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 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
20 #include "llvm/Constants.h"
21 #include "llvm/DerivedTypes.h"
22 #include "llvm/Function.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/Analysis/Dominators.h"
25 #include "llvm/Analysis/AliasSetTracker.h"
26 #include "llvm/ADT/StringExtras.h"
27 #include "llvm/Support/CFG.h"
28 #include "llvm/Support/StableBasicBlockNumbering.h"
32 /// isAllocaPromotable - Return true if this alloca is legal for promotion.
33 /// This is true if there are only loads and stores to the alloca.
35 bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
36 // FIXME: If the memory unit is of pointer or integer type, we can permit
37 // assignments to subsections of the memory unit.
39 // Only allow direct loads and stores...
40 for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
41 UI != UE; ++UI) // Loop over all of the uses of the alloca
42 if (isa<LoadInst>(*UI)) {
44 } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
45 if (SI->getOperand(0) == AI)
46 return false; // Don't allow a store OF the AI, only INTO the AI.
48 return false; // Not a load or store.
55 struct PromoteMem2Reg {
56 /// Allocas - The alloca instructions being promoted.
58 std::vector<AllocaInst*> Allocas;
59 std::vector<AllocaInst*> &RetryList;
61 DominanceFrontier &DF;
64 /// AST - An AliasSetTracker object to update. If null, don't update it.
68 /// AllocaLookup - Reverse mapping of Allocas.
70 std::map<AllocaInst*, unsigned> AllocaLookup;
72 /// NewPhiNodes - The PhiNodes we're adding.
74 std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes;
76 /// PointerAllocaValues - If we are updating an AliasSetTracker, then for
77 /// each alloca that is of pointer type, we keep track of what to copyValue
78 /// to the inserted PHI nodes here.
80 std::vector<Value*> PointerAllocaValues;
82 /// Visited - The set of basic blocks the renamer has already visited.
84 std::set<BasicBlock*> Visited;
86 /// BBNumbers - Contains a stable numbering of basic blocks to avoid
87 /// non-determinstic behavior.
88 StableBasicBlockNumbering BBNumbers;
91 PromoteMem2Reg(const std::vector<AllocaInst*> &A,
92 std::vector<AllocaInst*> &Retry, DominatorTree &dt,
93 DominanceFrontier &df, const TargetData &td,
95 : Allocas(A), RetryList(Retry), DT(dt), DF(df), TD(td), AST(ast) {}
99 /// properlyDominates - Return true if I1 properly dominates I2.
101 bool properlyDominates(Instruction *I1, Instruction *I2) const {
102 if (InvokeInst *II = dyn_cast<InvokeInst>(I1))
103 I1 = II->getNormalDest()->begin();
104 return DT[I1->getParent()]->properlyDominates(DT[I2->getParent()]);
107 /// dominates - Return true if BB1 dominates BB2 using the DominatorTree.
109 bool dominates(BasicBlock *BB1, BasicBlock *BB2) const {
110 return DT[BB1]->dominates(DT[BB2]);
114 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
115 std::set<PHINode*> &DeadPHINodes);
116 bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
117 void PromoteLocallyUsedAllocas(BasicBlock *BB,
118 const std::vector<AllocaInst*> &AIs);
120 void RenamePass(BasicBlock *BB, BasicBlock *Pred,
121 std::vector<Value*> &IncVals);
122 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
123 std::set<PHINode*> &InsertedPHINodes);
125 } // end of anonymous namespace
127 void PromoteMem2Reg::run() {
128 Function &F = *DF.getRoot()->getParent();
130 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
131 // only used in a single basic block. These instructions can be efficiently
132 // promoted by performing a single linear scan over that one block. Since
133 // individual basic blocks are sometimes large, we group together all allocas
134 // that are live in a single basic block by the basic block they are live in.
