-//===- PromoteMemoryToRegister.cpp - Convert memory refs to regs ----------===//
+//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
//
-// This pass is used to promote memory references to be register references. A
-// simple example of the transformation performed by this pass is:
+// The LLVM Compiler Infrastructure
//
-// FROM CODE TO CODE
-// %X = alloca int, uint 1 ret int 42
-// store int 42, int *%X
-// %Y = load int* %X
-// ret int %Y
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
-// To do this transformation, a simple analysis is done to ensure it is safe.
-// Currently this just loops over all alloca instructions, looking for
-// instructions that are only used in simple load and stores.
+//===----------------------------------------------------------------------===//
//
-// After this, the code is transformed by...something magical :)
+// This file promote memory references to be register references. It promotes
+// alloca instructions which only have loads and stores as uses. An alloca is
+// transformed by using dominator frontiers to place PHI nodes, then traversing
+// the function in depth-first order to rewrite loads and stores as appropriate.
+// This is just the standard SSA construction algorithm to construct "pruned"
+// SSA form.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Analysis/Dominators.h"
-#include "llvm/iMemory.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iTerminators.h"
+#define DEBUG_TYPE "mem2reg"
+#include "llvm/Transforms/Utils/PromoteMemToReg.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/Constant.h"
-#include "llvm/Type.h"
-#include "Support/StatisticReporter.h"
+#include "llvm/Instructions.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/AliasSetTracker.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+#include <algorithm>
+using namespace llvm;
+
+STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
+STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
+STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
+
+// Provide DenseMapKeyInfo for all pointers.
+namespace llvm {
+template<>
+struct DenseMapKeyInfo<std::pair<BasicBlock*, unsigned> > {
+ static inline std::pair<BasicBlock*, unsigned> getEmptyKey() {
+ return std::make_pair((BasicBlock*)-1, ~0U);
+ }
+ static inline std::pair<BasicBlock*, unsigned> getTombstoneKey() {
+ return std::make_pair((BasicBlock*)-2, 0U);
+ }
+ static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) {
+ return DenseMapKeyInfo<void*>::getHashValue(Val.first) + Val.second*2;
+ }
+ static bool isPod() { return true; }
+};
+}
+
+/// isAllocaPromotable - Return true if this alloca is legal for promotion.
+/// This is true if there are only loads and stores to the alloca.
+///
+bool llvm::isAllocaPromotable(const AllocaInst *AI) {
+ // FIXME: If the memory unit is of pointer or integer type, we can permit
+ // assignments to subsections of the memory unit.
-static Statistic<> NumPromoted("mem2reg\t\t- Number of alloca's promoted");
+ // Only allow direct loads and stores...
+ for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE; ++UI) // Loop over all of the uses of the alloca
+ if (isa<LoadInst>(*UI)) {
+ // noop
+ } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ if (SI->getOperand(0) == AI)
+ return false; // Don't allow a store OF the AI, only INTO the AI.
+ } else {
+ return false; // Not a load or store.
+ }
-using std::vector;
-using std::map;
-using std::set;
+ return true;
+}
namespace {
- struct PromotePass : public FunctionPass {
- vector<AllocaInst*> Allocas; // the alloca instruction..
- map<Instruction*, unsigned> AllocaLookup; // reverse mapping of above
+ struct AllocaInfo;
+
+ // Data package used by RenamePass()
+ class VISIBILITY_HIDDEN RenamePassData {
+ public:
+ typedef std::vector<Value *> ValVector;
+
+ RenamePassData() {}
+ RenamePassData(BasicBlock *B, BasicBlock *P,
+ const ValVector &V) : BB(B), Pred(P), Values(V) {}
+ BasicBlock *BB;
+ BasicBlock *Pred;
+ ValVector Values;
- vector<vector<BasicBlock*> > PhiNodes; // index corresponds to Allocas
+ void swap(RenamePassData &RHS) {
+ std::swap(BB, RHS.BB);
+ std::swap(Pred, RHS.Pred);
+ Values.swap(RHS.Values);
+ }
+ };
+
+ struct VISIBILITY_HIDDEN PromoteMem2Reg {
+ /// Allocas - The alloca instructions being promoted.
+ ///
+ std::vector<AllocaInst*> Allocas;
+ SmallVector<AllocaInst*, 16> &RetryList;
+ DominatorTree &DT;
+ DominanceFrontier &DF;
+
+ /// AST - An AliasSetTracker object to update. If null, don't update it.
+ ///
+ AliasSetTracker *AST;
+
+ /// AllocaLookup - Reverse mapping of Allocas.
+ ///
+ std::map<AllocaInst*, unsigned> AllocaLookup;
+
+ /// NewPhiNodes - The PhiNodes we're adding.
+ ///
+ DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*> NewPhiNodes;
- // List of instructions to remove at end of pass
- vector<Instruction *> KillList;
+ /// PhiToAllocaMap - For each PHI node, keep track of which entry in Allocas
+ /// it corresponds to.
