X64: Optimize access to external references.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 9653e1c94e82da41cafe2ccb6a6af5737bfc7b91..eb1f42d244b35deec43fa8225e2beb9ec4a84150 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -76,7 +76,49 @@ class MacroAssembler: public Assembler {
  public:
   MacroAssembler(void* buffer, int size);
 
+  // Prevent the use of the RootArray during the lifetime of this
+  // scope object.
+  class NoRootArrayScope BASE_EMBEDDED {
+   public:
+    explicit NoRootArrayScope(MacroAssembler* assembler)
+        : variable_(&assembler->root_array_available_),
+          old_value_(assembler->root_array_available_) {
+      assembler->root_array_available_ = false;
+    }
+    ~NoRootArrayScope() {
+      *variable_ = old_value_;
+    }
+   private:
+    bool* variable_;
+    bool old_value_;
+  };
+
+  // Operand pointing to an external reference.
+  // May emit code to set up the scratch register. The operand is
+  // only guaranteed to be correct as long as the scratch register
+  // isn't changed.
+  // If the operand is used more than once, use a scratch register
+  // that is guaranteed not to be clobbered.
+  Operand ExternalOperand(ExternalReference reference,
+                          Register scratch = kScratchRegister);
+  // Loads and stores the value of an external reference.
+  // Special case code for load and store to take advantage of
+  // load_rax/store_rax if possible/necessary.
+  // For other operations, just use:
+  //   Operand operand = ExternalOperand(extref);
+  //   operation(operand, ..);
+  void Load(Register destination, ExternalReference source);
+  void Store(ExternalReference destination, Register source);
+  // Loads the address of the external reference into the destination
+  // register.
+  void LoadAddress(Register destination, ExternalReference source);
+  // Returns the size of the code generated by LoadAddress.
+  // Used by CallSize(ExternalReference) to find the size of a call.
+  int LoadAddressSize(ExternalReference source);
+
+  // Operations on roots in the root-array.
   void LoadRoot(Register destination, Heap::RootListIndex index);
+  void StoreRoot(Register source, 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.
@@ -86,7 +128,6 @@ class MacroAssembler: public Assembler {
   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
@@ -634,9 +675,7 @@ class MacroAssembler: public Assembler {
   int CallSize(Address destination, RelocInfo::Mode rmode) {
     return kCallInstructionLength;
   }
-  int CallSize(ExternalReference ext) {
-    return kCallInstructionLength;
-  }
+  int CallSize(ExternalReference ext);
   int CallSize(Handle<Code> code_object) {
     // Code calls use 32-bit relative addressing.
     return kShortCallInstructionLength;
@@ -1024,6 +1063,7 @@ class MacroAssembler: public Assembler {
 
   bool generating_stub_;
   bool allow_stub_calls_;
+  bool root_array_available_;
 
   // Returns a register holding the smi value. The register MUST NOT be
   // modified. It may be the "smi 1 constant" register.