implement CoW semantics

Author: withinboredom

Zend/tests/data_class_005.phpt

@@ -0,0 +1,52 @@
+--TEST--
+Copy on write
+--FILE--
+<?php
+
+data class Point {
+    public function __construct(public int $x, public int $y) {}
+    public function add(Point $other): Point {
+        $this->x += $other->x;
+        $this->y += $other->y;
+        return $this;
+    }
+    public function __toString(): string {
+        return "({$this->x},{$this->y})";
+    }
+}
+
+$p1 = new Point(1, 2);
+$p2 = $p1;
+
+// p2 is copy on write (3,2)
+$p2->x = 3;
+echo "p1: $p1\n";
+echo "p2 (x+3): $p2\n";
+
+echo "p1->add(p2): " . $p1->add($p2) . "\n";
+echo "p1: $p1\n";
+$po = new Point(1,1);
+$p2 = $po;
+$p2->x++;
+echo "p2: $p2\n";
+echo "po: $po\n";
+
+function modify(Point $p): Point {
+    $p->y++;
+    return $p;
+}
+
+$p1 = new Point(1,1);
+$p2 = modify($p1);
+echo "p1: $p1\n";
+echo "p2: $p2\n";
+
+--EXPECT--
+p1: (1,2)
+p2 (x+3): (3,2)
+p1->add(p2): (4,4)
+p1: (1,2)
+p2: (2,1)
+po: (1,1)
+p1: (1,1)
+p2: (1,2)

Zend/zend_vm_def.h

@@ -1041,6 +1041,19 @@ ZEND_VM_HANDLER(28, ZEND_ASSIGN_OBJ_OP, VAR|UNUSED|THIS|CV, CONST|TMPVAR|CV, OP)
 ZEND_VM_C_LABEL(assign_op_object):
 		/* here we are sure we are dealing with an object */
 		zobj = Z_OBJ_P(object);
+
+		// if this is a data class, we may need to CoW
+		if (zobj->ce->ce_flags & ZEND_ACC_DATA_CLASS) {
+			if (GC_REFCOUNT(zobj) > 1) {
+				// clone the object
+				zend_object *new_obj = zend_objects_clone_obj(zobj);
+				// set the object zval to the new object
+				ZVAL_OBJ(object, new_obj);
+				GC_DELREF(zobj);
+				zobj = new_obj;
+			}
+		}
+
 		if (OP2_TYPE == IS_CONST) {
 			name = Z_STR_P(property);
 		} else {
@@ -1310,6 +1323,19 @@ ZEND_VM_HANDLER(132, ZEND_PRE_INC_OBJ, VAR|UNUSED|THIS|CV, CONST|TMPVAR|CV, CACH
 ZEND_VM_C_LABEL(pre_incdec_object):
 		/* here we are sure we are dealing with an object */
 		zobj = Z_OBJ_P(object);
+
+		// if this is a data class, we may need to CoW
+		if (zobj->ce->ce_flags & ZEND_ACC_DATA_CLASS) {
+			if (GC_REFCOUNT(zobj) > 1) {
+				// clone the object
+				zend_object *new_obj = zend_objects_clone_obj(zobj);
+				// set the object zval to the new object
+				ZVAL_OBJ(object, new_obj);
+				GC_DELREF(zobj);
+				zobj = new_obj;
+			}
+		}
+
 		if (OP2_TYPE == IS_CONST) {
 			name = Z_STR_P(property);
 		} else {
@@ -1380,6 +1406,19 @@ ZEND_VM_HANDLER(134, ZEND_POST_INC_OBJ, VAR|UNUSED|THIS|CV, CONST|TMPVAR|CV, CAC
 ZEND_VM_C_LABEL(post_incdec_object):
 		/* here we are sure we are dealing with an object */
 		zobj = Z_OBJ_P(object);
+
+		// if this is a data class, we may need to CoW
+		if (zobj->ce->ce_flags & ZEND_ACC_DATA_CLASS) {
+			if (GC_REFCOUNT(zobj) > 1) {
+				// clone the object
+				zend_object *new_obj = zend_objects_clone_obj(zobj);
+				// set the object zval to the new object
+				ZVAL_OBJ(object, new_obj);
+				GC_DELREF(zobj);
+				zobj = new_obj;
+			}
+		}
+
 		if (OP2_TYPE == IS_CONST) {
 			name = Z_STR_P(property);
 		} else {
@@ -2560,6 +2599,22 @@ ZEND_VM_C_LABEL(fast_assign_obj):
 		ZVAL_DEREF(value);
 	}
 
+	// if this is a data class, we may need to CoW
+	if (zobj->ce->ce_flags & ZEND_ACC_DATA_CLASS) {
+          // skip if in a constructor
+          if (EX(func)->common.fn_flags & ZEND_ACC_CTOR) {
+			// skip
+		  } else
+		if (GC_REFCOUNT(zobj) > 1) {
+			// clone the object
+			zend_object *new_obj = zend_objects_clone_obj(zobj);
+			// set the object zval to the new object
+			ZVAL_OBJ(object, new_obj);
+			GC_DELREF(zobj);
+			zobj = new_obj;
+		}
+	}
+
 	value = zobj->handlers->write_property(zobj, name, value, (OP2_TYPE == IS_CONST) ? CACHE_ADDR(opline->extended_value) : NULL);
 
 	if (OP2_TYPE != IS_CONST) {