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/Transforms/Utils/Local.h"
28 #include "llvm/Support/CFG.h"
29 #include "llvm/Support/StableBasicBlockNumbering.h"
33 /// isAllocaPromotable - Return true if this alloca is legal for promotion.
34 /// This is true if there are only loads and stores to the alloca.
36 bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
37 // FIXME: If the memory unit is of pointer or integer type, we can permit
38 // assignments to subsections of the memory unit.
40 // Only allow direct loads and stores...
41 for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
42 UI != UE; ++UI) // Loop over all of the uses of the alloca
43 if (isa<LoadInst>(*UI)) {
45 } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
46 if (SI->getOperand(0) == AI)
47 return false; // Don't allow a store OF the AI, only INTO the AI.
49 return false; // Not a load or store.
56 struct PromoteMem2Reg {
57 /// Allocas - The alloca instructions being promoted.
59 std::vector<AllocaInst*> Allocas;
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, DominatorTree &dt,
92 DominanceFrontier &df, const TargetData &td,
94 : Allocas(A), DT(dt), DF(df), TD(td), AST(ast) {}
98 /// dominates - Return true if BB1 dominates BB2 using the DT.
100 bool dominates(BasicBlock *BB1, BasicBlock *BB2) const {
101 return DT[BB1]->dominates(DT[BB2]);
105 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
106 std::set<PHINode*> &DeadPHINodes);
107 void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
108 void PromoteLocallyUsedAllocas(BasicBlock *BB,
109 const std::vector<AllocaInst*> &AIs);
111 void RenamePass(BasicBlock *BB, BasicBlock *Pred,
112 std::vector<Value*> &IncVals);
113 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
114 std::set<PHINode*> &InsertedPHINodes);
116 } // end of anonymous namespace
118 void PromoteMem2Reg::run() {
119 Function &F = *DF.getRoot()->getParent();
121 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
122 // only used in a single basic block. These instructions can be efficiently
123 // promoted by performing a single linear scan over that one block. Since
124 // individual basic blocks are sometimes large, we group together all allocas
125 // that are live in a single basic block by the basic block they are live in.
126 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
128 if (AST) PointerAllocaValues.resize(Allocas.size());
130 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
131 AllocaInst *AI = Allocas[AllocaNum];
133 assert(isAllocaPromotable(AI, TD) &&
134 "Cannot promote non-promotable alloca!");
135 assert(AI->getParent()->getParent() == &F &&
136 "All allocas should be in the same function, which is same as DF!");
138 if (AI->use_empty()) {
139 // If there are no uses of the alloca, just delete it now.
140 if (AST) AST->deleteValue(AI);
141 AI->getParent()->getInstList().erase(AI);
143 // Remove the alloca from the Allocas list, since it has been processed
144 Allocas[AllocaNum] = Allocas.back();
150 // Calculate the set of read and write-locations for each alloca. This is
151 // analogous to finding the 'uses' and 'definitions' of each variable.
152 std::vector<BasicBlock*> DefiningBlocks;
153 std::vector<BasicBlock*> UsingBlocks;
155 BasicBlock *OnlyBlock = 0;
156 bool OnlyUsedInOneBlock = true;
158 // As we scan the uses of the alloca instruction, keep track of stores, and
159 // decide whether all of the loads and stores to the alloca are within the
161 Value *AllocaPointerVal = 0;
162 for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
163 Instruction *User = cast<Instruction>(*U);
164 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
165 // Remember the basic blocks which define new values for the alloca
166 DefiningBlocks.push_back(SI->getParent());
167 AllocaPointerVal = SI->getOperand(0);
168 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
169 // Otherwise it must be a load instruction, keep track of variable reads
170 UsingBlocks.push_back(LI->getParent());
171 AllocaPointerVal = LI;
174 if (OnlyUsedInOneBlock) {
176 OnlyBlock = User->getParent();
177 else if (OnlyBlock != User->getParent())
178 OnlyUsedInOneBlock = false;
182 // If the alloca is only read and written in one basic block, just perform a
183 // linear sweep over the block to eliminate it.
184 if (OnlyUsedInOneBlock) {
185 LocallyUsedAllocas[OnlyBlock].push_back(AI);
187 // Remove the alloca from the Allocas list, since it will be processed.
188 Allocas[AllocaNum] = Allocas.back();
195 PointerAllocaValues[AllocaNum] = AllocaPointerVal;
197 // If we haven't computed a numbering for the BB's in the function, do so
199 BBNumbers.compute(F);
201 // Compute the locations where PhiNodes need to be inserted. Look at the
202 // dominance frontier of EACH basic-block we have a write in.
