ProcessImplicitDefs.cpp revision d13db2c59cc94162d6cf0a04187d408bfef6d4a7 
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;
29INITIALIZE_PASS(ProcessImplicitDefs, "processimpdefs",
30                "Process Implicit Definitions.", false, false);
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
45ProcessImplicitDefs::CanTurnIntoImplicitDef(MachineInstr *MI,
46                                            unsigned Reg, unsigned OpIdx,
47                                            const TargetInstrInfo *tii_,
48                                            SmallSet<unsigned, 8> &ImpDefRegs) {
49  switch(OpIdx) {
50  case 1:
51    return MI->isCopy() && (MI->getOperand(0).getSubReg() == 0 ||
52                            ImpDefRegs.count(MI->getOperand(0).getReg()));
53  case 2:
54    return MI->isSubregToReg() && (MI->getOperand(0).getSubReg() == 0 ||
55                                  ImpDefRegs.count(MI->getOperand(0).getReg()));
56  default: return false;
57  }
58}
59
60static bool isUndefCopy(MachineInstr *MI, unsigned Reg,
61                        const TargetInstrInfo *tii_,
62                        SmallSet<unsigned, 8> &ImpDefRegs) {
63  if (MI->isCopy()) {
64    MachineOperand &MO0 = MI->getOperand(0);
65    MachineOperand &MO1 = MI->getOperand(1);
66    if (MO1.getReg() != Reg)
67      return false;
68    if (!MO0.getSubReg() || ImpDefRegs.count(MO0.getReg()))
69      return true;
70    return false;
71  }
72  return false;
73}
74
75/// processImplicitDefs - Process IMPLICIT_DEF instructions and make sure
76/// there is one implicit_def for each use. Add isUndef marker to
77/// implicit_def defs and their uses.
78bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
79
80  DEBUG(dbgs() << "********** PROCESS IMPLICIT DEFS **********\n"
81               << "********** Function: "
82               << ((Value*)fn.getFunction())->getName() << '\n');
83
84  bool Changed = false;
85
86  const TargetInstrInfo *tii_ = fn.getTarget().getInstrInfo();
87  const TargetRegisterInfo *tri_ = fn.getTarget().getRegisterInfo();
88  MachineRegisterInfo *mri_ = &fn.getRegInfo();
89
90  LiveVariables *lv_ = &getAnalysis<LiveVariables>();
91
92  SmallSet<unsigned, 8> ImpDefRegs;
93  SmallVector<MachineInstr*, 8> ImpDefMIs;
94  SmallVector<MachineInstr*, 4> RUses;
95  SmallPtrSet<MachineBasicBlock*,16> Visited;
96  SmallPtrSet<MachineInstr*, 8> ModInsts;
97
98  MachineBasicBlock *Entry = fn.begin();
99  for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
100         DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
101       DFI != E; ++DFI) {
102    MachineBasicBlock *MBB = *DFI;
103    for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
104         I != E; ) {
105      MachineInstr *MI = &*I;
106      ++I;
107      if (MI->isImplicitDef()) {
108        if (MI->getOperand(0).getSubReg())
109          continue;
110        unsigned Reg = MI->getOperand(0).getReg();
111        ImpDefRegs.insert(Reg);
112        if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
113          for (const unsigned *SS = tri_->getSubRegisters(Reg); *SS; ++SS)
114            ImpDefRegs.insert(*SS);
115        }
116        ImpDefMIs.push_back(MI);
117        continue;
118      }
119
120      // Eliminate %reg1032:sub<def> = COPY undef.
121      if (MI->isCopy() && MI->getOperand(0).getSubReg()) {
122        MachineOperand &MO = MI->getOperand(1);
123        if (MO.isUndef() || ImpDefRegs.count(MO.getReg())) {
124          if (MO.isKill()) {
125            LiveVariables::VarInfo& vi = lv_->getVarInfo(MO.getReg());
126            vi.removeKill(MI);
127          }
128          MI->eraseFromParent();
129          Changed = true;
130          continue;
131        }
132      }
133
134      bool ChangedToImpDef = false;
135      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
136        MachineOperand& MO = MI->getOperand(i);
137        if (!MO.isReg() || (MO.isDef() && !MO.getSubReg()) || MO.isUndef())
138          continue;
139        unsigned Reg = MO.getReg();
140        if (!Reg)
141          continue;
142        if (!ImpDefRegs.count(Reg))
143          continue;
144        // Use is a copy, just turn it into an implicit_def.
145        if (CanTurnIntoImplicitDef(MI, Reg, i, tii_, ImpDefRegs)) {
146          bool isKill = MO.isKill();
147          MI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
148          for (int j = MI->getNumOperands() - 1, ee = 0; j > ee; --j)
149            MI->RemoveOperand(j);
150          if (isKill) {
151            ImpDefRegs.erase(Reg);
152            LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
153            vi.removeKill(MI);
154          }
155          ChangedToImpDef = true;
156          Changed = true;
157          break;
158        }
159
160        Changed = true;
161        MO.setIsUndef();
162        // This is a partial register redef of an implicit def.
