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PromoteMemoryToRegister.cpp

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00001 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
00002 // 
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 // 
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file promote memory references to be register references.  It promotes
00011 // alloca instructions which only have loads and stores as uses.  An alloca is
00012 // transformed by using dominator frontiers to place PHI nodes, then traversing
00013 // the function in depth-first order to rewrite loads and stores as appropriate.
00014 // This is just the standard SSA construction algorithm to construct "pruned"
00015 // SSA form.
00016 //
00017 //===----------------------------------------------------------------------===//
00018 
00019 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
00020 #include "llvm/Constants.h"
00021 #include "llvm/DerivedTypes.h"
00022 #include "llvm/Function.h"
00023 #include "llvm/Instructions.h"
00024 #include "llvm/Analysis/Dominators.h"
00025 #include "llvm/Analysis/AliasSetTracker.h"
00026 #include "llvm/ADT/StringExtras.h"
00027 #include "llvm/Transforms/Utils/Local.h"
00028 #include "llvm/Support/CFG.h"
00029 #include "llvm/Support/StableBasicBlockNumbering.h"
00030 #include <algorithm>
00031 using namespace llvm;
00032 
00033 /// isAllocaPromotable - Return true if this alloca is legal for promotion.
00034 /// This is true if there are only loads and stores to the alloca.
00035 ///
00036 bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
00037   // FIXME: If the memory unit is of pointer or integer type, we can permit
00038   // assignments to subsections of the memory unit.
00039 
00040   // Only allow direct loads and stores...
00041   for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
00042        UI != UE; ++UI)     // Loop over all of the uses of the alloca
00043     if (isa<LoadInst>(*UI)) {
00044       // noop
00045     } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
00046       if (SI->getOperand(0) == AI)
00047         return false;   // Don't allow a store OF the AI, only INTO the AI.
00048     } else {
00049       return false;   // Not a load or store.
00050     }
00051   
00052   return true;
00053 }
00054 
00055 namespace {
00056   struct PromoteMem2Reg {
00057     /// Allocas - The alloca instructions being promoted.
00058     ///
00059     std::vector<AllocaInst*> Allocas;
00060     DominatorTree &DT;
00061     DominanceFrontier &DF;
00062     const TargetData &TD;
00063 
00064     /// AST - An AliasSetTracker object to update.  If null, don't update it.
00065     ///
00066     AliasSetTracker *AST;
00067 
00068     /// AllocaLookup - Reverse mapping of Allocas.
00069     ///
00070     std::map<AllocaInst*, unsigned>  AllocaLookup;
00071 
00072     /// NewPhiNodes - The PhiNodes we're adding.
00073     ///
00074     std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes;
00075 
00076     /// PointerAllocaValues - If we are updating an AliasSetTracker, then for
00077     /// each alloca that is of pointer type, we keep track of what to copyValue
00078     /// to the inserted PHI nodes here.
00079     ///
00080     std::vector<Value*> PointerAllocaValues;
00081 
00082     /// Visited - The set of basic blocks the renamer has already visited.
00083     ///
00084     std::set<BasicBlock*> Visited;
00085 
00086     /// BBNumbers - Contains a stable numbering of basic blocks to avoid
00087     /// non-determinstic behavior.
00088     StableBasicBlockNumbering BBNumbers;
00089 
00090   public:
00091     PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
00092                    DominanceFrontier &df, const TargetData &td,
00093                    AliasSetTracker *ast)
00094       : Allocas(A), DT(dt), DF(df), TD(td), AST(ast) {}
00095 
00096     void run();
00097 
00098     /// dominates - Return true if I1 dominates I2 using the DominatorTree.
