[crankshaft] Remove the useless HMapEnumLength instruction.

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 <sstream>
 
 #include "src/allocation-site-scopes.h"
 #include "src/ast/ast-numbering.h"
@@ skipping 1257 matching lines @@
 
 HValue* HGraphBuilder::BuildGetElementsKind(HValue* object) {
   HValue* map = Add<HLoadNamedField>(object, nullptr, HObjectAccess::ForMap());
 
   HValue* bit_field2 =
       Add<HLoadNamedField>(map, nullptr, HObjectAccess::ForMapBitField2());
   return BuildDecodeField<Map::ElementsKindBits>(bit_field2);
 }
 
 
+HValue* HGraphBuilder::BuildEnumLength(HValue* map) {
+  NoObservableSideEffectsScope scope(this);
+  HValue* bit_field3 =
+      Add<HLoadNamedField>(map, nullptr, HObjectAccess::ForMapBitField3());
+  return BuildDecodeField<Map::EnumLengthBits>(bit_field3);
+}
+
+
 HValue* HGraphBuilder::BuildCheckHeapObject(HValue* obj) {
   if (obj->type().IsHeapObject()) return obj;
   return Add<HCheckHeapObject>(obj);
 }
 
 
 void HGraphBuilder::FinishExitWithHardDeoptimization(
     Deoptimizer::DeoptReason reason) {
   Add<HDeoptimize>(reason, Deoptimizer::EAGER);
   FinishExitCurrentBlock(New<HAbnormalExit>());
@@ skipping 4033 matching lines @@
   Add<HSimulate>(stmt->ToObjectId());
   if (fast) {
     map = Add<HForInPrepareMap>(enumerable);
     Push(map);
     Add<HSimulate>(stmt->EnumId());
     Drop(1);
     Add<HCheckMaps>(map, meta_map);
 
     array = Add<HForInCacheArray>(enumerable, map,
                                   DescriptorArray::kEnumCacheBridgeCacheIndex);
-    enum_length = Add<HMapEnumLength>(map);
+    enum_length = BuildEnumLength(map);
 
     HInstruction* index_cache = Add<HForInCacheArray>(
         enumerable, map, DescriptorArray::kEnumCacheBridgeIndicesCacheIndex);
     HForInCacheArray::cast(array)
         ->set_index_cache(HForInCacheArray::cast(index_cache));
   } else {
     Runtime::FunctionId function_id = Runtime::kGetPropertyNamesFast;
     Add<HPushArguments>(enumerable);
     array = Add<HCallRuntime>(Runtime::FunctionForId(function_id), 1);
     Push(array);
     Add<HSimulate>(stmt->EnumId());
     Drop(1);
     {
       NoObservableSideEffectsScope scope(this);
       IfBuilder if_fast(this);
       if_fast.If<HCompareMap>(array, meta_map);
       if_fast.Then();
       {
         HValue* cache_map = array;
         HForInCacheArray* cache = Add<HForInCacheArray>(
             enumerable, cache_map, DescriptorArray::kEnumCacheBridgeCacheIndex);
-        enum_length = Add<HMapEnumLength>(cache_map);
+        enum_length = BuildEnumLength(cache_map);
         Push(cache_map);
         Push(cache);
         Push(enum_length);
       }
       if_fast.Else();
       {
         Push(graph()->GetConstant1());
         Push(array);
         Push(AddLoadFixedArrayLength(array));
       }
@@ skipping 8244 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8