Avoid computing strlen() inside loops

Compiling with -O0 (no proper optimizations), strlen() call
in loops for comparing the size, isn't being called/initialized
before the actual loop gets started, which causes n-numbers of
strlen() calls (as long as the string is). Keeping the length
before entering in the loop is a good idea.

On some places, even with -O2, both GCC and Clang can't
recognize this pattern, which seem to happen in an array
of char pointer.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: rilysh <nightquick@proton.me>
Closes #16584

module/zcommon/zfs_prop.c

@@ -790,11 +790,12 @@ zfs_name_to_prop(const char *propname)
 boolean_t
 zfs_prop_user(const char *name)
 {
-	int i;
+	int i, len;
 	char c;
 	boolean_t foundsep = B_FALSE;
 
-	for (i = 0; i < strlen(name); i++) {
+	len = strlen(name);
+	for (i = 0; i < len; i++) {
 		c = name[i];
 		if (!zprop_valid_char(c))
 			return (B_FALSE);

module/zcommon/zpool_prop.c

@@ -473,11 +473,12 @@ vdev_name_to_prop(const char *propname)
 boolean_t
 vdev_prop_user(const char *name)
 {
-	int i;
+	int i, len;
 	char c;
 	boolean_t foundsep = B_FALSE;
 
-	for (i = 0; i < strlen(name); i++) {
+	len = strlen(name);
+	for (i = 0; i < len; i++) {
 		c = name[i];
 		if (!zprop_valid_char(c))
 			return (B_FALSE);