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/IntrinsicInst.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/TinyPtrVector.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/Support/AlignOf.h"
22 #include "llvm/Support/Allocator.h"
23 #include "llvm/Support/CFG.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
27 #include "llvm/Transforms/Utils/Local.h"
28 #include "llvm/Transforms/Utils/SSAUpdater.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 &getAvailableVals(AV);
45 /// Initialize - Reset this object to get ready for a new set of SSA
46 /// updates with type 'Ty'. PHI nodes get a name based on 'Name'.
47 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
49 AV = new AvailableValsTy();
51 getAvailableVals(AV).clear();
56 /// HasValueForBlock - Return true if the SSAUpdater already has a value for
57 /// the specified block.
58 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
59 return getAvailableVals(AV).count(BB);
62 /// AddAvailableValue - Indicate that a rewritten value is available in the
63 /// specified block with the specified value.
64 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
65 assert(ProtoType != 0 && "Need to initialize SSAUpdater");
66 assert(ProtoType == V->getType() &&
67 "All rewritten values must have the same type");
68 getAvailableVals(AV)[BB] = V;
71 /// IsEquivalentPHI - Check if PHI has the same incoming value as specified
72 /// in ValueMapping for each predecessor block.
73 static bool IsEquivalentPHI(PHINode *PHI,
74 DenseMap<BasicBlock*, Value*> &ValueMapping) {
75 unsigned PHINumValues = PHI->getNumIncomingValues();
76 if (PHINumValues != ValueMapping.size())
79 // Scan the phi to see if it matches.
80 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
81 if (ValueMapping[PHI->getIncomingBlock(i)] !=
82 PHI->getIncomingValue(i)) {
89 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
90 /// live at the end of the specified block.
91 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
92 Value *Res = GetValueAtEndOfBlockInternal(BB);
96 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
97 /// is live in the middle of the specified block.
99 /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
100 /// important case: if there is a definition of the rewritten value after the
101 /// 'use' in BB. Consider code like this:
107 /// br Cond, SomeBB, OutBB
109 /// In this case, there are two values (X1 and X2) added to the AvailableVals
110 /// set by the client of the rewriter, and those values are both live out of
111 /// their respective blocks. However, the use of X happens in the *middle* of
112 /// a block. Because of this, we need to insert a new PHI node in SomeBB to
113 /// merge the appropriate values, and this value isn't live out of the block.
115 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
116 // If there is no definition of the renamed variable in this block, just use
117 // GetValueAtEndOfBlock to do our work.
118 if (!HasValueForBlock(BB))
119 return GetValueAtEndOfBlock(BB);
121 // Otherwise, we have the hard case. Get the live-in values for each
123 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
124 Value *SingularValue = 0;
126 // We can get our predecessor info by walking the pred_iterator list, but it
127 // is relatively slow. If we already have PHI nodes in this block, walk one
128 // of them to get the predecessor list instead.
129 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
130 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
131 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
132 Value *PredVal = GetValueAtEndOfBlock(PredBB);
133 PredValues.push_back(std::make_pair(PredBB, PredVal));
135 // Compute SingularValue.
137 SingularValue = PredVal;
138 else if (PredVal != SingularValue)
142 bool isFirstPred = true;
143 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
144 BasicBlock *PredBB = *PI;
145 Value *PredVal = GetValueAtEndOfBlock(PredBB);
146 PredValues.push_back(std::make_pair(PredBB, PredVal));
148 // Compute SingularValue.
150 SingularValue = PredVal;
152 } else if (PredVal != SingularValue)
157 // If there are no predecessors, just return undef.
158 if (PredValues.empty())
159 return UndefValue::get(ProtoType);
161 // Otherwise, if all the merged values are the same, just use it.
162 if (SingularValue != 0)
163 return SingularValue;
165 // Otherwise, we do need a PHI: check to see if we already have one available
166 // in this block that produces the right value.
167 if (isa<PHINode>(BB->begin())) {
168 DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
171 for (BasicBlock::iterator It = BB->begin();
172 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
173 if (IsEquivalentPHI(SomePHI, ValueMapping))
178 // Ok, we have no way out, insert a new one now.
179 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
180 ProtoName, &BB->front());
182 // Fill in all the predecessors of the PHI.
