ProcessImplicitDefs.cpp revision e4454320b3cfffe926a487c33fbeb454366de2f8 
1//===---------------------- ProcessImplicitDefs.cpp -----------------------===//
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#define DEBUG_TYPE "processimplicitdefs"
11
12#include "llvm/CodeGen/ProcessImplicitDefs.h"
13
14#include "llvm/ADT/DepthFirstIterator.h"
15#include "llvm/ADT/SmallSet.h"
16#include "llvm/Analysis/AliasAnalysis.h"
17#include "llvm/CodeGen/LiveVariables.h"
18#include "llvm/CodeGen/MachineInstr.h"
19#include "llvm/CodeGen/MachineRegisterInfo.h"
20#include "llvm/CodeGen/Passes.h"
21#include "llvm/Support/Debug.h"
22#include "llvm/Target/TargetInstrInfo.h"
23#include "llvm/Target/TargetRegisterInfo.h"
24
25
26using namespace llvm;
27
28char ProcessImplicitDefs::ID = 0;
29static RegisterPass<ProcessImplicitDefs> X("processimpdefs",
30                                           "Process Implicit Definitions.");
31
32void ProcessImplicitDefs::getAnalysisUsage(AnalysisUsage &AU) const {
33  AU.setPreservesCFG();
34  AU.addPreserved<AliasAnalysis>();
35  AU.addPreserved<LiveVariables>();
36  AU.addRequired<LiveVariables>();
37  AU.addPreservedID(MachineLoopInfoID);
38  AU.addPreservedID(MachineDominatorsID);
39  AU.addPreservedID(TwoAddressInstructionPassID);
40  AU.addPreservedID(PHIEliminationID);
41  MachineFunctionPass::getAnalysisUsage(AU);
42}
43
44bool ProcessImplicitDefs::CanTurnIntoImplicitDef(MachineInstr *MI,
45                                                 unsigned Reg, unsigned OpIdx,
46                                                 const TargetInstrInfo *tii_) {
47  unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
48  if (tii_->isMoveInstr(*MI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
49      Reg == SrcReg)
50    return true;
51
52  if (OpIdx == 2 && MI->isSubregToReg())
53    return true;
54  if (OpIdx == 1 && MI->isExtractSubreg())
55    return true;
56  return false;
57}
58
59/// processImplicitDefs - Process IMPLICIT_DEF instructions and make sure
60/// there is one implicit_def for each use. Add isUndef marker to
61/// implicit_def defs and their uses.
62bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
63
64  DEBUG(dbgs() << "********** PROCESS IMPLICIT DEFS **********\n"
65               << "********** Function: "
66               << ((Value*)fn.getFunction())->getName() << '\n');
67
68  bool Changed = false;
69
70  const TargetInstrInfo *tii_ = fn.getTarget().getInstrInfo();
71  const TargetRegisterInfo *tri_ = fn.getTarget().getRegisterInfo();
72  MachineRegisterInfo *mri_ = &fn.getRegInfo();
73
74  LiveVariables *lv_ = &getAnalysis<LiveVariables>();
75
76  SmallSet<unsigned, 8> ImpDefRegs;
77  SmallVector<MachineInstr*, 8> ImpDefMIs;
78  SmallVector<MachineInstr*, 4> RUses;
79  SmallPtrSet<MachineBasicBlock*,16> Visited;
80  SmallPtrSet<MachineInstr*, 8> ModInsts;
81
82  MachineBasicBlock *Entry = fn.begin();
83  for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
84         DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
85       DFI != E; ++DFI) {
86    MachineBasicBlock *MBB = *DFI;
87    for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
88         I != E; ) {
89      MachineInstr *MI = &*I;
90      ++I;
91      if (MI->isImplicitDef()) {
92        unsigned Reg = MI->getOperand(0).getReg();
93        ImpDefRegs.insert(Reg);
94        if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
95          for (const unsigned *SS = tri_->getSubRegisters(Reg); *SS; ++SS)
96            ImpDefRegs.insert(*SS);
97        }
98        ImpDefMIs.push_back(MI);
99        continue;
100      }
101
102      if (MI->isInsertSubreg()) {
103        MachineOperand &MO = MI->getOperand(2);
104        if (ImpDefRegs.count(MO.getReg())) {
105          // %reg1032<def> = INSERT_SUBREG %reg1032, undef, 2
106          // This is an identity copy, eliminate it now.
107          if (MO.isKill()) {
108            LiveVariables::VarInfo& vi = lv_->getVarInfo(MO.getReg());
109            vi.removeKill(MI);
110          }
111          MI->eraseFromParent();
112          Changed = true;
113          continue;
114        }
115      }
116
117      bool ChangedToImpDef = false;
118      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
119        MachineOperand& MO = MI->getOperand(i);
120        if (!MO.isReg() || !MO.isUse() || MO.isUndef())
121          continue;
122        unsigned Reg = MO.getReg();
123        if (!Reg)
124          continue;
125        if (!ImpDefRegs.count(Reg))
126          continue;
127        // Use is a copy, just turn it into an implicit_def.
