[turbofan] Refactor the OSR environment merging to create an explicit environment.

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/ast.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/liveness-analyzer.h"
@@ skipping 561 matching lines @@
 
   // Copies this environment at a control-flow split point.
   Environment* CopyForConditional();
 
   // Copies this environment to a potentially unreachable control-flow point.
   Environment* CopyAsUnreachable();
 
   // Copies this environment at a loop header control-flow point.
   Environment* CopyForLoop(BitVector* assigned, bool is_osr = false);
 
+  // Copies this environment for Osr entry. This only produces environment
+  // of the right shape, the caller is responsible for filling in the right
+  // values and dependencies.
+  Environment* CopyForOsrEntry();
+
  private:
   AstGraphBuilder* builder_;
   int parameters_count_;
   int locals_count_;
   LivenessAnalyzerBlock* liveness_block_;
   NodeVector values_;
   NodeVector contexts_;
   Node* control_dependency_;
   Node* effect_dependency_;
   Node* parameters_node_;
   Node* locals_node_;
   Node* stack_node_;
 
   explicit Environment(Environment* copy,
                        LivenessAnalyzerBlock* liveness_block);
   Environment* CopyAndShareLiveness();
   void UpdateStateValues(Node** state_values, int offset, int count);
   void UpdateStateValuesWithCache(Node** state_values, int offset, int count);
   Zone* zone() const { return builder_->local_zone(); }
   Graph* graph() const { return builder_->graph(); }
   AstGraphBuilder* builder() const { return builder_; }
   CommonOperatorBuilder* common() { return builder_->common(); }
   NodeVector* values() { return &values_; }
   NodeVector* contexts() { return &contexts_; }
   LivenessAnalyzerBlock* liveness_block() { return liveness_block_; }
   bool IsLivenessAnalysisEnabled();
   bool IsLivenessBlockConsistent();
 
   // Prepare environment to be used as loop header.
-  void PrepareForLoop(BitVector* assigned, bool is_osr = false);
+  void PrepareForLoop(BitVector* assigned);
+  void PrepareForOsrEntry();
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_AST_GRAPH_BUILDER_H_