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/Constants.h"
16 #include "llvm/Instructions.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/Analysis/InstructionSimplify.h"
19 #include "llvm/Support/AlignOf.h"
20 #include "llvm/Support/Allocator.h"
21 #include "llvm/Support/CFG.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/raw_ostream.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/Transforms/Utils/SSAUpdater.h"
26 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
30 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
31 static AvailableValsTy &getAvailableVals(void *AV) {
32 return *static_cast<AvailableValsTy*>(AV);
35 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
36 : AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}
38 SSAUpdater::~SSAUpdater() {
39 delete &getAvailableVals(AV);
42 /// Initialize - Reset this object to get ready for a new set of SSA
43 /// updates with type 'Ty'. PHI nodes get a name based on 'Name'.
44 void SSAUpdater::Initialize(const Type *Ty, StringRef Name) {
46 AV = new AvailableValsTy();
48 getAvailableVals(AV).clear();
53 /// HasValueForBlock - Return true if the SSAUpdater already has a value for
54 /// the specified block.
55 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
56 return getAvailableVals(AV).count(BB);
59 /// AddAvailableValue - Indicate that a rewritten value is available in the
60 /// specified block with the specified value.
61 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
62 assert(ProtoType != 0 && "Need to initialize SSAUpdater");
63 assert(ProtoType == V->getType() &&
64 "All rewritten values must have the same type");
65 getAvailableVals(AV)[BB] = V;
68 /// IsEquivalentPHI - Check if PHI has the same incoming value as specified
69 /// in ValueMapping for each predecessor block.
70 static bool IsEquivalentPHI(PHINode *PHI,
71 DenseMap<BasicBlock*, Value*> &ValueMapping) {
72 unsigned PHINumValues = PHI->getNumIncomingValues();
73 if (PHINumValues != ValueMapping.size())
76 // Scan the phi to see if it matches.
77 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
78 if (ValueMapping[PHI->getIncomingBlock(i)] !=
79 PHI->getIncomingValue(i)) {
86 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
87 /// live at the end of the specified block.
88 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
89 Value *Res = GetValueAtEndOfBlockInternal(BB);
93 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
94 /// is live in the middle of the specified block.
96 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
97 /// important case: if there is a definition of the rewritten value after the
98 /// 'use' in BB. Consider code like this:
104 /// br Cond, SomeBB, OutBB
106 /// In this case, there are two values (X1 and X2) added to the AvailableVals
107 /// set by the client of the rewriter, and those values are both live out of
108 /// their respective blocks. However, the use of X happens in the *middle* of
109 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
110 /// merge the appropriate values, and this value isn't live out of the block.
112 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
113 // If there is no definition of the renamed variable in this block, just use
114 // GetValueAtEndOfBlock to do our work.
115 if (!HasValueForBlock(BB))
116 return GetValueAtEndOfBlock(BB);
118 // Otherwise, we have the hard case. Get the live-in values for each
120 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
121 Value *SingularValue = 0;
123 // We can get our predecessor info by walking the pred_iterator list, but it
124 // is relatively slow. If we already have PHI nodes in this block, walk one
125 // of them to get the predecessor list instead.
126 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
127 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
128 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
129 Value *PredVal = GetValueAtEndOfBlock(PredBB);
130 PredValues.push_back(std::make_pair(PredBB, PredVal));
132 // Compute SingularValue.
134 SingularValue = PredVal;
135 else if (PredVal != SingularValue)
139 bool isFirstPred = true;
140 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
141 BasicBlock *PredBB = *PI;
142 Value *PredVal = GetValueAtEndOfBlock(PredBB);
143 PredValues.push_back(std::make_pair(PredBB, PredVal));
145 // Compute SingularValue.
147 SingularValue = PredVal;
149 } else if (PredVal != SingularValue)
154 // If there are no predecessors, just return undef.
155 if (PredValues.empty())
156 return UndefValue::get(ProtoType);
158 // Otherwise, if all the merged values are the same, just use it.
159 if (SingularValue != 0)
160 return SingularValue;
162 // Otherwise, we do need a PHI: check to see if we already have one available
163 // in this block that produces the right value.
164 if (isa<PHINode>(BB->begin())) {
165 DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
168 for (BasicBlock::iterator It = BB->begin();
169 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
170 if (IsEquivalentPHI(SomePHI, ValueMapping))
175 // Ok, we have no way out, insert a new one now.
176 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
177 ProtoName, &BB->front());
179 // Fill in all the predecessors of the PHI.