204 unsigned CurrentVersion = 0;
205 std::set<PHINode*> InsertedPHINodes;
206 std::vector<unsigned> DFBlocks;
207 while (!DefiningBlocks.empty()) {
208 BasicBlock *BB = DefiningBlocks.back();
209 DefiningBlocks.pop_back();
211 // Look up the DF for this write, add it to PhiNodes
212 DominanceFrontier::const_iterator it = DF.find(BB);
213 if (it != DF.end()) {
214 const DominanceFrontier::DomSetType &S = it->second;
216 // In theory we don't need the indirection through the DFBlocks vector.
217 // In practice, the order of calling QueuePhiNode would depend on the
218 // (unspecified) ordering of basic blocks in the dominance frontier,
219 // which would give PHI nodes non-determinstic subscripts. Fix this by
220 // processing blocks in order of the occurance in the function.
221 for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end();
223 DFBlocks.push_back(BBNumbers.getNumber(*P));
225 // Sort by which the block ordering in the function.
226 std::sort(DFBlocks.begin(), DFBlocks.end());
228 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
229 BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]);
230 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
231 DefiningBlocks.push_back(BB);
237 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
238 // of the writes to the variable, scan through the reads of the variable,
239 // marking PHI nodes which are actually necessary as alive (by removing them
240 // from the InsertedPHINodes set). This is not perfect: there may PHI
241 // marked alive because of loads which are dominated by stores, but there
242 // will be no unmarked PHI nodes which are actually used.
244 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
245 MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
248 // If there are any PHI nodes which are now known to be dead, remove them!
249 for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
250 E = InsertedPHINodes.end(); I != E; ++I) {
252 std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
253 BBPNs[AllocaNum] = 0;
255 // Check to see if we just removed the last inserted PHI node from this
256 // basic block. If so, remove the entry for the basic block.
257 bool HasOtherPHIs = false;
258 for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
264 NewPhiNodes.erase(PN->getParent());
266 if (AST && isa<PointerType>(PN->getType()))
267 AST->deleteValue(PN);
268 PN->getParent()->getInstList().erase(PN);
271 // Keep the reverse mapping of the 'Allocas' array.
272 AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
275 // Process all allocas which are only used in a single basic block.
276 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
277 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
278 const std::vector<AllocaInst*> &Allocas = I->second;
279 assert(!Allocas.empty() && "empty alloca list??");
281 // It's common for there to only be one alloca in the list. Handle it
283 if (Allocas.size() == 1)
284 PromoteLocallyUsedAlloca(I->first, Allocas[0]);
286 PromoteLocallyUsedAllocas(I->first, Allocas);
290 return; // All of the allocas must have been trivial!
292 // Set the incoming values for the basic block to be null values for all of
293 // the alloca's. We do this in case there is a load of a value that has not
294 // been stored yet. In this case, it will get this null value.
296 std::vector<Value *> Values(Allocas.size());
297 for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
298 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
300 // Walks all basic blocks in the function performing the SSA rename algorithm
301 // and inserting the phi nodes we marked as necessary
303 RenamePass(F.begin(), 0, Values);
305 // The renamer uses the Visited set to avoid infinite loops. Clear it now.
308 // Remove the allocas themselves from the function...
309 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
310 Instruction *A = Allocas[i];
312 // If there are any uses of the alloca instructions left, they must be in
313 // sections of dead code that were not processed on the dominance frontier.
314 // Just delete the users now.
317 A->replaceAllUsesWith(UndefValue::get(A->getType()));
318 if (AST) AST->deleteValue(A);
319 A->getParent()->getInstList().erase(A);
322 // At this point, the renamer has added entries to PHI nodes for all reachable
323 // code. Unfortunately, there may be blocks which are not reachable, which
324 // the renamer hasn't traversed. If this is the case, the PHI nodes may not
325 // have incoming values for all predecessors. Loop over all PHI nodes we have
326 // created, inserting undef values if they are missing any incoming values.
328 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
329 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
331 std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
332 std::vector<PHINode*> &PNs = I->second;
333 assert(!PNs.empty() && "Empty PHI node list??");
335 // Loop over all of the PHI nodes and see if there are any that we can get
336 // rid of because they merge all of the same incoming values. This can
337 // happen due to undef values coming into the PHI nodes.
