# UNDF: UNDF-2026-000000213
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -3753,13 +3753,30 @@ static uint32_t zend_get_arg_num(const zend_function *fn, const zend_string *ar
 {
-	// TODO: Caching?
-	for (uint32_t i = 0; i < fn->common.num_args; i++) {
-		zend_arg_info *arg_info = &fn->op_array.arg_info[i];
-		if (zend_string_equals(arg_info->name, arg_name)) {
-			return i + 1;
-		}
-	}
-
-	/* Either an invalid argument name, or collected into a variadic argument. */
-	return (uint32_t) -1;
+	/*
+	 * Build a HashTable from arg_name -> (1-based position) on first call,
+	 * cache it on the zend_op_array.  Subsequent calls are O(1) lookups.
+	 * Replaces O(M) linear scan — was O(N*M) for N named args, M params.
+	 */
+	if (!fn->op_array.arg_name_map) {
+		HashTable *ht = emalloc(sizeof(HashTable));
+		zend_hash_init(ht, fn->common.num_args, NULL, NULL, 0);
+		for (uint32_t i = 0; i < fn->common.num_args; i++) {
+			zend_arg_info *arg_info = &fn->op_array.arg_info[i];
+			zval pos;
+			ZVAL_LONG(&pos, i + 1);
+			zend_hash_add(ht, arg_info->name, &pos);
+		}
+		((zend_op_array *)&fn->op_array)->arg_name_map = ht;
+	}
+
+	zval *zv = zend_hash_find(fn->op_array.arg_name_map, arg_name);
+	if (zv) {
+		return (uint32_t)Z_LVAL_P(zv);
+	}
+	return (uint32_t) -1;
 }