+ DenseMap<PHINode*, unsigned> PhiToAllocaMap;
- map<BasicBlock*,vector<PHINode*> > NewPhiNodes; // the PhiNodes we're adding
+ /// PointerAllocaValues - If we are updating an AliasSetTracker, then for
+ /// each alloca that is of pointer type, we keep track of what to copyValue
+ /// to the inserted PHI nodes here.
+ ///
+ std::vector<Value*> PointerAllocaValues;
- public:
- // runOnFunction - To run this pass, first we calculate the alloca
- // instructions that are safe for promotion, then we promote each one.
- //
- virtual bool runOnFunction(Function &F);
+ /// Visited - The set of basic blocks the renamer has already visited.
+ ///
+ SmallPtrSet<BasicBlock*, 16> Visited;
- // getAnalysisUsage - We need dominance frontiers
- //
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<DominanceFrontier>();
- AU.preservesCFG();
+ /// BBNumbers - Contains a stable numbering of basic blocks to avoid
+ /// non-determinstic behavior.
+ DenseMap<BasicBlock*, unsigned> BBNumbers;
+
+ public:
+ PromoteMem2Reg(const std::vector<AllocaInst*> &A,
+ SmallVector<AllocaInst*, 16> &Retry, DominatorTree &dt,
+ DominanceFrontier &df, AliasSetTracker *ast)
+ : Allocas(A), RetryList(Retry), DT(dt), DF(df), AST(ast) {}
+
+ void run();
+
+ /// properlyDominates - Return true if I1 properly dominates I2.
+ ///
+ bool properlyDominates(Instruction *I1, Instruction *I2) const {
+ if (InvokeInst *II = dyn_cast<InvokeInst>(I1))
+ I1 = II->getNormalDest()->begin();
+ return DT.properlyDominates(I1->getParent(), I2->getParent());
+ }
+
+ /// dominates - Return true if BB1 dominates BB2 using the DominatorTree.
+ ///
+ bool dominates(BasicBlock *BB1, BasicBlock *BB2) const {
+ return DT.dominates(BB1, BB2);
}
private:
- void Traverse(BasicBlock *BB, BasicBlock *Pred, vector<Value*> &IncVals,
- set<BasicBlock*> &Visited);
- bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx);
- void FindSafeAllocas(Function &F);
+ void RemoveFromAllocasList(unsigned &AllocaIdx) {
+ Allocas[AllocaIdx] = Allocas.back();
+ Allocas.pop_back();
+ --AllocaIdx;
+ }
+
+ void RewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info);
+
+ void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
+ SmallPtrSet<PHINode*, 16> &DeadPHINodes);
+ bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
+ void PromoteLocallyUsedAllocas(BasicBlock *BB,
+ const std::vector<AllocaInst*> &AIs);
+
+ void RenamePass(BasicBlock *BB, BasicBlock *Pred,
+ RenamePassData::ValVector &IncVals,
+ std::vector<RenamePassData> &Worklist);
+ bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
+ SmallPtrSet<PHINode*, 16> &InsertedPHINodes);
+ };
+
+ struct AllocaInfo {
+ std::vector<BasicBlock*> DefiningBlocks;
+ std::vector<BasicBlock*> UsingBlocks;
+
+ StoreInst *OnlyStore;
+ BasicBlock *OnlyBlock;
+ bool OnlyUsedInOneBlock;
+
+ Value *AllocaPointerVal;
+
+ void clear() {
+ DefiningBlocks.clear();
+ UsingBlocks.clear();
+ OnlyStore = 0;
+ OnlyBlock = 0;
+ OnlyUsedInOneBlock = true;
+ AllocaPointerVal = 0;
+ }
+
+ /// AnalyzeAlloca - Scan the uses of the specified alloca, filling in our
+ /// ivars.
+ void AnalyzeAlloca(AllocaInst *AI) {
+ clear();
+
+ // As we scan the uses of the alloca instruction, keep track of stores,
+ // and decide whether all of the loads and stores to the alloca are within
+ // the same basic block.
+ for (Value::use_iterator U = AI->use_begin(), E = AI->use_end();
+ U != E; ++U){
+ Instruction *User = cast<Instruction>(*U);
+ if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+ // Remember the basic blocks which define new values for the alloca
+ DefiningBlocks.push_back(SI->getParent());
+ AllocaPointerVal = SI->getOperand(0);
+ OnlyStore = SI;
+ } else {
+ LoadInst *LI = cast<LoadInst>(User);
+ // Otherwise it must be a load instruction, keep track of variable reads
+ UsingBlocks.push_back(LI->getParent());
+ AllocaPointerVal = LI;
+ }
+
+ if (OnlyUsedInOneBlock) {
+ if (OnlyBlock == 0)
+ OnlyBlock = User->getParent();
+ else if (OnlyBlock != User->getParent())
+ OnlyUsedInOneBlock = false;
+ }
+ }
+ }
};
- RegisterOpt<PromotePass> X("mem2reg", "Promote Memory to Register");
} // end of anonymous namespace
-// isSafeAlloca - This predicate controls what types of alloca instructions are
-// allowed to be promoted...