00099     ///
00100     bool dominates(Instruction *I1, Instruction *I2) const {
00101       if (InvokeInst *II = dyn_cast<InvokeInst>(I1))
00102         I1 = II->getNormalDest()->begin();
00103       return DT[I1->getParent()]->dominates(DT[I2->getParent()]);
00104     }
00105 
00106   private:
00107     void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
00108                                std::set<PHINode*> &DeadPHINodes);
00109     void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
00110     void PromoteLocallyUsedAllocas(BasicBlock *BB, 
00111                                    const std::vector<AllocaInst*> &AIs);
00112 
00113     void RenamePass(BasicBlock *BB, BasicBlock *Pred,
00114                     std::vector<Value*> &IncVals);
00115     bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
00116                       std::set<PHINode*> &InsertedPHINodes);
00117   };
00118 }  // end of anonymous namespace
00119 
00120 void PromoteMem2Reg::run() {
00121   Function &F = *DF.getRoot()->getParent();
00122 
00123   // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
00124   // only used in a single basic block.  These instructions can be efficiently
00125   // promoted by performing a single linear scan over that one block.  Since
00126   // individual basic blocks are sometimes large, we group together all allocas
00127   // that are live in a single basic block by the basic block they are live in.
00128   std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
00129 
00130   if (AST) PointerAllocaValues.resize(Allocas.size());
00131 
00132   for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
00133     AllocaInst *AI = Allocas[AllocaNum];
00134 
00135     assert(isAllocaPromotable(AI, TD) &&
00136            "Cannot promote non-promotable alloca!");
00137     assert(AI->getParent()->getParent() == &F &&
00138            "All allocas should be in the same function, which is same as DF!");
00139 
00140     if (AI->use_empty()) {
00141       // If there are no uses of the alloca, just delete it now.
00142       if (AST) AST->deleteValue(AI);
00143       AI->getParent()->getInstList().erase(AI);
00144 
00145       // Remove the alloca from the Allocas list, since it has been processed
00146       Allocas[AllocaNum] = Allocas.back();
00147       Allocas.pop_back();
00148       --AllocaNum;
00149       continue;
00150     }
00151 
00152     // Calculate the set of read and write-locations for each alloca.  This is
00153     // analogous to finding the 'uses' and 'definitions' of each variable.
00154     std::vector<BasicBlock*> DefiningBlocks;
00155     std::vector<BasicBlock*> UsingBlocks;
00156 
00157     BasicBlock *OnlyBlock = 0;
00158     bool OnlyUsedInOneBlock = true;
00159 
00160     // As we scan the uses of the alloca instruction, keep track of stores, and
00161     // decide whether all of the loads and stores to the alloca are within the
00162     // same basic block.
00163     Value *AllocaPointerVal = 0;
00164     for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
00165       Instruction *User = cast<Instruction>(*U);
00166       if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
00167         // Remember the basic blocks which define new values for the alloca
00168         DefiningBlocks.push_back(SI->getParent());
00169         AllocaPointerVal = SI->getOperand(0);
00170       } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
00171         // Otherwise it must be a load instruction, keep track of variable reads
00172         UsingBlocks.push_back(LI->getParent());
00173         AllocaPointerVal = LI;
00174       }
00175 
00176       if (OnlyUsedInOneBlock) {
00177         if (OnlyBlock == 0)
00178           OnlyBlock = User->getParent();
00179         else if (OnlyBlock != User->getParent())
00180           OnlyUsedInOneBlock = false;
00181       }
00182     }
00183 
00184     // If the alloca is only read and written in one basic block, just perform a
00185     // linear sweep over the block to eliminate it.
00186     if (OnlyUsedInOneBlock) {
00187       LocallyUsedAllocas[OnlyBlock].push_back(AI);
00188 
00189       // Remove the alloca from the Allocas list, since it will be processed.
00190       Allocas[AllocaNum] = Allocas.back();
00191       Allocas.pop_back();
00192       --AllocaNum;
00193       continue;
00194     }
00195 
00196     if (AST)
00197       PointerAllocaValues[AllocaNum] = AllocaPointerVal;
00198 
00199     // If we haven't computed a numbering for the BB's in the function, do so
00200     // now.
00201     BBNumbers.compute(F);
00202 
00203     // Compute the locations where PhiNodes need to be inserted.  Look at the
00204     // dominance frontier of EACH basic-block we have a write in.
