Addref static vars when not copying private method

While we don't need to give this method separate static vars, we
do still need to perform an addref, as there will be a corresponding
delref in the dtor.

Author: nikic

Zend/tests/static_variable_in_private_trait_method.phpt

@@ -0,0 +1,35 @@
+--TEST--
+Behavior of static variable in private trait method
+--FILE--
+<?php
+
+trait T {
+    private static function method() {
+        static $x;
+        if ($x === null) $x = new stdClass;
+        return $x;
+    }
+
+    public static function method2() {
+        return self::method();
+    }
+}
+
+class C {
+    use T;
+}
+
+var_dump(C::method2());
+
+class D extends C {
+    use T;
+}
+
+var_dump(D::method2());
+
+?>
+--EXPECT--
+object(stdClass)#1 (0) {
+}
+object(stdClass)#2 (0) {
+}

Zend/zend_inheritance.c

@@ -96,11 +96,19 @@ static zend_always_inline zend_function *zend_duplicate_function(zend_function *
 			(*func->op_array.refcount)++;
 		}
 		if (is_interface
-		 || EXPECTED(!func->op_array.static_variables)
-		 || (func->op_array.fn_flags & ZEND_ACC_PRIVATE)) {
+		 || EXPECTED(!func->op_array.static_variables)) {
 			/* reuse the same op_array structure */
 			return func;
 		}
+		if (func->op_array.fn_flags & ZEND_ACC_PRIVATE) {
+			/* For private methods we reuse the same op_array structure even if
+			 * static variables are used, because it will not end up being used
+			 * anyway. However we still need to addref as the dtor will delref. */
+			if (!(GC_FLAGS(func->op_array.static_variables) & IS_ARRAY_IMMUTABLE)) {
+				GC_ADDREF(func->op_array.static_variables);
+			}
+			return func;
+		}
 		return zend_duplicate_user_function(func);
 	}
 }