[turbofan] Desugar lookup slot optimization in graph builder.

src/compiler/ast-graph-builder.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_AST_GRAPH_BUILDER_H_
 #define V8_COMPILER_AST_GRAPH_BUILDER_H_
 
 #include "src/ast.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/liveness-analyzer.h"
@@ skipping 345 matching lines @@
 
   // ===========================================================================
   // The following build methods have the same contract as the above ones, but
   // they can also return {NULL} to indicate that no fragment was built. Note
   // that these are optimizations, disabling any of them should still produce
   // correct graphs.
 
   // Optimization for variable load from global object.
   Node* TryLoadGlobalConstant(Handle<Name> name);
 
+  // Optimization for variable load of dynamic lookup slot that is most likely
+  // to resolve to a global slot or context slot (inferred from scope chain).
+  Node* TryLoadDynamicVariable(Variable* variable, Handle<String> name,
+                               BailoutId bailout_id,
+                               FrameStateBeforeAndAfter& states,
+                               const VectorSlotPair& feedback,
+                               OutputFrameStateCombine combine,
+                               TypeofMode typeof_mode);
+
   // Optimizations for automatic type conversion.
   Node* TryFastToBoolean(Node* input);
   Node* TryFastToName(Node* input);
 
   // ===========================================================================
   // The following visitation methods all recursively visit a subtree of the
   // underlying AST and extent the graph. The operand stack is mutated in a way
   // consistent with other compilers:
   //  - Expressions pop operands and push result, depending on {AstContext}.
   //  - Statements keep the operand stack balanced.
@@ skipping 190 matching lines @@
 
   // Prepare environment to be used as loop header.
   void PrepareForLoop(BitVector* assigned, bool is_osr = false);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_AST_GRAPH_BUILDER_H_