New hydrogen instruction to reduce cost of growing an array on keyed stores.

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 80f9f0b49af0866250f99424541de692356ff2d7..1c4aa678ba3407fad6cbd86bce679e78907b15a0 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2375,6 +2375,21 @@ LInstruction* LChunkBuilder::DoTrapAllocationMemento(
 }
 
 
+LInstruction* LChunkBuilder::DoMaybeGrowElements(HMaybeGrowElements* instr) {
+  info()->MarkAsDeferredCalling();
+  LOperand* context = UseFixed(instr->context(), rsi);
+  LOperand* object = Use(instr->object());
+  LOperand* elements = UseAny(instr->elements());
+  LOperand* key = UseRegisterOrConstant(instr->key());
+  LOperand* current_capacity = UseRegisterOrConstant(instr->current_capacity());
+
+  LMaybeGrowElements* result = new (zone())
+      LMaybeGrowElements(context, object, elements, key, current_capacity);
+  DefineFixed(result, rax);
+  return AssignPointerMap(AssignEnvironment(result));
+}
+
+
 LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   bool is_in_object = instr->access().IsInobject();
   bool is_external_location = instr->access().IsExternalMemory() &&