1 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file promote memory references to be register references. It promotes
11 // alloca instructions which only have loads and stores as uses. An alloca is
12 // transformed by using dominator frontiers to place PHI nodes, then traversing
13 // the function in depth-first order to rewrite loads and stores as appropriate.
14 // This is just the standard SSA construction algorithm to construct "pruned"
17 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "mem2reg"
20 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Function.h"
24 #include "llvm/Instructions.h"
25 #include "llvm/Analysis/Dominators.h"
26 #include "llvm/Analysis/AliasSetTracker.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/ADT/StringExtras.h"
32 #include "llvm/Support/CFG.h"
33 #include "llvm/Support/Compiler.h"
37 STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
38 STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
39 STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
41 // Provide DenseMapKeyInfo for all pointers.
44 struct DenseMapKeyInfo<std::pair<BasicBlock*, unsigned> > {
45 static inline std::pair<BasicBlock*, unsigned> getEmptyKey() {
46 return std::make_pair((BasicBlock*)-1, ~0U);
48 static inline std::pair<BasicBlock*, unsigned> getTombstoneKey() {
49 return std::make_pair((BasicBlock*)-2, 0U);
51 static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) {
52 return DenseMapKeyInfo<void*>::getHashValue(Val.first) + Val.second*2;
54 static bool isPod() { return true; }
58 /// isAllocaPromotable - Return true if this alloca is legal for promotion.
59 /// This is true if there are only loads and stores to the alloca.
61 bool llvm::isAllocaPromotable(const AllocaInst *AI) {
62 // FIXME: If the memory unit is of pointer or integer type, we can permit
63 // assignments to subsections of the memory unit.
65 // Only allow direct loads and stores...
66 for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
67 UI != UE; ++UI) // Loop over all of the uses of the alloca
68 if (isa<LoadInst>(*UI)) {
70 } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
71 if (SI->getOperand(0) == AI)
72 return false; // Don't allow a store OF the AI, only INTO the AI.
74 return false; // Not a load or store.
83 // Data package used by RenamePass()
84 class VISIBILITY_HIDDEN RenamePassData {
86 typedef std::vector<Value *> ValVector;
89 RenamePassData(BasicBlock *B, BasicBlock *P,
90 const ValVector &V) : BB(B), Pred(P), Values(V) {}
95 void swap(RenamePassData &RHS) {
96 std::swap(BB, RHS.BB);
97 std::swap(Pred, RHS.Pred);
98 Values.swap(RHS.Values);
102 struct VISIBILITY_HIDDEN PromoteMem2Reg {
103 /// Allocas - The alloca instructions being promoted.
105 std::vector<AllocaInst*> Allocas;
106 SmallVector<AllocaInst*, 16> &RetryList;
108 DominanceFrontier &DF;
110 /// AST - An AliasSetTracker object to update. If null, don't update it.
112 AliasSetTracker *AST;
114 /// AllocaLookup - Reverse mapping of Allocas.
116 std::map<AllocaInst*, unsigned> AllocaLookup;
118 /// NewPhiNodes - The PhiNodes we're adding.
120 DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*> NewPhiNodes;
122 /// PhiToAllocaMap - For each PHI node, keep track of which entry in Allocas
123 /// it corresponds to.
124 DenseMap<PHINode*, unsigned> PhiToAllocaMap;
126 /// PointerAllocaValues - If we are updating an AliasSetTracker, then for
127 /// each alloca that is of pointer type, we keep track of what to copyValue
128 /// to the inserted PHI nodes here.
130 std::vector<Value*> PointerAllocaValues;
132 /// Visited - The set of basic blocks the renamer has already visited.
134 SmallPtrSet<BasicBlock*, 16> Visited;
136 /// BBNumbers - Contains a stable numbering of basic blocks to avoid
137 /// non-determinstic behavior.
138 DenseMap<BasicBlock*, unsigned> BBNumbers;
141 PromoteMem2Reg(const std::vector<AllocaInst*> &A,
142 SmallVector<AllocaInst*, 16> &Retry, DominatorTree &dt,
143 DominanceFrontier &df, AliasSetTracker *ast)
144 : Allocas(A), RetryList(Retry), DT(dt), DF(df), AST(ast) {}
148 /// properlyDominates - Return true if I1 properly dominates I2.
