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/CFG.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/Transforms/Utils/Local.h"
27 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
31 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
32 static AvailableValsTy &getAvailableVals(void *AV) {
33 return *static_cast<AvailableValsTy*>(AV);
36 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
37 : AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}
39 SSAUpdater::~SSAUpdater() {
40 delete static_cast<AvailableValsTy*>(AV);
43 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
45 AV = new AvailableValsTy();
47 getAvailableVals(AV).clear();
52 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
53 return getAvailableVals(AV).count(BB);
56 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
57 assert(ProtoType != 0 && "Need to initialize SSAUpdater");
58 assert(ProtoType == V->getType() &&
59 "All rewritten values must have the same type");
60 getAvailableVals(AV)[BB] = V;
63 static bool IsEquivalentPHI(PHINode *PHI,
64 SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
65 unsigned PHINumValues = PHI->getNumIncomingValues();
66 if (PHINumValues != ValueMapping.size())
69 // Scan the phi to see if it matches.
70 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
71 if (ValueMapping[PHI->getIncomingBlock(i)] !=
72 PHI->getIncomingValue(i)) {
79 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
80 Value *Res = GetValueAtEndOfBlockInternal(BB);
84 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
85 // If there is no definition of the renamed variable in this block, just use
86 // GetValueAtEndOfBlock to do our work.
87 if (!HasValueForBlock(BB))
88 return GetValueAtEndOfBlock(BB);
90 // Otherwise, we have the hard case. Get the live-in values for each
92 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
93 Value *SingularValue = 0;
95 // We can get our predecessor info by walking the pred_iterator list, but it
96 // is relatively slow. If we already have PHI nodes in this block, walk one
97 // of them to get the predecessor list instead.
98 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
99 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
100 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
101 Value *PredVal = GetValueAtEndOfBlock(PredBB);
102 PredValues.push_back(std::make_pair(PredBB, PredVal));
104 // Compute SingularValue.
106 SingularValue = PredVal;
107 else if (PredVal != SingularValue)
111 bool isFirstPred = true;
112 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
113 BasicBlock *PredBB = *PI;
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)
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.
131 if (SingularValue != 0)
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 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
251 Preds->push_back(*PI);
255 /// GetUndefVal - Get an undefined value of the same type as the value
257 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
258 return UndefValue::get(Updater->ProtoType);
261 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
262 /// Reserve space for the operands but do not fill them in yet.
263 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
264 SSAUpdater *Updater) {
265 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
266 Updater->ProtoName, &BB->front());
270 /// AddPHIOperand - Add the specified value as an operand of the PHI for
271 /// the specified predecessor block.
272 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
273 PHI->addIncoming(Val, Pred);
276 /// InstrIsPHI - Check if an instruction is a PHI.
278 static PHINode *InstrIsPHI(Instruction *I) {
279 return dyn_cast<PHINode>(I);
282 /// ValueIsPHI - Check if a value is a PHI.
284 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
285 return dyn_cast<PHINode>(Val);
288 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
289 /// operands, i.e., it was just added.
290 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
291 PHINode *PHI = ValueIsPHI(Val, Updater);
292 if (PHI && PHI->getNumIncomingValues() == 0)
297 /// GetPHIValue - For the specified PHI instruction, return the value
299 static Value *GetPHIValue(PHINode *PHI) {
304 } // End llvm namespace
306 /// Check to see if AvailableVals has an entry for the specified BB and if so,
307 /// return it. If not, construct SSA form by first calculating the required
308 /// placement of PHIs and then inserting new PHIs where needed.
309 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
310 AvailableValsTy &AvailableVals = getAvailableVals(AV);
311 if (Value *V = AvailableVals[BB])
314 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
315 return Impl.GetValue(BB);
318 //===----------------------------------------------------------------------===//
319 // LoadAndStorePromoter Implementation
320 //===----------------------------------------------------------------------===//
322 LoadAndStorePromoter::
323 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
324 SSAUpdater &S, StringRef BaseName) : SSA(S) {
325 if (Insts.empty()) return;
328 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
331 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
333 if (BaseName.empty())
334 BaseName = SomeVal->getName();
335 SSA.Initialize(SomeVal->getType(), BaseName);
339 void LoadAndStorePromoter::
340 run(const SmallVectorImpl<Instruction*> &Insts) const {
342 // First step: bucket up uses of the alloca by the block they occur in.
343 // This is important because we have to handle multiple defs/uses in a block
344 // ourselves: SSAUpdater is purely for cross-block references.
