1 //===- SSAUpdater.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 SSAUpdater class.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "ssaupdater"
15 #include "llvm/Instructions.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/Support/AlignOf.h"
18 #include "llvm/Support/Allocator.h"
19 #include "llvm/Support/CFG.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/raw_ostream.h"
22 #include "llvm/Transforms/Utils/SSAUpdater.h"
23 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
26 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
27 static AvailableValsTy &getAvailableVals(void *AV) {
28 return *static_cast<AvailableValsTy*>(AV);
31 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
32 : AV(0), PrototypeValue(0), InsertedPHIs(NewPHI) {}
34 SSAUpdater::~SSAUpdater() {
35 delete &getAvailableVals(AV);
38 /// Initialize - Reset this object to get ready for a new set of SSA
39 /// updates. ProtoValue is the value used to name PHI nodes.
40 void SSAUpdater::Initialize(Value *ProtoValue) {
42 AV = new AvailableValsTy();
44 getAvailableVals(AV).clear();
45 PrototypeValue = ProtoValue;
48 /// HasValueForBlock - Return true if the SSAUpdater already has a value for
49 /// the specified block.
50 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
51 return getAvailableVals(AV).count(BB);
54 /// AddAvailableValue - Indicate that a rewritten value is available in the
55 /// specified block with the specified value.
56 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
57 assert(PrototypeValue != 0 && "Need to initialize SSAUpdater");
58 assert(PrototypeValue->getType() == V->getType() &&
59 "All rewritten values must have the same type");
60 getAvailableVals(AV)[BB] = V;
63 /// IsEquivalentPHI - Check if PHI has the same incoming value as specified
64 /// in ValueMapping for each predecessor block.
65 static bool IsEquivalentPHI(PHINode *PHI,
66 DenseMap<BasicBlock*, Value*> &ValueMapping) {
67 unsigned PHINumValues = PHI->getNumIncomingValues();
68 if (PHINumValues != ValueMapping.size())
71 // Scan the phi to see if it matches.
72 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
73 if (ValueMapping[PHI->getIncomingBlock(i)] !=
74 PHI->getIncomingValue(i)) {
81 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
82 /// live at the end of the specified block.
83 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
84 Value *Res = GetValueAtEndOfBlockInternal(BB);
88 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
89 /// is live in the middle of the specified block.
91 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
92 /// important case: if there is a definition of the rewritten value after the
93 /// 'use' in BB. Consider code like this:
99 /// br Cond, SomeBB, OutBB
101 /// In this case, there are two values (X1 and X2) added to the AvailableVals
102 /// set by the client of the rewriter, and those values are both live out of
103 /// their respective blocks. However, the use of X happens in the *middle* of
104 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
105 /// merge the appropriate values, and this value isn't live out of the block.
107 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
108 // If there is no definition of the renamed variable in this block, just use
109 // GetValueAtEndOfBlock to do our work.
110 if (!HasValueForBlock(BB))
111 return GetValueAtEndOfBlock(BB);
113 // Otherwise, we have the hard case. Get the live-in values for each
115 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
116 Value *SingularValue = 0;
118 // We can get our predecessor info by walking the pred_iterator list, but it
119 // is relatively slow. If we already have PHI nodes in this block, walk one
120 // of them to get the predecessor list instead.
121 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
122 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
123 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
124 Value *PredVal = GetValueAtEndOfBlock(PredBB);
125 PredValues.push_back(std::make_pair(PredBB, PredVal));
127 // Compute SingularValue.
129 SingularValue = PredVal;
130 else if (PredVal != SingularValue)
134 bool isFirstPred = true;
135 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
136 BasicBlock *PredBB = *PI;
137 Value *PredVal = GetValueAtEndOfBlock(PredBB);
138 PredValues.push_back(std::make_pair(PredBB, PredVal));
140 // Compute SingularValue.
142 SingularValue = PredVal;
144 } else if (PredVal != SingularValue)
149 // If there are no predecessors, just return undef.
150 if (PredValues.empty())
151 return UndefValue::get(PrototypeValue->getType());
153 // Otherwise, if all the merged values are the same, just use it.
154 if (SingularValue != 0)
155 return SingularValue;
157 // Otherwise, we do need a PHI: check to see if we already have one available
158 // in this block that produces the right value.