00205     //
00206     unsigned CurrentVersion = 0;
00207     std::set<PHINode*> InsertedPHINodes;
00208     std::vector<unsigned> DFBlocks;
00209     while (!DefiningBlocks.empty()) {
00210       BasicBlock *BB = DefiningBlocks.back();
00211       DefiningBlocks.pop_back();
00212 
00213       // Look up the DF for this write, add it to PhiNodes
00214       DominanceFrontier::const_iterator it = DF.find(BB);
00215       if (it != DF.end()) {
00216         const DominanceFrontier::DomSetType &S = it->second;
00217 
00218         // In theory we don't need the indirection through the DFBlocks vector.
00219         // In practice, the order of calling QueuePhiNode would depend on the
00220         // (unspecified) ordering of basic blocks in the dominance frontier,
00221         // which would give PHI nodes non-determinstic subscripts.  Fix this by
00222         // processing blocks in order of the occurance in the function.
00223         for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
00224              PE = S.end(); P != PE; ++P)
00225           DFBlocks.push_back(BBNumbers.getNumber(*P));
00226 
00227         // Sort by which the block ordering in the function.
00228         std::sort(DFBlocks.begin(), DFBlocks.end());
00229 
00230         for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
00231           BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]);
00232           if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
00233             DefiningBlocks.push_back(BB);
00234         }
00235         DFBlocks.clear();
00236       }
00237     }
00238 
00239     // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
00240     // of the writes to the variable, scan through the reads of the variable,
00241     // marking PHI nodes which are actually necessary as alive (by removing them
00242     // from the InsertedPHINodes set).  This is not perfect: there may PHI
00243     // marked alive because of loads which are dominated by stores, but there
00244     // will be no unmarked PHI nodes which are actually used.
00245     //
00246     for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
00247       MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
00248     UsingBlocks.clear();
00249 
00250     // If there are any PHI nodes which are now known to be dead, remove them!
00251     for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
00252            E = InsertedPHINodes.end(); I != E; ++I) {
00253       PHINode *PN = *I;
00254       std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
00255       BBPNs[AllocaNum] = 0;
00256 
00257       // Check to see if we just removed the last inserted PHI node from this
00258       // basic block.  If so, remove the entry for the basic block.
00259       bool HasOtherPHIs = false;
00260       for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
00261         if (BBPNs[i]) {
00262           HasOtherPHIs = true;
00263           break;
00264         }
00265       if (!HasOtherPHIs)
00266         NewPhiNodes.erase(PN->getParent());
00267 
00268       if (AST && isa<PointerType>(PN->getType()))
00269         AST->deleteValue(PN);
00270       PN->getParent()->getInstList().erase(PN);      
00271     }
00272 
00273     // Keep the reverse mapping of the 'Allocas' array. 
00274     AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
00275   }
00276   
00277   // Process all allocas which are only used in a single basic block.
00278   for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
00279          LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
00280     const std::vector<AllocaInst*> &Allocas = I->second;
00281     assert(!Allocas.empty() && "empty alloca list??");
00282 
00283     // It's common for there to only be one alloca in the list.  Handle it
00284     // efficiently.
00285     if (Allocas.size() == 1)
00286       PromoteLocallyUsedAlloca(I->first, Allocas[0]);
00287     else
00288       PromoteLocallyUsedAllocas(I->first, Allocas);
00289   }
00290 
00291   if (Allocas.empty())
00292     return; // All of the allocas must have been trivial!
00293 
00294   // Set the incoming values for the basic block to be null values for all of
00295   // the alloca's.  We do this in case there is a load of a value that has not
00296   // been stored yet.  In this case, it will get this null value.
00297   //
00298   std::vector<Value *> Values(Allocas.size());
00299   for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
00300     Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
00301 
00302   // Walks all basic blocks in the function performing the SSA rename algorithm
00303   // and inserting the phi nodes we marked as necessary
00304   //
00305   RenamePass(F.begin(), 0, Values);
00306 
00307   // The renamer uses the Visited set to avoid infinite loops.  Clear it now.
00308   Visited.clear();
00309 
00310   // Remove the allocas themselves from the function...
00311   for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
00312     Instruction *A = Allocas[i];
00313 
00314     // If there are any uses of the alloca instructions left, they must be in
00315     // sections of dead code that were not processed on the dominance frontier.
00316     // Just delete the users now.
