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), ProtoType(0), ProtoName(), 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 with type 'Ty'. PHI nodes get a name based on 'Name'.
40 void SSAUpdater::Initialize(const Type *Ty, StringRef Name) {
42 AV = new AvailableValsTy();
44 getAvailableVals(AV).clear();
49 /// HasValueForBlock - Return true if the SSAUpdater already has a value for
50 /// the specified block.
51 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
52 return getAvailableVals(AV).count(BB);
55 /// AddAvailableValue - Indicate that a rewritten value is available in the
56 /// specified block with the specified value.
57 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
58 assert(ProtoType != 0 && "Need to initialize SSAUpdater");
59 assert(ProtoType == V->getType() &&
60 "All rewritten values must have the same type");
61 getAvailableVals(AV)[BB] = V;
64 /// IsEquivalentPHI - Check if PHI has the same incoming value as specified
65 /// in ValueMapping for each predecessor block.
66 static bool IsEquivalentPHI(PHINode *PHI,
67 DenseMap<BasicBlock*, Value*> &ValueMapping) {
68 unsigned PHINumValues = PHI->getNumIncomingValues();
69 if (PHINumValues != ValueMapping.size())
72 // Scan the phi to see if it matches.
73 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
74 if (ValueMapping[PHI->getIncomingBlock(i)] !=
75 PHI->getIncomingValue(i)) {
82 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
83 /// live at the end of the specified block.
84 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
85 Value *Res = GetValueAtEndOfBlockInternal(BB);
89 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
90 /// is live in the middle of the specified block.
92 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
93 /// important case: if there is a definition of the rewritten value after the
94 /// 'use' in BB. Consider code like this:
100 /// br Cond, SomeBB, OutBB
102 /// In this case, there are two values (X1 and X2) added to the AvailableVals
103 /// set by the client of the rewriter, and those values are both live out of
104 /// their respective blocks. However, the use of X happens in the *middle* of
105 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
106 /// merge the appropriate values, and this value isn't live out of the block.
108 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
109 // If there is no definition of the renamed variable in this block, just use
110 // GetValueAtEndOfBlock to do our work.
111 if (!HasValueForBlock(BB))
112 return GetValueAtEndOfBlock(BB);
114 // Otherwise, we have the hard case. Get the live-in values for each
116 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
117 Value *SingularValue = 0;
119 // We can get our predecessor info by walking the pred_iterator list, but it
120 // is relatively slow. If we already have PHI nodes in this block, walk one
121 // of them to get the predecessor list instead.
122 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
123 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
124 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
125 Value *PredVal = GetValueAtEndOfBlock(PredBB);
126 PredValues.push_back(std::make_pair(PredBB, PredVal));
128 // Compute SingularValue.
130 SingularValue = PredVal;
131 else if (PredVal != SingularValue)
135 bool isFirstPred = true;
136 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
137 BasicBlock *PredBB = *PI;
138 Value *PredVal = GetValueAtEndOfBlock(PredBB);
139 PredValues.push_back(std::make_pair(PredBB, PredVal));
141 // Compute SingularValue.
143 SingularValue = PredVal;
145 } else if (PredVal != SingularValue)
150 // If there are no predecessors, just return undef.
151 if (PredValues.empty())
152 return UndefValue::get(ProtoType);
154 // Otherwise, if all the merged values are the same, just use it.
155 if (SingularValue != 0)
156 return SingularValue;
158 // Otherwise, we do need a PHI: check to see if we already have one available
159 // in this block that produces the right value.
160 if (isa<PHINode>(BB->begin())) {
161 DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
164 for (BasicBlock::iterator It = BB->begin();
165 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
166 if (IsEquivalentPHI(SomePHI, ValueMapping))
171 // Ok, we have no way out, insert a new one now.
172 PHINode *InsertedPHI = PHINode::Create(ProtoType, ProtoName, &BB->front());
173 InsertedPHI->reserveOperandSpace(PredValues.size());
175 // Fill in all the predecessors of the PHI.
