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/Transforms/Utils/SSAUpdater.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/TinyPtrVector.h"
18 #include "llvm/Analysis/InstructionSimplify.h"
19 #include "llvm/IR/Constants.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/IntrinsicInst.h"
22 #include "llvm/Support/AlignOf.h"
23 #include "llvm/Support/Allocator.h"
24 #include "llvm/Support/CFG.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/Transforms/Utils/Local.h"
29 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
33 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
34 static AvailableValsTy &getAvailableVals(void *AV) {
35 return *static_cast<AvailableValsTy*>(AV);
38 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
39 : AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}
41 SSAUpdater::~SSAUpdater() {
42 delete static_cast<AvailableValsTy*>(AV);
45 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
47 AV = new AvailableValsTy();
49 getAvailableVals(AV).clear();
54 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
55 return getAvailableVals(AV).count(BB);
58 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
59 assert(ProtoType != 0 && "Need to initialize SSAUpdater");
60 assert(ProtoType == V->getType() &&
61 "All rewritten values must have the same type");
62 getAvailableVals(AV)[BB] = V;
65 static bool IsEquivalentPHI(PHINode *PHI,
66 SmallDenseMap<BasicBlock*, Value*, 8> &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 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
82 Value *Res = GetValueAtEndOfBlockInternal(BB);
86 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
87 // If there is no definition of the renamed variable in this block, just use
88 // GetValueAtEndOfBlock to do our work.
89 if (!HasValueForBlock(BB))
90 return GetValueAtEndOfBlock(BB);
92 // Otherwise, we have the hard case. Get the live-in values for each
94 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
95 Value *SingularValue = 0;
97 // We can get our predecessor info by walking the pred_iterator list, but it
98 // is relatively slow. If we already have PHI nodes in this block, walk one
99 // of them to get the predecessor list instead.
100 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
101 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
102 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
103 Value *PredVal = GetValueAtEndOfBlock(PredBB);
104 PredValues.push_back(std::make_pair(PredBB, PredVal));
106 // Compute SingularValue.
108 SingularValue = PredVal;
109 else if (PredVal != SingularValue)
113 bool isFirstPred = true;
114 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
115 BasicBlock *PredBB = *PI;
116 Value *PredVal = GetValueAtEndOfBlock(PredBB);
117 PredValues.push_back(std::make_pair(PredBB, PredVal));
119 // Compute SingularValue.
121 SingularValue = PredVal;
123 } else if (PredVal != SingularValue)
128 // If there are no predecessors, just return undef.
129 if (PredValues.empty())
130 return UndefValue::get(ProtoType);
132 // Otherwise, if all the merged values are the same, just use it.
133 if (SingularValue != 0)
134 return SingularValue;
136 // Otherwise, we do need a PHI: check to see if we already have one available
137 // in this block that produces the right value.
138 if (isa<PHINode>(BB->begin())) {
139 SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
142 for (BasicBlock::iterator It = BB->begin();
143 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
144 if (IsEquivalentPHI(SomePHI, ValueMapping))
149 // Ok, we have no way out, insert a new one now.
150 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
151 ProtoName, &BB->front());
153 // Fill in all the predecessors of the PHI.
154 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
155 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
157 // See if the PHI node can be merged to a single value. This can happen in
158 // loop cases when we get a PHI of itself and one other value.
159 if (Value *V = SimplifyInstruction(InsertedPHI)) {
160 InsertedPHI->eraseFromParent();
164 // Set the DebugLoc of the inserted PHI, if available.
166 if (const Instruction *I = BB->getFirstNonPHI())
167 DL = I->getDebugLoc();
168 InsertedPHI->setDebugLoc(DL);
170 // If the client wants to know about all new instructions, tell it.
171 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
173 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
177 void SSAUpdater::RewriteUse(Use &U) {
178 Instruction *User = cast<Instruction>(U.getUser());
181 if (PHINode *UserPN = dyn_cast<PHINode>(User))
182 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
184 V = GetValueInMiddleOfBlock(User->getParent());
186 // Notify that users of the existing value that it is being replaced.
