Age code to allow reclaiming old unexecuted functions

src/objects-visiting-inl.h

Index: src/objects-visiting-inl.h
diff --git a/src/objects-visiting-inl.h b/src/objects-visiting-inl.h
index d698a8df06f95a548b8da3b246f78a62cd3ddc01..1594377f4203a762736d6c8c1c087e068dedd2b8 100644
--- a/src/objects-visiting-inl.h
+++ b/src/objects-visiting-inl.h
@@ -225,6 +225,17 @@ void StaticMarkingVisitor<StaticVisitor>::VisitCodeTarget(
 
 
 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,
@@ -277,6 +288,9 @@ void StaticMarkingVisitor<StaticVisitor>::VisitCode(
     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());
+  }
 }
 
 
@@ -449,8 +463,10 @@ bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
   // 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;
   }
@@ -460,12 +476,16 @@ bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
     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);
+  }
 }
 
 
@@ -506,20 +526,20 @@ bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
     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.
-
-  // 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;
+  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;
+
+    // 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;
 }