135 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
137 if (AST) PointerAllocaValues.resize(Allocas.size());
139 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
140 AllocaInst *AI = Allocas[AllocaNum];
142 assert(isAllocaPromotable(AI, TD) &&
143 "Cannot promote non-promotable alloca!");
144 assert(AI->getParent()->getParent() == &F &&
145 "All allocas should be in the same function, which is same as DF!");
147 if (AI->use_empty()) {
148 // If there are no uses of the alloca, just delete it now.
149 if (AST) AST->deleteValue(AI);
150 AI->eraseFromParent();
152 // Remove the alloca from the Allocas list, since it has been processed
153 Allocas[AllocaNum] = Allocas.back();
159 // Calculate the set of read and write-locations for each alloca. This is
160 // analogous to finding the 'uses' and 'definitions' of each variable.
161 std::vector<BasicBlock*> DefiningBlocks;
162 std::vector<BasicBlock*> UsingBlocks;
164 StoreInst *OnlyStore = 0;
165 BasicBlock *OnlyBlock = 0;
166 bool OnlyUsedInOneBlock = true;
168 // As we scan the uses of the alloca instruction, keep track of stores, and
169 // decide whether all of the loads and stores to the alloca are within the
171 Value *AllocaPointerVal = 0;
172 for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
173 Instruction *User = cast<Instruction>(*U);
174 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
175 // Remember the basic blocks which define new values for the alloca
176 DefiningBlocks.push_back(SI->getParent());
177 AllocaPointerVal = SI->getOperand(0);
180 LoadInst *LI = cast<LoadInst>(User);
181 // Otherwise it must be a load instruction, keep track of variable reads
182 UsingBlocks.push_back(LI->getParent());
183 AllocaPointerVal = LI;
186 if (OnlyUsedInOneBlock) {
188 OnlyBlock = User->getParent();
189 else if (OnlyBlock != User->getParent())
190 OnlyUsedInOneBlock = false;
194 // If the alloca is only read and written in one basic block, just perform a
195 // linear sweep over the block to eliminate it.
196 if (OnlyUsedInOneBlock) {
197 LocallyUsedAllocas[OnlyBlock].push_back(AI);
199 // Remove the alloca from the Allocas list, since it will be processed.
200 Allocas[AllocaNum] = Allocas.back();
206 // If there is only a single store to this value, replace any loads of
207 // it that are directly dominated by the definition with the value stored.
208 if (DefiningBlocks.size() == 1) {
209 // Be aware of loads before the store.
210 std::set<BasicBlock*> ProcessedBlocks;
211 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
212 // If the store dominates the block and if we haven't processed it yet,
214 if (dominates(OnlyStore->getParent(), UsingBlocks[i]))
215 if (ProcessedBlocks.insert(UsingBlocks[i]).second) {
216 BasicBlock *UseBlock = UsingBlocks[i];
218 // If the use and store are in the same block, do a quick scan to
219 // verify that there are no uses before the store.
220 if (UseBlock == OnlyStore->getParent()) {
221 BasicBlock::iterator I = UseBlock->begin();
222 for (; &*I != OnlyStore; ++I) { // scan block for store.
223 if (isa<LoadInst>(I) && I->getOperand(0) == AI)
226 if (&*I != OnlyStore) break; // Do not handle this case.
229 // Otherwise, if this is a different block or if all uses happen
230 // after the store, do a simple linear scan to replace loads with
232 for (BasicBlock::iterator I = UseBlock->begin(),E = UseBlock->end();
234 if (LoadInst *LI = dyn_cast<LoadInst>(I++)) {
235 if (LI->getOperand(0) == AI) {
236 LI->replaceAllUsesWith(OnlyStore->getOperand(0));
237 if (AST && isa<PointerType>(LI->getType()))
238 AST->deleteValue(LI);
239 LI->eraseFromParent();
244 // Finally, remove this block from the UsingBlock set.
245 UsingBlocks[i] = UsingBlocks.back();
249 // Finally, after the scan, check to see if the store is all that is left.
250 if (UsingBlocks.empty()) {
251 // The alloca has been processed, move on.
