1 files changed, 66 insertions, 0 deletions
diff --git a/js/src/vm/ReceiverGuard.cpp b/js/src/vm/ReceiverGuard.cpp
new file mode 100644
index 000000000..97df908c3
--- /dev/null
+++ b/js/src/vm/ReceiverGuard.cpp
@@ -0,0 +1,66 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "vm/ReceiverGuard.h"
+
+#include "builtin/TypedObject.h"
+#include "vm/UnboxedObject.h"
+#include "jsobjinlines.h"
+
+using namespace js;
+
+ReceiverGuard::ReceiverGuard(JSObject* obj)
+  : group(nullptr), shape(nullptr)
+{
+    if (obj) {
+        if (obj->is<UnboxedPlainObject>()) {
+            group = obj->group();
+            if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
+                shape = expando->lastProperty();
+        } else if (obj->is<UnboxedArrayObject>() || obj->is<TypedObject>()) {
+            group = obj->group();
+        } else {
+            shape = obj->maybeShape();
+        }
+    }
+}
+
+ReceiverGuard::ReceiverGuard(ObjectGroup* group, Shape* shape)
+  : group(group), shape(shape)
+{
+    if (group) {
+        const Class* clasp = group->clasp();
+        if (clasp == &UnboxedPlainObject::class_) {
+            // Keep both group and shape.
+        } else if (clasp == &UnboxedArrayObject::class_ || IsTypedObjectClass(clasp)) {
+            this->shape = nullptr;
+        } else {
+            this->group = nullptr;
+        }
+    }
+}
+
+/* static */ int32_t
+HeapReceiverGuard::keyBits(JSObject* obj)
+{
+    if (obj->is<UnboxedPlainObject>()) {
+        // Both the group and shape need to be guarded for unboxed plain objects.
+        return obj->as<UnboxedPlainObject>().maybeExpando() ? 0 : 1;
+    }
+    if (obj->is<UnboxedArrayObject>() || obj->is<TypedObject>()) {
+        // Only the group needs to be guarded for unboxed arrays and typed objects.
+        return 2;
+    }
+    // Other objects only need the shape to be guarded.
+    return 3;
+}
+
+void
+HeapReceiverGuard::trace(JSTracer* trc)
+{
+    TraceNullableEdge(trc, &shape_, "receiver_guard_shape");
+    TraceNullableEdge(trc, &group_, "receiver_guard_group");
+}