Dynamically determine optimal instance size....

src/handles.cc

Index: src/handles.cc
===================================================================
--- src/handles.cc	(revision 5500)
+++ src/handles.cc	(working copy)
@@ -142,6 +142,12 @@
 
 
 void SetExpectedNofProperties(Handle<JSFunction> func, int nof) {
+  // If objects constructed from this function exist then changing
+  // 'estimated_nof_properties' is dangerous (even to the same value)
+  // since the inobject slack tracking logic might already have adjusted the
+  // previous value and compiled it into the fast construct stub.
+  if (func->shared()->live_objects_may_exist()) return;
+
   func->shared()->set_expected_nof_properties(nof);
   if (func->has_initial_map()) {
     Handle<Map> new_initial_map =
@@ -158,16 +164,25 @@
 
 
 static int ExpectedNofPropertiesFromEstimate(int estimate) {
-  // TODO(1231235): We need dynamic feedback to estimate the number
-  // of expected properties in an object. The static hack below
-  // is barely a solution.
-  if (estimate == 0) return 4;
-  return estimate + 2;
+  // If no properties are added in the constructor, they are more likely
+  // to be added later.
+  if (estimate == 0) estimate = 2;
+
+  // We do not shrink objects that go into a snapshot (yet), so we adjust
+  // the estimate conservatively.
+  if (Serializer::enabled()) return estimate + 2;
+
+  // Inobject slack tracking will reclaim redundant inobject space later,
+  // so we can afford to adjust the estimate generously.
+  return estimate + 6;
 }
 
 
 void SetExpectedNofPropertiesFromEstimate(Handle<SharedFunctionInfo> shared,
                                           int estimate) {
+  // See the comment in SetExpectedNofProperties.
+  if (shared->live_objects_may_exist()) return;
+
   shared->set_expected_nof_properties(
       ExpectedNofPropertiesFromEstimate(estimate));
 }