Only swap undefined for the global object if necessary in the prologue

src/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/hydrogen.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 3478 matching lines @@
       next_block_id_(0),
       entry_block_(NULL),
       blocks_(8, info->zone()),
       values_(16, info->zone()),
       phi_list_(NULL),
       uint32_instructions_(NULL),
       osr_(NULL),
       info_(info),
       zone_(info->zone()),
       is_recursive_(false),
-      this_has_uses_(false),
       use_optimistic_licm_(false),
       depends_on_empty_array_proto_elements_(false),
       type_change_checksum_(0),
       maximum_environment_size_(0),
       no_side_effects_scope_count_(0),
       disallow_adding_new_values_(false) {
   if (info->IsStub()) {
     CallInterfaceDescriptor descriptor =
         info->code_stub()->GetCallInterfaceDescriptor();
     start_environment_ = new (zone_)
@@ skipping 1885 matching lines @@
   while (length-- > 0) {
     context = Add<HLoadNamedField>(
         context, nullptr,
         HObjectAccess::ForContextSlot(Context::PREVIOUS_INDEX));
   }
   return context;
 }
 
 
 void HOptimizedGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
-  if (expr->is_this()) {
-    graph()->MarkThisHasUses();
-  }
-
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   Variable* variable = expr->var();
   switch (variable->location()) {
     case Variable::UNALLOCATED: {
       if (IsLexicalVariableMode(variable->mode())) {
         // TODO(rossberg): should this be an DCHECK?
         return Bailout(kReferenceToGlobalLexicalVariable);
       }
@@ skipping 7715 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal