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malloc: Optimize small memory clearing for calloc

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Add calloc-clear-memory.h to clear memory size up to 36 bytes (72 bytes
on 64-bit targets) for calloc.  Use repeated stores with 1 branch, instead
of up to 3 branches.  On x86-64, it is faster than memset since calling
memset needs 1 indirect branch, 1 broadcast, and up to 4 branches.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
This commit is contained in:
H.J. Lu
2024-11-26 16:15:25 +08:00
parent f43eb2cf30
commit 1c4cebb84b
3 changed files with 51 additions and 35 deletions
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36
malloc/malloc.c
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@ -3755,8 +3755,6 @@ __libc_calloc (size_t n, size_t elem_size)
INTERNAL_SIZE_T sz, oldtopsize;
void *mem;
unsigned long clearsize;
unsigned long nclears;
INTERNAL_SIZE_T *d;
ptrdiff_t bytes;
if (__glibc_unlikely (__builtin_mul_overflow (n, elem_size, &bytes)))
@ -3853,40 +3851,8 @@ __libc_calloc (size_t n, size_t elem_size)
}
#endif
/* Unroll clear of <= 36 bytes (72 if 8byte sizes). We know that
contents have an odd number of INTERNAL_SIZE_T-sized words;
minimally 3. */
d = (INTERNAL_SIZE_T *) mem;
clearsize = csz - SIZE_SZ;
nclears = clearsize / sizeof (INTERNAL_SIZE_T);
assert (nclears >= 3);
if (nclears > 9)
return memset (d, 0, clearsize);
else
{
*(d + 0) = 0;
*(d + 1) = 0;
*(d + 2) = 0;
if (nclears > 4)
{
*(d + 3) = 0;
*(d + 4) = 0;
if (nclears > 6)
{
*(d + 5) = 0;
*(d + 6) = 0;
if (nclears > 8)
{
*(d + 7) = 0;
*(d + 8) = 0;
}
}
}
}
return mem;
return clear_memory ((INTERNAL_SIZE_T *) mem, clearsize);
}
#endif /* IS_IN (libc) */