llvm/llvm/include/llvm/CodeGen/LivePhysRegs.h

//===- llvm/CodeGen/LivePhysRegs.h - Live Physical Register 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
/// This file implements the LivePhysRegs utility for tracking liveness of
/// physical registers. This can be used for ad-hoc liveness tracking after
/// register allocation. You can start with the live-ins/live-outs at the
/// beginning/end of a block and update the information while walking the
/// instructions inside the block. This implementation tracks the liveness on a
/// sub-register granularity.
///
/// We assume that the high bits of a physical super-register are not preserved
/// unless the instruction has an implicit-use operand reading the super-
/// register.
///
/// X86 Example:
/// %ymm0 = ...
/// %xmm0 = ... (Kills %xmm0, all %xmm0s sub-registers, and %ymm0)
///
/// %ymm0 = ...
/// %xmm0 = ..., implicit %ymm0 (%ymm0 and all its sub-registers are alive)
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_LIVEPHYSREGS_H
#define LLVM_CODEGEN_LIVEPHYSREGS_H

#include "llvm/ADT/SparseSet.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/MCRegister.h"
#include "llvm/MC/MCRegisterInfo.h"
#include <cassert>
#include <utility>

namespace llvm {

template <typename T> class ArrayRef;

class MachineInstr;
class MachineFunction;
class MachineOperand;
class MachineRegisterInfo;
class raw_ostream;

/// A set of physical registers with utility functions to track liveness
/// when walking backward/forward through a basic block.
class LivePhysRegs { … };

inline raw_ostream &operator<<(raw_ostream &OS, const LivePhysRegs& LR) { … }

/// Computes registers live-in to \p MBB assuming all of its successors
/// live-in lists are up-to-date. Puts the result into the given LivePhysReg
/// instance \p LiveRegs.
void computeLiveIns(LivePhysRegs &LiveRegs, const MachineBasicBlock &MBB);

/// Recomputes dead and kill flags in \p MBB.
void recomputeLivenessFlags(MachineBasicBlock &MBB);

/// Adds registers contained in \p LiveRegs to the block live-in list of \p MBB.
/// Does not add reserved registers.
void addLiveIns(MachineBasicBlock &MBB, const LivePhysRegs &LiveRegs);

/// Convenience function combining computeLiveIns() and addLiveIns().
void computeAndAddLiveIns(LivePhysRegs &LiveRegs,
                          MachineBasicBlock &MBB);

/// Convenience function for recomputing live-in's for a MBB. Returns true if
/// any changes were made.
static inline bool recomputeLiveIns(MachineBasicBlock &MBB) { … }

/// Convenience function for recomputing live-in's for a set of MBBs until the
/// computation converges.
inline void fullyRecomputeLiveIns(ArrayRef<MachineBasicBlock *> MBBs) { … }


} // end namespace llvm

#endif // LLVM_CODEGEN_LIVEPHYSREGS_H