[turbofan] Avoid some unnecessary write barriers.

src/compiler/js-global-object-specialization.cc

 // Copyright 2015 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/compiler/js-global-object-specialization.h"
 
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/js-graph.h"
@@ skipping 177 matching lines @@
       NodeProperties::MergeControlToEnd(graph(), common(), deoptimize);
       control = graph()->NewNode(common()->IfTrue(), branch);
       break;
     }
     case PropertyCellType::kConstantType: {
       // Store to constant-type property cell requires deoptimization support,
       // because we might even need to eager deoptimize for mismatch.
       if (!(flags() & kDeoptimizationEnabled)) return NoChange();
       dependencies()->AssumePropertyCell(property_cell);
       Node* check = graph()->NewNode(simplified()->ObjectIsSmi(), value);
+      Type* property_cell_value_type = Type::TaggedSigned();
       if (property_cell_value->IsHeapObject()) {
+        // Deoptimize if the {value} is a Smi.
         Node* branch = graph()->NewNode(common()->Branch(BranchHint::kFalse),
                                         check, control);
         Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
         Node* deoptimize = graph()->NewNode(common()->Deoptimize(), frame_state,
                                             effect, if_true);
         // TODO(bmeurer): This should be on the AdvancedReducer somehow.
         NodeProperties::MergeControlToEnd(graph(), common(), deoptimize);
         control = graph()->NewNode(common()->IfFalse(), branch);
-        Node* value_map =
+
+        // Load the {value} map check against the {property_cell} map.
+        Node* value_map = effect =
             graph()->NewNode(simplified()->LoadField(AccessBuilder::ForMap()),
                              value, effect, control);
         Handle<Map> property_cell_value_map(
             Handle<HeapObject>::cast(property_cell_value)->map(), isolate());
         check = graph()->NewNode(
             simplified()->ReferenceEqual(Type::Any()), value_map,
             jsgraph()->HeapConstant(property_cell_value_map));
+        property_cell_value_type = Type::TaggedPointer();
       }
       Node* branch =
           graph()->NewNode(common()->Branch(BranchHint::kTrue), check, control);
       Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
       Node* deoptimize = graph()->NewNode(common()->Deoptimize(), frame_state,
                                           effect, if_false);
       // TODO(bmeurer): This should be on the AdvancedReducer somehow.
       NodeProperties::MergeControlToEnd(graph(), common(), deoptimize);
       control = graph()->NewNode(common()->IfTrue(), branch);
       effect = graph()->NewNode(
-          simplified()->StoreField(AccessBuilder::ForPropertyCellValue()),
+          simplified()->StoreField(
+              AccessBuilder::ForPropertyCellValue(property_cell_value_type)),
           jsgraph()->HeapConstant(property_cell), value, effect, control);
       break;
     }
     case PropertyCellType::kMutable: {
       // Store to non-configurable, data property on the global can be lowered
       // to a field store, even without deoptimization, because the property
       // cannot be deleted or reconfigured to an accessor/interceptor property.
       if (property_details.IsConfigurable()) {
         // With deoptimization support, we can lower stores even to configurable
         // data properties on the global object, by adding a code dependency on
@@ skipping 49 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSGlobalObjectSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8