183 for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
184 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
186 // See if the PHI node can be merged to a single value. This can happen in
187 // loop cases when we get a PHI of itself and one other value.
188 if (Value *V = SimplifyInstruction(InsertedPHI)) {
189 InsertedPHI->eraseFromParent();
193 // Set the DebugLoc of the inserted PHI, if available.
195 if (const Instruction *I = BB->getFirstNonPHI())
196 DL = I->getDebugLoc();
197 InsertedPHI->setDebugLoc(DL);
199 // If the client wants to know about all new instructions, tell it.
200 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
202 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
206 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
207 /// which use their value in the corresponding predecessor.
208 void SSAUpdater::RewriteUse(Use &U) {
209 Instruction *User = cast<Instruction>(U.getUser());
212 if (PHINode *UserPN = dyn_cast<PHINode>(User))
213 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
215 V = GetValueInMiddleOfBlock(User->getParent());
220 /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However,
221 /// this version of the method can rewrite uses in the same block as a
222 /// definition, because it assumes that all uses of a value are below any
224 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
225 Instruction *User = cast<Instruction>(U.getUser());
228 if (PHINode *UserPN = dyn_cast<PHINode>(User))
229 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
231 V = GetValueAtEndOfBlock(User->getParent());
236 /// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
237 /// specialized for SSAUpdater.
240 class SSAUpdaterTraits<SSAUpdater> {
242 typedef BasicBlock BlkT;
244 typedef PHINode PhiT;
246 typedef succ_iterator BlkSucc_iterator;
247 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
248 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
256 explicit PHI_iterator(PHINode *P) // begin iterator
258 PHI_iterator(PHINode *P, bool) // end iterator
259 : PHI(P), idx(PHI->getNumIncomingValues()) {}
261 PHI_iterator &operator++() { ++idx; return *this; }
262 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
263 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
264 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
265 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
268 static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
269 static PHI_iterator PHI_end(PhiT *PHI) {
270 return PHI_iterator(PHI, true);
273 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
274 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
275 static void FindPredecessorBlocks(BasicBlock *BB,
276 SmallVectorImpl<BasicBlock*> *Preds) {
277 // We can get our predecessor info by walking the pred_iterator list,
278 // but it is relatively slow. If we already have PHI nodes in this
279 // block, walk one of them to get the predecessor list instead.
280 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
281 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
282 Preds->push_back(SomePhi->getIncomingBlock(PI));
284 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
285 Preds->push_back(*PI);
289 /// GetUndefVal - Get an undefined value of the same type as the value
291 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
292 return UndefValue::get(Updater->ProtoType);
295 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
296 /// Reserve space for the operands but do not fill them in yet.
297 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
298 SSAUpdater *Updater) {
299 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
300 Updater->ProtoName, &BB->front());
304 /// AddPHIOperand - Add the specified value as an operand of the PHI for
305 /// the specified predecessor block.
306 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
307 PHI->addIncoming(Val, Pred);
310 /// InstrIsPHI - Check if an instruction is a PHI.
312 static PHINode *InstrIsPHI(Instruction *I) {
313 return dyn_cast<PHINode>(I);
316 /// ValueIsPHI - Check if a value is a PHI.
318 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
319 return dyn_cast<PHINode>(Val);
322 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
323 /// operands, i.e., it was just added.
324 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
325 PHINode *PHI = ValueIsPHI(Val, Updater);
326 if (PHI && PHI->getNumIncomingValues() == 0)
331 /// GetPHIValue - For the specified PHI instruction, return the value
333 static Value *GetPHIValue(PHINode *PHI) {
338 } // End llvm namespace
340 /// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
341 /// for the specified BB and if so, return it. If not, construct SSA form by
342 /// first calculating the required placement of PHIs and then inserting new
343 /// PHIs where needed.
