[turbofan] Implement jump threading after register allocation.

src/compiler/schedule.h

 // Copyright 2013 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_SCHEDULE_H_
 #define V8_COMPILER_SCHEDULE_H_
 
 #include <iosfwd>
 #include <vector>
 
@@ skipping 43 matching lines @@
   class RpoNumber FINAL {
    public:
     int ToInt() const {
       DCHECK(IsValid());
       return index_;
     }
     size_t ToSize() const {
       DCHECK(IsValid());
       return static_cast<size_t>(index_);
     }
-    bool IsValid() const { return index_ != kInvalidRpoNumber; }
+    bool IsValid() const { return index_ >= 0; }
     static RpoNumber FromInt(int index) { return RpoNumber(index); }
     static RpoNumber Invalid() { return RpoNumber(kInvalidRpoNumber); }
 
     bool IsNext(const RpoNumber other) const {
       DCHECK(IsValid());
       return other.index_ == this->index_ + 1;
     }
 
     bool operator==(RpoNumber other) const {
       return this->index_ == other.index_;
@@ skipping 208 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(Schedule);
 };
 
 std::ostream& operator<<(std::ostream& os, const Schedule& s);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SCHEDULE_H_