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/STLExtras.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/TinyPtrVector.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/IR/BasicBlock.h"
22 #include "llvm/IR/CFG.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DebugLoc.h"
25 #include "llvm/IR/Instruction.h"
26 #include "llvm/IR/Instructions.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/IR/Use.h"
29 #include "llvm/IR/Value.h"
30 #include "llvm/IR/ValueHandle.h"
31 #include "llvm/Support/Casting.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
40 #define DEBUG_TYPE "ssaupdater"
42 typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
43 static AvailableValsTy &getAvailableVals(void *AV) {
44 return *static_cast<AvailableValsTy*>(AV);
47 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
48 : InsertedPHIs(NewPHI) {}
50 SSAUpdater::~SSAUpdater() {
51 delete static_cast<AvailableValsTy*>(AV);
54 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
56 AV = new AvailableValsTy();
58 getAvailableVals(AV).clear();
63 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
64 return getAvailableVals(AV).count(BB);
67 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
68 assert(ProtoType && "Need to initialize SSAUpdater");
69 assert(ProtoType == V->getType() &&
70 "All rewritten values must have the same type");
71 getAvailableVals(AV)[BB] = V;
74 static bool IsEquivalentPHI(PHINode *PHI,
75 SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
76 unsigned PHINumValues = PHI->getNumIncomingValues();
77 if (PHINumValues != ValueMapping.size())
80 // Scan the phi to see if it matches.
81 for (unsigned i = 0, e = PHINumValues; i != e; ++i)
82 if (ValueMapping[PHI->getIncomingBlock(i)] !=
83 PHI->getIncomingValue(i)) {
90 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
91 Value *Res = GetValueAtEndOfBlockInternal(BB);
95 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
96 // If there is no definition of the renamed variable in this block, just use
97 // GetValueAtEndOfBlock to do our work.
98 if (!HasValueForBlock(BB))
99 return GetValueAtEndOfBlock(BB);
101 // Otherwise, we have the hard case. Get the live-in values for each
103 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
104 Value *SingularValue = nullptr;
106 // We can get our predecessor info by walking the pred_iterator list, but it
107 // is relatively slow. If we already have PHI nodes in this block, walk one
108 // of them to get the predecessor list instead.
109 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
110 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
111 BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
112 Value *PredVal = GetValueAtEndOfBlock(PredBB);
113 PredValues.push_back(std::make_pair(PredBB, PredVal));
115 // Compute SingularValue.
117 SingularValue = PredVal;
118 else if (PredVal != SingularValue)
119 SingularValue = nullptr;
122 bool isFirstPred = true;
123 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
124 BasicBlock *PredBB = *PI;
125 Value *PredVal = GetValueAtEndOfBlock(PredBB);
126 PredValues.push_back(std::make_pair(PredBB, PredVal));
128 // Compute SingularValue.
130 SingularValue = PredVal;
132 } else if (PredVal != SingularValue)
133 SingularValue = nullptr;
137 // If there are no predecessors, just return undef.
138 if (PredValues.empty())
139 return UndefValue::get(ProtoType);
141 // Otherwise, if all the merged values are the same, just use it.
143 return SingularValue;
145 // Otherwise, we do need a PHI: check to see if we already have one available
146 // in this block that produces the right value.
147 if (isa<PHINode>(BB->begin())) {
148 SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
151 for (BasicBlock::iterator It = BB->begin();
152 (SomePHI = dyn_cast<PHINode>(It)); ++It) {
153 if (IsEquivalentPHI(SomePHI, ValueMapping))
158 // Ok, we have no way out, insert a new one now.
159 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
160 ProtoName, &BB->front());
162 // Fill in all the predecessors of the PHI.
163 for (const auto &PredValue : PredValues)
164 InsertedPHI->addIncoming(PredValue.second, PredValue.first);
166 // See if the PHI node can be merged to a single value. This can happen in
167 // loop cases when we get a PHI of itself and one other value.
169 SimplifyInstruction(InsertedPHI, BB->getModule()->getDataLayout())) {
170 InsertedPHI->eraseFromParent();
174 // Set the DebugLoc of the inserted PHI, if available.
176 if (const Instruction *I = BB->getFirstNonPHI())
177 DL = I->getDebugLoc();
178 InsertedPHI->setDebugLoc(DL);
180 // If the client wants to know about all new instructions, tell it.
