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 #include "llvm/Transforms/Utils/SSAUpdater.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/TinyPtrVector.h"
17 #include "llvm/Analysis/InstructionSimplify.h"
18 #include "llvm/IR/CFG.h"
19 #include "llvm/IR/Constants.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/IntrinsicInst.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/Local.h"
26 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
30 #define DEBUG_TYPE "ssaupdater"
32 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
33 static AvailableValsTy &getAvailableVals(void *AV) {
34 return *static_cast<AvailableValsTy*>(AV);
37 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
38 : AV(nullptr), ProtoType(nullptr), ProtoName(), InsertedPHIs(NewPHI) {}
40 SSAUpdater::~SSAUpdater() {
41 delete static_cast<AvailableValsTy*>(AV);
44 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
46 AV = new AvailableValsTy();
48 getAvailableVals(AV).clear();
53 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
54 return getAvailableVals(AV).count(BB);
57 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
58 assert(ProtoType && "Need to initialize SSAUpdater");
59 assert(ProtoType == V->getType() &&
60 "All rewritten values must have the same type");
61 getAvailableVals(AV)[BB] = V;
64 static bool IsEquivalentPHI(PHINode *PHI,
65 SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
66 unsigned PHINumValues = PHI->getNumIncomingValues();
67 if (PHINumValues != ValueMapping.size())
70 // Scan the phi to see if it matches.
71 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
72 if (ValueMapping[PHI->getIncomingBlock(i)] !=
73 PHI->getIncomingValue(i)) {
80 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
81 Value *Res = GetValueAtEndOfBlockInternal(BB);
85 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
86 // If there is no definition of the renamed variable in this block, just use
87 // GetValueAtEndOfBlock to do our work.
88 if (!HasValueForBlock(BB))
89 return GetValueAtEndOfBlock(BB);
91 // Otherwise, we have the hard case. Get the live-in values for each
93 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
94 Value *SingularValue = nullptr;
96 // We can get our predecessor info by walking the pred_iterator list, but it
97 // is relatively slow. If we already have PHI nodes in this block, walk one
98 // of them to get the predecessor list instead.
99 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
100 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
101 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
102 Value *PredVal = GetValueAtEndOfBlock(PredBB);
103 PredValues.push_back(std::make_pair(PredBB, PredVal));
105 // Compute SingularValue.
107 SingularValue = PredVal;
108 else if (PredVal != SingularValue)
109 SingularValue = nullptr;
112 bool isFirstPred = true;
113 for (BasicBlock *PredBB : predecessors(BB)) {
114 Value *PredVal = GetValueAtEndOfBlock(PredBB);
115 PredValues.push_back(std::make_pair(PredBB, PredVal));
117 // Compute SingularValue.
119 SingularValue = PredVal;
121 } else if (PredVal != SingularValue)
122 SingularValue = nullptr;
126 // If there are no predecessors, just return undef.
127 if (PredValues.empty())
128 return UndefValue::get(ProtoType);
130 // Otherwise, if all the merged values are the same, just use it.
132 return SingularValue;
134 // Otherwise, we do need a PHI: check to see if we already have one available
135 // in this block that produces the right value.
136 if (isa<PHINode>(BB->begin())) {
137 SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
140 for (BasicBlock::iterator It = BB->begin();
141 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
142 if (IsEquivalentPHI(SomePHI, ValueMapping))
147 // Ok, we have no way out, insert a new one now.
148 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
149 ProtoName, &BB->front());
151 // Fill in all the predecessors of the PHI.
152 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
153 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
155 // See if the PHI node can be merged to a single value. This can happen in
156 // loop cases when we get a PHI of itself and one other value.
157 if (Value *V = SimplifyInstruction(InsertedPHI)) {
158 InsertedPHI->eraseFromParent();
162 // Set the DebugLoc of the inserted PHI, if available.
164 if (const Instruction *I = BB->getFirstNonPHI())
165 DL = I->getDebugLoc();
166 InsertedPHI->setDebugLoc(DL);
168 // If the client wants to know about all new instructions, tell it.
169 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
171 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
175 void SSAUpdater::RewriteUse(Use &U) {
176 Instruction *User = cast<Instruction>(U.getUser());
179 if (PHINode *UserPN = dyn_cast<PHINode>(User))
180 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
182 V = GetValueInMiddleOfBlock(User->getParent());
184 // Notify that users of the existing value that it is being replaced.