180 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
181 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
183 // See if the PHI node can be merged to a single value. This can happen in
184 // loop cases when we get a PHI of itself and one other value.
185 if (Value *V = SimplifyInstruction(InsertedPHI)) {
186 InsertedPHI->eraseFromParent();
191 InsertedPHI->setDebugLoc(GetFirstDebugLocInBasicBlock(BB));
193 // If the client wants to know about all new instructions, tell it.
194 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
196 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
200 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
201 /// which use their value in the corresponding predecessor.
202 void SSAUpdater::RewriteUse(Use &U) {
203 Instruction *User = cast<Instruction>(U.getUser());
206 if (PHINode *UserPN = dyn_cast<PHINode>(User))
207 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
209 V = GetValueInMiddleOfBlock(User->getParent());
214 /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However,
215 /// this version of the method can rewrite uses in the same block as a
216 /// definition, because it assumes that all uses of a value are below any
218 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
219 Instruction *User = cast<Instruction>(U.getUser());
222 if (PHINode *UserPN = dyn_cast<PHINode>(User))
223 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
225 V = GetValueAtEndOfBlock(User->getParent());
230 /// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
231 /// in the SSAUpdaterImpl template.
239 explicit PHIiter(PHINode *P) // begin iterator
241 PHIiter(PHINode *P, bool) // end iterator
242 : PHI(P), idx(PHI->getNumIncomingValues()) {}
244 PHIiter &operator++() { ++idx; return *this; }
245 bool operator==(const PHIiter& x) const { return idx == x.idx; }
246 bool operator!=(const PHIiter& x) const { return !operator==(x); }
247 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
248 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
252 /// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
253 /// specialized for SSAUpdater.
256 class SSAUpdaterTraits<SSAUpdater> {
258 typedef BasicBlock BlkT;
260 typedef PHINode PhiT;
262 typedef succ_iterator BlkSucc_iterator;
263 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
264 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
266 typedef PHIiter PHI_iterator;
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 Info->BB into the Preds
273 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
274 static void FindPredecessorBlocks(BasicBlock *BB,
275 SmallVectorImpl<BasicBlock*> *Preds) {
276 // We can get our predecessor info by walking the pred_iterator list,
277 // but it is relatively slow. If we already have PHI nodes in this
278 // block, walk one of them to get the predecessor list instead.
279 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
280 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
281 Preds->push_back(SomePhi->getIncomingBlock(PI));
283 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
284 Preds->push_back(*PI);
288 /// GetUndefVal - Get an undefined value of the same type as the value
290 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
291 return UndefValue::get(Updater->ProtoType);
294 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
295 /// Reserve space for the operands but do not fill them in yet.
296 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
297 SSAUpdater *Updater) {
298 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
299 Updater->ProtoName, &BB->front());
303 /// AddPHIOperand - Add the specified value as an operand of the PHI for
304 /// the specified predecessor block.
305 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
306 PHI->addIncoming(Val, Pred);
309 /// InstrIsPHI - Check if an instruction is a PHI.
311 static PHINode *InstrIsPHI(Instruction *I) {
312 return dyn_cast<PHINode>(I);
315 /// ValueIsPHI - Check if a value is a PHI.
317 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
318 return dyn_cast<PHINode>(Val);
321 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
322 /// operands, i.e., it was just added.
323 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
324 PHINode *PHI = ValueIsPHI(Val, Updater);
325 if (PHI && PHI->getNumIncomingValues() == 0)
330 /// GetPHIValue - For the specified PHI instruction, return the value
332 static Value *GetPHIValue(PHINode *PHI) {
337 } // End llvm namespace
339 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
340 /// for the specified BB and if so, return it. If not, construct SSA form by
341 /// first calculating the required placement of PHIs and then inserting new
342 /// PHIs where needed.
343 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
344 AvailableValsTy &AvailableVals = getAvailableVals(AV);
345 if (Value *V = AvailableVals[BB])
348 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
349 return Impl.GetValue(BB);
352 //===----------------------------------------------------------------------===//
353 // LoadAndStorePromoter Implementation
354 //===----------------------------------------------------------------------===//
356 LoadAndStorePromoter::
357 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
358 SSAUpdater &S, StringRef BaseName) : SSA(S) {
359 if (Insts.empty()) return;
362 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
365 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
367 if (BaseName.empty())
368 BaseName = SomeVal->getName();
369 SSA.Initialize(SomeVal->getType(), BaseName);
373 void LoadAndStorePromoter::
374 run(const SmallVectorImpl<Instruction*> &Insts) const {
376 // First step: bucket up uses of the alloca by the block they occur in.
