Age code to allow reclaiming old unexecuted functions

src/objects-visiting-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 207 matching lines @@
           Serializer::enabled() || target->ic_age() != heap->global_ic_age())) {
     IC::Clear(rinfo->pc());
     target = Code::GetCodeFromTargetAddress(rinfo->target_address());
   }
   heap->mark_compact_collector()->RecordRelocSlot(rinfo, target);
   StaticVisitor::MarkObject(heap, target);
 }
 
 
 template<typename StaticVisitor>
+void StaticMarkingVisitor<StaticVisitor>::VisitCodeAgeSequence(
+    Heap* heap, RelocInfo* rinfo) {
+  ASSERT(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
+  Code* target = rinfo->code_age_stub();
+  ASSERT(target != NULL);
+  heap->mark_compact_collector()->RecordRelocSlot(rinfo, target);
+  StaticVisitor::MarkObject(heap, target);
+}
+
+
+template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitNativeContext(
     Map* map, HeapObject* object) {
   FixedBodyVisitor<StaticVisitor,
                    Context::MarkCompactBodyDescriptor,
                    void>::Visit(map, object);
 
   MarkCompactCollector* collector = map->GetHeap()->mark_compact_collector();
   for (int idx = Context::FIRST_WEAK_SLOT;
        idx < Context::NATIVE_CONTEXT_SLOTS;
        ++idx) {
@@ skipping 32 matching lines @@
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitCode(
     Map* map, HeapObject* object) {
   Heap* heap = map->GetHeap();
   Code* code = Code::cast(object);
   if (FLAG_cleanup_code_caches_at_gc) {
     code->ClearTypeFeedbackCells(heap);
   }
   code->CodeIterateBody<StaticVisitor>(heap);
+  if (FLAG_age_code && !Serializer::enabled()) {

[Michael Starzinger, 2012/11/02 15:29:34]

Technically it shouldn't make any difference in this case, but I would sleep
better if we could do the mutation before we scan the code body. Can we move
this block to before we call CodeIterateBody() here?

[danno, 2012/11/09 13:05:30]

Done.

+    code->MakeOlder(heap->mark_compact_collector()->marking_parity());
+  }
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitSharedFunctionInfo(
     Map* map, HeapObject* object) {
   Heap* heap = map->GetHeap();
   SharedFunctionInfo* shared = SharedFunctionInfo::cast(object);
   if (shared->ic_age() != heap->global_ic_age()) {
     shared->ResetForNewContext(heap->global_ic_age());
@@ skipping 152 matching lines @@
 
 template<typename StaticVisitor>
 bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
     Heap* heap, JSFunction* function) {
   SharedFunctionInfo* shared_info = function->unchecked_shared();
 
   // Code is either on stack, in compilation cache or referenced
   // by optimized version of function.
   MarkBit code_mark = Marking::MarkBitFrom(function->code());
   if (code_mark.Get()) {
-    if (!Marking::MarkBitFrom(shared_info).Get()) {
-      shared_info->set_code_age(0);
+    if (!FLAG_age_code) {
+      if (!Marking::MarkBitFrom(shared_info).Get()) {
+        shared_info->set_code_age(0);
+      }
     }
     return false;
   }
 
   // The function must have a valid context and not be a builtin.
   if (!IsValidNonBuiltinContext(function->unchecked_context())) {
     return false;
   }
 
-  // We do not flush code for optimized functions.
-  if (function->code() != shared_info->code()) {
-    return false;
+  if (FLAG_age_code) {
+    return function->code()->IsOld() && IsFlushable(heap, shared_info);

[Michael Starzinger, 2012/11/02 15:29:34]

We cannot yet flush optimized code because they are not recorded as candidates.
I will be working on that next. For now we need to leave in the original check
in place.

Also, can we do the age-check as a separate step behind the FLAG_age_code flag
and in the end always call through to IsFlushable() for the shared function? I
think that's easier to read.

// Check age of optimized code.
if (FLAG_age_code && !function->code()->IsOld()) {
  return false;
}

return IsFlushable(heap, shared_info);

[danno, 2012/11/09 13:05:30]

Done.

+  } else {
+    // We do not flush code for optimized functions.
+    if (function->code() != shared_info->code()) {
+      return false;
+    }
+
+    return IsFlushable(heap, shared_info);
   }
-
-  return IsFlushable(heap, shared_info);
 }
 
 
 template<typename StaticVisitor>
 bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
     Heap* heap, SharedFunctionInfo* shared_info) {
   // Code is either on stack, in compilation cache or referenced
   // by optimized version of function.
   MarkBit code_mark = Marking::MarkBitFrom(shared_info->code());
   if (code_mark.Get()) {
@@ skipping 20 matching lines @@
   // Function must be lazy compilable.
   if (!shared_info->allows_lazy_compilation()) {
     return false;
   }
 
   // If this is a full script wrapped in a function we do no flush the code.
   if (shared_info->is_toplevel()) {
     return false;
   }
 
-  // TODO(mstarzinger): The following will soon be replaced by a new way of
-  // aging code, that is based on an aging stub in the function prologue.
+  if (FLAG_age_code) {
+    return shared_info->code()->IsOld();
+  } else {
+    // How many collections newly compiled code object will survive before being
+    // flushed.
+    static const int kCodeAgeThreshold = 5;
 
-  // How many collections newly compiled code object will survive before being
-  // flushed.
-  static const int kCodeAgeThreshold = 5;
-
-  // Age this shared function info.
-  if (shared_info->code_age() < kCodeAgeThreshold) {
-    shared_info->set_code_age(shared_info->code_age() + 1);
-    return false;
+    // Age this shared function info.
+    if (shared_info->code_age() < kCodeAgeThreshold) {
+      shared_info->set_code_age(shared_info->code_age() + 1);
+      return false;
+    }
+    return true;
   }
-
-  return true;
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitSharedFunctionInfoStrongCode(
     Heap* heap, HeapObject* object) {
   StaticVisitor::BeforeVisitingSharedFunctionInfo(object);
   Object** start_slot =
       HeapObject::RawField(object,
                            SharedFunctionInfo::BodyDescriptor::kStartOffset);
@@ skipping 121 matching lines @@
   RelocIterator it(this, mode_mask);
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_INL_H_