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.

2 files changed, 7 insertions, 0 deletions

diff --git a/string/test-memcpy.c b/string/test-memcpy.c
index 2a0994ca98..cb072f8674 100644
--- a/string/test-memcpy.c
+++ b/string/test-memcpy.c
@@ -53,6 +53,12 @@ static void
 do_one_test (impl_t *impl, char *dst, const char *src,
 	     size_t len)
 {
+  size_t i;
+
+  /* Must clear the destination buffer set by the previous run.  */
+  for (i = 0; i < len; i++)
+    dst[i] = 0;
+
   if (CALL (impl, dst, src, len) != MEMCPY_RESULT (dst, len))
     {
       error (0, 0, "Wrong result in function %s %p %p", impl->name,
diff --git a/string/test-memmove.c b/string/test-memmove.c
index d2ab3f3c8d..43433297e5 100644
--- a/string/test-memmove.c
+++ b/string/test-memmove.c
@@ -68,6 +68,7 @@ static void
 do_one_test (impl_t *impl, char *dst, char *src, const char *orig_src,
 	     size_t len)
 {
+  /* This also clears the destination buffer set by the previous run.  */
   memcpy (src, orig_src, len);
 #ifdef TEST_BCOPY
   CALL (impl, src, dst, len);