Experimental: thread live register references to deferred code....

src/register-allocator-ia32.h

 // Copyright 2008 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 50 matching lines @@
 
   // Record that a register will no longer be used by decrementing its
   // reference count.
   void Unuse(Register reg) {
     ASSERT(is_used(reg.code()));
     if (is_used(reg.code())) {
       ref_counts_[reg.code()]--;
     }
   }
 
+  // Copy the reference counts from this register file to the other.
+  void CopyTo(RegisterFile* other);
+
+#ifdef DEBUG
+  // True if the reference counts all match the other register file.
+  bool Equals(RegisterFile* other);
+#endif
+
   static const int kNumRegisters = 8;
 
  private:
   int ref_counts_[kNumRegisters];
 };
 
 
 // -------------------------------------------------------------------------
 // Register allocator
 //
 
 class RegisterAllocator BASE_EMBEDDED {
  public:
-  RegisterAllocator(CodeGenerator* cgen) : code_generator_(cgen) {}
+  explicit RegisterAllocator(CodeGenerator* cgen) : code_generator_(cgen) {}
 
   int num_registers() const { return RegisterFile::kNumRegisters; }
 
   int count(int reg_code) { return registers_.count(reg_code); }
 
   // Explicitly record a reference to a register.
   void Use(Register reg) { registers_.Use(reg); }
 
   // Explicitly record that a register will no lonber be used.
   void Unuse(Register reg) { registers_.Unuse(reg); }
 
   // Initialize the register allocator for entry to a JS function.  On
   // entry, esp, ebp, esi, and edi are externally referenced (ie, outside
   // the virtual frame); and the other registers are free.
   void Initialize();
 
   // Allocate a free register if possible or fail by returning no_reg.
   Register Allocate();
 
   // Allocate a free register without spilling any or fail and return
   // no_reg.
   Register AllocateWithoutSpilling();
 
+  // Copy the internal state to a register file, to be restored later
+  // by RestoreFrom.
+  void SaveTo(RegisterFile* register_file) {
+    registers_.CopyTo(register_file);
+  }
+
+  void RestoreFrom(RegisterFile* register_file) {
+    register_file->CopyTo(&registers_);
+  }
+
+#ifdef DEBUG
+  // True if the reference counts of this allocator match those saved in the
+  // given register file.
+  bool Matches(RegisterFile* register_file) {
+    return registers_.Equals(register_file);
+  }
+#endif
+
  private:
   CodeGenerator* code_generator_;
   RegisterFile registers_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_REGISTER_ALLOCATOR_IA32_H_