150 bool properlyDominates(Instruction *I1, Instruction *I2) const {
151 if (InvokeInst *II = dyn_cast<InvokeInst>(I1))
152 I1 = II->getNormalDest()->begin();
153 return DT.properlyDominates(I1->getParent(), I2->getParent());
156 /// dominates - Return true if BB1 dominates BB2 using the DominatorTree.
158 bool dominates(BasicBlock *BB1, BasicBlock *BB2) const {
159 return DT.dominates(BB1, BB2);
163 void RemoveFromAllocasList(unsigned &AllocaIdx) {
164 Allocas[AllocaIdx] = Allocas.back();
169 void RewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info);
171 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
172 SmallPtrSet<PHINode*, 16> &DeadPHINodes);
173 bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
174 void PromoteLocallyUsedAllocas(BasicBlock *BB,
175 const std::vector<AllocaInst*> &AIs);
177 void RenamePass(BasicBlock *BB, BasicBlock *Pred,
178 RenamePassData::ValVector &IncVals,
179 std::vector<RenamePassData> &Worklist);
180 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
181 SmallPtrSet<PHINode*, 16> &InsertedPHINodes);
185 std::vector<BasicBlock*> DefiningBlocks;
186 std::vector<BasicBlock*> UsingBlocks;
188 StoreInst *OnlyStore;
189 BasicBlock *OnlyBlock;
190 bool OnlyUsedInOneBlock;
192 Value *AllocaPointerVal;
195 DefiningBlocks.clear();
199 OnlyUsedInOneBlock = true;
200 AllocaPointerVal = 0;
203 /// AnalyzeAlloca - Scan the uses of the specified alloca, filling in our
205 void AnalyzeAlloca(AllocaInst *AI) {
208 // As we scan the uses of the alloca instruction, keep track of stores,
209 // and decide whether all of the loads and stores to the alloca are within
210 // the same basic block.
211 for (Value::use_iterator U = AI->use_begin(), E = AI->use_end();
213 Instruction *User = cast<Instruction>(*U);
214 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
215 // Remember the basic blocks which define new values for the alloca
216 DefiningBlocks.push_back(SI->getParent());
217 AllocaPointerVal = SI->getOperand(0);
220 LoadInst *LI = cast<LoadInst>(User);
221 // Otherwise it must be a load instruction, keep track of variable reads
222 UsingBlocks.push_back(LI->getParent());
223 AllocaPointerVal = LI;
226 if (OnlyUsedInOneBlock) {
228 OnlyBlock = User->getParent();
229 else if (OnlyBlock != User->getParent())
230 OnlyUsedInOneBlock = false;
236 } // end of anonymous namespace
239 void PromoteMem2Reg::run() {
240 Function &F = *DF.getRoot()->getParent();
242 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
243 // only used in a single basic block. These instructions can be efficiently
244 // promoted by performing a single linear scan over that one block. Since
245 // individual basic blocks are sometimes large, we group together all allocas
246 // that are live in a single basic block by the basic block they are live in.
247 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
249 if (AST) PointerAllocaValues.resize(Allocas.size());
253 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
254 AllocaInst *AI = Allocas[AllocaNum];
256 assert(isAllocaPromotable(AI) &&
257 "Cannot promote non-promotable alloca!");
258 assert(AI->getParent()->getParent() == &F &&
259 "All allocas should be in the same function, which is same as DF!");
261 if (AI->use_empty()) {
262 // If there are no uses of the alloca, just delete it now.
263 if (AST) AST->deleteValue(AI);
264 AI->eraseFromParent();
266 // Remove the alloca from the Allocas list, since it has been processed
267 RemoveFromAllocasList(AllocaNum);
272 // Calculate the set of read and write-locations for each alloca. This is
273 // analogous to finding the 'uses' and 'definitions' of each variable.
274 Info.AnalyzeAlloca(AI);
276 // If the alloca is only read and written in one basic block, just perform a
277 // linear sweep over the block to eliminate it.
