[turbofan] Strip useless sign-extension for store8/store16.

src/compiler/machine-operator-reducer.h

 // 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.
 
 #ifndef V8_COMPILER_MACHINE_OPERATOR_REDUCER_H_
 #define V8_COMPILER_MACHINE_OPERATOR_REDUCER_H_
 
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/machine-operator.h"
 
@@ skipping 47 matching lines @@
     return Replace(Uint32Constant(value));
   }
   Reduction ReplaceInt64(int64_t value) {
     return Replace(Int64Constant(value));
   }
 
   Reduction ReduceInt32Div(Node* node);
   Reduction ReduceUint32Div(Node* node);
   Reduction ReduceInt32Mod(Node* node);
   Reduction ReduceUint32Mod(Node* node);
+  Reduction ReduceStore(Node* node);
   Reduction ReduceProjection(size_t index, Node* node);
 
   Graph* graph() const;
   JSGraph* jsgraph() const { return jsgraph_; }
   CommonOperatorBuilder* common() const;
   MachineOperatorBuilder* machine() const;
 
   JSGraph* jsgraph_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_REDUCER_H_