Optimize loads from root-array in X64.

src/x64/macro-assembler-x64.h

 // Copyright 2011 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 34 matching lines @@
 };
 
 // Default scratch register used by MacroAssembler (and other code that needs
 // a spare register). The register isn't callee save, and not used by the
 // function calling convention.
 static const Register kScratchRegister = { 10 };      // r10.
 static const Register kSmiConstantRegister = { 15 };  // r15 (callee save).
 static const Register kRootRegister = { 13 };         // r13 (callee save).
 // Value of smi in kSmiConstantRegister.
 static const int kSmiConstantRegisterValue = 1;
+// Actual value of root register is offset from the root array's start
+// to take advantage of negitive 8-bit displacement values.
+static const int kRootRegisterBias = 128;
 
 // Convenience for platform-independent signatures.
 typedef Operand MemOperand;
 
 // Forward declaration.
 class JumpTarget;
 class PostCallGenerator;
 
 struct SmiIndex {
   SmiIndex(Register index_register, ScaleFactor scale)
       : reg(index_register),
         scale(scale) {}
   Register reg;
   ScaleFactor scale;
 };
 
 // MacroAssembler implements a collection of frequently used macros.
 class MacroAssembler: public Assembler {
  public:
   MacroAssembler(void* buffer, int size);
 
   void LoadRoot(Register destination, Heap::RootListIndex index);
+  // Load a root value where the index (or part of it) is variable.
+  // The variable_offset register is added to the fixed_offset value
+  // to get the index into the root-array.
+  void LoadRootIndexed(Register destination,
+                       Register variable_offset,
+                       int fixed_offset);
   void CompareRoot(Register with, Heap::RootListIndex index);
   void CompareRoot(const Operand& with, Heap::RootListIndex index);
   void PushRoot(Heap::RootListIndex index);
   void StoreRoot(Register source, Heap::RootListIndex index);
 
   // ---------------------------------------------------------------------------
   // GC Support
 
   // For page containing |object| mark region covering |addr| dirty.
   // RecordWriteHelper only works if the object is not in new
@@ skipping 82 matching lines @@
   void LeaveApiExitFrame();
 
   // Push and pop the registers that can hold pointers.
   void PushSafepointRegisters() { Pushad(); }
   void PopSafepointRegisters() { Popad(); }
   // Store the value in register src in the safepoint register stack
   // slot for register dst.
   void StoreToSafepointRegisterSlot(Register dst, Register src);
   void LoadFromSafepointRegisterSlot(Register dst, Register src);
 
+  void InitializeRootRegister() {
+    ExternalReference roots_address = ExternalReference::roots_address();
+    movq(kRootRegister, roots_address);
+    addq(kRootRegister, Immediate(kRootRegisterBias));
+  }
+
   // ---------------------------------------------------------------------------
   // JavaScript invokes
 
   // Invoke the JavaScript function code by either calling or jumping.
   void InvokeCode(Register code,
                   const ParameterCount& expected,
                   const ParameterCount& actual,
                   InvokeFlag flag,
                   PostCallGenerator* post_call_generator = NULL);
 
@@ skipping 1654 matching lines @@
       Jump(adaptor, RelocInfo::CODE_TARGET);
     }
     bind(&invoke);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_