HSubAllocatedObject instruction allows hydrogen code to carve up

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 009df374d36ad079d5ffebda0979aba3de7a7c97..11cb3684368d589846d5dbaae2d59ff854f94f99 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -292,6 +292,13 @@ void LTypeofIsAndBranch::PrintDataTo(StringStream* stream) {
 }
 
 
+void LSubAllocatedObject::PrintDataTo(StringStream* stream) {
+  stream->Add(" = ");
+  base_object()->PrintTo(stream);
+  stream->Add("+%d", offset());
+}
+
+
 void LCallConstantFunction::PrintDataTo(StringStream* stream) {
   stream->Add("#%d / ", arity());
 }
@@ -1024,6 +1031,16 @@ LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoSubAllocatedObject(
+    HSubAllocatedObject* sub_object) {
+  bool zero_offset = sub_object->offset() == 0;
+  LOperand* base_object = UseRegister(sub_object->base_object());
+  LSubAllocatedObject* result =
+      new(zone()) LSubAllocatedObject(base_object);
+  return zero_offset ? DefineSameAsFirst(result) : DefineAsRegister(result);
+}
+
+
 LInstruction* LChunkBuilder::DoThisFunction(HThisFunction* instr) {
   return instr->HasNoUses()
       ? NULL