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 /// dominates - Return true if I1 dominates I2 using the DominatorTree.
101 bool dominates(Instruction *I1, Instruction *I2) const {
102 if (InvokeInst *II = dyn_cast<InvokeInst>(I1))
103 I1 = II->getNormalDest()->begin();
104 return DT[I1->getParent()]->dominates(DT[I2->getParent()]);
108 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
109 std::set<PHINode*> &DeadPHINodes);
110 bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
111 void PromoteLocallyUsedAllocas(BasicBlock *BB,
112 const std::vector<AllocaInst*> &AIs);
114 void RenamePass(BasicBlock *BB, BasicBlock *Pred,
115 std::vector<Value*> &IncVals);
116 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
117 std::set<PHINode*> &InsertedPHINodes);
119 } // end of anonymous namespace
121 void PromoteMem2Reg::run() {
122 Function &F = *DF.getRoot()->getParent();
124 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
125 // only used in a single basic block. These instructions can be efficiently
126 // promoted by performing a single linear scan over that one block. Since
127 // individual basic blocks are sometimes large, we group together all allocas
128 // that are live in a single basic block by the basic block they are live in.
129 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
131 if (AST) PointerAllocaValues.resize(Allocas.size());
133 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
134 AllocaInst *AI = Allocas[AllocaNum];
136 assert(isAllocaPromotable(AI, TD) &&
137 "Cannot promote non-promotable alloca!");
138 assert(AI->getParent()->getParent() == &F &&
139 "All allocas should be in the same function, which is same as DF!");
141 if (AI->use_empty()) {
142 // If there are no uses of the alloca, just delete it now.
143 if (AST) AST->deleteValue(AI);
144 AI->getParent()->getInstList().erase(AI);
146 // Remove the alloca from the Allocas list, since it has been processed
147 Allocas[AllocaNum] = Allocas.back();
153 // Calculate the set of read and write-locations for each alloca. This is
154 // analogous to finding the 'uses' and 'definitions' of each variable.
155 std::vector<BasicBlock*> DefiningBlocks;
156 std::vector<BasicBlock*> UsingBlocks;
158 BasicBlock *OnlyBlock = 0;
159 bool OnlyUsedInOneBlock = true;
161 // As we scan the uses of the alloca instruction, keep track of stores, and
162 // decide whether all of the loads and stores to the alloca are within the
164 Value *AllocaPointerVal = 0;
165 for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
166 Instruction *User = cast<Instruction>(*U);
167 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
168 // Remember the basic blocks which define new values for the alloca
169 DefiningBlocks.push_back(SI->getParent());
170 AllocaPointerVal = SI->getOperand(0);
171 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
172 // Otherwise it must be a load instruction, keep track of variable reads
173 UsingBlocks.push_back(LI->getParent());
174 AllocaPointerVal = LI;
177 if (OnlyUsedInOneBlock) {
179 OnlyBlock = User->getParent();
180 else if (OnlyBlock != User->getParent())
181 OnlyUsedInOneBlock = false;
185 // If the alloca is only read and written in one basic block, just perform a
186 // linear sweep over the block to eliminate it.
187 if (OnlyUsedInOneBlock) {
188 LocallyUsedAllocas[OnlyBlock].push_back(AI);
190 // Remove the alloca from the Allocas list, since it will be processed.
191 Allocas[AllocaNum] = Allocas.back();
198 PointerAllocaValues[AllocaNum] = AllocaPointerVal;
200 // If we haven't computed a numbering for the BB's in the function, do so
202 BBNumbers.compute(F);
204 // Compute the locations where PhiNodes need to be inserted. Look at the
205 // dominance frontier of EACH basic-block we have a write in.
207 unsigned CurrentVersion = 0;
208 std::set<PHINode*> InsertedPHINodes;
209 std::vector<unsigned> DFBlocks;
210 while (!DefiningBlocks.empty()) {
211 BasicBlock *BB = DefiningBlocks.back();
212 DefiningBlocks.pop_back();
214 // Look up the DF for this write, add it to PhiNodes
215 DominanceFrontier::const_iterator it = DF.find(BB);
216 if (it != DF.end()) {
217 const DominanceFrontier::DomSetType &S = it->second;
219 // In theory we don't need the indirection through the DFBlocks vector.
220 // In practice, the order of calling QueuePhiNode would depend on the
221 // (unspecified) ordering of basic blocks in the dominance frontier,
222 // which would give PHI nodes non-determinstic subscripts. Fix this by
223 // processing blocks in order of the occurance in the function.
224 for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
225 PE = S.end(); P != PE; ++P)
226 DFBlocks.push_back(BBNumbers.getNumber(*P));
228 // Sort by which the block ordering in the function.
229 std::sort(DFBlocks.begin(), DFBlocks.end());
231 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
232 BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]);
233 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
234 DefiningBlocks.push_back(BB);
240 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
241 // of the writes to the variable, scan through the reads of the variable,
242 // marking PHI nodes which are actually necessary as alive (by removing them
243 // from the InsertedPHINodes set). This is not perfect: there may PHI
244 // marked alive because of loads which are dominated by stores, but there
245 // will be no unmarked PHI nodes which are actually used.
247 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
248 MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
251 // If there are any PHI nodes which are now known to be dead, remove them!
252 for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
253 E = InsertedPHINodes.end(); I != E; ++I) {
255 std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
256 BBPNs[AllocaNum] = 0;
258 // Check to see if we just removed the last inserted PHI node from this
259 // basic block. If so, remove the entry for the basic block.
260 bool HasOtherPHIs = false;
261 for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
267 NewPhiNodes.erase(PN->getParent());
269 if (AST && isa<PointerType>(PN->getType()))
270 AST->deleteValue(PN);
271 PN->getParent()->getInstList().erase(PN);
274 // Keep the reverse mapping of the 'Allocas' array.
275 AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
278 // Process all allocas which are only used in a single basic block.
279 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
280 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
281 const std::vector<AllocaInst*> &LocAllocas = I->second;
282 assert(!LocAllocas.empty() && "empty alloca list??");
284 // It's common for there to only be one alloca in the list. Handle it
286 if (LocAllocas.size() == 1) {
287 // If we can do the quick promotion pass, do so now.
288 if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0]))
289 RetryList.push_back(LocAllocas[0]); // Failed, retry later.
291 // Locally promote anything possible. Note that if this is unable to
292 // promote a particular alloca, it puts the alloca onto the Allocas vector
293 // for global processing.
294 PromoteLocallyUsedAllocas(I->first, LocAllocas);
299 return; // All of the allocas must have been trivial!
301 // Set the incoming values for the basic block to be null values for all of
302 // the alloca's. We do this in case there is a load of a value that has not
303 // been stored yet. In this case, it will get this null value.
305 std::vector<Value *> Values(Allocas.size());
306 for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
307 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
309 // Walks all basic blocks in the function performing the SSA rename algorithm
310 // and inserting the phi nodes we marked as necessary
312 RenamePass(F.begin(), 0, Values);
314 // The renamer uses the Visited set to avoid infinite loops. Clear it now.
317 // Remove the allocas themselves from the function...
318 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
319 Instruction *A = Allocas[i];
321 // If there are any uses of the alloca instructions left, they must be in
322 // sections of dead code that were not processed on the dominance frontier.
323 // Just delete the users now.
326 A->replaceAllUsesWith(UndefValue::get(A->getType()));
327 if (AST) AST->deleteValue(A);
328 A->getParent()->getInstList().erase(A);
331 // At this point, the renamer has added entries to PHI nodes for all reachable
332 // code. Unfortunately, there may be blocks which are not reachable, which
333 // the renamer hasn't traversed. If this is the case, the PHI nodes may not
334 // have incoming values for all predecessors. Loop over all PHI nodes we have
335 // created, inserting undef values if they are missing any incoming values.
337 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
338 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
340 std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
341 std::vector<PHINode*> &PNs = I->second;
342 assert(!PNs.empty() && "Empty PHI node list??");
344 // Loop over all of the PHI nodes and see if there are any that we can get
345 // rid of because they merge all of the same incoming values. This can
346 // happen due to undef values coming into the PHI nodes.
347 PHINode *SomePHI = 0;
348 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
350 if (Value *V = PNs[i]->hasConstantValue(true)) {
351 if (!isa<Instruction>(V) || dominates(cast<Instruction>(V), PNs[i])) {
352 if (AST && isa<PointerType>(PNs[i]->getType()))
353 AST->deleteValue(PNs[i]);
354 PNs[i]->replaceAllUsesWith(V);
355 PNs[i]->eraseFromParent();
363 // Only do work here if there the PHI nodes are missing incoming values. We
364 // know that all PHI nodes that were inserted in a block will have the same
365 // number of incoming values, so we can just check any PHI node.
366 if (SomePHI && Preds.size() != SomePHI->getNumIncomingValues()) {
367 // Ok, now we know that all of the PHI nodes are missing entries for some
368 // basic blocks. Start by sorting the incoming predecessors for efficient
370 std::sort(Preds.begin(), Preds.end());
372 // Now we loop through all BB's which have entries in SomePHI and remove
373 // them from the Preds list.
374 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
375 // Do a log(n) search of the Preds list for the entry we want.
376 std::vector<BasicBlock*>::iterator EntIt =
377 std::lower_bound(Preds.begin(), Preds.end(),
378 SomePHI->getIncomingBlock(i));
379 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
380 "PHI node has entry for a block which is not a predecessor!");
386 // At this point, the blocks left in the preds list must have dummy
387 // entries inserted into every PHI nodes for the block.
388 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
389 if (PHINode *PN = PNs[i]) {
390 Value *UndefVal = UndefValue::get(PN->getType());
391 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
392 PN->addIncoming(UndefVal, Preds[pred]);
398 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
399 // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
400 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
401 // each read of the variable. For each block that reads the variable, this
402 // function is called, which removes used PHI nodes from the DeadPHINodes set.
403 // After all of the reads have been processed, any PHI nodes left in the
404 // DeadPHINodes set are removed.
406 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
407 std::set<PHINode*> &DeadPHINodes) {
408 // Scan the immediate dominators of this block looking for a block which has a
409 // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
410 for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
411 BasicBlock *DomBB = N->getBlock();
412 std::map<BasicBlock*, std::vector<PHINode*> >::iterator
413 I = NewPhiNodes.find(DomBB);
414 if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
415 // Ok, we found an inserted PHI node which dominates this value.
416 PHINode *DominatingPHI = I->second[AllocaNum];
418 // Find out if we previously thought it was dead.
419 std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
420 if (DPNI != DeadPHINodes.end()) {
421 // Ok, until now, we thought this PHI node was dead. Mark it as being
423 DeadPHINodes.erase(DPNI);
425 // Now that we have marked the PHI node alive, also mark any PHI nodes
426 // which it might use as being alive as well.
427 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
429 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
435 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
436 /// block. If this is the case, avoid traversing the CFG and inserting a lot of
437 /// potentially useless PHI nodes by just performing a single linear pass over
438 /// the basic block using the Alloca.
440 /// If we cannot promote this alloca (because it is read before it is written),
441 /// return true. This is necessary in cases where, due to control flow, the
442 /// alloca is potentially undefined on some control flow paths. e.g. code like
443 /// this is potentially correct:
445 /// for (...) { if (c) { A = undef; undef = B; } }
447 /// ... so long as A is not used before undef is set.
449 bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
450 assert(!AI->use_empty() && "There are no uses of the alloca!");
452 // Handle degenerate cases quickly.
453 if (AI->hasOneUse()) {
454 Instruction *U = cast<Instruction>(AI->use_back());
455 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
456 // Must be a load of uninitialized value.
457 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
458 if (AST && isa<PointerType>(LI->getType()))
459 AST->deleteValue(LI);
461 // Otherwise it must be a store which is never read.
462 assert(isa<StoreInst>(U));
464 BB->getInstList().erase(U);
466 // Uses of the uninitialized memory location shall get undef.
469 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
470 Instruction *Inst = I++;
471 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
472 if (LI->getOperand(0) == AI) {
473 if (!CurVal) return true; // Could not locally promote!
475 // Loads just returns the "current value"...
476 LI->replaceAllUsesWith(CurVal);
477 if (AST && isa<PointerType>(LI->getType()))
478 AST->deleteValue(LI);
479 BB->getInstList().erase(LI);
481 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
482 if (SI->getOperand(1) == AI) {
483 // Store updates the "current value"...
484 CurVal = SI->getOperand(0);
485 BB->getInstList().erase(SI);
491 // After traversing the basic block, there should be no more uses of the
492 // alloca, remove it now.
493 assert(AI->use_empty() && "Uses of alloca from more than one BB??");
494 if (AST) AST->deleteValue(AI);
495 AI->getParent()->getInstList().erase(AI);
499 /// PromoteLocallyUsedAllocas - This method is just like
500 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca
501 /// instructions in parallel. This is important in cases where we have large
502 /// basic blocks, as we don't want to rescan the entire basic block for each
503 /// alloca which is locally used in it (which might be a lot).
504 void PromoteMem2Reg::
505 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
506 std::map<AllocaInst*, Value*> CurValues;
507 for (unsigned i = 0, e = AIs.size(); i != e; ++i)
508 CurValues[AIs[i]] = 0; // Insert with null value
510 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
511 Instruction *Inst = I++;
512 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
513 // Is this a load of an alloca we are tracking?
514 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
515 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
516 if (AIt != CurValues.end()) {
517 // If loading an uninitialized value, allow the inter-block case to
518 // handle it. Due to control flow, this might actually be ok.
519 if (AIt->second == 0) { // Use of locally uninitialized value??
520 RetryList.push_back(AI); // Retry elsewhere.
521 CurValues.erase(AIt); // Stop tracking this here.
522 if (CurValues.empty()) return;
524 // Loads just returns the "current value"...