185 Value *OldVal = U.get();
186 if (OldVal != V && OldVal->hasValueHandle())
187 ValueHandleBase::ValueIsRAUWd(OldVal, V);
192 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
193 Instruction *User = cast<Instruction>(U.getUser());
196 if (PHINode *UserPN = dyn_cast<PHINode>(User))
197 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
199 V = GetValueAtEndOfBlock(User->getParent());
206 class SSAUpdaterTraits<SSAUpdater> {
208 typedef BasicBlock BlkT;
210 typedef PHINode PhiT;
212 typedef succ_iterator BlkSucc_iterator;
213 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
214 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
222 explicit PHI_iterator(PHINode *P) // begin iterator
224 PHI_iterator(PHINode *P, bool) // end iterator
225 : PHI(P), idx(PHI->getNumIncomingValues()) {}
227 PHI_iterator &operator++() { ++idx; return *this; }
228 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
229 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
230 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
231 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
234 static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
235 static PHI_iterator PHI_end(PhiT *PHI) {
236 return PHI_iterator(PHI, true);
239 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
240 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
241 static void FindPredecessorBlocks(BasicBlock *BB,
242 SmallVectorImpl<BasicBlock*> *Preds) {
243 // We can get our predecessor info by walking the pred_iterator list,
244 // but it is relatively slow. If we already have PHI nodes in this
245 // block, walk one of them to get the predecessor list instead.
246 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
247 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
248 Preds->push_back(SomePhi->getIncomingBlock(PI));
250 Preds->insert(Preds->end(), pred_begin(BB), pred_end(BB));
254 /// GetUndefVal - Get an undefined value of the same type as the value
256 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
257 return UndefValue::get(Updater->ProtoType);
260 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
261 /// Reserve space for the operands but do not fill them in yet.
262 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
263 SSAUpdater *Updater) {
264 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
265 Updater->ProtoName, &BB->front());
269 /// AddPHIOperand - Add the specified value as an operand of the PHI for
270 /// the specified predecessor block.
271 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
272 PHI->addIncoming(Val, Pred);
275 /// InstrIsPHI - Check if an instruction is a PHI.
277 static PHINode *InstrIsPHI(Instruction *I) {
278 return dyn_cast<PHINode>(I);
281 /// ValueIsPHI - Check if a value is a PHI.
283 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
284 return dyn_cast<PHINode>(Val);
287 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
288 /// operands, i.e., it was just added.
289 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
290 PHINode *PHI = ValueIsPHI(Val, Updater);
291 if (PHI && PHI->getNumIncomingValues() == 0)
296 /// GetPHIValue - For the specified PHI instruction, return the value
298 static Value *GetPHIValue(PHINode *PHI) {
303 } // End llvm namespace
305 /// Check to see if AvailableVals has an entry for the specified BB and if so,
306 /// return it. If not, construct SSA form by first calculating the required
307 /// placement of PHIs and then inserting new PHIs where needed.
308 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
309 AvailableValsTy &AvailableVals = getAvailableVals(AV);
310 if (Value *V = AvailableVals[BB])
313 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
314 return Impl.GetValue(BB);
317 //===----------------------------------------------------------------------===//
318 // LoadAndStorePromoter Implementation
319 //===----------------------------------------------------------------------===//
321 LoadAndStorePromoter::
322 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
323 SSAUpdater &S, StringRef BaseName) : SSA(S) {
324 if (Insts.empty()) return;
327 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
330 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
332 if (BaseName.empty())
333 BaseName = SomeVal->getName();
334 SSA.Initialize(SomeVal->getType(), BaseName);
338 void LoadAndStorePromoter::
339 run(const SmallVectorImpl<Instruction*> &Insts) const {
341 // First step: bucket up uses of the alloca by the block they occur in.
342 // This is important because we have to handle multiple defs/uses in a block
343 // ourselves: SSAUpdater is purely for cross-block references.
