Use linear backing store for hidden properties to save memory.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "execution.h"
 #include "factory.h"
 #include "macro-assembler.h"
 #include "global-handles.h"
@@ skipping 1948 matching lines @@
     }
     CHECK(t->IsSlicedString());
     CHECK(!HEAP->InNewSpace(*t));
     *slice.location() = *t.location();
   }
 
   CHECK(SlicedString::cast(*slice)->parent()->IsSeqAsciiString());
   HEAP->CollectAllGarbage(Heap::kNoGCFlags);
   CHECK(SlicedString::cast(*slice)->parent()->IsSeqAsciiString());
 }
+
+
+TEST(Regress2211) {
+  static const int kLoops = 16;
+  InitializeVM();
+  v8::HandleScope scope;
+  Handle<JSObject> object = v8::Utils::OpenHandle(*v8::Object::New());
+  Handle<String> key[kLoops];
+  Handle<String> val[kLoops];
+
+  // Test adding entries and backing store size.
+  for (int i = 0; i < kLoops; i++) {
+    ScopedVector<char> key_string(8);
+    ScopedVector<char> val_string(8);
+    OS::SNPrintF(key_string, "key #%d", i);
+    OS::SNPrintF(val_string, "val #%d", i);
+    key[i] = v8::Utils::OpenHandle(*v8::String::New(key_string.start()));
+    val[i] = v8::Utils::OpenHandle(*v8::String::New(val_string.start()));
+    JSObject::SetHiddenProperty(object, key[i], val[i]);
+    // Get size of backing store.
+    DescriptorArray* descriptors = object->map()->instance_descriptors();
+    HiddenPropertiesArray* hidden = HiddenPropertiesArray::cast(
+        object->FastPropertyAt(descriptors->GetFieldIndex(0)));
+    int size = hidden->SizeFor(hidden->length());
+    printf("%d: %d\n", i, size);
+    // Size is smaller than FixedArray header + twice the entries (key + value).
+    CHECK(size < FixedArray::kHeaderSize + 2 * (2 * (i + 1)) * kPointerSize);
+  }
+
+  // Test stored entries with new key strings.
+  for (int i = 0; i < kLoops; i++) {
+    ScopedVector<char> key_string(8);
+    OS::SNPrintF(key_string, "key #%d", i);
+    key[i] = v8::Utils::OpenHandle(*v8::String::New(key_string.start()));
+    CHECK(String::cast(object->GetHiddenProperty(*key[i]))->Equals(*val[i]));
+  }
+
+  // Test delete entry.
+  object->DeleteHiddenProperty(*key[3]);
+
+  for (int i = 0; i < kLoops; i++) {
+    if (i == 3) {
+      CHECK(object->GetHiddenProperty(*key[i])->IsUndefined());
+    } else {
+      CHECK(String::cast(object->GetHiddenProperty(*key[i]))->Equals(*val[i]));
+    }
+  }
+
+  // Test re-add entry.
+  key[3] = v8::Utils::OpenHandle(*v8::String::New("re-add key"));
+  val[3] = v8::Utils::OpenHandle(*v8::String::New("re-add val"));
+  JSObject::SetHiddenProperty(object, key[3], val[3]);
+
+  for (int i = 0; i < kLoops; i++) {
+    CHECK(String::cast(object->GetHiddenProperty(*key[i]))->Equals(*val[i]));
+  }
+}