[turbofan] Introduce a dedicated StringCharAt operator.

src/compiler/simplified-operator.cc

 // Copyright 2012 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.h"
 
 #include "src/base/lazy-instance.h"
 #include "src/compiler/opcodes.h"
 #include "src/compiler/operator.h"
 #include "src/compiler/types.h"
@@ skipping 383 matching lines @@
   V(NumberSinh, Operator::kNoProperties, 1, 0)                   \
   V(NumberSqrt, Operator::kNoProperties, 1, 0)                   \
   V(NumberTan, Operator::kNoProperties, 1, 0)                    \
   V(NumberTanh, Operator::kNoProperties, 1, 0)                   \
   V(NumberTrunc, Operator::kNoProperties, 1, 0)                  \
   V(NumberToBoolean, Operator::kNoProperties, 1, 0)              \
   V(NumberToInt32, Operator::kNoProperties, 1, 0)                \
   V(NumberToUint32, Operator::kNoProperties, 1, 0)               \
   V(NumberToUint8Clamped, Operator::kNoProperties, 1, 0)         \
   V(NumberSilenceNaN, Operator::kNoProperties, 1, 0)             \
+  V(StringCharAt, Operator::kNoProperties, 2, 1)                 \
   V(StringCharCodeAt, Operator::kNoProperties, 2, 1)             \
   V(StringFromCharCode, Operator::kNoProperties, 1, 0)           \
   V(PlainPrimitiveToNumber, Operator::kNoProperties, 1, 0)       \
   V(PlainPrimitiveToWord32, Operator::kNoProperties, 1, 0)       \
   V(PlainPrimitiveToFloat64, Operator::kNoProperties, 1, 0)      \
   V(ChangeTaggedSignedToInt32, Operator::kNoProperties, 1, 0)    \
   V(ChangeTaggedToInt32, Operator::kNoProperties, 1, 0)          \
   V(ChangeTaggedToUint32, Operator::kNoProperties, 1, 0)         \
   V(ChangeTaggedToFloat64, Operator::kNoProperties, 1, 0)        \
   V(ChangeFloat64ToTagged, Operator::kNoProperties, 1, 0)        \
@@ skipping 432 matching lines @@
                         Operator::kNoDeopt | Operator::kNoThrow | properties,  \
                         #Name, value_input_count, 1, control_input_count,      \
                         output_count, 1, 0, access);                           \
   }
 ACCESS_OP_LIST(ACCESS)
 #undef ACCESS
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8