[turbofan] Introduce dedicated StringIndexOf operator.

src/compiler/simplified-lowering.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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 2222 matching lines @@
       case IrOpcode::kStringFromCharCode: {
         VisitUnop(node, UseInfo::TruncatingWord32(),
                   MachineRepresentation::kTaggedPointer);
         return;
       }
       case IrOpcode::kStringFromCodePoint: {
         VisitUnop(node, UseInfo::TruncatingWord32(),
                   MachineRepresentation::kTaggedPointer);
         return;
       }
+      case IrOpcode::kStringIndexOf: {
+        ProcessInput(node, 0, UseInfo::AnyTagged());
+        ProcessInput(node, 1, UseInfo::AnyTagged());
+        ProcessInput(node, 2, UseInfo::TaggedSigned());
+        SetOutput(node, MachineRepresentation::kTaggedSigned);
+        return;
+      }
 
       case IrOpcode::kCheckBounds: {
         Type* index_type = TypeOf(node->InputAt(0));
         Type* length_type = TypeOf(node->InputAt(1));
         if (index_type->Is(Type::Unsigned32())) {
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
           if (lower() && index_type->Max() < length_type->Min()) {
             // The bounds check is redundant if we already know that
             // the index is within the bounds of [0.0, length[.
@@ skipping 1254 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8