[turbofan] Introduce explicit loop exits markers.

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 522 matching lines @@
     DCHECK(depth >= 0 && depth <= stack_height());
     values()->erase(values()->end() - depth, values()->end());
   }
 
   // Preserve a checkpoint of the environment for the IR graph. Any
   // further mutation of the environment will not affect checkpoints.
   Node* Checkpoint(BailoutId ast_id, OutputFrameStateCombine combine =
                                          OutputFrameStateCombine::Ignore(),
                    bool node_has_exception = false);
 
+  // Inserts a loop exit control node and renames the environment.
+  // This is useful for loop peeling to insert phis at loop exits.
+  void PrepareForLoopExit(Node* loop, BitVector* assigned_variables);
+
   // Control dependency tracked by this environment.
   Node* GetControlDependency() { return control_dependency_; }
   void UpdateControlDependency(Node* dependency) {
     control_dependency_ = dependency;
   }
 
   // Effect dependency tracked by this environment.
   Node* GetEffectDependency() { return effect_dependency_; }
   void UpdateEffectDependency(Node* dependency) {
     effect_dependency_ = dependency;
@@ skipping 50 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_