[turbofan] Introduce a dedicated StringCharAt operator.

src/compiler/simplified-operator.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_SIMPLIFIED_OPERATOR_H_
 #define V8_COMPILER_SIMPLIFIED_OPERATOR_H_
 
 #include <iosfwd>
 
 #include "src/base/compiler-specific.h"
@@ skipping 278 matching lines @@
 
   const Operator* SpeculativeNumberLessThan(NumberOperationHint hint);
   const Operator* SpeculativeNumberLessThanOrEqual(NumberOperationHint hint);
   const Operator* SpeculativeNumberEqual(NumberOperationHint hint);
 
   const Operator* ReferenceEqual();
 
   const Operator* StringEqual();
   const Operator* StringLessThan();
   const Operator* StringLessThanOrEqual();
+  const Operator* StringCharAt();
   const Operator* StringCharCodeAt();
   const Operator* StringFromCharCode();
   const Operator* StringFromCodePoint(UnicodeEncoding encoding);
 
   const Operator* PlainPrimitiveToNumber();
   const Operator* PlainPrimitiveToWord32();
   const Operator* PlainPrimitiveToFloat64();
 
   const Operator* ChangeTaggedSignedToInt32();
   const Operator* ChangeTaggedToInt32();
@@ skipping 96 matching lines @@
   Zone* const zone_;
 
   DISALLOW_COPY_AND_ASSIGN(SimplifiedOperatorBuilder);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_OPERATOR_H_