X64: Added unimplemented method in codegen-x64.cc.

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 719bdf4d58ad0bf821a9e1b1bd7db9cb63e31414..d143558bc4bc3d6f441cb865773acb609ea0f72c 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -3816,8 +3816,28 @@ Operand CodeGenerator::SlotOperand(Slot* slot, Register tmp) {
 Operand CodeGenerator::ContextSlotOperandCheckExtensions(Slot* slot,
                                                          Result tmp,
                                                          JumpTarget* slow) {
-  UNIMPLEMENTED();
-  return Operand(rsp, 0);
+  ASSERT(slot->type() == Slot::CONTEXT);
+  ASSERT(tmp.is_register());
+  Register context = rsi;
+
+  for (Scope* s = scope(); s != slot->var()->scope(); s = s->outer_scope()) {
+    if (s->num_heap_slots() > 0) {
+      if (s->calls_eval()) {
+        // Check that extension is NULL.
+        __ cmpq(ContextOperand(context, Context::EXTENSION_INDEX),
+                Immediate(0));
+        slow->Branch(not_equal, not_taken);
+      }
+      __ movq(tmp.reg(), ContextOperand(context, Context::CLOSURE_INDEX));
+      __ movq(tmp.reg(), FieldOperand(tmp.reg(), JSFunction::kContextOffset));
+      context = tmp.reg();
+    }
+  }
+  // Check that last extension is NULL.
+  __ cmpq(ContextOperand(context, Context::EXTENSION_INDEX), Immediate(0));
+  slow->Branch(not_equal, not_taken);
+  __ movq(tmp.reg(), ContextOperand(context, Context::FCONTEXT_INDEX));
+  return ContextOperand(tmp.reg(), slot->index());
 }