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malloc: Change calloc when tagging is disabled

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When glibc is built with memory tagging support (USE_MTAG) but it is not
enabled at runtime (mtag_enabled) then unconditional memset was used
even though that can be often avoided.

This is for performance when tagging is supported but not enabled.
The extra check should have no overhead: tag_new_zero_region already
had a runtime check which the compiler can now optimize away.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Szabolcs Nagy 2021-02-16 17:02:44 +00:00
parent c076a0bc69
commit 9d61722b59
1 changed files with 4 additions and 6 deletions
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10
malloc/malloc.c
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@ -3591,11 +3591,9 @@ __libc_calloc (size_t n, size_t elem_size)
mchunkptr oldtop;
INTERNAL_SIZE_T sz, oldtopsize;
void *mem;
#ifndef USE_MTAG
unsigned long clearsize;
unsigned long nclears;
INTERNAL_SIZE_T *d;
#endif
ptrdiff_t bytes;
if (__glibc_unlikely (__builtin_mul_overflow (n, elem_size, &bytes)))
@ -3674,12 +3672,13 @@ __libc_calloc (size_t n, size_t elem_size)
return 0;
mchunkptr p = mem2chunk (mem);
/* If we are using memory tagging, then we need to set the tags
regardless of MORECORE_CLEARS, so we zero the whole block while
doing so. */
#ifdef USE_MTAG
return tag_new_zero_region (mem, CHUNK_AVAILABLE_SIZE (p) - CHUNK_HDR_SZ);
#else
if (__glibc_unlikely (mtag_enabled))
return tag_new_zero_region (mem, CHUNK_AVAILABLE_SIZE (p) - CHUNK_HDR_SZ);
INTERNAL_SIZE_T csz = chunksize (p);
/* Two optional cases in which clearing not necessary */
@ -3733,7 +3732,6 @@ __libc_calloc (size_t n, size_t elem_size)
}
return mem;
#endif
}
/*