344 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
345 AvailableValsTy &AvailableVals = getAvailableVals(AV);
346 if (Value *V = AvailableVals[BB])
349 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
350 return Impl.GetValue(BB);
353 //===----------------------------------------------------------------------===//
354 // LoadAndStorePromoter Implementation
355 //===----------------------------------------------------------------------===//
357 LoadAndStorePromoter::
358 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
359 SSAUpdater &S, StringRef BaseName) : SSA(S) {
360 if (Insts.empty()) return;
363 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
366 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
368 if (BaseName.empty())
369 BaseName = SomeVal->getName();
370 SSA.Initialize(SomeVal->getType(), BaseName);
374 void LoadAndStorePromoter::
375 run(const SmallVectorImpl<Instruction*> &Insts) const {
377 // First step: bucket up uses of the alloca by the block they occur in.
378 // This is important because we have to handle multiple defs/uses in a block
379 // ourselves: SSAUpdater is purely for cross-block references.
380 DenseMap<BasicBlock*, TinyPtrVector<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 TinyPtrVector<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)) {
407 SSA.AddAvailableValue(BB, SI->getOperand(0));
409 // Otherwise it is a load, queue it to rewrite as a live-in load.
410 LiveInLoads.push_back(cast<LoadInst>(User));
415 // Otherwise, check to see if this block is all loads.
416 bool HasStore = false;
417 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
418 if (isa<StoreInst>(BlockUses[i])) {
424 // If so, we can queue them all as live in loads. We don't have an
425 // efficient way to tell which on is first in the block and don't want to
426 // scan large blocks, so just add all loads as live ins.
428 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
429 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
434 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
435 // Since SSAUpdater is purely for cross-block values, we need to determine
436 // the order of these instructions in the block. If the first use in the
437 // block is a load, then it uses the live in value. The last store defines
438 // the live out value. We handle this by doing a linear scan of the block.
439 Value *StoredValue = 0;
440 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
441 if (LoadInst *L = dyn_cast<LoadInst>(II)) {
442 // If this is a load from an unrelated pointer, ignore it.
443 if (!isInstInList(L, Insts)) continue;
445 // If we haven't seen a store yet, this is a live in use, otherwise
446 // use the stored value.
448 replaceLoadWithValue(L, StoredValue);
449 L->replaceAllUsesWith(StoredValue);
450 ReplacedLoads[L] = StoredValue;
452 LiveInLoads.push_back(L);
457 if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
458 // If this is a store to an unrelated pointer, ignore it.
459 if (!isInstInList(SI, Insts)) continue;
462 // Remember that this is the active value in the block.
463 StoredValue = SI->getOperand(0);
467 // The last stored value that happened is the live-out for the block.
468 assert(StoredValue && "Already checked that there is a store in block");
469 SSA.AddAvailableValue(BB, StoredValue);
473 // Okay, now we rewrite all loads that use live-in values in the loop,
474 // inserting PHI nodes as necessary.
475 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
476 LoadInst *ALoad = LiveInLoads[i];
477 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
478 replaceLoadWithValue(ALoad, NewVal);
480 // Avoid assertions in unreachable code.
481 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
482 ALoad->replaceAllUsesWith(NewVal);
483 ReplacedLoads[ALoad] = NewVal;
486 // Allow the client to do stuff before we start nuking things.
487 doExtraRewritesBeforeFinalDeletion();
489 // Now that everything is rewritten, delete the old instructions from the
490 // function. They should all be dead now.
491 for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
492 Instruction *User = Insts[i];
494 // If this is a load that still has uses, then the load must have been added
495 // as a live value in the SSAUpdate data structure for a block (e.g. because
496 // the loaded value was stored later). In this case, we need to recursively
497 // propagate the updates until we get to the real value.
498 if (!User->use_empty()) {
499 Value *NewVal = ReplacedLoads[User];
500 assert(NewVal && "not a replaced load?");
502 // Propagate down to the ultimate replacee. The intermediately loads
503 // could theoretically already have been deleted, so we don't want to
504 // dereference the Value*'s.
505 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
506 while (RLI != ReplacedLoads.end()) {
507 NewVal = RLI->second;
508 RLI = ReplacedLoads.find(NewVal);
511 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
512 User->replaceAllUsesWith(NewVal);
515 instructionDeleted(User);
516 User->eraseFromParent();
521 LoadAndStorePromoter::isInstInList(Instruction *I,
522 const SmallVectorImpl<Instruction*> &Insts)
524 return std::find(Insts.begin(), Insts.end(), I) != Insts.end();