[turbofan] Use special constant type for RPO block number operands.

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 314 matching lines @@
       return os << constant.ToInt64() << "l";
     case Constant::kFloat32:
       return os << constant.ToFloat32() << "f";
     case Constant::kFloat64:
       return os << constant.ToFloat64();
     case Constant::kExternalReference:
       return os << static_cast<const void*>(
                        constant.ToExternalReference().address());
     case Constant::kHeapObject:
       return os << Brief(*constant.ToHeapObject());
+    case Constant::kRpoNumber:
+      return os << "RPO" << constant.ToRpoNumber().ToInt();
   }
   UNREACHABLE();
   return os;
 }
 
 
 InstructionBlock::InstructionBlock(Zone* zone, BasicBlock::Id id,
                                    BasicBlock::RpoNumber ao_number,
                                    BasicBlock::RpoNumber rpo_number,
                                    BasicBlock::RpoNumber loop_header,
@@ skipping 325 matching lines @@
       os << " B" << succ_block->id();
     }
     os << "\n";
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8