Do not store fp and sp values in TickSample

src/sampler.h

 // Copyright 2013 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 26 matching lines @@
 
 class Isolate;
 
 // ----------------------------------------------------------------------------
 // Sampler
 //
 // A sampler periodically samples the state of the VM and optionally
 // (if used for profiling) the program counter and stack pointer for
 // the thread that created it.
 
+struct RegisterState {
+  RegisterState() : pc(NULL), sp(NULL), fp(NULL) {}
+  Address pc;      // Instruction pointer.
+  Address sp;      // Stack pointer.
+  Address fp;      // Frame pointer.
+};
+
 // TickSample captures the information collected for each sample.
 struct TickSample {
   TickSample()
       : state(OTHER),
         pc(NULL),
-        sp(NULL),
-        fp(NULL),
         external_callback(NULL),
         frames_count(0),
         has_external_callback(false),
         top_frame_type(StackFrame::NONE) {}
-  void Trace(Isolate* isolate);
+  void Init(Isolate* isolate, const RegisterState& state);
   StateTag state;  // The state of the VM.
   Address pc;      // Instruction pointer.
-  Address sp;      // Stack pointer.
-  Address fp;      // Frame pointer.
   union {
     Address tos;   // Top stack value (*sp).
     Address external_callback;
   };
   static const int kMaxFramesCount = 64;
   Address stack[kMaxFramesCount];  // Call stack.
   int frames_count : 8;  // Number of captured frames.
   bool has_external_callback : 1;
   StackFrame::Type top_frame_type : 4;
 };
 
 class Sampler {
  public:
   // Initializes the Sampler support. Called once at VM startup.
   static void SetUp();
   static void TearDown();
 
   // Initialize sampler.
   Sampler(Isolate* isolate, int interval);
   virtual ~Sampler();
 
   Isolate* isolate() const { return isolate_; }
   int interval() const { return interval_; }
 
   // Performs stack sampling.
-  void SampleStack(TickSample* sample);
-
-  // This method is called for each sampling period with the current
-  // program counter.
-  virtual void Tick(TickSample* sample) = 0;
+  void SampleStack(const RegisterState& regs);
 
   // Start and stop sampler.
   void Start();
   void Stop();
 
   // Is the sampler used for profiling?
   bool IsProfiling() const { return NoBarrier_Load(&profiling_) > 0; }
   void IncreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, 1); }
   void DecreaseProfilingDepth() { NoBarrier_AtomicIncrement(&profiling_, -1); }
 
   // Whether the sampler is running (that is, consumes resources).
   bool IsActive() const { return NoBarrier_Load(&active_); }
 
   // Used in tests to make sure that stack sampling is performed.
   int samples_taken() const { return samples_taken_; }
   void ResetSamplesTaken() { samples_taken_ = 0; }
 
   class PlatformData;
   PlatformData* platform_data() const { return data_; }
 
+ protected:
+  // This method is called for each sampling period with the current
+  // program counter.
+  virtual void Tick(TickSample* sample) = 0;
+
  private:
   void SetActive(bool value) { NoBarrier_Store(&active_, value); }
 
   Isolate* isolate_;
   const int interval_;
   Atomic32 profiling_;
   Atomic32 active_;
   PlatformData* data_;  // Platform specific data.
   int samples_taken_;  // Counts stack samples taken.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SAMPLER_H_