278 if (Info.OnlyUsedInOneBlock) {
279 LocallyUsedAllocas[Info.OnlyBlock].push_back(AI);
281 // Remove the alloca from the Allocas list, since it will be processed.
282 RemoveFromAllocasList(AllocaNum);
286 // If there is only a single store to this value, replace any loads of
287 // it that are directly dominated by the definition with the value stored.
288 if (Info.DefiningBlocks.size() == 1) {
289 RewriteSingleStoreAlloca(AI, Info);
291 // Finally, after the scan, check to see if the store is all that is left.
292 if (Info.UsingBlocks.empty()) {
294 // The alloca has been processed, move on.
295 RemoveFromAllocasList(AllocaNum);
302 PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
304 // If we haven't computed a numbering for the BB's in the function, do so
306 if (BBNumbers.empty()) {
308 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
312 // Compute the locations where PhiNodes need to be inserted. Look at the
313 // dominance frontier of EACH basic-block we have a write in.
315 unsigned CurrentVersion = 0;
316 SmallPtrSet<PHINode*, 16> InsertedPHINodes;
317 std::vector<std::pair<unsigned, BasicBlock*> > DFBlocks;
318 while (!Info.DefiningBlocks.empty()) {
319 BasicBlock *BB = Info.DefiningBlocks.back();
320 Info.DefiningBlocks.pop_back();
322 // Look up the DF for this write, add it to PhiNodes
323 DominanceFrontier::const_iterator it = DF.find(BB);
324 if (it != DF.end()) {
325 const DominanceFrontier::DomSetType &S = it->second;
327 // In theory we don't need the indirection through the DFBlocks vector.
328 // In practice, the order of calling QueuePhiNode would depend on the
329 // (unspecified) ordering of basic blocks in the dominance frontier,
330 // which would give PHI nodes non-determinstic subscripts. Fix this by
331 // processing blocks in order of the occurance in the function.
332 for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
333 PE = S.end(); P != PE; ++P)
334 DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P));
336 // Sort by which the block ordering in the function.
337 std::sort(DFBlocks.begin(), DFBlocks.end());
339 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
340 BasicBlock *BB = DFBlocks[i].second;
341 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
342 Info.DefiningBlocks.push_back(BB);
348 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
349 // of the writes to the variable, scan through the reads of the variable,
350 // marking PHI nodes which are actually necessary as alive (by removing them
351 // from the InsertedPHINodes set). This is not perfect: there may PHI
352 // marked alive because of loads which are dominated by stores, but there
353 // will be no unmarked PHI nodes which are actually used.
355 for (unsigned i = 0, e = Info.UsingBlocks.size(); i != e; ++i)
356 MarkDominatingPHILive(Info.UsingBlocks[i], AllocaNum, InsertedPHINodes);
357 Info.UsingBlocks.clear();
359 // If there are any PHI nodes which are now known to be dead, remove them!
360 for (SmallPtrSet<PHINode*, 16>::iterator I = InsertedPHINodes.begin(),
361 E = InsertedPHINodes.end(); I != E; ++I) {
363 bool Erased=NewPhiNodes.erase(std::make_pair(PN->getParent(), AllocaNum));
365 assert(Erased && "PHI already removed?");
367 if (AST && isa<PointerType>(PN->getType()))
368 AST->deleteValue(PN);
369 PN->eraseFromParent();
370 PhiToAllocaMap.erase(PN);
373 // Keep the reverse mapping of the 'Allocas' array.
374 AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
377 // Process all allocas which are only used in a single basic block.
378 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
379 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
380 const std::vector<AllocaInst*> &LocAllocas = I->second;
381 assert(!LocAllocas.empty() && "empty alloca list??");
383 // It's common for there to only be one alloca in the list. Handle it
385 if (LocAllocas.size() == 1) {
386 // If we can do the quick promotion pass, do so now.
387 if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0]))
388 RetryList.push_back(LocAllocas[0]); // Failed, retry later.
390 // Locally promote anything possible. Note that if this is unable to
391 // promote a particular alloca, it puts the alloca onto the Allocas vector
392 // for global processing.
