1 //===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the MachineSSAUpdater class. It's based on SSAUpdater
11 // class in lib/Transforms/Utils.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/CodeGen/MachineSSAUpdater.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/CodeGen/MachineInstr.h"
19 #include "llvm/CodeGen/MachineInstrBuilder.h"
20 #include "llvm/CodeGen/MachineRegisterInfo.h"
21 #include "llvm/Support/AlignOf.h"
22 #include "llvm/Support/Allocator.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/ErrorHandling.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Target/TargetMachine.h"
28 #include "llvm/Target/TargetRegisterInfo.h"
29 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
32 typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
33 static AvailableValsTy &getAvailableVals(void *AV) {
34 return *static_cast<AvailableValsTy*>(AV);
37 MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
38 SmallVectorImpl<MachineInstr*> *NewPHI)
39 : AV(0), InsertedPHIs(NewPHI) {
40 TII = MF.getTarget().getInstrInfo();
41 MRI = &MF.getRegInfo();
44 MachineSSAUpdater::~MachineSSAUpdater() {
45 delete static_cast<AvailableValsTy*>(AV);
48 /// Initialize - Reset this object to get ready for a new set of SSA
49 /// updates. ProtoValue is the value used to name PHI nodes.
50 void MachineSSAUpdater::Initialize(unsigned V) {
52 AV = new AvailableValsTy();
54 getAvailableVals(AV).clear();
57 VRC = MRI->getRegClass(VR);
60 /// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
61 /// the specified block.
62 bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
63 return getAvailableVals(AV).count(BB);
66 /// AddAvailableValue - Indicate that a rewritten value is available in the
67 /// specified block with the specified value.
68 void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
69 getAvailableVals(AV)[BB] = V;
72 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
73 /// live at the end of the specified block.
74 unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
75 return GetValueAtEndOfBlockInternal(BB);
79 unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
80 SmallVectorImpl<std::pair<MachineBasicBlock*, unsigned> > &PredValues) {
84 MachineBasicBlock::iterator I = BB->begin();
88 AvailableValsTy AVals;
89 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
90 AVals[PredValues[i].first] = PredValues[i].second;
91 while (I != BB->end() && I->isPHI()) {
93 for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
94 unsigned SrcReg = I->getOperand(i).getReg();
95 MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
96 if (AVals[SrcBB] != SrcReg) {
102 return I->getOperand(0).getReg();
108 /// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
109 /// a value of the given register class at the start of the specified basic
110 /// block. It returns the virtual register defined by the instruction.
112 MachineInstrBuilder InsertNewDef(unsigned Opcode,
113 MachineBasicBlock *BB, MachineBasicBlock::iterator I,
114 const TargetRegisterClass *RC,
115 MachineRegisterInfo *MRI,
116 const TargetInstrInfo *TII) {
117 unsigned NewVR = MRI->createVirtualRegister(RC);
118 return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
121 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
122 /// is live in the middle of the specified block.
124 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
125 /// important case: if there is a definition of the rewritten value after the
126 /// 'use' in BB. Consider code like this:
132 /// br Cond, SomeBB, OutBB
134 /// In this case, there are two values (X1 and X2) added to the AvailableVals
135 /// set by the client of the rewriter, and those values are both live out of
136 /// their respective blocks. However, the use of X happens in the *middle* of
137 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
138 /// merge the appropriate values, and this value isn't live out of the block.
140 unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
141 // If there is no definition of the renamed variable in this block, just use
142 // GetValueAtEndOfBlock to do our work.
143 if (!HasValueForBlock(BB))
144 return GetValueAtEndOfBlockInternal(BB);
146 // If there are no predecessors, just return undef.
147 if (BB->pred_empty()) {
148 // Insert an implicit_def to represent an undef value.
149 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
150 BB, BB->getFirstTerminator(),
152 return NewDef->getOperand(0).getReg();
155 // Otherwise, we have the hard case. Get the live-in values for each
157 SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
158 unsigned SingularValue = 0;
160 bool isFirstPred = true;
161 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
162 E = BB->pred_end(); PI != E; ++PI) {
163 MachineBasicBlock *PredBB = *PI;
164 unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
165 PredValues.push_back(std::make_pair(PredBB, PredVal));
167 // Compute SingularValue.
169 SingularValue = PredVal;
171 } else if (PredVal != SingularValue)
175 // Otherwise, if all the merged values are the same, just use it.
