[turbofan] Enable typed lowering of string addition.

test/unittests/compiler/simplified-operator-unittest.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/opcodes.h"
 #include "src/compiler/operator.h"
 #include "src/compiler/operator-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/types-inl.h"
 #include "test/unittests/test-utils.h"
@@ skipping 36 matching lines @@
     PURE(NumberSubtract, Operator::kNoProperties, 2),
     PURE(NumberMultiply, Operator::kCommutative, 2),
     PURE(NumberDivide, Operator::kNoProperties, 2),
     PURE(NumberModulus, Operator::kNoProperties, 2),
     PURE(NumberToInt32, Operator::kNoProperties, 1),
     PURE(NumberToUint32, Operator::kNoProperties, 1),
     PURE(PlainPrimitiveToNumber, Operator::kNoProperties, 1),
     PURE(StringEqual, Operator::kCommutative, 2),
     PURE(StringLessThan, Operator::kNoProperties, 2),
     PURE(StringLessThanOrEqual, Operator::kNoProperties, 2),
-    PURE(StringAdd, Operator::kNoProperties, 2),
     PURE(ChangeTaggedToInt32, Operator::kNoProperties, 1),
     PURE(ChangeTaggedToUint32, Operator::kNoProperties, 1),
     PURE(ChangeTaggedToFloat64, Operator::kNoProperties, 1),
     PURE(ChangeInt32ToTagged, Operator::kNoProperties, 1),
     PURE(ChangeUint32ToTagged, Operator::kNoProperties, 1),
     PURE(ChangeFloat64ToTagged, Operator::kNoProperties, 1),
     PURE(ChangeBoolToBit, Operator::kNoProperties, 1),
     PURE(ChangeBitToBool, Operator::kNoProperties, 1),
     PURE(ObjectIsSmi, Operator::kNoProperties, 1),
     PURE(ObjectIsNonNegativeSmi, Operator::kNoProperties, 1)
@@ skipping 211 matching lines @@
 }
 
 
 INSTANTIATE_TEST_CASE_P(SimplifiedOperatorTest,
                         SimplifiedElementAccessOperatorTest,
                         ::testing::ValuesIn(kElementAccesses));
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8