163        // Make sure the whole register is defined by the instruction.
164        if (MO.isDef()) {
165          MI->addRegisterDefined(Reg);
166          continue;
167        }
168        if (MO.isKill() || MI->isRegTiedToDefOperand(i)) {
169          // Make sure other uses of
170          for (unsigned j = i+1; j != e; ++j) {
171            MachineOperand &MOJ = MI->getOperand(j);
172            if (MOJ.isReg() && MOJ.isUse() && MOJ.getReg() == Reg)
173              MOJ.setIsUndef();
174          }
175          ImpDefRegs.erase(Reg);
176        }
177      }
178
179      if (ChangedToImpDef) {
180        // Backtrack to process this new implicit_def.
181        --I;
182      } else {
183        for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
184          MachineOperand& MO = MI->getOperand(i);
185          if (!MO.isReg() || !MO.isDef())
186            continue;
187          ImpDefRegs.erase(MO.getReg());
188        }
189      }
190    }
191
192    // Any outstanding liveout implicit_def's?
193    for (unsigned i = 0, e = ImpDefMIs.size(); i != e; ++i) {
194      MachineInstr *MI = ImpDefMIs[i];
195      unsigned Reg = MI->getOperand(0).getReg();
196      if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
197          !ImpDefRegs.count(Reg)) {
198        // Delete all "local" implicit_def's. That include those which define
199        // physical registers since they cannot be liveout.
200        MI->eraseFromParent();
201        Changed = true;
202        continue;
203      }
204
205      // If there are multiple defs of the same register and at least one
206      // is not an implicit_def, do not insert implicit_def's before the
207      // uses.
208      bool Skip = false;
209      SmallVector<MachineInstr*, 4> DeadImpDefs;
210      for (MachineRegisterInfo::def_iterator DI = mri_->def_begin(Reg),
211             DE = mri_->def_end(); DI != DE; ++DI) {
212        MachineInstr *DeadImpDef = &*DI;
213        if (!DeadImpDef->isImplicitDef()) {
214          Skip = true;
215          break;
216        }
217        DeadImpDefs.push_back(DeadImpDef);
218      }
219      if (Skip)
220        continue;
221
222      // The only implicit_def which we want to keep are those that are live
223      // out of its block.
224      for (unsigned j = 0, ee = DeadImpDefs.size(); j != ee; ++j)
225        DeadImpDefs[j]->eraseFromParent();
226      Changed = true;
227
228      // Process each use instruction once.
229      for (MachineRegisterInfo::use_iterator UI = mri_->use_begin(Reg),
230             UE = mri_->use_end(); UI != UE; ++UI) {
231        if (UI.getOperand().isUndef())
232          continue;
233        MachineInstr *RMI = &*UI;
234        if (ModInsts.insert(RMI))
235          RUses.push_back(RMI);
236      }
237
238      for (unsigned i = 0, e = RUses.size(); i != e; ++i) {
239        MachineInstr *RMI = RUses[i];
240
241        // Turn a copy use into an implicit_def.
242        if (isUndefCopy(RMI, Reg, tii_, ImpDefRegs)) {
243          RMI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
244
245          bool isKill = false;
246          SmallVector<unsigned, 4> Ops;
247          for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
248            MachineOperand &RRMO = RMI->getOperand(j);
249            if (RRMO.isReg() && RRMO.getReg() == Reg) {
250              Ops.push_back(j);
251              if (RRMO.isKill())
252                isKill = true;
253            }
254          }
255          // Leave the other operands along.
256          for (unsigned j = 0, ee = Ops.size(); j != ee; ++j) {
257            unsigned OpIdx = Ops[j];
258            RMI->RemoveOperand(OpIdx-j);
259          }
260
261          // Update LiveVariables varinfo if the instruction is a kill.
262          if (isKill) {
263            LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
264            vi.removeKill(RMI);
265          }
266          continue;
267        }
268
269        // Replace Reg with a new vreg that's marked implicit.
270        const TargetRegisterClass* RC = mri_->getRegClass(Reg);
271        unsigned NewVReg = mri_->createVirtualRegister(RC);
272        bool isKill = true;
273        for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
274          MachineOperand &RRMO = RMI->getOperand(j);
275          if (RRMO.isReg() && RRMO.getReg() == Reg) {
276            RRMO.setReg(NewVReg);
277            RRMO.setIsUndef();
278            if (isKill) {
279              // Only the first operand of NewVReg is marked kill.
280              RRMO.setIsKill();
281              isKill = false;
282            }
283          }
284        }
285      }
286      RUses.clear();
287      ModInsts.clear();
288    }
289    ImpDefRegs.clear();
290    ImpDefMIs.clear();
291  }
292
293  return Changed;
294}
295
296