159 if (isa<PHINode>(BB->begin())) {
160 DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
163 for (BasicBlock::iterator It = BB->begin();
164 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
165 if (IsEquivalentPHI(SomePHI, ValueMapping))
170 // Ok, we have no way out, insert a new one now.
171 PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
172 PrototypeValue->getName(),
174 InsertedPHI->reserveOperandSpace(PredValues.size());
176 // Fill in all the predecessors of the PHI.
177 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
178 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
180 // See if the PHI node can be merged to a single value. This can happen in
181 // loop cases when we get a PHI of itself and one other value.
182 if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
183 InsertedPHI->eraseFromParent();
187 // If the client wants to know about all new instructions, tell it.
188 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
190 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
194 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
195 /// which use their value in the corresponding predecessor.
196 void SSAUpdater::RewriteUse(Use &U) {
197 Instruction *User = cast<Instruction>(U.getUser());
200 if (PHINode *UserPN = dyn_cast<PHINode>(User))
201 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
203 V = GetValueInMiddleOfBlock(User->getParent());
208 /// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
209 /// in the SSAUpdaterImpl template.
217 explicit PHIiter(PHINode *P) // begin iterator
219 PHIiter(PHINode *P, bool) // end iterator
220 : PHI(P), idx(PHI->getNumIncomingValues()) {}
222 PHIiter &operator++() { ++idx; return *this; }
223 bool operator==(const PHIiter& x) const { return idx == x.idx; }
224 bool operator!=(const PHIiter& x) const { return !operator==(x); }
225 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
226 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
230 /// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
231 /// specialized for SSAUpdater.
234 class SSAUpdaterTraits<SSAUpdater> {
236 typedef BasicBlock BlkT;
238 typedef PHINode PhiT;
240 typedef succ_iterator BlkSucc_iterator;
241 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
242 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
244 typedef PHIiter PHI_iterator;
245 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
246 static inline PHI_iterator PHI_end(PhiT *PHI) {
247 return PHI_iterator(PHI, true);
250 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
251 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
252 static void FindPredecessorBlocks(BasicBlock *BB,
253 SmallVectorImpl<BasicBlock*> *Preds) {
254 // We can get our predecessor info by walking the pred_iterator list,
255 // but it is relatively slow. If we already have PHI nodes in this
256 // block, walk one of them to get the predecessor list instead.
257 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
258 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
259 Preds->push_back(SomePhi->getIncomingBlock(PI));
261 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
262 Preds->push_back(*PI);
266 /// GetUndefVal - Get an undefined value of the same type as the value
268 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
269 return UndefValue::get(Updater->PrototypeValue->getType());
272 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
273 /// Reserve space for the operands but do not fill them in yet.
274 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
275 SSAUpdater *Updater) {
276 PHINode *PHI = PHINode::Create(Updater->PrototypeValue->getType(),
277 Updater->PrototypeValue->getName(),
279 PHI->reserveOperandSpace(NumPreds);
283 /// AddPHIOperand - Add the specified value as an operand of the PHI for
284 /// the specified predecessor block.
285 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
286 PHI->addIncoming(Val, Pred);
289 /// InstrIsPHI - Check if an instruction is a PHI.
291 static PHINode *InstrIsPHI(Instruction *I) {
292 return dyn_cast<PHINode>(I);
295 /// ValueIsPHI - Check if a value is a PHI.
297 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
298 return dyn_cast<PHINode>(Val);
301 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
302 /// operands, i.e., it was just added.
303 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
304 PHINode *PHI = ValueIsPHI(Val, Updater);
305 if (PHI && PHI->getNumIncomingValues() == 0)
310 /// GetPHIValue - For the specified PHI instruction, return the value
312 static Value *GetPHIValue(PHINode *PHI) {
317 } // End llvm namespace
319 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
320 /// for the specified BB and if so, return it. If not, construct SSA form by
321 /// first calculating the required placement of PHIs and then inserting new
322 /// PHIs where needed.
323 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
324 AvailableValsTy &AvailableVals = getAvailableVals(AV);
325 if (Value *V = AvailableVals[BB])
328 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
329 return Impl.GetValue(BB);