252 Allocas[AllocaNum] = Allocas.back();
261 PointerAllocaValues[AllocaNum] = AllocaPointerVal;
263 // If we haven't computed a numbering for the BB's in the function, do so
265 BBNumbers.compute(F);
267 // Compute the locations where PhiNodes need to be inserted. Look at the
268 // dominance frontier of EACH basic-block we have a write in.
270 unsigned CurrentVersion = 0;
271 std::set<PHINode*> InsertedPHINodes;
272 std::vector<unsigned> DFBlocks;
273 while (!DefiningBlocks.empty()) {
274 BasicBlock *BB = DefiningBlocks.back();
275 DefiningBlocks.pop_back();
277 // Look up the DF for this write, add it to PhiNodes
278 DominanceFrontier::const_iterator it = DF.find(BB);
279 if (it != DF.end()) {
280 const DominanceFrontier::DomSetType &S = it->second;
282 // In theory we don't need the indirection through the DFBlocks vector.
283 // In practice, the order of calling QueuePhiNode would depend on the
284 // (unspecified) ordering of basic blocks in the dominance frontier,
285 // which would give PHI nodes non-determinstic subscripts. Fix this by
286 // processing blocks in order of the occurance in the function.
287 for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
288 PE = S.end(); P != PE; ++P)
289 DFBlocks.push_back(BBNumbers.getNumber(*P));
291 // Sort by which the block ordering in the function.
292 std::sort(DFBlocks.begin(), DFBlocks.end());
294 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
295 BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]);
296 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
297 DefiningBlocks.push_back(BB);
303 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
304 // of the writes to the variable, scan through the reads of the variable,
305 // marking PHI nodes which are actually necessary as alive (by removing them
306 // from the InsertedPHINodes set). This is not perfect: there may PHI
307 // marked alive because of loads which are dominated by stores, but there
308 // will be no unmarked PHI nodes which are actually used.
310 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
311 MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
314 // If there are any PHI nodes which are now known to be dead, remove them!
315 for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
316 E = InsertedPHINodes.end(); I != E; ++I) {
318 std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
319 BBPNs[AllocaNum] = 0;
321 // Check to see if we just removed the last inserted PHI node from this
322 // basic block. If so, remove the entry for the basic block.
323 bool HasOtherPHIs = false;
324 for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
330 NewPhiNodes.erase(PN->getParent());
332 if (AST && isa<PointerType>(PN->getType()))
333 AST->deleteValue(PN);
334 PN->eraseFromParent();
337 // Keep the reverse mapping of the 'Allocas' array.
338 AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
341 // Process all allocas which are only used in a single basic block.
342 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
343 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
344 const std::vector<AllocaInst*> &LocAllocas = I->second;
345 assert(!LocAllocas.empty() && "empty alloca list??");
347 // It's common for there to only be one alloca in the list. Handle it
349 if (LocAllocas.size() == 1) {
350 // If we can do the quick promotion pass, do so now.
351 if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0]))
352 RetryList.push_back(LocAllocas[0]); // Failed, retry later.
354 // Locally promote anything possible. Note that if this is unable to
355 // promote a particular alloca, it puts the alloca onto the Allocas vector
356 // for global processing.
357 PromoteLocallyUsedAllocas(I->first, LocAllocas);
362 return; // All of the allocas must have been trivial!
364 // Set the incoming values for the basic block to be null values for all of
365 // the alloca's. We do this in case there is a load of a value that has not
366 // been stored yet. In this case, it will get this null value.
368 std::vector<Value *> Values(Allocas.size());
369 for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
370 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
372 // Walks all basic blocks in the function performing the SSA rename algorithm
373 // and inserting the phi nodes we marked as necessary
375 RenamePass(F.begin(), 0, Values);
377 // The renamer uses the Visited set to avoid infinite loops. Clear it now.
380 // Remove the allocas themselves from the function.
381 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
382 Instruction *A = Allocas[i];
384 // If there are any uses of the alloca instructions left, they must be in
385 // sections of dead code that were not processed on the dominance frontier.
