In the toplevel code generator, suppor local context allocation...

src/x64/fast-codegen-x64.cc

 // Copyright 2009 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 49 matching lines @@
   __ push(rsi);  // Callee's context.
   __ push(rdi);  // Callee's JS Function.
 
   { Comment cmnt(masm_, "[ Allocate locals");
     int locals_count = fun->scope()->num_stack_slots();
     for (int i = 0; i < locals_count; i++) {
       __ PushRoot(Heap::kUndefinedValueRootIndex);
     }
   }
 
+  // Possibly allocate a local context.
+  if (fun->scope()->num_heap_slots() > 0) {
+    Comment cmnt(masm_, "[ Allocate local context");
+    // Argument to NewContext is the function, still in rdi.
+    __ push(rdi);
+    __ CallRuntime(Runtime::kNewContext, 1);
+    // Context is returned in both rax and rsi.  It replaces the context
+    // passed to us.  It's saved in the stack and kept live in rsi.
+    __ movq(Operand(rbp, StandardFrameConstants::kContextOffset), rsi);
+#ifdef DEBUG
+    // Assert we do not have to copy any parameters into the context.
+    for (int i = 0, len = fun->scope()->num_parameters(); i < len; i++) {
+      Slot* slot = fun->scope()->parameter(i)->slot();
+      ASSERT(slot != NULL && slot->type() != Slot::CONTEXT);
+    }
+#endif
+  }
+
   { Comment cmnt(masm_, "[ Stack check");
     Label ok;
     __ CompareRoot(rsp, Heap::kStackLimitRootIndex);
     __ j(above_equal, &ok);
     StackCheckStub stub;
     __ CallStub(&stub);
     __ bind(&ok);
   }
 
   { Comment cmnt(masm_, "[ Declarations");
@@ skipping 1201 matching lines @@
   true_label_ = saved_true;
   false_label_ = saved_false;
   // Convert current context to test context: End post-test code.
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal