[turbofan] Implement jump threading after register allocation.

src/compiler/instruction.cc

 // 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.
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 
 namespace v8 {
@@ skipping 102 matching lines @@
 
 
 bool ParallelMove::IsRedundant() const {
   for (int i = 0; i < move_operands_.length(); ++i) {
     if (!move_operands_[i].IsRedundant()) return false;
   }
   return true;
 }
 
 
+bool GapInstruction::IsRedundant() const {
+  for (int i = GapInstruction::FIRST_INNER_POSITION;
+       i <= GapInstruction::LAST_INNER_POSITION; i++) {
+    if (parallel_moves_[i] != NULL && !parallel_moves_[i]->IsRedundant())
+      return false;
+  }
+  return true;
+}
+
+
 std::ostream& operator<<(std::ostream& os,
                          const PrintableParallelMove& printable) {
   const ParallelMove& pm = *printable.parallel_move_;
   bool first = true;
   for (ZoneList<MoveOperands>::iterator move = pm.move_operands()->begin();
        move != pm.move_operands()->end(); ++move) {
     if (move->IsEliminated()) continue;
     if (!first) os << " ";
     first = false;
     PrintableMoveOperands pmo = {printable.register_configuration_, move};
@@ skipping 539 matching lines @@
       os << " B" << succ_block->id();
     }
     os << "\n";
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8