[turbofan] Eliminate redundant CheckString based on types.

src/compiler/js-typed-lowering.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_JS_TYPED_LOWERING_H_
 #define V8_COMPILER_JS_TYPED_LOWERING_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/opcodes.h"
@@ skipping 60 matching lines @@
   Reduction ReduceJSToObject(Node* node);
   Reduction ReduceJSConvertReceiver(Node* node);
   Reduction ReduceJSCallConstruct(Node* node);
   Reduction ReduceJSCallFunction(Node* node);
   Reduction ReduceJSForInDone(Node* node);
   Reduction ReduceJSForInNext(Node* node);
   Reduction ReduceJSForInStep(Node* node);
   Reduction ReduceJSGeneratorStore(Node* node);
   Reduction ReduceJSGeneratorRestoreContinuation(Node* node);
   Reduction ReduceJSGeneratorRestoreRegister(Node* node);
+  Reduction ReduceCheckString(Node* node);
   Reduction ReduceNumberRoundop(Node* node);
   Reduction ReduceSelect(Node* node);
   Reduction ReduceJSSubtract(Node* node);
   Reduction ReduceJSDivide(Node* node);
   Reduction ReduceInt32Binop(Node* node, const Operator* intOp);
   Reduction ReduceShiftLeft(Node* node);
   Reduction ReduceUI32Shift(Node* node, Signedness left_signedness,
                             const Operator* shift_op);
 
   Node* EmptyFrameState();
@@ skipping 19 matching lines @@
   TypeCache const& type_cache_;
 };
 
 DEFINE_OPERATORS_FOR_FLAGS(JSTypedLowering::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_TYPED_LOWERING_H_