393 PromoteLocallyUsedAllocas(I->first, LocAllocas);
398 return; // All of the allocas must have been trivial!
400 // Set the incoming values for the basic block to be null values for all of
401 // the alloca's. We do this in case there is a load of a value that has not
402 // been stored yet. In this case, it will get this null value.
404 RenamePassData::ValVector Values(Allocas.size());
405 for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
406 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
408 // Walks all basic blocks in the function performing the SSA rename algorithm
409 // and inserting the phi nodes we marked as necessary
411 std::vector<RenamePassData> RenamePassWorkList;
412 RenamePassWorkList.push_back(RenamePassData(F.begin(), 0, Values));
413 while (!RenamePassWorkList.empty()) {
415 RPD.swap(RenamePassWorkList.back());
416 RenamePassWorkList.pop_back();
417 // RenamePass may add new worklist entries.
418 RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
421 // The renamer uses the Visited set to avoid infinite loops. Clear it now.
424 // Remove the allocas themselves from the function.
425 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
426 Instruction *A = Allocas[i];
428 // If there are any uses of the alloca instructions left, they must be in
429 // sections of dead code that were not processed on the dominance frontier.
430 // Just delete the users now.
433 A->replaceAllUsesWith(UndefValue::get(A->getType()));
434 if (AST) AST->deleteValue(A);
435 A->eraseFromParent();
439 // Loop over all of the PHI nodes and see if there are any that we can get
440 // rid of because they merge all of the same incoming values. This can
441 // happen due to undef values coming into the PHI nodes. This process is
442 // iterative, because eliminating one PHI node can cause others to be removed.
443 bool EliminatedAPHI = true;
444 while (EliminatedAPHI) {
445 EliminatedAPHI = false;
447 for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
448 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) {
449 PHINode *PN = I->second;
451 // If this PHI node merges one value and/or undefs, get the value.
452 if (Value *V = PN->hasConstantValue(true)) {
453 if (!isa<Instruction>(V) ||
454 properlyDominates(cast<Instruction>(V), PN)) {
455 if (AST && isa<PointerType>(PN->getType()))
456 AST->deleteValue(PN);
457 PN->replaceAllUsesWith(V);
458 PN->eraseFromParent();
459 NewPhiNodes.erase(I++);
460 EliminatedAPHI = true;
468 // At this point, the renamer has added entries to PHI nodes for all reachable
469 // code. Unfortunately, there may be unreachable blocks which the renamer
470 // hasn't traversed. If this is the case, the PHI nodes may not
471 // have incoming values for all predecessors. Loop over all PHI nodes we have
472 // created, inserting undef values if they are missing any incoming values.
474 for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
475 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
476 // We want to do this once per basic block. As such, only process a block
477 // when we find the PHI that is the first entry in the block.
478 PHINode *SomePHI = I->second;
479 BasicBlock *BB = SomePHI->getParent();
480 if (&BB->front() != SomePHI)
483 // Count the number of preds for BB.
484 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
486 // Only do work here if there the PHI nodes are missing incoming values. We
487 // know that all PHI nodes that were inserted in a block will have the same
488 // number of incoming values, so we can just check any of them.
489 if (SomePHI->getNumIncomingValues() == Preds.size())
492 // Ok, now we know that all of the PHI nodes are missing entries for some
493 // basic blocks. Start by sorting the incoming predecessors for efficient
495 std::sort(Preds.begin(), Preds.end());
497 // Now we loop through all BB's which have entries in SomePHI and remove
498 // them from the Preds list.
499 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
500 // Do a log(n) search of the Preds list for the entry we want.
501 SmallVector<BasicBlock*, 16>::iterator EntIt =
502 std::lower_bound(Preds.begin(), Preds.end(),
503 SomePHI->getIncomingBlock(i));
504 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
505 "PHI node has entry for a block which is not a predecessor!");
511 // At this point, the blocks left in the preds list must have dummy
512 // entries inserted into every PHI nodes for the block. Update all the phi
513 // nodes in this block that we are inserting (there could be phis before
515 unsigned NumBadPreds = SomePHI->getNumIncomingValues();
516 BasicBlock::iterator BBI = BB->begin();
517 while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
518 SomePHI->getNumIncomingValues() == NumBadPreds) {
519 Value *UndefVal = UndefValue::get(SomePHI->getType());
520 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
521 SomePHI->addIncoming(UndefVal, Preds[pred]);
529 /// RewriteSingleStoreAlloca - If there is only a single store to this value,
530 /// replace any loads of it that are directly dominated by the definition with
531 /// the value stored.
