_ALIGNMENT)
mark_maybe_object (*(Lisp_Object *) ((char *) p + i));
/* Mark Lisp data pointed to. This is necessary because, in some
situations, the C compiler optimizes Lisp objects away, so that
only a pointer to them remains. Example:
......@@ -4310,17 +4320,10 @@ mark_memory (void *start, void *end)
for (pp = start; (void *) pp < end; pp++)
for (i = 0; i < sizeof *pp; i += GC_POINTER_ALIGNMENT)
{
void *w = *(void **) ((char *) pp + i);
mark_maybe_pointer (w);
#ifdef USE_LSB_TAG
/* A host where a Lisp_Object is wider than a pointer might
allocate a Lisp_Object in non-adjacent halves. If
USE_LSB_TAG, the bottom half is not a valid pointer, so
widen it to to a Lisp_Object and check it that way. */
if (sizeof w < sizeof (Lisp_Object))
mark_maybe_object (widen_to_Lisp_Object (w));
#endif
void *p = *(void **) ((char *) pp + i);
mark_maybe_pointer (p);
if (POINTERS_MIGHT_HIDE_IN_OBJECTS)
mark_maybe_object (widen_to_Lisp_Object (p));
}
}
......
......@@ -146,9 +146,6 @@ along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */
|| defined __ia64__ || defined __sh__
#define GC_SETJMP_WORKS 1
#define GC_MARK_STACK GC_MAKE_GCPROS_NOOPS
#ifdef __mc68000__
#define GC_LISP_OBJECT_ALIGNMENT 2
#endif
#ifdef __ia64__
#define GC_MARK_SECONDARY_STACK() \
do { \
......
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