[turbofan] Boost performance of Array.prototype.shift by 4x.

src/crankshaft/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/crankshaft/hydrogen.h"
 
 #include <memory>
 #include <sstream>
 
 #include "src/allocation-site-scopes.h"
@@ skipping 8563 matching lines @@
       // If there currently can be no elements accessors on the prototype chain,
       // it doesn't mean that there won't be any later. Install a full prototype
       // chain check to trap element accessors being installed on the prototype
       // chain, which would cause elements to go to dictionary mode and result
       // in a map change.
       BuildCheckPrototypeMaps(
           handle(JSObject::cast(receiver_map->prototype()), isolate()),
           Handle<JSObject>::null(), true);
 
       // Threshold for fast inlined Array.shift().
-      HConstant* inline_threshold = Add<HConstant>(static_cast<int32_t>(16));
+      HConstant* inline_threshold = Add<HConstant>(JSArray::kMaxCopyElements);
 
       Drop(args_count_no_receiver);
       HValue* result;
       HValue* receiver = Pop();
       HValue* checked_object = AddCheckMap(receiver, receiver_map);
       HValue* length = Add<HLoadNamedField>(
           receiver, checked_object, HObjectAccess::ForArrayLength(kind));
 
       Drop(1);  // Function.
       {
@@ skipping 3926 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8