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bmomjianbmomjian
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Split MemSet into three parts to constant comparisons can be optimized
away by the compiler; used by palloc0.
1 parent 266c367 commit aaa3a0c

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3 files changed

+39
-25
lines changed

3 files changed

+39
-25
lines changed

‎src/backend/utils/mmgr/mcxt.c

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@
1414
*
1515
*
1616
* IDENTIFICATION
17-
* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/mcxt.c,v 1.35 2002/11/10 02:17:25 momjian Exp $
17+
* $Header: /cvsroot/pgsql/src/backend/utils/mmgr/mcxt.c,v 1.36 2002/11/13 00:37:06 momjian Exp $
1818
*
1919
*-------------------------------------------------------------------------
2020
*/
@@ -453,14 +453,14 @@ MemoryContextAlloc(MemoryContext context, Size size)
453453
}
454454

455455
/*
456-
* MemoryContextAllocZero
456+
* MemoryContextAllocPalloc0
457457
* Like MemoryContextAlloc, but clears allocated memory
458458
*
459459
* We could just call MemoryContextAlloc then clear the memory, but this
460460
* function is called too many times, so we have a separate version.
461461
*/
462462
void *
463-
MemoryContextAllocZero(MemoryContext context, Size size)
463+
MemoryContextAllocPalloc0(MemoryContext context, Size size)
464464
{
465465
void *ret;
466466

@@ -471,7 +471,7 @@ MemoryContextAllocZero(MemoryContext context, Size size)
471471
(unsigned long) size);
472472

473473
ret = (*context->methods->alloc) (context, size);
474-
MemSet(ret, 0, size);
474+
MemSetLoop(ret, 0, size);
475475
return ret;
476476
}
477477

‎src/include/c.h

Lines changed: 28 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@
1212
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
1313
* Portions Copyright (c) 1994, Regents of the University of California
1414
*
15-
* $Id: c.h,v 1.131 2002/11/11 03:02:19 momjian Exp $
15+
* $Id: c.h,v 1.132 2002/11/13 00:37:06 momjian Exp $
1616
*
1717
*-------------------------------------------------------------------------
1818
*/
@@ -577,26 +577,36 @@ typedef NameData *Name;
577577
* memset() functions. More research needs to be done, perhaps with
578578
* platform-specific MEMSET_LOOP_LIMIT values or tests in configure.
579579
*
580+
* MemSet has been split into two parts so MemSetTest can be optimized
581+
* away for constant 'val' and 'len'. This is used by palloc0().
582+
*
583+
* Note, arguments are evaluated more than once.
584+
*
580585
* bjm 2002-10-08
581586
*/
582-
#define MemSet(start, val, len) \
583-
do \
584-
{ \
585-
int32 * _start = (int32 *) (start); \
586-
int _val = (val); \
587-
Size _len = (len); \
587+
#define MemSetTest(val, len) \
588+
( ((len) & INT_ALIGN_MASK) == 0 && \
589+
(len) <= MEMSET_LOOP_LIMIT && \
590+
(val) == 0 )
591+
592+
#define MemSetLoop(start, val, len) \
593+
do \
594+
{ \
595+
int32 * _start = (int32 *) (start); \
596+
int32 * _stop = (int32 *) ((char *) _start + (len)); \
588597
\
589-
if ((( ((long) _start) | _len) & INT_ALIGN_MASK) == 0 && \
590-
_val == 0 && \
591-
_len <= MEMSET_LOOP_LIMIT) \
592-
{ \
593-
int32 * _stop = (int32 *) ((char *) _start + _len); \
594-
while (_start < _stop) \
595-
*_start++ = 0; \
596-
} \
597-
else \
598-
memset((char *) _start, _val, _len); \
599-
} while (0)
598+
while (_start < _stop) \
599+
*_start++ = 0; \
600+
} while (0)
601+
602+
#define MemSet(start, val, len) \
603+
do \
604+
{ \
605+
if (MemSetTest(val, len) && ((long)(start) & INT_ALIGN_MASK) == 0 ) \
606+
MemSetLoop(start, val, len); \
607+
else \
608+
memset((char *)(start), (val), (len)); \
609+
} while (0)
600610

601611
#define MEMSET_LOOP_LIMIT 1024
602612

‎src/include/utils/palloc.h

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -21,7 +21,7 @@
2121
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
2222
* Portions Copyright (c) 1994, Regents of the University of California
2323
*
24-
* $Id: palloc.h,v 1.22 2002/11/10 02:17:25 momjian Exp $
24+
* $Id: palloc.h,v 1.23 2002/11/13 00:37:06 momjian Exp $
2525
*
2626
*-------------------------------------------------------------------------
2727
*/
@@ -46,11 +46,15 @@ extern DLLIMPORT MemoryContext CurrentMemoryContext;
4646
* Fundamental memory-allocation operations (more are in utils/memutils.h)
4747
*/
4848
extern void *MemoryContextAlloc(MemoryContext context, Size size);
49-
extern void *MemoryContextAllocZero(MemoryContext context, Size size);
49+
extern void *MemoryContextAllocPalloc0(MemoryContext context, Size size);
5050

5151
#define palloc(sz) MemoryContextAlloc(CurrentMemoryContext, (sz))
5252

53-
#define palloc0(sz) MemoryContextAllocZero(CurrentMemoryContext, (sz))
53+
/* We assume palloc() is already int-aligned */
54+
#define palloc0(sz) \
55+
( MemSetTest(0, (sz)) ? \
56+
MemoryContextAllocPalloc0(CurrentMemoryContext, (sz)) : \
57+
memset(palloc(sz), 0, (sz)))
5458

5559
extern void pfree(void *pointer);
5660

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