176 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
177 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
179 // See if the PHI node can be merged to a single value. This can happen in
180 // loop cases when we get a PHI of itself and one other value.
181 if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
182 InsertedPHI->eraseFromParent();
186 // If the client wants to know about all new instructions, tell it.
187 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
189 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
193 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
194 /// which use their value in the corresponding predecessor.
195 void SSAUpdater::RewriteUse(Use &U) {
196 Instruction *User = cast<Instruction>(U.getUser());
199 if (PHINode *UserPN = dyn_cast<PHINode>(User))
200 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
202 V = GetValueInMiddleOfBlock(User->getParent());
207 /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However,
208 /// this version of the method can rewrite uses in the same block as a
209 /// definition, because it assumes that all uses of a value are below any
211 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
212 Instruction *User = cast<Instruction>(U.getUser());
215 if (PHINode *UserPN = dyn_cast<PHINode>(User))
216 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
218 V = GetValueAtEndOfBlock(User->getParent());
223 /// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
224 /// in the SSAUpdaterImpl template.
232 explicit PHIiter(PHINode *P) // begin iterator
234 PHIiter(PHINode *P, bool) // end iterator
235 : PHI(P), idx(PHI->getNumIncomingValues()) {}
237 PHIiter &operator++() { ++idx; return *this; }
238 bool operator==(const PHIiter& x) const { return idx == x.idx; }
239 bool operator!=(const PHIiter& x) const { return !operator==(x); }
240 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
241 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
245 /// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
246 /// specialized for SSAUpdater.
249 class SSAUpdaterTraits<SSAUpdater> {
251 typedef BasicBlock BlkT;
253 typedef PHINode PhiT;
255 typedef succ_iterator BlkSucc_iterator;
256 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
257 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
259 typedef PHIiter PHI_iterator;
260 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
261 static inline PHI_iterator PHI_end(PhiT *PHI) {
262 return PHI_iterator(PHI, true);
265 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
266 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
267 static void FindPredecessorBlocks(BasicBlock *BB,
268 SmallVectorImpl<BasicBlock*> *Preds) {
269 // We can get our predecessor info by walking the pred_iterator list,
270 // but it is relatively slow. If we already have PHI nodes in this
271 // block, walk one of them to get the predecessor list instead.
272 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
273 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
274 Preds->push_back(SomePhi->getIncomingBlock(PI));
276 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
277 Preds->push_back(*PI);
281 /// GetUndefVal - Get an undefined value of the same type as the value
283 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
284 return UndefValue::get(Updater->ProtoType);
287 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
288 /// Reserve space for the operands but do not fill them in yet.
289 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
290 SSAUpdater *Updater) {
291 PHINode *PHI = PHINode::Create(Updater->ProtoType, Updater->ProtoName,
293 PHI->reserveOperandSpace(NumPreds);
297 /// AddPHIOperand - Add the specified value as an operand of the PHI for
298 /// the specified predecessor block.
299 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
300 PHI->addIncoming(Val, Pred);
303 /// InstrIsPHI - Check if an instruction is a PHI.
305 static PHINode *InstrIsPHI(Instruction *I) {
306 return dyn_cast<PHINode>(I);
309 /// ValueIsPHI - Check if a value is a PHI.
311 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
312 return dyn_cast<PHINode>(Val);
315 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
316 /// operands, i.e., it was just added.
317 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
318 PHINode *PHI = ValueIsPHI(Val, Updater);
319 if (PHI && PHI->getNumIncomingValues() == 0)
324 /// GetPHIValue - For the specified PHI instruction, return the value
326 static Value *GetPHIValue(PHINode *PHI) {
331 } // End llvm namespace
333 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
334 /// for the specified BB and if so, return it. If not, construct SSA form by
335 /// first calculating the required placement of PHIs and then inserting new
336 /// PHIs where needed.
337 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
338 AvailableValsTy &AvailableVals = getAvailableVals(AV);
339 if (Value *V = AvailableVals[BB])
342 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
343 return Impl.GetValue(BB);