345 DenseMap<BasicBlock*, TinyPtrVector<Instruction*> > UsesByBlock;
347 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
348 Instruction *User = Insts[i];
349 UsesByBlock[User->getParent()].push_back(User);
352 // Okay, now we can iterate over all the blocks in the function with uses,
353 // processing them. Keep track of which loads are loading a live-in value.
354 // Walk the uses in the use-list order to be determinstic.
355 SmallVector<LoadInst*, 32> LiveInLoads;
356 DenseMap<Value*, Value*> ReplacedLoads;
358 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
359 Instruction *User = Insts[i];
360 BasicBlock *BB = User->getParent();
361 TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
363 // If this block has already been processed, ignore this repeat use.
364 if (BlockUses.empty()) continue;
366 // Okay, this is the first use in the block. If this block just has a
367 // single user in it, we can rewrite it trivially.
368 if (BlockUses.size() == 1) {
369 // If it is a store, it is a trivial def of the value in the block.
370 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
372 SSA.AddAvailableValue(BB, SI->getOperand(0));
374 // Otherwise it is a load, queue it to rewrite as a live-in load.
375 LiveInLoads.push_back(cast<LoadInst>(User));
380 // Otherwise, check to see if this block is all loads.
381 bool HasStore = false;
382 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
383 if (isa<StoreInst>(BlockUses[i])) {
389 // If so, we can queue them all as live in loads. We don't have an
390 // efficient way to tell which on is first in the block and don't want to
391 // scan large blocks, so just add all loads as live ins.
393 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
394 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
399 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
400 // Since SSAUpdater is purely for cross-block values, we need to determine
401 // the order of these instructions in the block. If the first use in the
402 // block is a load, then it uses the live in value. The last store defines
403 // the live out value. We handle this by doing a linear scan of the block.
404 Value *StoredValue = 0;
405 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
406 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
407 // If this is a load from an unrelated pointer, ignore it.
408 if (!isInstInList(L, Insts)) continue;
410 // If we haven't seen a store yet, this is a live in use, otherwise
411 // use the stored value.
413 replaceLoadWithValue(L, StoredValue);
414 L->replaceAllUsesWith(StoredValue);
415 ReplacedLoads[L] = StoredValue;
417 LiveInLoads.push_back(L);
422 if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
423 // If this is a store to an unrelated pointer, ignore it.
424 if (!isInstInList(SI, Insts)) continue;
427 // Remember that this is the active value in the block.
428 StoredValue = SI->getOperand(0);
432 // The last stored value that happened is the live-out for the block.
433 assert(StoredValue && "Already checked that there is a store in block");
434 SSA.AddAvailableValue(BB, StoredValue);
438 // Okay, now we rewrite all loads that use live-in values in the loop,
439 // inserting PHI nodes as necessary.
440 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
441 LoadInst *ALoad = LiveInLoads[i];
442 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
443 replaceLoadWithValue(ALoad, NewVal);
445 // Avoid assertions in unreachable code.
446 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
447 ALoad->replaceAllUsesWith(NewVal);
448 ReplacedLoads[ALoad] = NewVal;
451 // Allow the client to do stuff before we start nuking things.
452 doExtraRewritesBeforeFinalDeletion();
454 // Now that everything is rewritten, delete the old instructions from the
455 // function. They should all be dead now.
456 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
457 Instruction *User = Insts[i];
459 // If this is a load that still has uses, then the load must have been added
460 // as a live value in the SSAUpdate data structure for a block (e.g. because
461 // the loaded value was stored later). In this case, we need to recursively
462 // propagate the updates until we get to the real value.
463 if (!User->use_empty()) {
464 Value *NewVal = ReplacedLoads[User];
465 assert(NewVal && "not a replaced load?");
467 // Propagate down to the ultimate replacee. The intermediately loads
468 // could theoretically already have been deleted, so we don't want to
469 // dereference the Value*'s.
470 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
471 while (RLI != ReplacedLoads.end()) {
472 NewVal = RLI->second;
473 RLI = ReplacedLoads.find(NewVal);
476 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
477 User->replaceAllUsesWith(NewVal);
480 instructionDeleted(User);
481 User->eraseFromParent();
486 LoadAndStorePromoter::isInstInList(Instruction *I,
487 const SmallVectorImpl<Instruction*> &Insts)
489 return std::find(Insts.begin(), Insts.end(), I) != Insts.end();