377 // This is important because we have to handle multiple defs/uses in a block
378 // ourselves: SSAUpdater is purely for cross-block references.
379 // FIXME: Want a TinyVector<Instruction*> since there is often 0/1 element.
380 DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock;
382 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
383 Instruction *User = Insts[i];
384 UsesByBlock[User->getParent()].push_back(User);
387 // Okay, now we can iterate over all the blocks in the function with uses,
388 // processing them. Keep track of which loads are loading a live-in value.
389 // Walk the uses in the use-list order to be determinstic.
390 SmallVector<LoadInst*, 32> LiveInLoads;
391 DenseMap<Value*, Value*> ReplacedLoads;
393 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
394 Instruction *User = Insts[i];
395 BasicBlock *BB = User->getParent();
396 std::vector<Instruction*> &BlockUses = UsesByBlock[BB];
398 // If this block has already been processed, ignore this repeat use.
399 if (BlockUses.empty()) continue;
401 // Okay, this is the first use in the block. If this block just has a
402 // single user in it, we can rewrite it trivially.
403 if (BlockUses.size() == 1) {
404 // If it is a store, it is a trivial def of the value in the block.
405 if (StoreInst *SI = dyn_cast<StoreInst>(User))
406 SSA.AddAvailableValue(BB, SI->getOperand(0));
408 // Otherwise it is a load, queue it to rewrite as a live-in load.
409 LiveInLoads.push_back(cast<LoadInst>(User));
414 // Otherwise, check to see if this block is all loads.
415 bool HasStore = false;
416 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
417 if (isa<StoreInst>(BlockUses[i])) {
423 // If so, we can queue them all as live in loads. We don't have an
424 // efficient way to tell which on is first in the block and don't want to
425 // scan large blocks, so just add all loads as live ins.
427 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
428 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
433 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
434 // Since SSAUpdater is purely for cross-block values, we need to determine
435 // the order of these instructions in the block. If the first use in the
436 // block is a load, then it uses the live in value. The last store defines
437 // the live out value. We handle this by doing a linear scan of the block.
438 Value *StoredValue = 0;
439 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
440 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
441 // If this is a load from an unrelated pointer, ignore it.
442 if (!isInstInList(L, Insts)) continue;
444 // If we haven't seen a store yet, this is a live in use, otherwise
445 // use the stored value.
447 replaceLoadWithValue(L, StoredValue);
448 L->replaceAllUsesWith(StoredValue);
449 ReplacedLoads[L] = StoredValue;
451 LiveInLoads.push_back(L);
456 if (StoreInst *S = dyn_cast<StoreInst>(II)) {
457 // If this is a store to an unrelated pointer, ignore it.
458 if (!isInstInList(S, Insts)) continue;
460 // Remember that this is the active value in the block.
461 StoredValue = S->getOperand(0);
465 // The last stored value that happened is the live-out for the block.
466 assert(StoredValue && "Already checked that there is a store in block");
467 SSA.AddAvailableValue(BB, StoredValue);
471 // Okay, now we rewrite all loads that use live-in values in the loop,
472 // inserting PHI nodes as necessary.
473 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
474 LoadInst *ALoad = LiveInLoads[i];
475 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
476 replaceLoadWithValue(ALoad, NewVal);
478 // Avoid assertions in unreachable code.
479 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
480 ALoad->replaceAllUsesWith(NewVal);
481 ReplacedLoads[ALoad] = NewVal;
484 // Allow the client to do stuff before we start nuking things.
485 doExtraRewritesBeforeFinalDeletion();
487 // Now that everything is rewritten, delete the old instructions from the
488 // function. They should all be dead now.
489 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
490 Instruction *User = Insts[i];
492 // If this is a load that still has uses, then the load must have been added
493 // as a live value in the SSAUpdate data structure for a block (e.g. because
494 // the loaded value was stored later). In this case, we need to recursively
495 // propagate the updates until we get to the real value.
496 if (!User->use_empty()) {
497 Value *NewVal = ReplacedLoads[User];
498 assert(NewVal && "not a replaced load?");
500 // Propagate down to the ultimate replacee. The intermediately loads
501 // could theoretically already have been deleted, so we don't want to
502 // dereference the Value*'s.
503 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
504 while (RLI != ReplacedLoads.end()) {
505 NewVal = RLI->second;
506 RLI = ReplacedLoads.find(NewVal);
509 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
510 User->replaceAllUsesWith(NewVal);
513 instructionDeleted(User);
514 User->eraseFromParent();