Age code to allow reclaiming old unexecuted functions

src/objects.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 176 matching lines @@
 };
 
 
 // Indicates whether we are only interested in the descriptors of a particular
 // map, or in all descriptors in the descriptor array.
 enum DescriptorFlag {
   ALL_DESCRIPTORS,
   OWN_DESCRIPTORS
 };
 
+// The GC maintains a bit of information, the MarkingParity, which toggles
+// from odd to even and back every time marking is completed. Incremental
+// marking can visit an object twice during a marking phase, so algorithms that
+// that piggy-back on marking can use the parity to ensure that they only
+// perform an operation on an object once per marking phase: they record the
+// MarkingParity when they visit an object, and only re-visit the object when it
+// is marked again and the MarkingParity changes.
+enum MarkingParity {
+  NO_MARKING_PARITY,
+  ODD_MARKING_PARITY,
+  EVEN_MARKING_PARITY
+};
 
 // Instance size sentinel for objects of variable size.
 const int kVariableSizeSentinel = 0;
 
 const int kStubMajorKeyBits = 6;
 const int kStubMinorKeyBits = kBitsPerInt - kSmiTagSize - kStubMajorKeyBits;
 
 // All Maps have a field instance_type containing a InstanceType.
 // It describes the type of the instances.
 //
@@ skipping 4308 matching lines @@
   inline void CodePrint() {
     CodePrint(stdout);
   }
   void CodePrint(FILE* out);
 #endif
   DECLARE_VERIFIER(Code)
 
   void ClearInlineCaches();
   void ClearTypeFeedbackCells(Heap* heap);
 
+#define DECLARE_CODE_AGE_ENUM(X) k##X##CodeAge,
+  enum Age {
+    kNoAge = 0,
+    CODE_AGE_LIST(DECLARE_CODE_AGE_ENUM)
+    kAfterLastCodeAge,
+    kLastCodeAge = kAfterLastCodeAge - 1,
+    kCodeAgeCount = kAfterLastCodeAge - 1
+  };
+#undef DECLARE_CODE_AGE_ENUM
+
+  // Code aging
+  static void MakeCodeAgeSequenceYoung(byte* sequence);
+  void MakeYoung();
+  void MakeOlder(MarkingParity);
+  static bool IsYoungSequence(byte* sequence);
+  bool IsOld();
+
   // Max loop nesting marker used to postpose OSR. We don't take loop
   // nesting that is deeper than 5 levels into account.
   static const int kMaxLoopNestingMarker = 6;
 
   // Layout description.
   static const int kInstructionSizeOffset = HeapObject::kHeaderSize;
   static const int kRelocationInfoOffset = kInstructionSizeOffset + kIntSize;
   static const int kHandlerTableOffset = kRelocationInfoOffset + kPointerSize;
   static const int kDeoptimizationDataOffset =
       kHandlerTableOffset + kPointerSize;
@@ skipping 108 matching lines @@
 
   // Signed field cannot be encoded using the BitField class.
   static const int kArgumentsCountShift = 14;
   static const int kArgumentsCountMask = ~((1 << kArgumentsCountShift) - 1);
 
   // This constant should be encodable in an ARM instruction.
   static const int kFlagsNotUsedInLookup =
       TypeField::kMask | CacheHolderField::kMask;
 
  private:
+  friend class RelocIterator;
+
+  // Code aging
+  byte* FindCodeAgeSequence();
+  static void  GetCodeAgeAndParity(Code* code, Age* age,
+                                   MarkingParity* parity);
+  static void GetCodeAgeAndParity(byte* sequence, Age* age,
+                                  MarkingParity* parity);
+  static Code* GetCodeAgeStub(Age age, MarkingParity parity);
+
+  // Code aging -- platform-specific
+  byte* FindPlatformCodeAgeSequence();
+  static void PatchPlatformCodeAge(byte* sequence, Age age,
+                                   MarkingParity parity);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Code);
 };
 
 
 // All heap objects have a Map that describes their structure.
 //  A Map contains information about:
 //  - Size information about the object
 //  - How to iterate over an object (for garbage collection)
 class Map: public HeapObject {
  public:
@@ skipping 4227 matching lines @@
 
   // Visits the resource of an ASCII or two-byte string.
   virtual void VisitExternalAsciiString(
       v8::String::ExternalAsciiStringResource** resource) {}
   virtual void VisitExternalTwoByteString(
       v8::String::ExternalStringResource** resource) {}
 
   // Visits a debug call target in the instruction stream.
   virtual void VisitDebugTarget(RelocInfo* rinfo);
 
+  // Visits the byte sequence in a function's prologue that contains information
+  // about the code's age.
+  virtual void VisitCodeAgeSequence(RelocInfo* rinfo);
+
   // Handy shorthand for visiting a single pointer.
   virtual void VisitPointer(Object** p) { VisitPointers(p, p + 1); }
 
   // Visit pointer embedded into a code object.
   virtual void VisitEmbeddedPointer(RelocInfo* rinfo);
 
   // Visits a contiguous arrays of external references (references to the C++
   // heap) in the half-open range [start, end). Any or all of the values
   // may be modified on return.
   virtual void VisitExternalReferences(Address* start, Address* end) {}
@@ skipping 45 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_