AllocationOrder.h

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//===-- llvm/CodeGen/AllocationOrder.h - Allocation Order -*- C++ -*-------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements an allocation order for virtual registers.
//
// The preferred allocation order for a virtual register depends on allocation
// hints and target hooks. The AllocationOrder class encapsulates all of that.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_ALLOCATIONORDER_H
#define LLVM_CODEGEN_ALLOCATIONORDER_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/MC/MCRegisterInfo.h"

namespace llvm {

class RegisterClassInfo;
class VirtRegMap;

class AllocationOrder {
  SmallVector<MCPhysReg, 16> Hints;
  ArrayRef<MCPhysReg> Order;
  int Pos;

public:
  /// Create a new AllocationOrder for VirtReg.
  /// @param VirtReg      Virtual register to allocate for.
  /// @param VRM          Virtual register map for function.
  /// @param RegClassInfo Information about reserved and allocatable registers.
  AllocationOrder(unsigned VirtReg,
                  const VirtRegMap &VRM,
                  const RegisterClassInfo &RegClassInfo);

  /// Get the allocation order without reordered hints.
  ArrayRef<MCPhysReg> getOrder() const { return Order; }

  /// Return the next physical register in the allocation order, or 0.
  /// It is safe to call next() again after it returned 0, it will keep
  /// returning 0 until rewind() is called.
  unsigned next() {
    if (Pos < 0)
      return Hints.end()[Pos++];
    while (Pos < int(Order.size())) {
      unsigned Reg = Order[Pos++];
      if (!isHint(Reg))
        return Reg;
    }
    return 0;
  }

  /// As next(), but allow duplicates to be returned, and stop before the
  /// Limit'th register in the RegisterClassInfo allocation order.
  ///
  /// This can produce more than Limit registers if there are hints.
  unsigned nextWithDups(unsigned Limit) {
    if (Pos < 0)
      return Hints.end()[Pos++];
    if (Pos < int(Limit))
      return Order[Pos++];
    return 0;
  }

  /// Start over from the beginning.
  void rewind() { Pos = -int(Hints.size()); }

  /// Return true if the last register returned from next() was a preferred register.
  bool isHint() const { return Pos <= 0; }

  /// Return true if PhysReg is a preferred register.
  bool isHint(unsigned PhysReg) const {
    return std::find(Hints.begin(), Hints.end(), PhysReg) != Hints.end();
  }
};

} // end namespace llvm

#endif