[compiler] Introduce code stubs for string relational comparisons.

src/compiler/simplified-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_SIMPLIFIED_LOWERING_H_
 #define V8_COMPILER_SIMPLIFIED_LOWERING_H_
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
@@ skipping 19 matching lines @@
   ~SimplifiedLowering() {}
 
   void LowerAllNodes();
 
   // TODO(turbofan): The representation can be removed once the result of the
   // representation analysis is stored in the node bounds.
   void DoLoadBuffer(Node* node, MachineRepresentation rep,
                     RepresentationChanger* changer);
   void DoStoreBuffer(Node* node);
   void DoShift(Node* node, Operator const* op, Type* rhs_type);
-  void DoStringLessThan(Node* node);
-  void DoStringLessThanOrEqual(Node* node);
 
   // TODO(bmeurer): This is a gigantic hack to support the gigantic LoadBuffer
   // typing hack to support the gigantic "asm.js should be fast without proper
   // verifier"-hack, ... Kill this! Soon! Really soon! I'm serious!
   bool abort_compilation_ = false;
 
  private:
   JSGraph* const jsgraph_;
   Zone* const zone_;
   TypeCache const& type_cache_;
 
   // TODO(danno): SimplifiedLowering shouldn't know anything about the source
   // positions table, but must for now since there currently is no other way to
   // pass down source position information to nodes created during
   // lowering. Once this phase becomes a vanilla reducer, it should get source
   // position information via the SourcePositionWrapper like all other reducers.
   SourcePositionTable* source_positions_;
 
-  Node* StringComparison(Node* node);
   Node* Int32Div(Node* const node);
   Node* Int32Mod(Node* const node);
   Node* Uint32Div(Node* const node);
   Node* Uint32Mod(Node* const node);
 
   friend class RepresentationSelector;
 
   Isolate* isolate() { return jsgraph_->isolate(); }
   Zone* zone() { return jsgraph_->zone(); }
   JSGraph* jsgraph() { return jsgraph_; }
   Graph* graph() { return jsgraph()->graph(); }
   CommonOperatorBuilder* common() { return jsgraph()->common(); }
   MachineOperatorBuilder* machine() { return jsgraph()->machine(); }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_LOWERING_H_