532 void PromoteMem2Reg::RewriteSingleStoreAlloca(AllocaInst *AI,
534 StoreInst *OnlyStore = Info.OnlyStore;
536 // Be aware of loads before the store.
537 SmallPtrSet<BasicBlock*, 32> ProcessedBlocks;
538 for (unsigned i = 0, e = Info.UsingBlocks.size(); i != e; ++i) {
539 // If the store dominates the block and if we haven't processed it yet,
541 if (!dominates(OnlyStore->getParent(), Info.UsingBlocks[i]))
544 BasicBlock *UseBlock = Info.UsingBlocks[i];
545 if (!ProcessedBlocks.insert(UseBlock))
548 // If the use and store are in the same block, do a quick scan to
549 // verify that there are no uses before the store.
550 if (UseBlock == OnlyStore->getParent()) {
551 BasicBlock::iterator I = UseBlock->begin();
552 for (; &*I != OnlyStore; ++I) { // scan block for store.
553 if (isa<LoadInst>(I) && I->getOperand(0) == AI)
556 if (&*I != OnlyStore) break; // Do not handle this case.
559 // Otherwise, if this is a different block or if all uses happen
560 // after the store, do a simple linear scan to replace loads with
562 for (BasicBlock::iterator I = UseBlock->begin(), E = UseBlock->end();
564 if (LoadInst *LI = dyn_cast<LoadInst>(I++)) {
565 if (LI->getOperand(0) == AI) {
566 LI->replaceAllUsesWith(OnlyStore->getOperand(0));
567 if (AST && isa<PointerType>(LI->getType()))
568 AST->deleteValue(LI);
569 LI->eraseFromParent();
574 // Finally, remove this block from the UsingBlock set.
575 Info.UsingBlocks[i] = Info.UsingBlocks.back();
576 Info.UsingBlocks.pop_back();
582 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
583 // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
584 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
585 // each read of the variable. For each block that reads the variable, this
586 // function is called, which removes used PHI nodes from the DeadPHINodes set.
587 // After all of the reads have been processed, any PHI nodes left in the
588 // DeadPHINodes set are removed.
590 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
591 SmallPtrSet<PHINode*, 16> &DeadPHINodes) {
592 // Scan the immediate dominators of this block looking for a block which has a
593 // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
594 DomTreeNode *IDomNode = DT.getNode(BB);
595 for (DomTreeNode *IDom = IDomNode; IDom; IDom = IDom->getIDom()) {
596 BasicBlock *DomBB = IDom->getBlock();
597 DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator
598 I = NewPhiNodes.find(std::make_pair(DomBB, AllocaNum));
599 if (I != NewPhiNodes.end()) {
600 // Ok, we found an inserted PHI node which dominates this value.
601 PHINode *DominatingPHI = I->second;
603 // Find out if we previously thought it was dead. If so, mark it as being
604 // live by removing it from the DeadPHINodes set.
605 if (DeadPHINodes.erase(DominatingPHI)) {
606 // Now that we have marked the PHI node alive, also mark any PHI nodes
607 // which it might use as being alive as well.
608 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
610 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
616 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
617 /// block. If this is the case, avoid traversing the CFG and inserting a lot of
618 /// potentially useless PHI nodes by just performing a single linear pass over
619 /// the basic block using the Alloca.
621 /// If we cannot promote this alloca (because it is read before it is written),
622 /// return true. This is necessary in cases where, due to control flow, the
623 /// alloca is potentially undefined on some control flow paths. e.g. code like
624 /// this is potentially correct:
626 /// for (...) { if (c) { A = undef; undef = B; } }
628 /// ... so long as A is not used before undef is set.