176 if (SingularValue != 0)
177 return SingularValue;
179 // If an identical PHI is already in BB, just reuse it.
180 unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
184 // Otherwise, we do need a PHI: insert one now.
185 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
186 MachineInstrBuilder InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB,
189 // Fill in all the predecessors of the PHI.
190 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
191 InsertedPHI.addReg(PredValues[i].second).addMBB(PredValues[i].first);
193 // See if the PHI node can be merged to a single value. This can happen in
194 // loop cases when we get a PHI of itself and one other value.
195 if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
196 InsertedPHI->eraseFromParent();
200 // If the client wants to know about all new instructions, tell it.
201 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
203 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
204 return InsertedPHI->getOperand(0).getReg();
208 MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
210 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
211 if (&MI->getOperand(i) == U)
212 return MI->getOperand(i+1).getMBB();
215 llvm_unreachable("MachineOperand::getParent() failure?");
218 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
219 /// which use their value in the corresponding predecessor.
220 void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
221 MachineInstr *UseMI = U.getParent();
223 if (UseMI->isPHI()) {
224 MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
225 NewVR = GetValueAtEndOfBlockInternal(SourceBB);
227 NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
233 /// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
234 /// template, specialized for MachineSSAUpdater.
237 class SSAUpdaterTraits<MachineSSAUpdater> {
239 typedef MachineBasicBlock BlkT;
240 typedef unsigned ValT;
241 typedef MachineInstr PhiT;
243 typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
244 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
245 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
247 /// Iterator for PHI operands.
254 explicit PHI_iterator(MachineInstr *P) // begin iterator
256 PHI_iterator(MachineInstr *P, bool) // end iterator
257 : PHI(P), idx(PHI->getNumOperands()) {}
259 PHI_iterator &operator++() { idx += 2; return *this; }
260 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
261 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
262 unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
263 MachineBasicBlock *getIncomingBlock() {
264 return PHI->getOperand(idx+1).getMBB();
267 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
268 static inline PHI_iterator PHI_end(PhiT *PHI) {
269 return PHI_iterator(PHI, true);
272 /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
274 static void FindPredecessorBlocks(MachineBasicBlock *BB,
275 SmallVectorImpl<MachineBasicBlock*> *Preds){
276 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
277 E = BB->pred_end(); PI != E; ++PI)
278 Preds->push_back(*PI);
281 /// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
282 /// Add it into the specified block and return the register.
283 static unsigned GetUndefVal(MachineBasicBlock *BB,
284 MachineSSAUpdater *Updater) {
285 // Insert an implicit_def to represent an undef value.
286 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
287 BB, BB->getFirstTerminator(),
288 Updater->VRC, Updater->MRI,
290 return NewDef->getOperand(0).getReg();
293 /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
294 /// Add it into the specified block and return the register.
295 static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
296 MachineSSAUpdater *Updater) {
297 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
298 MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
299 Updater->VRC, Updater->MRI,
301 return PHI->getOperand(0).getReg();
304 /// AddPHIOperand - Add the specified value as an operand of the PHI for
305 /// the specified predecessor block.
306 static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
307 MachineBasicBlock *Pred) {
308 MachineInstrBuilder(*Pred->getParent(), PHI).addReg(Val).addMBB(Pred);
311 /// InstrIsPHI - Check if an instruction is a PHI.
313 static MachineInstr *InstrIsPHI(MachineInstr *I) {
319 /// ValueIsPHI - Check if the instruction that defines the specified register
320 /// is a PHI instruction.
321 static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
322 return InstrIsPHI(Updater->MRI->getVRegDef(Val));
325 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
326 /// operands, i.e., it was just added.
327 static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
328 MachineInstr *PHI = ValueIsPHI(Val, Updater);
329 if (PHI && PHI->getNumOperands() <= 1)
334 /// GetPHIValue - For the specified PHI instruction, return the register
336 static unsigned GetPHIValue(MachineInstr *PHI) {
337 return PHI->getOperand(0).getReg();
341 } // End llvm namespace
343 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
344 /// for the specified BB and if so, return it. If not, construct SSA form by
345 /// first calculating the required placement of PHIs and then inserting new
346 /// PHIs where needed.
347 unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
348 AvailableValsTy &AvailableVals = getAvailableVals(AV);
349 if (unsigned V = AvailableVals[BB])
352 SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
353 return Impl.GetValue(BB);