LiveRegUnits.h

Go to the documentation of this file.

//===- llvm/CodeGen/LiveRegUnits.h - Register Unit Set ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file
/// A set of register units. It is intended for register liveness tracking.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_LIVEREGUNITS_H
#define LLVM_CODEGEN_LIVEREGUNITS_H
 
#include "llvm/ADT/BitVector.h"
#include "llvm/CodeGen/MachineInstrBundle.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCRegisterInfo.h"
#include <cstdint>
 
namespace llvm {
 
class MachineInstr;
class MachineBasicBlock;
 
/// A set of register units used to track register liveness.
class LiveRegUnits {
  const TargetRegisterInfo *TRI = nullptr;
  BitVector Units;
 
public:
  /// Constructs a new empty LiveRegUnits set.
  LiveRegUnits() = default;
 
  /// Constructs and initialize an empty LiveRegUnits set.
  LiveRegUnits(const TargetRegisterInfo &TRI) {
    init(TRI);
  }
 
  /// For a machine instruction \p MI, adds all register units used in
  /// \p UsedRegUnits and defined or clobbered in \p ModifiedRegUnits. This is
  /// useful when walking over a range of instructions to track registers
  /// used or defined separately.
  static void accumulateUsedDefed(const MachineInstr &MI,
                                  LiveRegUnits &ModifiedRegUnits,
                                  LiveRegUnits &UsedRegUnits,
                                  const TargetRegisterInfo *TRI) {
    for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
      if (O->isRegMask())
        ModifiedRegUnits.addRegsInMask(O->getRegMask());
      if (!O->isReg())
        continue;
      Register Reg = O->getReg();
      if (!Reg.isPhysical())
        continue;
      if (O->isDef()) {
        // Some architectures (e.g. AArch64 XZR/WZR) have registers that are
        // constant and may be used as destinations to indicate the generated
        // value is discarded. No need to track such case as a def.
        if (!TRI->isConstantPhysReg(Reg))
          ModifiedRegUnits.addReg(Reg);
      } else {
        assert(O->isUse() && "Reg operand not a def and not a use");
        UsedRegUnits.addReg(Reg);
      }
    }
  }
 
  /// Initialize and clear the set.
  void init(const TargetRegisterInfo &TRI) {
    this->TRI = &TRI;
    Units.reset();
    Units.resize(TRI.getNumRegUnits());
  }
 
  /// Clears the set.
  void clear() { Units.reset(); }
 
  /// Returns true if the set is empty.
  bool empty() const { return Units.none(); }
 
  /// Adds register units covered by physical register \p Reg.
  void addReg(MCPhysReg Reg) {
    for (MCRegUnit Unit : TRI->regunits(Reg))
      Units.set(Unit);
  }
 
  /// Adds register units covered by physical register \p Reg that are
  /// part of the lanemask \p Mask.
  void addRegMasked(MCPhysReg Reg, LaneBitmask Mask) {
    for (MCRegUnitMaskIterator Unit(Reg, TRI); Unit.isValid(); ++Unit) {
      LaneBitmask UnitMask = (*Unit).second;
      if ((UnitMask & Mask).any())
        Units.set((*Unit).first);
    }
  }
 
  /// Removes all register units covered by physical register \p Reg.
  void removeReg(MCPhysReg Reg) {
    for (MCRegUnit Unit : TRI->regunits(Reg))
      Units.reset(Unit);
  }
 
  /// Removes register units not preserved by the regmask \p RegMask.
  /// The regmask has the same format as the one in the RegMask machine operand.
  void removeRegsNotPreserved(const uint32_t *RegMask);
 
  /// Adds register units not preserved by the regmask \p RegMask.
  /// The regmask has the same format as the one in the RegMask machine operand.
  void addRegsInMask(const uint32_t *RegMask);
 
  /// Returns true if no part of physical register \p Reg is live.
  bool available(MCPhysReg Reg) const {
    for (MCRegUnit Unit : TRI->regunits(Reg)) {
      if (Units.test(Unit))
        return false;
    }
    return true;
  }
 
  /// Updates liveness when stepping backwards over the instruction \p MI.
  /// This removes all register units defined or clobbered in \p MI and then
  /// adds the units used (as in use operands) in \p MI.
  void stepBackward(const MachineInstr &MI);
 
  /// Adds all register units used, defined or clobbered in \p MI.
  /// This is useful when walking over a range of instruction to find registers
  /// unused over the whole range.
  void accumulate(const MachineInstr &MI);
 
  /// Adds registers living out of block \p MBB.
  /// Live out registers are the union of the live-in registers of the successor
  /// blocks and pristine registers. Live out registers of the end block are the
  /// callee saved registers.
  void addLiveOuts(const MachineBasicBlock &MBB);
 
  /// Adds registers living into block \p MBB.
  void addLiveIns(const MachineBasicBlock &MBB);
 
  /// Adds all register units marked in the bitvector \p RegUnits.
  void addUnits(const BitVector &RegUnits) {
    Units |= RegUnits;
  }
  /// Removes all register units marked in the bitvector \p RegUnits.
  void removeUnits(const BitVector &RegUnits) {
    Units.reset(RegUnits);
  }
  /// Return the internal bitvector representation of the set.
  const BitVector &getBitVector() const {
    return Units;
  }
 
private:
  /// Adds pristine registers. Pristine registers are callee saved registers
  /// that are unused in the function.
  void addPristines(const MachineFunction &MF);
};
 
/// Returns an iterator range over all physical register and mask operands for
/// \p MI and bundled instructions. This also skips any debug operands.
inline iterator_range<
    filter_iterator<ConstMIBundleOperands, bool (*)(const MachineOperand &)>>
phys_regs_and_masks(const MachineInstr &MI) {
  auto Pred = [](const MachineOperand &MOP) {
    return MOP.isRegMask() ||
           (MOP.isReg() && !MOP.isDebug() && MOP.getReg().isPhysical());
  };
  return make_filter_range(const_mi_bundle_ops(MI),
                           static_cast<bool (*)(const MachineOperand &)>(Pred));
}
 
} // end namespace llvm
 
#endif // LLVM_CODEGEN_LIVEREGUNITS_H