[turbofan] Add poor man's store elimination for storing to fields.

src/compiler/simplified-operator-reducer.cc

 // Copyright 2014 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/simplified-operator-reducer.h"
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/operator-properties.h"
@@ skipping 82 matching lines @@
                       m.node()->InputAt(0));
       }
       if (m.IsChangeUint32ToTagged()) return Replace(m.node()->InputAt(0));
       break;
     }
     case IrOpcode::kChangeUint32ToTagged: {
       Uint32Matcher m(node->InputAt(0));
       if (m.HasValue()) return ReplaceNumber(FastUI2D(m.Value()));
       break;
     }
+    case IrOpcode::kStoreField: {
+      // TODO(turbofan): Poor man's store elimination, remove this once we have
+      // a fully featured store elimination in place.
+      Node* const effect = node->InputAt(2);
+      if (effect->op()->Equals(node->op()) && effect->OwnedBy(node) &&
+          effect->InputAt(0) == node->InputAt(0)) {
+        // The {effect} is a store to the same field in the same object, and
+        // {node} is the only effect observer, so we can kill {effect} and
+        // instead make {node} depend on the incoming effect to {effect}.
+        node->ReplaceInput(2, effect->InputAt(2));
+        effect->Kill();
+        return Changed(node);
+      }
+      break;
+    }
     default:
       break;
   }
   return NoChange();
 }
 
 
 Reduction SimplifiedOperatorReducer::Change(Node* node, const Operator* op,
                                             Node* a) {
   DCHECK_EQ(node->InputCount(), OperatorProperties::GetTotalInputCount(op));
@@ skipping 32 matching lines @@
 }
 
 
 MachineOperatorBuilder* SimplifiedOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8