386 // Just delete the users now.
389 A->replaceAllUsesWith(UndefValue::get(A->getType()));
390 if (AST) AST->deleteValue(A);
391 A->eraseFromParent();
395 // Loop over all of the PHI nodes and see if there are any that we can get
396 // rid of because they merge all of the same incoming values. This can
397 // happen due to undef values coming into the PHI nodes. This process is
398 // iterative, because eliminating one PHI node can cause others to be removed.
399 bool EliminatedAPHI = true;
400 while (EliminatedAPHI) {
401 EliminatedAPHI = false;
403 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
404 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
405 std::vector<PHINode*> &PNs = I->second;
406 for (unsigned i = 0, e = PNs.size(); i != e; ++i) {
407 if (!PNs[i]) continue;
409 // If this PHI node merges one value and/or undefs, get the value.
410 if (Value *V = PNs[i]->hasConstantValue(true)) {
411 if (!isa<Instruction>(V) ||
412 properlyDominates(cast<Instruction>(V), PNs[i])) {
413 if (AST && isa<PointerType>(PNs[i]->getType()))
414 AST->deleteValue(PNs[i]);
415 PNs[i]->replaceAllUsesWith(V);
416 PNs[i]->eraseFromParent();
418 EliminatedAPHI = true;
426 // At this point, the renamer has added entries to PHI nodes for all reachable
427 // code. Unfortunately, there may be blocks which are not reachable, which
428 // the renamer hasn't traversed. If this is the case, the PHI nodes may not
429 // have incoming values for all predecessors. Loop over all PHI nodes we have
430 // created, inserting undef values if they are missing any incoming values.
432 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
433 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
435 std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
436 std::vector<PHINode*> &PNs = I->second;
437 assert(!PNs.empty() && "Empty PHI node list??");
438 PHINode *SomePHI = 0;
439 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
445 // Only do work here if there the PHI nodes are missing incoming values. We
446 // know that all PHI nodes that were inserted in a block will have the same
447 // number of incoming values, so we can just check any PHI node.
448 if (SomePHI && Preds.size() != SomePHI->getNumIncomingValues()) {
449 // Ok, now we know that all of the PHI nodes are missing entries for some
450 // basic blocks. Start by sorting the incoming predecessors for efficient
452 std::sort(Preds.begin(), Preds.end());
454 // Now we loop through all BB's which have entries in SomePHI and remove
455 // them from the Preds list.
456 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
457 // Do a log(n) search of the Preds list for the entry we want.
458 std::vector<BasicBlock*>::iterator EntIt =
459 std::lower_bound(Preds.begin(), Preds.end(),
460 SomePHI->getIncomingBlock(i));
461 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
462 "PHI node has entry for a block which is not a predecessor!");
468 // At this point, the blocks left in the preds list must have dummy
469 // entries inserted into every PHI nodes for the block.
470 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
471 if (PHINode *PN = PNs[i]) {
472 Value *UndefVal = UndefValue::get(PN->getType());
473 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
474 PN->addIncoming(UndefVal, Preds[pred]);
480 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
481 // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
482 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
483 // each read of the variable. For each block that reads the variable, this
484 // function is called, which removes used PHI nodes from the DeadPHINodes set.
485 // After all of the reads have been processed, any PHI nodes left in the
486 // DeadPHINodes set are removed.
488 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
489 std::set<PHINode*> &DeadPHINodes) {
490 // Scan the immediate dominators of this block looking for a block which has a
491 // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
492 for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
493 BasicBlock *DomBB = N->getBlock();
494 std::map<BasicBlock*, std::vector<PHINode*> >::iterator
495 I = NewPhiNodes.find(DomBB);
496 if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
497 // Ok, we found an inserted PHI node which dominates this value.
498 PHINode *DominatingPHI = I->second[AllocaNum];
500 // Find out if we previously thought it was dead.