00317     //
00318     if (!A->use_empty())
00319       A->replaceAllUsesWith(UndefValue::get(A->getType()));
00320     if (AST) AST->deleteValue(A);
00321     A->getParent()->getInstList().erase(A);
00322   }
00323 
00324   // At this point, the renamer has added entries to PHI nodes for all reachable
00325   // code.  Unfortunately, there may be blocks which are not reachable, which
00326   // the renamer hasn't traversed.  If this is the case, the PHI nodes may not
00327   // have incoming values for all predecessors.  Loop over all PHI nodes we have
00328   // created, inserting undef values if they are missing any incoming values.
00329   //
00330   for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I = 
00331          NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
00332 
00333     std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
00334     std::vector<PHINode*> &PNs = I->second;
00335     assert(!PNs.empty() && "Empty PHI node list??");
00336 
00337     // Loop over all of the PHI nodes and see if there are any that we can get
00338     // rid of because they merge all of the same incoming values.  This can
00339     // happen due to undef values coming into the PHI nodes.
00340     PHINode *SomePHI = 0;
00341     for (unsigned i = 0, e = PNs.size(); i != e; ++i)
00342       if (PNs[i]) {
00343         if (Value *V = hasConstantValue(PNs[i])) {
00344           if (!isa<Instruction>(V) || dominates(cast<Instruction>(V), PNs[i])) {
00345             if (AST && isa<PointerType>(PNs[i]->getType()))
00346               AST->deleteValue(PNs[i]);
00347             PNs[i]->replaceAllUsesWith(V);
00348             PNs[i]->eraseFromParent();
00349             PNs[i] = 0;
00350           }
00351         }
00352         if (PNs[i])
00353           SomePHI = PNs[i];
00354       }
00355 
00356     // Only do work here if there the PHI nodes are missing incoming values.  We
00357     // know that all PHI nodes that were inserted in a block will have the same
00358     // number of incoming values, so we can just check any PHI node.
00359     if (SomePHI && Preds.size() != SomePHI->getNumIncomingValues()) {
00360       // Ok, now we know that all of the PHI nodes are missing entries for some
00361       // basic blocks.  Start by sorting the incoming predecessors for efficient
00362       // access.
00363       std::sort(Preds.begin(), Preds.end());
00364 
00365       // Now we loop through all BB's which have entries in SomePHI and remove
00366       // them from the Preds list.
00367       for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
00368         // Do a log(n) search of the Preds list for the entry we want.
00369         std::vector<BasicBlock*>::iterator EntIt =
00370           std::lower_bound(Preds.begin(), Preds.end(),
00371                            SomePHI->getIncomingBlock(i));
00372         assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
00373                "PHI node has entry for a block which is not a predecessor!");
00374 
00375         // Remove the entry
00376         Preds.erase(EntIt);
00377       }
00378 
00379       // At this point, the blocks left in the preds list must have dummy
00380       // entries inserted into every PHI nodes for the block.
00381       for (unsigned i = 0, e = PNs.size(); i != e; ++i)
00382         if (PHINode *PN = PNs[i]) {
00383           Value *UndefVal = UndefValue::get(PN->getType());
00384           for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
00385             PN->addIncoming(UndefVal, Preds[pred]);
00386         }
00387     }
00388   }
00389 }
00390 
00391 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
00392 // "minimal" SSA form.  To do this, it inserts all of the PHI nodes on the IDF
00393 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
00394 // each read of the variable.  For each block that reads the variable, this
00395 // function is called, which removes used PHI nodes from the DeadPHINodes set.
00396 // After all of the reads have been processed, any PHI nodes left in the
00397 // DeadPHINodes set are removed.
00398 //
00399 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
00400                                            std::set<PHINode*> &DeadPHINodes) {
00401   // Scan the immediate dominators of this block looking for a block which has a
00402   // PHI node for Alloca num.  If we find it, mark the PHI node as being alive!
00403   for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
00404     BasicBlock *DomBB = N->getBlock();
00405     std::map<BasicBlock*, std::vector<PHINode*> >::iterator
00406       I = NewPhiNodes.find(DomBB);
00407     if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
00408       // Ok, we found an inserted PHI node which dominates this value.