344 DenseMap<BasicBlock*, TinyPtrVector<Instruction*> > UsesByBlock;
346 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
347 Instruction *User = Insts[i];
348 UsesByBlock[User->getParent()].push_back(User);
351 // Okay, now we can iterate over all the blocks in the function with uses,
352 // processing them. Keep track of which loads are loading a live-in value.
353 // Walk the uses in the use-list order to be determinstic.
354 SmallVector<LoadInst*, 32> LiveInLoads;
355 DenseMap<Value*, Value*> ReplacedLoads;
357 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
358 Instruction *User = Insts[i];
359 BasicBlock *BB = User->getParent();
360 TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
362 // If this block has already been processed, ignore this repeat use.
363 if (BlockUses.empty()) continue;
365 // Okay, this is the first use in the block. If this block just has a
366 // single user in it, we can rewrite it trivially.
367 if (BlockUses.size() == 1) {
368 // If it is a store, it is a trivial def of the value in the block.
369 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
371 SSA.AddAvailableValue(BB, SI->getOperand(0));
373 // Otherwise it is a load, queue it to rewrite as a live-in load.
374 LiveInLoads.push_back(cast<LoadInst>(User));
379 // Otherwise, check to see if this block is all loads.
380 bool HasStore = false;
381 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
382 if (isa<StoreInst>(BlockUses[i])) {
388 // If so, we can queue them all as live in loads. We don't have an
389 // efficient way to tell which on is first in the block and don't want to
390 // scan large blocks, so just add all loads as live ins.
392 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
393 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
398 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
399 // Since SSAUpdater is purely for cross-block values, we need to determine
400 // the order of these instructions in the block. If the first use in the
401 // block is a load, then it uses the live in value. The last store defines
402 // the live out value. We handle this by doing a linear scan of the block.
403 Value *StoredValue = nullptr;
404 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
405 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
406 // If this is a load from an unrelated pointer, ignore it.
407 if (!isInstInList(L, Insts)) continue;
409 // If we haven't seen a store yet, this is a live in use, otherwise
410 // use the stored value.
412 replaceLoadWithValue(L, StoredValue);
413 L->replaceAllUsesWith(StoredValue);
414 ReplacedLoads[L] = StoredValue;
416 LiveInLoads.push_back(L);
421 if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
422 // If this is a store to an unrelated pointer, ignore it.
423 if (!isInstInList(SI, Insts)) continue;
426 // Remember that this is the active value in the block.
427 StoredValue = SI->getOperand(0);
431 // The last stored value that happened is the live-out for the block.
432 assert(StoredValue && "Already checked that there is a store in block");
433 SSA.AddAvailableValue(BB, StoredValue);
437 // Okay, now we rewrite all loads that use live-in values in the loop,
438 // inserting PHI nodes as necessary.
439 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
440 LoadInst *ALoad = LiveInLoads[i];
441 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
442 replaceLoadWithValue(ALoad, NewVal);
444 // Avoid assertions in unreachable code.
445 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
446 ALoad->replaceAllUsesWith(NewVal);
447 ReplacedLoads[ALoad] = NewVal;
450 // Allow the client to do stuff before we start nuking things.
451 doExtraRewritesBeforeFinalDeletion();
453 // Now that everything is rewritten, delete the old instructions from the
454 // function. They should all be dead now.
455 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
456 Instruction *User = Insts[i];
458 // If this is a load that still has uses, then the load must have been added
459 // as a live value in the SSAUpdate data structure for a block (e.g. because
460 // the loaded value was stored later). In this case, we need to recursively
461 // propagate the updates until we get to the real value.
462 if (!User->use_empty()) {
463 Value *NewVal = ReplacedLoads[User];
464 assert(NewVal && "not a replaced load?");
466 // Propagate down to the ultimate replacee. The intermediately loads
467 // could theoretically already have been deleted, so we don't want to
468 // dereference the Value*'s.
469 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
470 while (RLI != ReplacedLoads.end()) {
471 NewVal = RLI->second;
472 RLI = ReplacedLoads.find(NewVal);
475 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
476 User->replaceAllUsesWith(NewVal);
479 instructionDeleted(User);
480 User->eraseFromParent();
485 LoadAndStorePromoter::isInstInList(Instruction *I,
486 const SmallVectorImpl<Instruction*> &Insts)
488 return std::find(Insts.begin(), Insts.end(), I) != Insts.end();