coccinelle: convert hashcpy() with null_sha1 to hashclr()

hashcpy with null_sha1 as the source is equivalent to hashclr.  In
addition to being simpler, using hashclr may give the compiler a chance
to optimize better.  Convert instances of hashcpy with the source
argument of null_sha1 to hashclr.

This transformation was implemented using the following semantic patch:

@@
expression E1;
@@
-hashcpy(E1, null_sha1);
+hashclr(E1);
Signed-off-by: Nbrian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -1530,7 +1530,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	     * Stash away the local changes so that we can try more than one.
 	     */
 	    save_state(stash))
-		hashcpy(stash, null_sha1);
+		hashclr(stash);
 
 	for (i = 0; i < use_strategies_nr; i++) {
 		int ret;

builtin/unpack-objects.c

@@ -355,7 +355,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			return; /* we are done */
 		else {
 			/* cannot resolve yet --- queue it */
-			hashcpy(obj_list[nr].sha1, null_sha1);
+			hashclr(obj_list[nr].sha1);
 			add_delta_to_list(nr, base_sha1, 0, delta_data, delta_size);
 			return;
 		}
@@ -406,7 +406,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			 * The delta base object is itself a delta that
 			 * has not been resolved yet.
 			 */
-			hashcpy(obj_list[nr].sha1, null_sha1);
+			hashclr(obj_list[nr].sha1);
 			add_delta_to_list(nr, null_sha1, base_offset, delta_data, delta_size);
 			return;
 		}

diff.c

@@ -3134,7 +3134,7 @@ static void diff_fill_sha1_info(struct diff_filespec *one)
 		if (!one->sha1_valid) {
 			struct stat st;
 			if (one->is_stdin) {
-				hashcpy(one->sha1, null_sha1);
+				hashclr(one->sha1);
 				return;
 			}
 			if (lstat(one->path, &st) < 0)

submodule-config.c

@@ -368,7 +368,7 @@ static int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
 	int ret = 0;
 
 	if (is_null_sha1(commit_sha1)) {
-		hashcpy(gitmodules_sha1, null_sha1);
+		hashclr(gitmodules_sha1);
 		return 1;
 	}
 

t/helper/test-submodule-config.c

@@ -49,7 +49,7 @@ int main(int argc, char **argv)
 		path_or_name = arg[1];
 
 		if (commit[0] == '\0')
-			hashcpy(commit_sha1, null_sha1);
+			hashclr(commit_sha1);
 		else if (get_sha1(commit, commit_sha1) < 0)
 			die_usage(argc, argv, "Commit not found.");