00409       PHINode *DominatingPHI = I->second[AllocaNum];
00410 
00411       // Find out if we previously thought it was dead.
00412       std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
00413       if (DPNI != DeadPHINodes.end()) {
00414         // Ok, until now, we thought this PHI node was dead.  Mark it as being
00415         // alive/needed.
00416         DeadPHINodes.erase(DPNI);
00417 
00418         // Now that we have marked the PHI node alive, also mark any PHI nodes
00419         // which it might use as being alive as well.
00420         for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
00421              PI != PE; ++PI)
00422           MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
00423       }
00424     }
00425   }
00426 }
00427 
00428 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
00429 /// block.  If this is the case, avoid traversing the CFG and inserting a lot of
00430 /// potentially useless PHI nodes by just performing a single linear pass over
00431 /// the basic block using the Alloca.
00432 ///
00433 void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
00434   assert(!AI->use_empty() && "There are no uses of the alloca!");
00435 
00436   // Handle degenerate cases quickly.
00437   if (AI->hasOneUse()) {
00438     Instruction *U = cast<Instruction>(AI->use_back());
00439     if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
00440       // Must be a load of uninitialized value.
00441       LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
00442       if (AST && isa<PointerType>(LI->getType()))
00443         AST->deleteValue(LI);
00444     } else {
00445       // Otherwise it must be a store which is never read.
00446       assert(isa<StoreInst>(U));
00447     }
00448     BB->getInstList().erase(U);
00449   } else {
00450     // Uses of the uninitialized memory location shall get undef.
00451     Value *CurVal = UndefValue::get(AI->getAllocatedType());
00452   
00453     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
00454       Instruction *Inst = I++;
00455       if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
00456         if (LI->getOperand(0) == AI) {
00457           // Loads just returns the "current value"...
00458           LI->replaceAllUsesWith(CurVal);
00459           if (AST && isa<PointerType>(LI->getType()))
00460             AST->deleteValue(LI);
00461           BB->getInstList().erase(LI);
00462         }
00463       } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
00464         if (SI->getOperand(1) == AI) {
00465           // Store updates the "current value"...
00466           CurVal = SI->getOperand(0);
00467           BB->getInstList().erase(SI);
00468         }
00469       }
00470     }
00471   }
00472 
00473   // After traversing the basic block, there should be no more uses of the
00474   // alloca, remove it now.
00475   assert(AI->use_empty() && "Uses of alloca from more than one BB??");
00476   if (AST) AST->deleteValue(AI);
00477   AI->getParent()->getInstList().erase(AI);
00478 }
00479 
00480 /// PromoteLocallyUsedAllocas - This method is just like
00481 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca
00482 /// instructions in parallel.  This is important in cases where we have large
00483 /// basic blocks, as we don't want to rescan the entire basic block for each
00484 /// alloca which is locally used in it (which might be a lot).
00485 void PromoteMem2Reg::
00486 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
00487   std::map<AllocaInst*, Value*> CurValues;
00488   for (unsigned i = 0, e = AIs.size(); i != e; ++i)
00489     CurValues[AIs[i]] = 0; // Insert with null value
00490 
00491   for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
00492     Instruction *Inst = I++;
00493     if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
00494       // Is this a load of an alloca we are tracking?
00495       if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
00496         std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
00497         if (AIt != CurValues.end()) {
00498           // Loads just returns the "current value"...
00499           if (AIt->second == 0)   // Uninitialized value??
00500             AIt->second = UndefValue::get(AIt->first->getAllocatedType());
00501           LI->replaceAllUsesWith(AIt->second);
00502           if (AST && isa<PointerType>(LI->getType()))
00503             AST->deleteValue(LI);
00504           BB->getInstList().erase(LI);
00505         }
00506       }
00507     } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
00508       if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
00509         std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
00510         if (AIt != CurValues.end()) {
00511           // Store updates the "current value"...
00512           AIt->second = SI->getOperand(0);
00513           BB->getInstList().erase(SI);
00514         }
00515       }
00516     }
00517   }
00518 }
00519 
00520 
00521 
00522 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
00523 // Alloca returns true if there wasn't already a phi-node for that variable
00524 //
00525 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
00526                                   unsigned &Version,
00527                                   std::set<PHINode*> &InsertedPHINodes) {
00528   // Look up the basic-block in question.
