Preallocate result array size in xpath (#12105)

We know what size they're going to be, and we know they are packed
arrays. Prevent reallocations and initialisation overhead by setting the
initial size and initializing it as packed from the start.

Author: ndossche

ext/dom/xpath.c

@@ -95,7 +95,8 @@ static void dom_xpath_ext_function_php(xmlXPathParserContextPtr ctxt, int nargs,
 				} else if (type == 2) {
 					int j;
 					if (obj->nodesetval && obj->nodesetval->nodeNr > 0) {
-						array_init(&fci.params[i]);
+						array_init_size(&fci.params[i], obj->nodesetval->nodeNr);
+						zend_hash_real_init_packed(Z_ARRVAL_P(&fci.params[i]));
 						for (j = 0; j < obj->nodesetval->nodeNr; j++) {
 							xmlNodePtr node = obj->nodesetval->nodeTab[j];
 							zval child;
@@ -408,8 +409,8 @@ static void php_xpath_eval(INTERNAL_FUNCTION_PARAMETERS, int type) /* {{{ */
 			xmlNodeSetPtr nodesetp;
 
 			if (xpathobjp->type == XPATH_NODESET && NULL != (nodesetp = xpathobjp->nodesetval) && nodesetp->nodeNr) {
-
-				array_init(&retval);
+				array_init_size(&retval, nodesetp->nodeNr);
+				zend_hash_real_init_packed(Z_ARRVAL_P(&retval));
 				for (i = 0; i < nodesetp->nodeNr; i++) {
 					xmlNodePtr node = nodesetp->nodeTab[i];
 					zval child;