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 #define DEBUG_TYPE "machine-ssaupdater"
34 typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
35 static AvailableValsTy &getAvailableVals(void *AV) {
36 return *static_cast<AvailableValsTy*>(AV);
39 MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
40 SmallVectorImpl<MachineInstr*> *NewPHI)
41 : AV(nullptr), InsertedPHIs(NewPHI) {
42 TII = MF.getTarget().getInstrInfo();
43 MRI = &MF.getRegInfo();
46 MachineSSAUpdater::~MachineSSAUpdater() {
47 delete static_cast<AvailableValsTy*>(AV);
50 /// Initialize - Reset this object to get ready for a new set of SSA
51 /// updates. ProtoValue is the value used to name PHI nodes.
52 void MachineSSAUpdater::Initialize(unsigned V) {
54 AV = new AvailableValsTy();
56 getAvailableVals(AV).clear();
59 VRC = MRI->getRegClass(VR);
62 /// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
63 /// the specified block.
64 bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
65 return getAvailableVals(AV).count(BB);
68 /// AddAvailableValue - Indicate that a rewritten value is available in the
69 /// specified block with the specified value.
70 void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
71 getAvailableVals(AV)[BB] = V;
74 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
75 /// live at the end of the specified block.
76 unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
77 return GetValueAtEndOfBlockInternal(BB);
81 unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
82 SmallVectorImpl<std::pair<MachineBasicBlock*, unsigned> > &PredValues) {
86 MachineBasicBlock::iterator I = BB->begin();
90 AvailableValsTy AVals;
91 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
92 AVals[PredValues[i].first] = PredValues[i].second;
93 while (I != BB->end() && I->isPHI()) {
95 for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
96 unsigned SrcReg = I->getOperand(i).getReg();
97 MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
98 if (AVals[SrcBB] != SrcReg) {
104 return I->getOperand(0).getReg();
110 /// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
111 /// a value of the given register class at the start of the specified basic
112 /// block. It returns the virtual register defined by the instruction.
114 MachineInstrBuilder InsertNewDef(unsigned Opcode,
115 MachineBasicBlock *BB, MachineBasicBlock::iterator I,
116 const TargetRegisterClass *RC,
117 MachineRegisterInfo *MRI,
118 const TargetInstrInfo *TII) {
119 unsigned NewVR = MRI->createVirtualRegister(RC);
120 return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
123 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
124 /// is live in the middle of the specified block.
126 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
127 /// important case: if there is a definition of the rewritten value after the
128 /// 'use' in BB. Consider code like this:
134 /// br Cond, SomeBB, OutBB
136 /// In this case, there are two values (X1 and X2) added to the AvailableVals
137 /// set by the client of the rewriter, and those values are both live out of
138 /// their respective blocks. However, the use of X happens in the *middle* of
139 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
140 /// merge the appropriate values, and this value isn't live out of the block.
142 unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
143 // If there is no definition of the renamed variable in this block, just use
144 // GetValueAtEndOfBlock to do our work.
145 if (!HasValueForBlock(BB))
146 return GetValueAtEndOfBlockInternal(BB);
148 // If there are no predecessors, just return undef.
149 if (BB->pred_empty()) {
150 // Insert an implicit_def to represent an undef value.
151 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
152 BB, BB->getFirstTerminator(),
154 return NewDef->getOperand(0).getReg();
157 // Otherwise, we have the hard case. Get the live-in values for each
159 SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
160 unsigned SingularValue = 0;
162 bool isFirstPred = true;
163 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
164 E = BB->pred_end(); PI != E; ++PI) {
165 MachineBasicBlock *PredBB = *PI;
166 unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
167 PredValues.push_back(std::make_pair(PredBB, PredVal));
169 // Compute SingularValue.
171 SingularValue = PredVal;
173 } else if (PredVal != SingularValue)
177 // Otherwise, if all the merged values are the same, just use it.
178 if (SingularValue != 0)
179 return SingularValue;
181 // If an identical PHI is already in BB, just reuse it.
182 unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
186 // Otherwise, we do need a PHI: insert one now.
187 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
188 MachineInstrBuilder InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB,
191 // Fill in all the predecessors of the PHI.