00529   std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
00530   if (BBPNs.empty()) BBPNs.resize(Allocas.size());
00531 
00532   // If the BB already has a phi node added for the i'th alloca then we're done!
00533   if (BBPNs[AllocaNo]) return false;
00534 
00535   // Create a PhiNode using the dereferenced type... and add the phi-node to the
00536   // BasicBlock.
00537   PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
00538                             Allocas[AllocaNo]->getName() + "." +
00539                                         utostr(Version++), BB->begin());
00540   BBPNs[AllocaNo] = PN;
00541   InsertedPHINodes.insert(PN);
00542 
00543   if (AST && isa<PointerType>(PN->getType()))
00544     AST->copyValue(PointerAllocaValues[AllocaNo], PN);
00545 
00546   return true;
00547 }
00548 
00549 
00550 // RenamePass - Recursively traverse the CFG of the function, renaming loads and
00551 // stores to the allocas which we are promoting.  IncomingVals indicates what
00552 // value each Alloca contains on exit from the predecessor block Pred.
00553 //
00554 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
00555                                 std::vector<Value*> &IncomingVals) {
00556 
00557   // If this BB needs a PHI node, update the PHI node for each variable we need
00558   // PHI nodes for.
00559   std::map<BasicBlock*, std::vector<PHINode *> >::iterator
00560     BBPNI = NewPhiNodes.find(BB);
00561   if (BBPNI != NewPhiNodes.end()) {
00562     std::vector<PHINode *> &BBPNs = BBPNI->second;
00563     for (unsigned k = 0; k != BBPNs.size(); ++k)
00564       if (PHINode *PN = BBPNs[k]) {
00565         // Add this incoming value to the PHI node.
00566         PN->addIncoming(IncomingVals[k], Pred);
00567 
00568         // The currently active variable for this block is now the PHI.
00569         IncomingVals[k] = PN;
00570       }
00571   }
00572 
00573   // don't revisit nodes
00574   if (Visited.count(BB)) return;
00575   
00576   // mark as visited
00577   Visited.insert(BB);
00578 
00579   for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
00580     Instruction *I = II++; // get the instruction, increment iterator
00581 
00582     if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
00583       if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
00584         std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
00585         if (AI != AllocaLookup.end()) {
00586           Value *V = IncomingVals[AI->second];
00587 
00588           // walk the use list of this load and replace all uses with r
00589           LI->replaceAllUsesWith(V);
00590           if (AST && isa<PointerType>(LI->getType()))
00591             AST->deleteValue(LI);
00592           BB->getInstList().erase(LI);
00593         }
00594       }
00595     } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
00596       // Delete this instruction and mark the name as the current holder of the
00597       // value
00598       if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
00599         std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
00600         if (ai != AllocaLookup.end()) {
00601           // what value were we writing?
00602           IncomingVals[ai->second] = SI->getOperand(0);
00603           BB->getInstList().erase(SI);
00604         }
00605       }
00606     }
00607   }
00608 
00609   // Recurse to our successors.
00610   TerminatorInst *TI = BB->getTerminator();
00611   for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
00612     std::vector<Value*> OutgoingVals(IncomingVals);
00613     RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
00614   }
00615 }
00616 
00617 /// PromoteMemToReg - Promote the specified list of alloca instructions into
00618 /// scalar registers, inserting PHI nodes as appropriate.  This function makes
00619 /// use of DominanceFrontier information.  This function does not modify the CFG
00620 /// of the function at all.  All allocas must be from the same function.
00621 ///
00622 /// If AST is specified, the specified tracker is updated to reflect changes
00623 /// made to the IR.
00624 ///
00625 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
00626                            DominatorTree &DT, DominanceFrontier &DF,
00627                            const TargetData &TD, AliasSetTracker *AST) {
00628   // If there is nothing to do, bail out...
00629   if (Allocas.empty()) return;
00630   PromoteMem2Reg(Allocas, DT, DF, TD, AST).run();
00631 }