630 bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
631 assert(!AI->use_empty() && "There are no uses of the alloca!");
633 // Handle degenerate cases quickly.
634 if (AI->hasOneUse()) {
635 Instruction *U = cast<Instruction>(AI->use_back());
636 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
637 // Must be a load of uninitialized value.
638 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
639 if (AST && isa<PointerType>(LI->getType()))
640 AST->deleteValue(LI);
642 // Otherwise it must be a store which is never read.
643 assert(isa<StoreInst>(U));
645 BB->getInstList().erase(U);
647 // Uses of the uninitialized memory location shall get undef.
650 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
651 Instruction *Inst = I++;
652 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
653 if (LI->getOperand(0) == AI) {
654 if (!CurVal) return true; // Could not locally promote!
656 // Loads just returns the "current value"...
657 LI->replaceAllUsesWith(CurVal);
658 if (AST && isa<PointerType>(LI->getType()))
659 AST->deleteValue(LI);
660 BB->getInstList().erase(LI);
662 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
663 if (SI->getOperand(1) == AI) {
664 // Store updates the "current value"...
665 CurVal = SI->getOperand(0);
666 BB->getInstList().erase(SI);
672 // After traversing the basic block, there should be no more uses of the
673 // alloca, remove it now.
674 assert(AI->use_empty() && "Uses of alloca from more than one BB??");
675 if (AST) AST->deleteValue(AI);
676 AI->getParent()->getInstList().erase(AI);
682 /// PromoteLocallyUsedAllocas - This method is just like
683 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca
684 /// instructions in parallel. This is important in cases where we have large
685 /// basic blocks, as we don't want to rescan the entire basic block for each
686 /// alloca which is locally used in it (which might be a lot).
687 void PromoteMem2Reg::
688 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
689 std::map<AllocaInst*, Value*> CurValues;
690 for (unsigned i = 0, e = AIs.size(); i != e; ++i)
691 CurValues[AIs[i]] = 0; // Insert with null value
693 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
694 Instruction *Inst = I++;
695 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
696 // Is this a load of an alloca we are tracking?
697 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
698 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
699 if (AIt != CurValues.end()) {
700 // If loading an uninitialized value, allow the inter-block case to
701 // handle it. Due to control flow, this might actually be ok.
702 if (AIt->second == 0) { // Use of locally uninitialized value??
703 RetryList.push_back(AI); // Retry elsewhere.
704 CurValues.erase(AIt); // Stop tracking this here.
705 if (CurValues.empty()) return;
707 // Loads just returns the "current value"...
708 LI->replaceAllUsesWith(AIt->second);
709 if (AST && isa<PointerType>(LI->getType()))
710 AST->deleteValue(LI);
711 BB->getInstList().erase(LI);
715 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
716 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
717 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
718 if (AIt != CurValues.end()) {
719 // Store updates the "current value"...
720 AIt->second = SI->getOperand(0);
721 BB->getInstList().erase(SI);
730 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
731 // Alloca returns true if there wasn't already a phi-node for that variable
733 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
735 SmallPtrSet<PHINode*, 16> &InsertedPHINodes) {
736 // Look up the basic-block in question.
737 PHINode *&PN = NewPhiNodes[std::make_pair(BB, AllocaNo)];
739 // If the BB already has a phi node added for the i'th alloca then we're done!
740 if (PN) return false;
742 // Create a PhiNode using the dereferenced type... and add the phi-node to the
744 PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
745 Allocas[AllocaNo]->getName() + "." +
746 utostr(Version++), BB->begin());
747 PhiToAllocaMap[PN] = AllocaNo;
749 InsertedPHINodes.insert(PN);
751 if (AST && isa<PointerType>(PN->getType()))
752 AST->copyValue(PointerAllocaValues[AllocaNo], PN);
758 // RenamePass - Recursively traverse the CFG of the function, renaming loads and
759 // stores to the allocas which we are promoting. IncomingVals indicates what
760 // value each Alloca contains on exit from the predecessor block Pred.
762 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
763 RenamePassData::ValVector &IncomingVals,
764 std::vector<RenamePassData> &Worklist) {
765 // If we are inserting any phi nodes into this BB, they will already be in the
767 if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
768 // Pred may have multiple edges to BB. If so, we want to add N incoming
769 // values to each PHI we are inserting on the first time we see the edge.