128        if (CanTurnIntoImplicitDef(MI, Reg, i, tii_)) {
129          bool isKill = MO.isKill();
130          MI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
131          for (int j = MI->getNumOperands() - 1, ee = 0; j > ee; --j)
132            MI->RemoveOperand(j);
133          if (isKill) {
134            ImpDefRegs.erase(Reg);
135            LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
136            vi.removeKill(MI);
137          }
138          ChangedToImpDef = true;
139          Changed = true;
140          break;
141        }
142
143        Changed = true;
144        MO.setIsUndef();
145        if (MO.isKill() || MI->isRegTiedToDefOperand(i)) {
146          // Make sure other uses of
147          for (unsigned j = i+1; j != e; ++j) {
148            MachineOperand &MOJ = MI->getOperand(j);
149            if (MOJ.isReg() && MOJ.isUse() && MOJ.getReg() == Reg)
150              MOJ.setIsUndef();
151          }
152          ImpDefRegs.erase(Reg);
153        }
154      }
155
156      if (ChangedToImpDef) {
157        // Backtrack to process this new implicit_def.
158        --I;
159      } else {
160        for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
161          MachineOperand& MO = MI->getOperand(i);
162          if (!MO.isReg() || !MO.isDef())
163            continue;
164          ImpDefRegs.erase(MO.getReg());
165        }
166      }
167    }
168
169    // Any outstanding liveout implicit_def's?
170    for (unsigned i = 0, e = ImpDefMIs.size(); i != e; ++i) {
171      MachineInstr *MI = ImpDefMIs[i];
172      unsigned Reg = MI->getOperand(0).getReg();
173      if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
174          !ImpDefRegs.count(Reg)) {
175        // Delete all "local" implicit_def's. That include those which define
176        // physical registers since they cannot be liveout.
177        MI->eraseFromParent();
178        Changed = true;
179        continue;
180      }
181
182      // If there are multiple defs of the same register and at least one
183      // is not an implicit_def, do not insert implicit_def's before the
184      // uses.
185      bool Skip = false;
186      SmallVector<MachineInstr*, 4> DeadImpDefs;
187      for (MachineRegisterInfo::def_iterator DI = mri_->def_begin(Reg),
188             DE = mri_->def_end(); DI != DE; ++DI) {
189        MachineInstr *DeadImpDef = &*DI;
190        if (!DeadImpDef->isImplicitDef()) {
191          Skip = true;
192          break;
193        }
194        DeadImpDefs.push_back(DeadImpDef);
195      }
196      if (Skip)
197        continue;
198
199      // The only implicit_def which we want to keep are those that are live
200      // out of its block.
201      for (unsigned j = 0, ee = DeadImpDefs.size(); j != ee; ++j)
202        DeadImpDefs[j]->eraseFromParent();
203      Changed = true;
204
205      // Process each use instruction once.
206      for (MachineRegisterInfo::use_iterator UI = mri_->use_begin(Reg),
207             UE = mri_->use_end(); UI != UE; ++UI) {
208        if (UI.getOperand().isUndef())
209          continue;
210        MachineInstr *RMI = &*UI;
211        if (ModInsts.insert(RMI))
212          RUses.push_back(RMI);
213      }
214
215      for (unsigned i = 0, e = RUses.size(); i != e; ++i) {
216        MachineInstr *RMI = RUses[i];
217
218        // Turn a copy use into an implicit_def.
219        unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
220        if (tii_->isMoveInstr(*RMI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
221            Reg == SrcReg) {
222          RMI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
223
224          bool isKill = false;
225          SmallVector<unsigned, 4> Ops;
226          for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
227            MachineOperand &RRMO = RMI->getOperand(j);
228            if (RRMO.isReg() && RRMO.getReg() == Reg) {
229              Ops.push_back(j);
230              if (RRMO.isKill())
231                isKill = true;
232            }
233          }
234          // Leave the other operands along.
235          for (unsigned j = 0, ee = Ops.size(); j != ee; ++j) {
236            unsigned OpIdx = Ops[j];
237            RMI->RemoveOperand(OpIdx-j);
238          }
239
240          // Update LiveVariables varinfo if the instruction is a kill.
241          if (isKill) {
242            LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
243            vi.removeKill(RMI);
244          }
245          continue;
246        }
247
248        // Replace Reg with a new vreg that's marked implicit.
249        const TargetRegisterClass* RC = mri_->getRegClass(Reg);
250        unsigned NewVReg = mri_->createVirtualRegister(RC);
251        bool isKill = true;
252        for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
253          MachineOperand &RRMO = RMI->getOperand(j);
254          if (RRMO.isReg() && RRMO.getReg() == Reg) {
255            RRMO.setReg(NewVReg);
256            RRMO.setIsUndef();
257            if (isKill) {
258              // Only the first operand of NewVReg is marked kill.
259              RRMO.setIsKill();
260              isKill = false;
261            }
262          }
263        }
264      }
265      RUses.clear();
266      ModInsts.clear();
267    }
268    ImpDefRegs.clear();
269    ImpDefMIs.clear();
270  }
271
272  return Changed;
273}
274
275