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//===--- LivePhysRegs.cpp - Live Physical Register Set --------------------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file implements the LivePhysRegs utility for tracking liveness of
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// physical registers across machine instructions in forward or backward order.
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// A more detailed description can be found in the corresponding header file.
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/LivePhysRegs.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineInstrBundle.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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/// \brief Remove all registers from the set that get clobbered by the register
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/// The clobbers set will be the list of live registers clobbered
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void LivePhysRegs::removeRegsInMask(const MachineOperand &MO,
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SmallVectorImpl<std::pair<unsigned, const MachineOperand*>> *Clobbers) {
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SparseSet<unsigned>::iterator LRI = LiveRegs.begin();
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while (LRI != LiveRegs.end()) {
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if (MO.clobbersPhysReg(*LRI)) {
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Clobbers->push_back(std::make_pair(*LRI, &MO));
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LRI = LiveRegs.erase(LRI);
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/// Simulates liveness when stepping backwards over an instruction(bundle):
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/// Remove Defs, add uses. This is the recommended way of calculating liveness.
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void LivePhysRegs::stepBackward(const MachineInstr &MI) {
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// Remove defined registers and regmask kills from the set.
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for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
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unsigned Reg = O->getReg();
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} else if (O->isRegMask())
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removeRegsInMask(*O, nullptr);
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// Add uses to the set.
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for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
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if (!O->isReg() || !O->readsReg() || O->isUndef())
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unsigned Reg = O->getReg();
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/// Simulates liveness when stepping forward over an instruction(bundle): Remove
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/// killed-uses, add defs. This is the not recommended way, because it depends
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/// on accurate kill flags. If possible use stepBackwards() instead of this
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void LivePhysRegs::stepForward(const MachineInstr &MI,
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SmallVectorImpl<std::pair<unsigned, const MachineOperand*>> &Clobbers) {
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// Remove killed registers from the set.
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for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
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unsigned Reg = O->getReg();
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// Note, dead defs are still recorded. The caller should decide how to
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Clobbers.push_back(std::make_pair(Reg, &*O));
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} else if (O->isRegMask())
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removeRegsInMask(*O, &Clobbers);
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// Add defs to the set.
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for (auto Reg : Clobbers) {
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// Skip dead defs. They shouldn't be added to the set.
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if (Reg.second->isReg() && Reg.second->isDead())
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/// Prin the currently live registers to OS.
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void LivePhysRegs::print(raw_ostream &OS) const {
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OS << "Live Registers:";
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OS << " (uninitialized)\n";
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for (const_iterator I = begin(), E = end(); I != E; ++I)
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OS << " " << PrintReg(*I, TRI);
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/// Dumps the currently live registers to the debug output.
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void LivePhysRegs::dump() const {
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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dbgs() << " " << *this;
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/// Add live-in registers of basic block \p MBB to \p LiveRegs.
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static void addLiveIns(LivePhysRegs &LiveRegs, const MachineBasicBlock &MBB) {
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for (unsigned Reg : make_range(MBB.livein_begin(), MBB.livein_end()))
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LiveRegs.addReg(Reg);
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/// Add pristine registers to the given \p LiveRegs. This function removes
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/// actually saved callee save registers when \p InPrologueEpilogue is false.
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static void addPristines(LivePhysRegs &LiveRegs, const MachineFunction &MF,
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const TargetRegisterInfo &TRI) {
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const MachineFrameInfo &MFI = *MF.getFrameInfo();
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if (!MFI.isCalleeSavedInfoValid())
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for (const MCPhysReg *CSR = TRI.getCalleeSavedRegs(&MF); CSR && *CSR; ++CSR)
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LiveRegs.addReg(*CSR);
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for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
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LiveRegs.removeReg(Info.getReg());
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void LivePhysRegs::addLiveOuts(const MachineBasicBlock *MBB,
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const MachineFunction &MF = *MBB->getParent();
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addPristines(*this, MF, *TRI);
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for (const MachineBasicBlock *Succ : MBB->successors())
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::addLiveIns(*this, *Succ);
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void LivePhysRegs::addLiveIns(const MachineBasicBlock *MBB,
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const MachineFunction &MF = *MBB->getParent();
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addPristines(*this, MF, *TRI);
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::addLiveIns(*this, *MBB);