187 Value *OldVal = U.get();
188 if (OldVal != V && OldVal->hasValueHandle())
189 ValueHandleBase::ValueIsRAUWd(OldVal, V);
194 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
195 Instruction *User = cast<Instruction>(U.getUser());
198 if (PHINode *UserPN = dyn_cast<PHINode>(User))
199 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
201 V = GetValueAtEndOfBlock(User->getParent());
208 class SSAUpdaterTraits<SSAUpdater> {
210 typedef BasicBlock BlkT;
212 typedef PHINode PhiT;
214 typedef succ_iterator BlkSucc_iterator;
215 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
216 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
224 explicit PHI_iterator(PHINode *P) // begin iterator
226 PHI_iterator(PHINode *P, bool) // end iterator
227 : PHI(P), idx(PHI->getNumIncomingValues()) {}
229 PHI_iterator &operator++() { ++idx; return *this; }
230 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
231 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
232 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
233 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
236 static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
237 static PHI_iterator PHI_end(PhiT *PHI) {
238 return PHI_iterator(PHI, true);
241 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
242 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
243 static void FindPredecessorBlocks(BasicBlock *BB,
244 SmallVectorImpl<BasicBlock*> *Preds) {
245 // We can get our predecessor info by walking the pred_iterator list,
246 // but it is relatively slow. If we already have PHI nodes in this
247 // block, walk one of them to get the predecessor list instead.
248 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
249 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
250 Preds->push_back(SomePhi->getIncomingBlock(PI));
252 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
253 Preds->push_back(*PI);
257 /// GetUndefVal - Get an undefined value of the same type as the value
259 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
260 return UndefValue::get(Updater->ProtoType);
263 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
264 /// Reserve space for the operands but do not fill them in yet.
265 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
266 SSAUpdater *Updater) {
267 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
268 Updater->ProtoName, &BB->front());
272 /// AddPHIOperand - Add the specified value as an operand of the PHI for
273 /// the specified predecessor block.
274 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
275 PHI->addIncoming(Val, Pred);
278 /// InstrIsPHI - Check if an instruction is a PHI.
280 static PHINode *InstrIsPHI(Instruction *I) {
281 return dyn_cast<PHINode>(I);
284 /// ValueIsPHI - Check if a value is a PHI.
286 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
287 return dyn_cast<PHINode>(Val);
290 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
291 /// operands, i.e., it was just added.
292 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
293 PHINode *PHI = ValueIsPHI(Val, Updater);
294 if (PHI && PHI->getNumIncomingValues() == 0)
299 /// GetPHIValue - For the specified PHI instruction, return the value
301 static Value *GetPHIValue(PHINode *PHI) {
306 } // End llvm namespace
308 /// Check to see if AvailableVals has an entry for the specified BB and if so,
309 /// return it. If not, construct SSA form by first calculating the required
310 /// placement of PHIs and then inserting new PHIs where needed.
311 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
312 AvailableValsTy &AvailableVals = getAvailableVals(AV);
313 if (Value *V = AvailableVals[BB])
316 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
317 return Impl.GetValue(BB);
320 //===----------------------------------------------------------------------===//
321 // LoadAndStorePromoter Implementation
322 //===----------------------------------------------------------------------===//
324 LoadAndStorePromoter::
325 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
326 SSAUpdater &S, StringRef BaseName) : SSA(S) {
327 if (Insts.empty()) return;
330 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
333 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
335 if (BaseName.empty())
336 BaseName = SomeVal->getName();
337 SSA.Initialize(SomeVal->getType(), BaseName);
341 void LoadAndStorePromoter::
342 run(const SmallVectorImpl<Instruction*> &Insts) const {
344 // First step: bucket up uses of the alloca by the block they occur in.
345 // This is important because we have to handle multiple defs/uses in a block
346 // ourselves: SSAUpdater is purely for cross-block references.
347 DenseMap<BasicBlock*, TinyPtrVector<Instruction*> > UsesByBlock;
349 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
350 Instruction *User = Insts[i];
351 UsesByBlock[User->getParent()].push_back(User);
354 // Okay, now we can iterate over all the blocks in the function with uses,
355 // processing them. Keep track of which loads are loading a live-in value.