192 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
193 InsertedPHI.addReg(PredValues[i].second).addMBB(PredValues[i].first);
195 // See if the PHI node can be merged to a single value. This can happen in
196 // loop cases when we get a PHI of itself and one other value.
197 if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
198 InsertedPHI->eraseFromParent();
202 // If the client wants to know about all new instructions, tell it.
203 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
205 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
206 return InsertedPHI->getOperand(0).getReg();
210 MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
212 for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
213 if (&MI->getOperand(i) == U)
214 return MI->getOperand(i+1).getMBB();
217 llvm_unreachable("MachineOperand::getParent() failure?");
220 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
221 /// which use their value in the corresponding predecessor.
222 void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
223 MachineInstr *UseMI = U.getParent();
225 if (UseMI->isPHI()) {
226 MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
227 NewVR = GetValueAtEndOfBlockInternal(SourceBB);
229 NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
235 /// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
236 /// template, specialized for MachineSSAUpdater.
239 class SSAUpdaterTraits<MachineSSAUpdater> {
241 typedef MachineBasicBlock BlkT;
242 typedef unsigned ValT;
243 typedef MachineInstr PhiT;
245 typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
246 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
247 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
249 /// Iterator for PHI operands.
256 explicit PHI_iterator(MachineInstr *P) // begin iterator
258 PHI_iterator(MachineInstr *P, bool) // end iterator
259 : PHI(P), idx(PHI->getNumOperands()) {}
261 PHI_iterator &operator++() { idx += 2; return *this; }
262 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
263 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
264 unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
265 MachineBasicBlock *getIncomingBlock() {
266 return PHI->getOperand(idx+1).getMBB();
269 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
270 static inline PHI_iterator PHI_end(PhiT *PHI) {
271 return PHI_iterator(PHI, true);
274 /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
276 static void FindPredecessorBlocks(MachineBasicBlock *BB,
277 SmallVectorImpl<MachineBasicBlock*> *Preds){
278 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
279 E = BB->pred_end(); PI != E; ++PI)
280 Preds->push_back(*PI);
283 /// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
284 /// Add it into the specified block and return the register.
285 static unsigned GetUndefVal(MachineBasicBlock *BB,
286 MachineSSAUpdater *Updater) {
287 // Insert an implicit_def to represent an undef value.
288 MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
289 BB, BB->getFirstTerminator(),
290 Updater->VRC, Updater->MRI,
292 return NewDef->getOperand(0).getReg();
295 /// CreateEmptyPHI - Create a PHI instruction that defines a new register.
296 /// Add it into the specified block and return the register.
297 static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
298 MachineSSAUpdater *Updater) {
299 MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
300 MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
301 Updater->VRC, Updater->MRI,
303 return PHI->getOperand(0).getReg();
306 /// AddPHIOperand - Add the specified value as an operand of the PHI for
307 /// the specified predecessor block.
308 static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
309 MachineBasicBlock *Pred) {
310 MachineInstrBuilder(*Pred->getParent(), PHI).addReg(Val).addMBB(Pred);
313 /// InstrIsPHI - Check if an instruction is a PHI.
315 static MachineInstr *InstrIsPHI(MachineInstr *I) {
321 /// ValueIsPHI - Check if the instruction that defines the specified register
322 /// is a PHI instruction.
323 static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
324 return InstrIsPHI(Updater->MRI->getVRegDef(Val));
327 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
328 /// operands, i.e., it was just added.
329 static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
330 MachineInstr *PHI = ValueIsPHI(Val, Updater);
331 if (PHI && PHI->getNumOperands() <= 1)
336 /// GetPHIValue - For the specified PHI instruction, return the register
338 static unsigned GetPHIValue(MachineInstr *PHI) {
339 return PHI->getOperand(0).getReg();
343 } // End llvm namespace
345 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
346 /// for the specified BB and if so, return it. If not, construct SSA form by
347 /// first calculating the required placement of PHIs and then inserting new
348 /// PHIs where needed.
349 unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
350 AvailableValsTy &AvailableVals = getAvailableVals(AV);
351 if (unsigned V = AvailableVals[BB])
354 SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
355 return Impl.GetValue(BB);