[PATCH] aarch64: revert memcpy optimze for kunpeng to avoid performance degradation

[Shuo Wang]

In commit 863d775c481704baaa41855fc93e5a1ca2dc6bf6, kunpeng920 is added to default memcpy version,
however, there is performance degradation when the copy size is some large bytes, eg: 100k. 
This is the result, tested in glibc-2.28:
             before backport  after backport	 Performance improvement
memcpy_1k      0.005              0.005                 0.00%
memcpy_10k     0.032              0.029                 10.34%
memcpy_100k    0.356              0.429                 -17.02%
memcpy_1m      7.470              11.153                -33.02%

This is the demo
#include "stdio.h"
#include "string.h"
#include "stdlib.h"

char a[1024*1024] = {12};
char b[1024*1024] = {13};
int main(int argc, char *argv[])
{
    int i = atoi(argv[1]);
    int j;
    int size = atoi(argv[2]);
    
    for (j = 0; j < i; j++)
        memcpy(b, a, size*1024);
    return 0;
}

# gcc -g -O0 memcpy.c -o memcpy
# time taskset -c 10 ./memcpy 100000 1024

Co-authored-by: liqingqing <liqingqing3@huawei.com>

---
 sysdeps/aarch64/multiarch/memcpy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/aarch64/multiarch/memcpy.c b/sysdeps/aarch64/multiarch/memcpy.c
index 27259d3386..0e0a5cbcfb 100644
--- a/sysdeps/aarch64/multiarch/memcpy.c
+++ b/sysdeps/aarch64/multiarch/memcpy.c
@@ -37,7 +37,7 @@ extern __typeof (__redirect_memcpy) __memcpy_falkor attribute_hidden;
 libc_ifunc (__libc_memcpy,
             (IS_THUNDERX (midr)
 	     ? __memcpy_thunderx
-	     : (IS_FALKOR (midr) || IS_PHECDA (midr) || IS_KUNPENG920 (midr)
+	     : (IS_FALKOR (midr) || IS_PHECDA (midr)
 		? __memcpy_falkor
 		: (IS_THUNDERX2 (midr) || IS_THUNDERX2PA (midr)
 		  ? __memcpy_thunderx2
-- 
2.23.0