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Tweak GC performance if !USE_LSB_TAG

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Performance issue reported by Eli Zaretskii (Bug#41321#149).
* src/alloc.c (GC_OBJECT_ALIGNMENT_MINIMUM): New constant.
(maybe_lisp_pointer): Use it instead of GCALIGNMENT.
This commit is contained in:
Paul Eggert 2020-05-26 15:47:59 -07:00
parent 5467aac131
commit 0fc4989f34
1 changed files with 19 additions and 2 deletions
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21
src/alloc.c
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@ -4687,16 +4687,33 @@ mark_maybe_objects (Lisp_Object const *array, ptrdiff_t nelts)
mark_maybe_object (*array);
}
/* A lower bound on the alignment of Lisp objects that need marking.
Although 1 is safe, higher values speed up mark_maybe_pointer.
If USE_LSB_TAG, this value is typically GCALIGNMENT; otherwise,
it's determined by the natural alignment of Lisp structs.
All vectorlike objects have alignment at least that of union
vectorlike_header and it's unlikely they all have alignment greater,
so use the union as a safe and likely-accurate standin for
vectorlike objects. */
enum { GC_OBJECT_ALIGNMENT_MINIMUM
= max (GCALIGNMENT,
min (alignof (union vectorlike_header),
min (min (alignof (struct Lisp_Cons),
alignof (struct Lisp_Float)),
min (alignof (struct Lisp_String),
alignof (struct Lisp_Symbol))))) };
/* Return true if P might point to Lisp data that can be garbage
collected, and false otherwise (i.e., false if it is easy to see
that P cannot point to Lisp data that can be garbage collected).
Symbols are implemented via offsets not pointers, but the offsets
are also multiples of GCALIGNMENT. */
are also multiples of GC_OBJECT_ALIGNMENT_MINIMUM. */
static bool
maybe_lisp_pointer (void *p)
{
return (uintptr_t) p % GCALIGNMENT == 0;
return (uintptr_t) p % GC_OBJECT_ALIGNMENT_MINIMUM == 0;
}
/* If P points to Lisp data, mark that as live if it isn't already