From: ishell <ishell@chromium.org>
Date: Tue, 3 Feb 2015 10:28:18 +0000 (-0800)
Subject: Avoid issuing write barriers for unboxed double fields in Heap::CopyJSObject().
X-Git-Tag: upstream/4.7.83~4646
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=ba8409d2f66ee56fd18198019591f49c9c675244;p=platform%2Fupstream%2Fv8.git

Avoid issuing write barriers for unboxed double fields in Heap::CopyJSObject().

Review URL: https://codereview.chromium.org/880043003

Cr-Commit-Position: refs/heads/master@{#26394}
---

diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 52bd70a..d5417ac 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -3906,9 +3906,33 @@ AllocationResult Heap::CopyJSObject(JSObject* source, AllocationSite* site) {
     }
     Address clone_address = clone->address();
     CopyBlock(clone_address, source->address(), object_size);
-    // Update write barrier for all fields that lie beyond the header.
-    RecordWrites(clone_address, JSObject::kHeaderSize,
-                 (object_size - JSObject::kHeaderSize) / kPointerSize);
+
+    // Update write barrier for all tagged fields that lie beyond the header.
+    const int start_offset = JSObject::kHeaderSize;
+    const int end_offset = object_size;
+
+#if V8_DOUBLE_FIELDS_UNBOXING
+    LayoutDescriptorHelper helper(map);
+    bool has_only_tagged_fields = helper.all_fields_tagged();
+
+    if (!has_only_tagged_fields) {
+      for (int offset = start_offset; offset < end_offset;) {
+        int end_of_region_offset;
+        if (helper.IsTagged(offset, end_offset, &end_of_region_offset)) {
+          RecordWrites(clone_address, offset,
+                       (end_of_region_offset - offset) / kPointerSize);
+        }
+        offset = end_of_region_offset;
+      }
+    } else {
+#endif
+      // Object has only tagged fields.
+      RecordWrites(clone_address, start_offset,
+                   (end_offset - start_offset) / kPointerSize);
+#if V8_DOUBLE_FIELDS_UNBOXING
+    }
+#endif
+
   } else {
     wb_mode = SKIP_WRITE_BARRIER;
 
diff --git a/test/cctest/test-unboxed-doubles.cc b/test/cctest/test-unboxed-doubles.cc
index ca78455..a783ce6 100644
--- a/test/cctest/test-unboxed-doubles.cc
+++ b/test/cctest/test-unboxed-doubles.cc
@@ -1223,4 +1223,89 @@ TEST(StoreBufferScanOnScavenge) {
   CHECK_EQ(boom_value, GetDoubleFieldValue(*obj, field_index));
 }
 
+
+static int LenFromSize(int size) {
+  return (size - FixedArray::kHeaderSize) / kPointerSize;
+}
+
+
+TEST(WriteBarriersInCopyJSObject) {
+  FLAG_max_semi_space_size = 1;  // Ensure new space is not growing.
+  CcTest::InitializeVM();
+  Isolate* isolate = CcTest::i_isolate();
+  TestHeap* heap = CcTest::test_heap();
+
+  v8::HandleScope scope(CcTest::isolate());
+
+  // The plan: create JSObject which contains unboxed double value that looks
+  // like a reference to an object in new space.
+  // Then clone this object (forcing it to go into old space) and check
+  // that the value of the unboxed double property of the cloned object has
+  // was not corrupted by GC.
+
+  // Step 1: prepare a map for the object. We add unboxed double property to it.
+  // Create a map with single inobject property.
+  Handle<Map> my_map = Map::Create(isolate, 1);
+  Handle<String> name = isolate->factory()->InternalizeUtf8String("foo");
+  my_map = Map::CopyWithField(my_map, name, HeapType::Any(isolate), NONE,
+                              Representation::Double(),
+                              INSERT_TRANSITION).ToHandleChecked();
+  my_map->set_pre_allocated_property_fields(1);
+  int n_properties = my_map->InitialPropertiesLength();
+  CHECK_GE(n_properties, 0);
+
+  int object_size = my_map->instance_size();
+
+  // Step 2: allocate a lot of objects so to almost fill new space: we need
+  // just enough room to allocate JSObject and thus fill the newspace.
+
+  int allocation_amount =
+      Min(FixedArray::kMaxSize, Page::kMaxRegularHeapObjectSize + kPointerSize);
+  int allocation_len = LenFromSize(allocation_amount);
+  NewSpace* new_space = heap->new_space();
+  Address* top_addr = new_space->allocation_top_address();
+  Address* limit_addr = new_space->allocation_limit_address();
+  while ((*limit_addr - *top_addr) > allocation_amount) {
+    CHECK(!heap->always_allocate());
+    Object* array = heap->AllocateFixedArray(allocation_len).ToObjectChecked();
+    CHECK(new_space->Contains(array));
+  }
+
+  // Step 3: now allocate fixed array and JSObject to fill the whole new space.
+  int to_fill = static_cast<int>(*limit_addr - *top_addr - object_size);
+  int fixed_array_len = LenFromSize(to_fill);
+  CHECK(fixed_array_len < FixedArray::kMaxLength);
+
+  CHECK(!heap->always_allocate());
+  Object* array = heap->AllocateFixedArray(fixed_array_len).ToObjectChecked();
+  CHECK(new_space->Contains(array));
+
+  Object* object = heap->AllocateJSObjectFromMap(*my_map).ToObjectChecked();
+  CHECK(new_space->Contains(object));
+  JSObject* jsobject = JSObject::cast(object);
+  CHECK_EQ(0, FixedArray::cast(jsobject->elements())->length());
+  CHECK_EQ(0, jsobject->properties()->length());
+
+  // Construct a double value that looks like a pointer to the new space object
+  // and store it into the obj.
+  Address fake_object = reinterpret_cast<Address>(array) + kPointerSize;
+  double boom_value = bit_cast<double>(fake_object);
+  FieldIndex index = FieldIndex::ForDescriptor(*my_map, 0);
+  jsobject->RawFastDoublePropertyAtPut(index, boom_value);
+
+  CHECK_EQ(0, static_cast<int>(*limit_addr - *top_addr));
+
+  // Step 4: clone jsobject, but force always allocate first to create a clone
+  // in old pointer space.
+  AlwaysAllocateScope aa_scope(isolate);
+  Object* clone_obj = heap->CopyJSObject(jsobject).ToObjectChecked();
+  Handle<JSObject> clone(JSObject::cast(clone_obj));
+  CHECK(heap->old_pointer_space()->Contains(clone->address()));
+
+  CcTest::heap()->CollectGarbage(NEW_SPACE, "boom");
+
+  // The value in cloned object should not be corrupted by GC.
+  CHECK_EQ(boom_value, clone->RawFastDoublePropertyAt(index));
+}
+
 #endif