338 PHINode *SomePHI = 0;
339 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
341 if (Value *V = hasConstantValue(PNs[i])) {
342 if (!isa<Instruction>(V) ||
343 dominates(cast<Instruction>(V)->getParent(), I->first)) {
344 PNs[i]->replaceAllUsesWith(V);
345 PNs[i]->eraseFromParent();
353 // Only do work here if there the PHI nodes are missing incoming values. We
354 // know that all PHI nodes that were inserted in a block will have the same
355 // number of incoming values, so we can just check any PHI node.
356 if (SomePHI && Preds.size() != SomePHI->getNumIncomingValues()) {
357 // Ok, now we know that all of the PHI nodes are missing entries for some
358 // basic blocks. Start by sorting the incoming predecessors for efficient
360 std::sort(Preds.begin(), Preds.end());
362 // Now we loop through all BB's which have entries in SomePHI and remove
363 // them from the Preds list.
364 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
365 // Do a log(n) search of the Preds list for the entry we want.
366 std::vector<BasicBlock*>::iterator EntIt =
367 std::lower_bound(Preds.begin(), Preds.end(),
368 SomePHI->getIncomingBlock(i));
369 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
370 "PHI node has entry for a block which is not a predecessor!");
376 // At this point, the blocks left in the preds list must have dummy
377 // entries inserted into every PHI nodes for the block.
378 for (unsigned i = 0, e = PNs.size(); i != e; ++i)
379 if (PHINode *PN = PNs[i]) {
380 Value *UndefVal = UndefValue::get(PN->getType());
381 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
382 PN->addIncoming(UndefVal, Preds[pred]);
388 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
389 // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
390 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
391 // each read of the variable. For each block that reads the variable, this
392 // function is called, which removes used PHI nodes from the DeadPHINodes set.
393 // After all of the reads have been processed, any PHI nodes left in the
394 // DeadPHINodes set are removed.
396 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
397 std::set<PHINode*> &DeadPHINodes) {
398 // Scan the immediate dominators of this block looking for a block which has a
399 // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
400 for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
401 BasicBlock *DomBB = N->getBlock();
402 std::map<BasicBlock*, std::vector<PHINode*> >::iterator
403 I = NewPhiNodes.find(DomBB);
404 if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
405 // Ok, we found an inserted PHI node which dominates this value.
406 PHINode *DominatingPHI = I->second[AllocaNum];
408 // Find out if we previously thought it was dead.
409 std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
410 if (DPNI != DeadPHINodes.end()) {
411 // Ok, until now, we thought this PHI node was dead. Mark it as being
413 DeadPHINodes.erase(DPNI);
415 // Now that we have marked the PHI node alive, also mark any PHI nodes
416 // which it might use as being alive as well.
417 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
419 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
425 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
426 /// block. If this is the case, avoid traversing the CFG and inserting a lot of
427 /// potentially useless PHI nodes by just performing a single linear pass over
428 /// the basic block using the Alloca.
430 void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
431 assert(!AI->use_empty() && "There are no uses of the alloca!");
433 // Handle degenerate cases quickly.
434 if (AI->hasOneUse()) {
435 Instruction *U = cast<Instruction>(AI->use_back());
436 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
437 // Must be a load of uninitialized value.
438 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
439 if (AST && isa<PointerType>(LI->getType()))
440 AST->deleteValue(LI);
442 // Otherwise it must be a store which is never read.
443 assert(isa<StoreInst>(U));
445 BB->getInstList().erase(U);
447 // Uses of the uninitialized memory location shall get undef.
448 Value *CurVal = UndefValue::get(AI->getAllocatedType());
450 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
451 Instruction *Inst = I++;
452 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
453 if (LI->getOperand(0) == AI) {
454 // Loads just returns the "current value"...
455 LI->replaceAllUsesWith(CurVal);
456 if (AST && isa<PointerType>(LI->getType()))
457 AST->deleteValue(LI);
458 BB->getInstList().erase(LI);
460 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
461 if (SI->getOperand(1) == AI) {
462 // Store updates the "current value"...
463 CurVal = SI->getOperand(0);
464 BB->getInstList().erase(SI);
470 // After traversing the basic block, there should be no more uses of the
471 // alloca, remove it now.
472 assert(AI->use_empty() && "Uses of alloca from more than one BB??");
473 if (AST) AST->deleteValue(AI);
474 AI->getParent()->getInstList().erase(AI);
477 /// PromoteLocallyUsedAllocas - This method is just like
478 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca
479 /// instructions in parallel. This is important in cases where we have large
480 /// basic blocks, as we don't want to rescan the entire basic block for each
481 /// alloca which is locally used in it (which might be a lot).
