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

src/compiler/instruction-selector-impl.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_INSTRUCTION_SELECTOR_IMPL_H_
 #define V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_
 
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/instruction-selector.h"
@@ skipping 119 matching lines @@
     return ImmediateOperand::Create(index, zone());
   }
 
   InstructionOperand* TempLocation(LinkageLocation location, MachineType type) {
     UnallocatedOperand* op = ToUnallocatedOperand(location, type);
     op->set_virtual_register(sequence()->NextVirtualRegister());
     return op;
   }
 
   InstructionOperand* Label(BasicBlock* block) {
-    // TODO(bmeurer): We misuse ImmediateOperand here.
-    return TempImmediate(block->rpo_number());
+    int index = sequence()->AddImmediate(Constant(block->GetRpoNumber()));
+    return ImmediateOperand::Create(index, zone());
   }
 
  protected:
   InstructionSelector* selector() const { return selector_; }
   InstructionSequence* sequence() const { return selector()->sequence(); }
   Isolate* isolate() const { return zone()->isolate(); }
   Zone* zone() const { return selector()->instruction_zone(); }
 
  private:
   static Constant ToConstant(const Node* node) {
@@ skipping 207 matching lines @@
                : (frame_state_descriptor->GetTotalSize() +
                   1);  // Include deopt id.
   }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_