501 std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
502 if (DPNI != DeadPHINodes.end()) {
503 // Ok, until now, we thought this PHI node was dead. Mark it as being
505 DeadPHINodes.erase(DPNI);
507 // Now that we have marked the PHI node alive, also mark any PHI nodes
508 // which it might use as being alive as well.
509 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
511 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
517 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
518 /// block. If this is the case, avoid traversing the CFG and inserting a lot of
519 /// potentially useless PHI nodes by just performing a single linear pass over
520 /// the basic block using the Alloca.
522 /// If we cannot promote this alloca (because it is read before it is written),
523 /// return true. This is necessary in cases where, due to control flow, the
524 /// alloca is potentially undefined on some control flow paths. e.g. code like
525 /// this is potentially correct:
527 /// for (...) { if (c) { A = undef; undef = B; } }
529 /// ... so long as A is not used before undef is set.
531 bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
532 assert(!AI->use_empty() && "There are no uses of the alloca!");
534 // Handle degenerate cases quickly.
535 if (AI->hasOneUse()) {
536 Instruction *U = cast<Instruction>(AI->use_back());
537 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
538 // Must be a load of uninitialized value.
539 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
540 if (AST && isa<PointerType>(LI->getType()))
541 AST->deleteValue(LI);
543 // Otherwise it must be a store which is never read.
544 assert(isa<StoreInst>(U));
546 BB->getInstList().erase(U);
548 // Uses of the uninitialized memory location shall get undef.
551 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
552 Instruction *Inst = I++;
553 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
554 if (LI->getOperand(0) == AI) {
555 if (!CurVal) return true; // Could not locally promote!
557 // Loads just returns the "current value"...
558 LI->replaceAllUsesWith(CurVal);
559 if (AST && isa<PointerType>(LI->getType()))
560 AST->deleteValue(LI);
561 BB->getInstList().erase(LI);
563 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
564 if (SI->getOperand(1) == AI) {
565 // Store updates the "current value"...
566 CurVal = SI->getOperand(0);
567 BB->getInstList().erase(SI);
573 // After traversing the basic block, there should be no more uses of the
574 // alloca, remove it now.
575 assert(AI->use_empty() && "Uses of alloca from more than one BB??");
576 if (AST) AST->deleteValue(AI);
577 AI->getParent()->getInstList().erase(AI);
581 /// PromoteLocallyUsedAllocas - This method is just like
582 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca
583 /// instructions in parallel. This is important in cases where we have large
584 /// basic blocks, as we don't want to rescan the entire basic block for each
585 /// alloca which is locally used in it (which might be a lot).
586 void PromoteMem2Reg::
587 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
588 std::map<AllocaInst*, Value*> CurValues;
589 for (unsigned i = 0, e = AIs.size(); i != e; ++i)
590 CurValues[AIs[i]] = 0; // Insert with null value
592 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
593 Instruction *Inst = I++;
594 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
595 // Is this a load of an alloca we are tracking?
596 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
597 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
598 if (AIt != CurValues.end()) {
599 // If loading an uninitialized value, allow the inter-block case to
600 // handle it. Due to control flow, this might actually be ok.
601 if (AIt->second == 0) { // Use of locally uninitialized value??
602 RetryList.push_back(AI); // Retry elsewhere.
603 CurValues.erase(AIt); // Stop tracking this here.
604 if (CurValues.empty()) return;
606 // Loads just returns the "current value"...
607 LI->replaceAllUsesWith(AIt->second);
608 if (AST && isa<PointerType>(LI->getType()))
609 AST->deleteValue(LI);
610 BB->getInstList().erase(LI);
614 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
615 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
616 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
617 if (AIt != CurValues.end()) {
618 // Store updates the "current value"...
619 AIt->second = SI->getOperand(0);
620 BB->getInstList().erase(SI);
629 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
630 // Alloca returns true if there wasn't already a phi-node for that variable
632 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
634 std::set<PHINode*> &InsertedPHINodes) {
635 // Look up the basic-block in question.