482 void PromoteMem2Reg::
483 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
484 std::map<AllocaInst*, Value*> CurValues;
485 for (unsigned i = 0, e = AIs.size(); i != e; ++i)
486 CurValues[AIs[i]] = 0; // Insert with null value
488 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
489 Instruction *Inst = I++;
490 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
491 // Is this a load of an alloca we are tracking?
492 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
493 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
494 if (AIt != CurValues.end()) {
495 // Loads just returns the "current value"...
496 if (AIt->second == 0) // Uninitialized value??
497 AIt->second = UndefValue::get(AIt->first->getAllocatedType());
498 LI->replaceAllUsesWith(AIt->second);
499 if (AST && isa<PointerType>(LI->getType()))
500 AST->deleteValue(LI);
501 BB->getInstList().erase(LI);
504 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
505 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
506 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
507 if (AIt != CurValues.end()) {
508 // Store updates the "current value"...
509 AIt->second = SI->getOperand(0);
510 BB->getInstList().erase(SI);
519 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
520 // Alloca returns true if there wasn't already a phi-node for that variable
522 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
524 std::set<PHINode*> &InsertedPHINodes) {
525 // Look up the basic-block in question.
526 std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
527 if (BBPNs.empty()) BBPNs.resize(Allocas.size());
529 // If the BB already has a phi node added for the i'th alloca then we're done!
530 if (BBPNs[AllocaNo]) return false;
532 // Create a PhiNode using the dereferenced type... and add the phi-node to the
534 PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
535 Allocas[AllocaNo]->getName() + "." +
536 utostr(Version++), BB->begin());
537 BBPNs[AllocaNo] = PN;
538 InsertedPHINodes.insert(PN);
540 if (AST && isa<PointerType>(PN->getType()))
541 AST->copyValue(PointerAllocaValues[AllocaNo], PN);
547 // RenamePass - Recursively traverse the CFG of the function, renaming loads and
548 // stores to the allocas which we are promoting. IncomingVals indicates what
549 // value each Alloca contains on exit from the predecessor block Pred.
551 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
552 std::vector<Value*> &IncomingVals) {
554 // If this BB needs a PHI node, update the PHI node for each variable we need
556 std::map<BasicBlock*, std::vector<PHINode *> >::iterator
557 BBPNI = NewPhiNodes.find(BB);
558 if (BBPNI != NewPhiNodes.end()) {
559 std::vector<PHINode *> &BBPNs = BBPNI->second;
560 for (unsigned k = 0; k != BBPNs.size(); ++k)
561 if (PHINode *PN = BBPNs[k]) {
562 // Add this incoming value to the PHI node.
563 PN->addIncoming(IncomingVals[k], Pred);
565 // The currently active variable for this block is now the PHI.
566 IncomingVals[k] = PN;
570 // don't revisit nodes
571 if (Visited.count(BB)) return;
576 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
577 Instruction *I = II++; // get the instruction, increment iterator
579 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
580 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
581 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
582 if (AI != AllocaLookup.end()) {
583 Value *V = IncomingVals[AI->second];
585 // walk the use list of this load and replace all uses with r
586 LI->replaceAllUsesWith(V);
587 if (AST && isa<PointerType>(LI->getType()))
588 AST->deleteValue(LI);
589 BB->getInstList().erase(LI);
592 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
593 // Delete this instruction and mark the name as the current holder of the
595 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
596 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
597 if (ai != AllocaLookup.end()) {
598 // what value were we writing?
599 IncomingVals[ai->second] = SI->getOperand(0);
600 BB->getInstList().erase(SI);
606 // Recurse to our successors.
607 TerminatorInst *TI = BB->getTerminator();
608 for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
609 std::vector<Value*> OutgoingVals(IncomingVals);
610 RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
614 /// PromoteMemToReg - Promote the specified list of alloca instructions into
615 /// scalar registers, inserting PHI nodes as appropriate. This function makes
616 /// use of DominanceFrontier information. This function does not modify the CFG
617 /// of the function at all. All allocas must be from the same function.
619 /// If AST is specified, the specified tracker is updated to reflect changes
622 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
623 DominatorTree &DT, DominanceFrontier &DF,
624 const TargetData &TD, AliasSetTracker *AST) {
625 // If there is nothing to do, bail out...
626 if (Allocas.empty()) return;
627 PromoteMem2Reg(Allocas, DT, DF, TD, AST).run();