[glibc/nsz/mtag] malloc: Change calloc when tagging is disabled

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f33e5f9a8301e7905985301b479fc4bc29d0063d

commit f33e5f9a8301e7905985301b479fc4bc29d0063d
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Tue Feb 16 17:02:44 2021 +0000

    malloc: Change calloc when tagging is disabled
    
    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>

Diff:
---
 malloc/malloc.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 01cf6e9325..0b2aff3768 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -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
 }
 
 /*