181 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
183 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
187 void SSAUpdater::RewriteUse(Use &U) {
188 Instruction *User = cast<Instruction>(U.getUser());
191 if (PHINode *UserPN = dyn_cast<PHINode>(User))
192 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
194 V = GetValueInMiddleOfBlock(User->getParent());
196 // Notify that users of the existing value that it is being replaced.
197 Value *OldVal = U.get();
198 if (OldVal != V && OldVal->hasValueHandle())
199 ValueHandleBase::ValueIsRAUWd(OldVal, V);
204 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
205 Instruction *User = cast<Instruction>(U.getUser());
208 if (PHINode *UserPN = dyn_cast<PHINode>(User))
209 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
211 V = GetValueAtEndOfBlock(User->getParent());
219 class SSAUpdaterTraits<SSAUpdater> {
221 typedef BasicBlock BlkT;
223 typedef PHINode PhiT;
225 typedef succ_iterator BlkSucc_iterator;
226 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
227 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
235 explicit PHI_iterator(PHINode *P) // begin iterator
237 PHI_iterator(PHINode *P, bool) // end iterator
238 : PHI(P), idx(PHI->getNumIncomingValues()) {}
240 PHI_iterator &operator++() { ++idx; return *this; }
241 bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
242 bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
244 Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
245 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
248 static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
249 static PHI_iterator PHI_end(PhiT *PHI) {
250 return PHI_iterator(PHI, true);
253 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
254 /// vector, set Info->NumPreds, and allocate space in Info->Preds.
255 static void FindPredecessorBlocks(BasicBlock *BB,
256 SmallVectorImpl<BasicBlock*> *Preds) {
257 // We can get our predecessor info by walking the pred_iterator list,
258 // but it is relatively slow. If we already have PHI nodes in this
259 // block, walk one of them to get the predecessor list instead.
260 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
261 Preds->append(SomePhi->block_begin(), SomePhi->block_end());
263 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
264 Preds->push_back(*PI);
268 /// GetUndefVal - Get an undefined value of the same type as the value
270 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
271 return UndefValue::get(Updater->ProtoType);
274 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
275 /// Reserve space for the operands but do not fill them in yet.
276 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
277 SSAUpdater *Updater) {
278 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
279 Updater->ProtoName, &BB->front());
283 /// AddPHIOperand - Add the specified value as an operand of the PHI for
284 /// the specified predecessor block.
285 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
286 PHI->addIncoming(Val, Pred);
289 /// InstrIsPHI - Check if an instruction is a PHI.
291 static PHINode *InstrIsPHI(Instruction *I) {
292 return dyn_cast<PHINode>(I);
295 /// ValueIsPHI - Check if a value is a PHI.
297 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
298 return dyn_cast<PHINode>(Val);
301 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
302 /// operands, i.e., it was just added.
303 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
304 PHINode *PHI = ValueIsPHI(Val, Updater);
305 if (PHI && PHI->getNumIncomingValues() == 0)
310 /// GetPHIValue - For the specified PHI instruction, return the value
312 static Value *GetPHIValue(PHINode *PHI) {
317 } // end namespace llvm
319 /// Check to see if AvailableVals has an entry for the specified BB and if so,
320 /// return it. If not, construct SSA form by first calculating the required
321 /// placement of PHIs and then inserting new PHIs where needed.
322 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
323 AvailableValsTy &AvailableVals = getAvailableVals(AV);
324 if (Value *V = AvailableVals[BB])
327 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
328 return Impl.GetValue(BB);
331 //===----------------------------------------------------------------------===//
332 // LoadAndStorePromoter Implementation
333 //===----------------------------------------------------------------------===//
335 LoadAndStorePromoter::
336 LoadAndStorePromoter(ArrayRef<const Instruction*> Insts,
337 SSAUpdater &S, StringRef BaseName) : SSA(S) {
338 if (Insts.empty()) return;
340 const Value *SomeVal;
341 if (const LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
344 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
346 if (BaseName.empty())
347 BaseName = SomeVal->getName();
348 SSA.Initialize(SomeVal->getType(), BaseName);
351 void LoadAndStorePromoter::
352 run(const SmallVectorImpl<Instruction*> &Insts) const {
353 // First step: bucket up uses of the alloca by the block they occur in.
354 // This is important because we have to handle multiple defs/uses in a block
355 // ourselves: SSAUpdater is purely for cross-block references.
356 DenseMap<BasicBlock*, TinyPtrVector<Instruction*>> UsesByBlock;
358 for (Instruction *User : Insts)
359 UsesByBlock[User->getParent()].push_back(User);
361 // Okay, now we can iterate over all the blocks in the function with uses,
362 // processing them. Keep track of which loads are loading a live-in value.
