Clear destination buffer updated by the previous run

Clear the destination buffer updated by the previous run in bench-memcpy.c
and test-memcpy.c to catch the error when the following implementations do
not copy anything.

	[BZ #19907]
	* benchtests/bench-memcpy.c (do_one_test): Clear the destination
	buffer updated by the previous run.
	* string/test-memcpy.c (do_one_test): Likewise.
	* benchtests/bench-memmove.c (do_one_test): Add a comment.
	* string/test-memmove.c (do_one_test): Likewise.

1 files changed, 1 insertions, 0 deletions

diff --git a/benchtests/bench-memmove.c b/benchtests/bench-memmove.c
index c38596b41e..3858f2ac52 100644
--- a/benchtests/bench-memmove.c
+++ b/benchtests/bench-memmove.c
@@ -70,6 +70,7 @@ do_one_test (impl_t *impl, char *dst, char *src, const char *orig_src,
   size_t i, iters = INNER_LOOP_ITERS;
   timing_t start, stop, cur;
 
+  /* This also clears the destination buffer set by the previous run.  */
   memcpy (src, orig_src, len);
 #ifdef TEST_BCOPY
   CALL (impl, src, dst, len);