1//===--- LivePhysRegs.cpp - Live Physical Register Set --------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the LivePhysRegs utility for tracking liveness of
11// physical registers across machine instructions in forward or backward order.
12// A more detailed description can be found in the corresponding header file.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/CodeGen/LivePhysRegs.h"
17#include "llvm/CodeGen/MachineFrameInfo.h"
18#include "llvm/CodeGen/MachineFunction.h"
19#include "llvm/CodeGen/MachineInstrBundle.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/raw_ostream.h"
22using namespace llvm;
23
24
25/// \brief Remove all registers from the set that get clobbered by the register
26/// mask.
27/// The clobbers set will be the list of live registers clobbered
28/// by the regmask.
29void LivePhysRegs::removeRegsInMask(const MachineOperand &MO,
30        SmallVectorImpl<std::pair<unsigned, const MachineOperand*>> *Clobbers) {
31  SparseSet<unsigned>::iterator LRI = LiveRegs.begin();
32  while (LRI != LiveRegs.end()) {
33    if (MO.clobbersPhysReg(*LRI)) {
34      if (Clobbers)
35        Clobbers->push_back(std::make_pair(*LRI, &MO));
36      LRI = LiveRegs.erase(LRI);
37    } else
38      ++LRI;
39  }
40}
41
42/// Simulates liveness when stepping backwards over an instruction(bundle):
43/// Remove Defs, add uses. This is the recommended way of calculating liveness.
44void LivePhysRegs::stepBackward(const MachineInstr &MI) {
45  // Remove defined registers and regmask kills from the set.
46  for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
47    if (O->isReg()) {
48      if (!O->isDef())
49        continue;
50      unsigned Reg = O->getReg();
51      if (Reg == 0)
52        continue;
53      removeReg(Reg);
54    } else if (O->isRegMask())
55      removeRegsInMask(*O, nullptr);
56  }
57
58  // Add uses to the set.
59  for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
60    if (!O->isReg() || !O->readsReg() || O->isUndef())
61      continue;
62    unsigned Reg = O->getReg();
63    if (Reg == 0)
64      continue;
65    addReg(Reg);
66  }
67}
68
69/// Simulates liveness when stepping forward over an instruction(bundle): Remove
70/// killed-uses, add defs. This is the not recommended way, because it depends
71/// on accurate kill flags. If possible use stepBackward() instead of this
72/// function.
73void LivePhysRegs::stepForward(const MachineInstr &MI,
74        SmallVectorImpl<std::pair<unsigned, const MachineOperand*>> &Clobbers) {
75  // Remove killed registers from the set.
76  for (ConstMIBundleOperands O(&MI); O.isValid(); ++O) {
77    if (O->isReg()) {
78      unsigned Reg = O->getReg();
79      if (Reg == 0)
80        continue;
81      if (O->isDef()) {
82        // Note, dead defs are still recorded.  The caller should decide how to
83        // handle them.
84        Clobbers.push_back(std::make_pair(Reg, &*O));
85      } else {
86        if (!O->isKill())
87          continue;
88        assert(O->isUse());
89        removeReg(Reg);
90      }
91    } else if (O->isRegMask())
92      removeRegsInMask(*O, &Clobbers);
93  }
94
95  // Add defs to the set.
96  for (auto Reg : Clobbers) {
97    // Skip dead defs.  They shouldn't be added to the set.
98    if (Reg.second->isReg() && Reg.second->isDead())
99      continue;
100    addReg(Reg.first);
101  }
102}
103
104/// Prin the currently live registers to OS.
105void LivePhysRegs::print(raw_ostream &OS) const {
106  OS << "Live Registers:";
107  if (!TRI) {
108    OS << " (uninitialized)\n";
109    return;
110  }
111
112  if (empty()) {
113    OS << " (empty)\n";
114    return;
115  }
116
117  for (const_iterator I = begin(), E = end(); I != E; ++I)
118    OS << " " << PrintReg(*I, TRI);
119  OS << "\n";
120}
121
122/// Dumps the currently live registers to the debug output.
123void LivePhysRegs::dump() const {
124#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
125  dbgs() << "  " << *this;
126#endif
127}
128
129/// Add live-in registers of basic block \p MBB to \p LiveRegs.
130static void addLiveIns(LivePhysRegs &LiveRegs, const MachineBasicBlock &MBB) {
131  for (const auto &LI : MBB.liveins())
132    LiveRegs.addReg(LI.PhysReg);
133}
134
135/// Add pristine registers to the given \p LiveRegs. This function removes
136/// actually saved callee save registers when \p InPrologueEpilogue is false.
137static void addPristines(LivePhysRegs &LiveRegs, const MachineFunction &MF,
138                         const TargetRegisterInfo &TRI) {
139  const MachineFrameInfo &MFI = *MF.getFrameInfo();
140  if (!MFI.isCalleeSavedInfoValid())
141    return;
142
143  for (const MCPhysReg *CSR = TRI.getCalleeSavedRegs(&MF); CSR && *CSR; ++CSR)
144    LiveRegs.addReg(*CSR);
145  for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
146    LiveRegs.removeReg(Info.getReg());
147}
148
149void LivePhysRegs::addLiveOuts(const MachineBasicBlock *MBB,
150                               bool AddPristinesAndCSRs) {
151  if (AddPristinesAndCSRs) {
152    const MachineFunction &MF = *MBB->getParent();
153    addPristines(*this, MF, *TRI);
154    if (!MBB->isReturnBlock()) {
155      // The return block has no successors whose live-ins we could merge
156      // below. So instead we add the callee saved registers manually.
157      for (const MCPhysReg *I = TRI->getCalleeSavedRegs(&MF); *I; ++I)
158        addReg(*I);
159    }
160  }
161
162  // To get the live-outs we simply merge the live-ins of all successors.
163  for (const MachineBasicBlock *Succ : MBB->successors())
164    ::addLiveIns(*this, *Succ);
165}
166
167void LivePhysRegs::addLiveIns(const MachineBasicBlock *MBB,
168                              bool AddPristines) {
169  if (AddPristines) {
170    const MachineFunction &MF = *MBB->getParent();
171    addPristines(*this, MF, *TRI);
172  }
173  ::addLiveIns(*this, *MBB);
174}
175