356 // Walk the uses in the use-list order to be determinstic.
357 SmallVector<LoadInst*, 32> LiveInLoads;
358 DenseMap<Value*, Value*> ReplacedLoads;
360 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
361 Instruction *User = Insts[i];
362 BasicBlock *BB = User->getParent();
363 TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
365 // If this block has already been processed, ignore this repeat use.
366 if (BlockUses.empty()) continue;
368 // Okay, this is the first use in the block. If this block just has a
369 // single user in it, we can rewrite it trivially.
370 if (BlockUses.size() == 1) {
371 // If it is a store, it is a trivial def of the value in the block.
372 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
374 SSA.AddAvailableValue(BB, SI->getOperand(0));
376 // Otherwise it is a load, queue it to rewrite as a live-in load.
377 LiveInLoads.push_back(cast<LoadInst>(User));
382 // Otherwise, check to see if this block is all loads.
383 bool HasStore = false;
384 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
385 if (isa<StoreInst>(BlockUses[i])) {
391 // If so, we can queue them all as live in loads. We don't have an
392 // efficient way to tell which on is first in the block and don't want to
393 // scan large blocks, so just add all loads as live ins.
395 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
396 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
401 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
402 // Since SSAUpdater is purely for cross-block values, we need to determine
403 // the order of these instructions in the block. If the first use in the
404 // block is a load, then it uses the live in value. The last store defines
405 // the live out value. We handle this by doing a linear scan of the block.
406 Value *StoredValue = 0;
407 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
408 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
409 // If this is a load from an unrelated pointer, ignore it.
410 if (!isInstInList(L, Insts)) continue;
412 // If we haven't seen a store yet, this is a live in use, otherwise
413 // use the stored value.
415 replaceLoadWithValue(L, StoredValue);
416 L->replaceAllUsesWith(StoredValue);
417 ReplacedLoads[L] = StoredValue;
419 LiveInLoads.push_back(L);
424 if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
425 // If this is a store to an unrelated pointer, ignore it.
426 if (!isInstInList(SI, Insts)) continue;
429 // Remember that this is the active value in the block.
430 StoredValue = SI->getOperand(0);
434 // The last stored value that happened is the live-out for the block.
435 assert(StoredValue && "Already checked that there is a store in block");
436 SSA.AddAvailableValue(BB, StoredValue);
440 // Okay, now we rewrite all loads that use live-in values in the loop,
441 // inserting PHI nodes as necessary.
442 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
443 LoadInst *ALoad = LiveInLoads[i];
444 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
445 replaceLoadWithValue(ALoad, NewVal);
447 // Avoid assertions in unreachable code.
448 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
449 ALoad->replaceAllUsesWith(NewVal);
450 ReplacedLoads[ALoad] = NewVal;
453 // Allow the client to do stuff before we start nuking things.
454 doExtraRewritesBeforeFinalDeletion();
456 // Now that everything is rewritten, delete the old instructions from the
457 // function. They should all be dead now.
458 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
459 Instruction *User = Insts[i];
461 // If this is a load that still has uses, then the load must have been added
462 // as a live value in the SSAUpdate data structure for a block (e.g. because
463 // the loaded value was stored later). In this case, we need to recursively
464 // propagate the updates until we get to the real value.
465 if (!User->use_empty()) {
466 Value *NewVal = ReplacedLoads[User];
467 assert(NewVal && "not a replaced load?");
469 // Propagate down to the ultimate replacee. The intermediately loads
470 // could theoretically already have been deleted, so we don't want to
471 // dereference the Value*'s.
472 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
473 while (RLI != ReplacedLoads.end()) {
474 NewVal = RLI->second;
475 RLI = ReplacedLoads.find(NewVal);
478 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
479 User->replaceAllUsesWith(NewVal);
482 instructionDeleted(User);
483 User->eraseFromParent();
488 LoadAndStorePromoter::isInstInList(Instruction *I,
489 const SmallVectorImpl<Instruction*> &Insts)
491 return std::find(Insts.begin(), Insts.end(), I) != Insts.end();