770 // Check to see if APN already has incoming values from Pred. This also
771 // prevents us from modifying PHI nodes that are not currently being
773 bool HasPredEntries = false;
774 for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
775 if (APN->getIncomingBlock(i) == Pred) {
776 HasPredEntries = true;
781 // If we have PHI nodes to update, compute the number of edges from Pred to
783 if (!HasPredEntries) {
784 TerminatorInst *PredTerm = Pred->getTerminator();
785 unsigned NumEdges = 0;
786 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) {
787 if (PredTerm->getSuccessor(i) == BB)
790 assert(NumEdges && "Must be at least one edge from Pred to BB!");
792 // Add entries for all the phis.
793 BasicBlock::iterator PNI = BB->begin();
795 unsigned AllocaNo = PhiToAllocaMap[APN];
797 // Add N incoming values to the PHI node.
798 for (unsigned i = 0; i != NumEdges; ++i)
799 APN->addIncoming(IncomingVals[AllocaNo], Pred);
801 // The currently active variable for this block is now the PHI.
802 IncomingVals[AllocaNo] = APN;
804 // Get the next phi node.
806 APN = dyn_cast<PHINode>(PNI);
809 // Verify it doesn't already have entries for Pred. If it does, it is
810 // not being inserted by this mem2reg invocation.
811 HasPredEntries = false;
812 for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
813 if (APN->getIncomingBlock(i) == Pred) {
814 HasPredEntries = true;
818 } while (!HasPredEntries);
822 // Don't revisit blocks.
823 if (!Visited.insert(BB)) return;
825 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
826 Instruction *I = II++; // get the instruction, increment iterator
828 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
829 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
830 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
831 if (AI != AllocaLookup.end()) {
832 Value *V = IncomingVals[AI->second];
834 // walk the use list of this load and replace all uses with r
835 LI->replaceAllUsesWith(V);
836 if (AST && isa<PointerType>(LI->getType()))
837 AST->deleteValue(LI);
838 BB->getInstList().erase(LI);
841 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
842 // Delete this instruction and mark the name as the current holder of the
844 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
845 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
846 if (ai != AllocaLookup.end()) {
847 // what value were we writing?
848 IncomingVals[ai->second] = SI->getOperand(0);
849 BB->getInstList().erase(SI);
855 // Recurse to our successors.
856 TerminatorInst *TI = BB->getTerminator();
857 for (unsigned i = 0; i != TI->getNumSuccessors(); i++)
858 Worklist.push_back(RenamePassData(TI->getSuccessor(i), BB, IncomingVals));
861 /// PromoteMemToReg - Promote the specified list of alloca instructions into
862 /// scalar registers, inserting PHI nodes as appropriate. This function makes
863 /// use of DominanceFrontier information. This function does not modify the CFG
864 /// of the function at all. All allocas must be from the same function.
866 /// If AST is specified, the specified tracker is updated to reflect changes
869 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
870 DominatorTree &DT, DominanceFrontier &DF,
871 AliasSetTracker *AST) {
872 // If there is nothing to do, bail out...
873 if (Allocas.empty()) return;
875 SmallVector<AllocaInst*, 16> RetryList;
876 PromoteMem2Reg(Allocas, RetryList, DT, DF, AST).run();
878 // PromoteMem2Reg may not have been able to promote all of the allocas in one
879 // pass, run it again if needed.
880 std::vector<AllocaInst*> NewAllocas;
881 while (!RetryList.empty()) {
882 // If we need to retry some allocas, this is due to there being no store
883 // before a read in a local block. To counteract this, insert a store of
884 // undef into the alloca right after the alloca itself.
885 for (unsigned i = 0, e = RetryList.size(); i != e; ++i) {
886 BasicBlock::iterator BBI = RetryList[i];
888 new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()),
889 RetryList[i], ++BBI);
892 NewAllocas.assign(RetryList.begin(), RetryList.end());
894 PromoteMem2Reg(NewAllocas, RetryList, DT, DF, AST).run();