363 // Walk the uses in the use-list order to be determinstic.
364 SmallVector<LoadInst*, 32> LiveInLoads;
365 DenseMap<Value*, Value*> ReplacedLoads;
367 for (Instruction *User : Insts) {
368 BasicBlock *BB = User->getParent();
369 TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
371 // If this block has already been processed, ignore this repeat use.
372 if (BlockUses.empty()) continue;
374 // Okay, this is the first use in the block. If this block just has a
375 // single user in it, we can rewrite it trivially.
376 if (BlockUses.size() == 1) {
377 // If it is a store, it is a trivial def of the value in the block.
378 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
380 SSA.AddAvailableValue(BB, SI->getOperand(0));
382 // Otherwise it is a load, queue it to rewrite as a live-in load.
383 LiveInLoads.push_back(cast<LoadInst>(User));
388 // Otherwise, check to see if this block is all loads.
389 bool HasStore = false;
390 for (Instruction *I : BlockUses) {
391 if (isa<StoreInst>(I)) {
397 // If so, we can queue them all as live in loads. We don't have an
398 // efficient way to tell which on is first in the block and don't want to
399 // scan large blocks, so just add all loads as live ins.
401 for (Instruction *I : BlockUses)
402 LiveInLoads.push_back(cast<LoadInst>(I));
407 // Otherwise, we have mixed loads and stores (or just a bunch of stores).
408 // Since SSAUpdater is purely for cross-block values, we need to determine
409 // the order of these instructions in the block. If the first use in the
410 // block is a load, then it uses the live in value. The last store defines
411 // the live out value. We handle this by doing a linear scan of the block.
412 Value *StoredValue = nullptr;
413 for (Instruction &I : *BB) {
414 if (LoadInst *L = dyn_cast<LoadInst>(&I)) {
415 // If this is a load from an unrelated pointer, ignore it.
416 if (!isInstInList(L, Insts)) continue;
418 // If we haven't seen a store yet, this is a live in use, otherwise
419 // use the stored value.
421 replaceLoadWithValue(L, StoredValue);
422 L->replaceAllUsesWith(StoredValue);
423 ReplacedLoads[L] = StoredValue;
425 LiveInLoads.push_back(L);
430 if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
431 // If this is a store to an unrelated pointer, ignore it.
432 if (!isInstInList(SI, Insts)) continue;
435 // Remember that this is the active value in the block.
436 StoredValue = SI->getOperand(0);
440 // The last stored value that happened is the live-out for the block.
441 assert(StoredValue && "Already checked that there is a store in block");
442 SSA.AddAvailableValue(BB, StoredValue);
446 // Okay, now we rewrite all loads that use live-in values in the loop,
447 // inserting PHI nodes as necessary.
448 for (LoadInst *ALoad : LiveInLoads) {
449 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
450 replaceLoadWithValue(ALoad, NewVal);
452 // Avoid assertions in unreachable code.
453 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
454 ALoad->replaceAllUsesWith(NewVal);
455 ReplacedLoads[ALoad] = NewVal;
458 // Allow the client to do stuff before we start nuking things.
459 doExtraRewritesBeforeFinalDeletion();
461 // Now that everything is rewritten, delete the old instructions from the
462 // function. They should all be dead now.
463 for (Instruction *User : Insts) {
464 // If this is a load that still has uses, then the load must have been added
465 // as a live value in the SSAUpdate data structure for a block (e.g. because
466 // the loaded value was stored later). In this case, we need to recursively
467 // propagate the updates until we get to the real value.
468 if (!User->use_empty()) {
469 Value *NewVal = ReplacedLoads[User];
470 assert(NewVal && "not a replaced load?");
472 // Propagate down to the ultimate replacee. The intermediately loads
473 // could theoretically already have been deleted, so we don't want to
474 // dereference the Value*'s.
475 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
476 while (RLI != ReplacedLoads.end()) {
477 NewVal = RLI->second;
478 RLI = ReplacedLoads.find(NewVal);
481 replaceLoadWithValue(cast<LoadInst>(User), NewVal);
482 User->replaceAllUsesWith(NewVal);
485 instructionDeleted(User);
486 User->eraseFromParent();
491 LoadAndStorePromoter::isInstInList(Instruction *I,
492 const SmallVectorImpl<Instruction*> &Insts)
494 return is_contained(Insts, I);