Optimize array_fill_keys()

Move the refcount update outside of the loop.

For the following benchmark:
```php
$r = range(0, 1000);
$v = new stdClass();

for ($i = 0; $i < 100000; $i++) {
    array_fill_keys($r, $v);
}
```

On an i7-4790:
```
Benchmark 1: ./sapi/cli/php_old ../x.php
  Time (mean ± σ):     507.5 ms ±   4.8 ms    [User: 505.1 ms, System: 1.2 ms]
  Range (min … max):   501.2 ms … 518.4 ms    10 runs

Benchmark 2: ./sapi/cli/php ../x.php
  Time (mean ± σ):     479.8 ms ±   3.1 ms    [User: 476.8 ms, System: 1.8 ms]
  Range (min … max):   475.0 ms … 486.7 ms    10 runs

Summary
  ./sapi/cli/php ../x.php ran
    1.06 ± 0.01 times faster than ./sapi/cli/php_old ../x.php
```

On an i7-1185G7:
```
Benchmark 1: ./sapi/cli/php x.php
  Time (mean ± σ):     343.9 ms ±   3.1 ms    [User: 341.1 ms, System: 2.3 ms]
  Range (min … max):   337.9 ms … 347.8 ms    10 runs

Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):     357.8 ms ±   2.3 ms    [User: 355.7 ms, System: 1.6 ms]
  Range (min … max):   355.0 ms … 362.6 ms    10 runs

Summary
  ./sapi/cli/php x.php ran
    1.04 ± 0.01 times faster than ./sapi/cli/php_old x.php
```

Author: ndossche

Zend/zend_hash.h

@@ -473,6 +473,17 @@ static zend_always_inline bool zend_hash_str_exists_ind(const HashTable *ht, con
 			Z_TYPE_P(Z_INDIRECT_P(zv)) != IS_UNDEF);
 }
 
+static zend_always_inline zval *zend_symtable_add(HashTable *ht, zend_string *key, zval *pData)
+{
+	zend_ulong idx;
+
+	if (ZEND_HANDLE_NUMERIC(key, idx)) {
+		return zend_hash_index_add(ht, idx, pData);
+	} else {
+		return zend_hash_add(ht, key, pData);
+	}
+}
+
 static zend_always_inline zval *zend_symtable_add_new(HashTable *ht, zend_string *key, zval *pData)
 {
 	zend_ulong idx;

ext/standard/array.c

@@ -2826,20 +2826,28 @@ PHP_FUNCTION(array_fill_keys)
 	ZEND_PARSE_PARAMETERS_END();
 
 	/* Initialize return array */
-	array_init_size(return_value, zend_hash_num_elements(Z_ARRVAL_P(keys)));
+	uint32_t keys_count = zend_hash_num_elements(Z_ARRVAL_P(keys));
+	array_init_size(return_value, keys_count);
+
+	if (Z_REFCOUNTED_P(val)) {
+		GC_ADDREF_EX(Z_COUNTED_P(val), keys_count);
+	}
 
 	ZEND_HASH_FOREACH_VAL(Z_ARRVAL_P(keys), entry) {
 		ZVAL_DEREF(entry);
-		Z_TRY_ADDREF_P(val);
 		if (Z_TYPE_P(entry) == IS_LONG) {
-			zend_hash_index_update(Z_ARRVAL_P(return_value), Z_LVAL_P(entry), val);
+			zend_hash_index_add(Z_ARRVAL_P(return_value), Z_LVAL_P(entry), val);
 		} else {
 			zend_string *tmp_key;
 			zend_string *key = zval_get_tmp_string(entry, &tmp_key);
-			zend_symtable_update(Z_ARRVAL_P(return_value), key, val);
+			zend_symtable_add(Z_ARRVAL_P(return_value), key, val);
 			zend_tmp_string_release(tmp_key);
 		}
 	} ZEND_HASH_FOREACH_END();
+
+	if (Z_REFCOUNTED_P(val)) {
+		GC_DELREF_EX(Z_COUNTED_P(val), keys_count - zend_hash_num_elements(Z_ARRVAL_P(return_value)));
+	}
 }
 /* }}} */