525 LI->replaceAllUsesWith(AIt->second);
526 if (AST && isa<PointerType>(LI->getType()))
527 AST->deleteValue(LI);
528 BB->getInstList().erase(LI);
532 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
533 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
534 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
535 if (AIt != CurValues.end()) {
536 // Store updates the "current value"...
537 AIt->second = SI->getOperand(0);
538 BB->getInstList().erase(SI);
547 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
548 // Alloca returns true if there wasn't already a phi-node for that variable
550 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
552 std::set<PHINode*> &InsertedPHINodes) {
553 // Look up the basic-block in question.
554 std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
555 if (BBPNs.empty()) BBPNs.resize(Allocas.size());
557 // If the BB already has a phi node added for the i'th alloca then we're done!
558 if (BBPNs[AllocaNo]) return false;
560 // Create a PhiNode using the dereferenced type... and add the phi-node to the
562 PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
563 Allocas[AllocaNo]->getName() + "." +
564 utostr(Version++), BB->begin());
565 BBPNs[AllocaNo] = PN;
566 InsertedPHINodes.insert(PN);
568 if (AST && isa<PointerType>(PN->getType()))
569 AST->copyValue(PointerAllocaValues[AllocaNo], PN);
575 // RenamePass - Recursively traverse the CFG of the function, renaming loads and
576 // stores to the allocas which we are promoting. IncomingVals indicates what
577 // value each Alloca contains on exit from the predecessor block Pred.
579 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
580 std::vector<Value*> &IncomingVals) {
582 // If this BB needs a PHI node, update the PHI node for each variable we need
584 std::map<BasicBlock*, std::vector<PHINode *> >::iterator
585 BBPNI = NewPhiNodes.find(BB);
586 if (BBPNI != NewPhiNodes.end()) {
587 std::vector<PHINode *> &BBPNs = BBPNI->second;
588 for (unsigned k = 0; k != BBPNs.size(); ++k)
589 if (PHINode *PN = BBPNs[k]) {
590 // Add this incoming value to the PHI node.
591 PN->addIncoming(IncomingVals[k], Pred);
593 // The currently active variable for this block is now the PHI.
594 IncomingVals[k] = PN;
598 // don't revisit nodes
599 if (Visited.count(BB)) return;
604 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
605 Instruction *I = II++; // get the instruction, increment iterator
607 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
608 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
609 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
610 if (AI != AllocaLookup.end()) {
611 Value *V = IncomingVals[AI->second];
613 // walk the use list of this load and replace all uses with r
614 LI->replaceAllUsesWith(V);
615 if (AST && isa<PointerType>(LI->getType()))
616 AST->deleteValue(LI);
617 BB->getInstList().erase(LI);
620 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
621 // Delete this instruction and mark the name as the current holder of the
623 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
624 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
625 if (ai != AllocaLookup.end()) {
626 // what value were we writing?
627 IncomingVals[ai->second] = SI->getOperand(0);
628 BB->getInstList().erase(SI);
634 // Recurse to our successors.
635 TerminatorInst *TI = BB->getTerminator();
636 for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
637 std::vector<Value*> OutgoingVals(IncomingVals);
638 RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
642 /// PromoteMemToReg - Promote the specified list of alloca instructions into
643 /// scalar registers, inserting PHI nodes as appropriate. This function makes
644 /// use of DominanceFrontier information. This function does not modify the CFG
645 /// of the function at all. All allocas must be from the same function.
647 /// If AST is specified, the specified tracker is updated to reflect changes
650 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
651 DominatorTree &DT, DominanceFrontier &DF,
652 const TargetData &TD, AliasSetTracker *AST) {
653 // If there is nothing to do, bail out...
654 if (Allocas.empty()) return;
656 std::vector<AllocaInst*> RetryList;
657 PromoteMem2Reg(Allocas, RetryList, DT, DF, TD, AST).run();
659 // PromoteMem2Reg may not have been able to promote all of the allocas in one
660 // pass, run it again if needed.
661 while (!RetryList.empty()) {
662 // If we need to retry some allocas, this is due to there being no store
663 // before a read in a local block. To counteract this, insert a store of
664 // undef into the alloca right after the alloca itself.
665 for (unsigned i = 0, e = RetryList.size(); i != e; ++i) {
666 BasicBlock::iterator BBI = RetryList[i];
668 new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()),
669 RetryList[i], ++BBI);
672 std::vector<AllocaInst*> NewAllocas;
673 std::swap(NewAllocas, RetryList);
674 PromoteMem2Reg(NewAllocas, RetryList, DT, DF, TD, AST).run();