[turbofan] Use the typer to statically detect Smis.

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 39 matching lines @@
   // 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* SmiTag(Node* node);
   Node* IsTagged(Node* node);
   Node* Untag(Node* node);
   Node* OffsetMinusTagConstant(int32_t offset);
-  WriteBarrierKind ComputeWriteBarrierKind(BaseTaggedness base_is_tagged,
-                                           MachineType representation,
-                                           Node* value);
   Node* ComputeIndex(const ElementAccess& access, Node* const key);
   Node* StringComparison(Node* node, bool requires_ordering);
   Node* Int32Div(Node* const node);
   Node* Int32Mod(Node* const node);
   Node* Uint32Div(Node* const node);
   Node* Uint32Mod(Node* const node);
 
   friend class RepresentationSelector;
 
   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_