636 std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
637 if (BBPNs.empty()) BBPNs.resize(Allocas.size());
639 // If the BB already has a phi node added for the i'th alloca then we're done!
640 if (BBPNs[AllocaNo]) return false;
642 // Create a PhiNode using the dereferenced type... and add the phi-node to the
644 PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
645 Allocas[AllocaNo]->getName() + "." +
646 utostr(Version++), BB->begin());
647 BBPNs[AllocaNo] = PN;
648 InsertedPHINodes.insert(PN);
650 if (AST && isa<PointerType>(PN->getType()))
651 AST->copyValue(PointerAllocaValues[AllocaNo], PN);
657 // RenamePass - Recursively traverse the CFG of the function, renaming loads and
658 // stores to the allocas which we are promoting. IncomingVals indicates what
659 // value each Alloca contains on exit from the predecessor block Pred.
661 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
662 std::vector<Value*> &IncomingVals) {
664 // If this BB needs a PHI node, update the PHI node for each variable we need
666 std::map<BasicBlock*, std::vector<PHINode *> >::iterator
667 BBPNI = NewPhiNodes.find(BB);
668 if (BBPNI != NewPhiNodes.end()) {
669 std::vector<PHINode *> &BBPNs = BBPNI->second;
670 for (unsigned k = 0; k != BBPNs.size(); ++k)
671 if (PHINode *PN = BBPNs[k]) {
672 // Add this incoming value to the PHI node.
673 PN->addIncoming(IncomingVals[k], Pred);
675 // The currently active variable for this block is now the PHI.
676 IncomingVals[k] = PN;
680 // don't revisit nodes
681 if (Visited.count(BB)) return;
686 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
687 Instruction *I = II++; // get the instruction, increment iterator
689 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
690 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
691 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
692 if (AI != AllocaLookup.end()) {
693 Value *V = IncomingVals[AI->second];
695 // walk the use list of this load and replace all uses with r
696 LI->replaceAllUsesWith(V);
697 if (AST && isa<PointerType>(LI->getType()))
698 AST->deleteValue(LI);
699 BB->getInstList().erase(LI);
702 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
703 // Delete this instruction and mark the name as the current holder of the
705 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
706 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
707 if (ai != AllocaLookup.end()) {
708 // what value were we writing?
709 IncomingVals[ai->second] = SI->getOperand(0);
710 BB->getInstList().erase(SI);
716 // Recurse to our successors.
717 TerminatorInst *TI = BB->getTerminator();
718 for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
719 std::vector<Value*> OutgoingVals(IncomingVals);
720 RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
724 /// PromoteMemToReg - Promote the specified list of alloca instructions into
725 /// scalar registers, inserting PHI nodes as appropriate. This function makes
726 /// use of DominanceFrontier information. This function does not modify the CFG
727 /// of the function at all. All allocas must be from the same function.
729 /// If AST is specified, the specified tracker is updated to reflect changes
732 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
733 DominatorTree &DT, DominanceFrontier &DF,
734 const TargetData &TD, AliasSetTracker *AST) {
735 // If there is nothing to do, bail out...
736 if (Allocas.empty()) return;
738 std::vector<AllocaInst*> RetryList;
739 PromoteMem2Reg(Allocas, RetryList, DT, DF, TD, AST).run();
741 // PromoteMem2Reg may not have been able to promote all of the allocas in one
742 // pass, run it again if needed.
743 while (!RetryList.empty()) {
744 // If we need to retry some allocas, this is due to there being no store
745 // before a read in a local block. To counteract this, insert a store of
746 // undef into the alloca right after the alloca itself.
747 for (unsigned i = 0, e = RetryList.size(); i != e; ++i) {
748 BasicBlock::iterator BBI = RetryList[i];
750 new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()),
751 RetryList[i], ++BBI);
754 std::vector<AllocaInst*> NewAllocas;
755 std::swap(NewAllocas, RetryList);
756 PromoteMem2Reg(NewAllocas, RetryList, DT, DF, TD, AST).run();