-//
-static inline bool isSafeAlloca(const AllocaInst *AI) {
- if (AI->isArrayAllocation()) return false;
+void PromoteMem2Reg::run() {
+ Function &F = *DF.getRoot()->getParent();
- // Only allow direct loads and stores...
- for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
- UI != UE; ++UI) // Loop over all of the uses of the alloca
- if (!isa<LoadInst>(*UI) && !isa<StoreInst>(*UI))
- return false; // Not a load or store?
-
- return true;
-}
+ // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
+ // only used in a single basic block. These instructions can be efficiently
+ // promoted by performing a single linear scan over that one block. Since
+ // individual basic blocks are sometimes large, we group together all allocas
+ // that are live in a single basic block by the basic block they are live in.
+ std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
-// FindSafeAllocas - Find allocas that are safe to promote
-//
-void PromotePass::FindSafeAllocas(Function &F) {
- BasicBlock &BB = F.getEntryNode(); // Get the entry node for the function
-
- // Look at all instructions in the entry node
- for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
- if (AllocaInst *AI = dyn_cast<AllocaInst>(&*I)) // Is it an alloca?
- if (isSafeAlloca(AI)) { // If safe alloca, add alloca to safe list
- AllocaLookup[AI] = Allocas.size(); // Keep reverse mapping
- Allocas.push_back(AI);
- }
-}
+ if (AST) PointerAllocaValues.resize(Allocas.size());
+ AllocaInfo Info;
+ for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
+ AllocaInst *AI = Allocas[AllocaNum];
-bool PromotePass::runOnFunction(Function &F) {
- // Calculate the set of safe allocas
- FindSafeAllocas(F);
+ assert(isAllocaPromotable(AI) &&
+ "Cannot promote non-promotable alloca!");
+ assert(AI->getParent()->getParent() == &F &&
+ "All allocas should be in the same function, which is same as DF!");
- // If there is nothing to do, bail out...
- if (Allocas.empty()) return false;
-
- // Add each alloca to the KillList. Note: KillList is destroyed MOST recently
- // added to least recently.
- KillList.assign(Allocas.begin(), Allocas.end());
-
- // Calculate the set of write-locations for each alloca. This is analogous to
- // counting the number of 'redefinitions' of each variable.
- vector<vector<BasicBlock*> > WriteSets; // index corresponds to Allocas
- WriteSets.resize(Allocas.size());
- for (unsigned i = 0; i != Allocas.size(); ++i) {
- AllocaInst *AI = Allocas[i];
- for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E; ++U)
- if (StoreInst *SI = dyn_cast<StoreInst>(*U))
- // jot down the basic-block it came from
- WriteSets[i].push_back(SI->getParent());
- }
+ if (AI->use_empty()) {
+ // If there are no uses of the alloca, just delete it now.
+ if (AST) AST->deleteValue(AI);
+ AI->eraseFromParent();
- // Get dominance frontier information...
- DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
+ // Remove the alloca from the Allocas list, since it has been processed
+ RemoveFromAllocasList(AllocaNum);
+ ++NumDeadAlloca;
+ continue;
+ }
+
+ // Calculate the set of read and write-locations for each alloca. This is
+ // analogous to finding the 'uses' and 'definitions' of each variable.
+ Info.AnalyzeAlloca(AI);
+
+ // If the alloca is only read and written in one basic block, just perform a
+ // linear sweep over the block to eliminate it.
+ if (Info.OnlyUsedInOneBlock) {
+ LocallyUsedAllocas[Info.OnlyBlock].push_back(AI);
+
+ // Remove the alloca from the Allocas list, since it will be processed.
+ RemoveFromAllocasList(AllocaNum);
+ continue;
+ }
- // Compute the locations where PhiNodes need to be inserted. Look at the
- // dominance frontier of EACH basic-block we have a write in
- //
- PhiNodes.resize(Allocas.size());
- for (unsigned i = 0; i != Allocas.size(); ++i) {
- for (unsigned j = 0; j != WriteSets[i].size(); j++) {
- // Look up the DF for this write, add it to PhiNodes
- DominanceFrontier::const_iterator it = DF.find(WriteSets[i][j]);
- DominanceFrontier::DomSetType S = it->second;
- for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
- P != PE; ++P)
- QueuePhiNode(*P, i);
+ // If there is only a single store to this value, replace any loads of
+ // it that are directly dominated by the definition with the value stored.
+ if (Info.DefiningBlocks.size() == 1) {
+ RewriteSingleStoreAlloca(AI, Info);
+
+ // Finally, after the scan, check to see if the store is all that is left.
+ if (Info.UsingBlocks.empty()) {
+ ++NumSingleStore;
+ // The alloca has been processed, move on.
+ RemoveFromAllocasList(AllocaNum);
+ continue;
+ }
}
- // Perform iterative step
- for (unsigned k = 0; k != PhiNodes[i].size(); k++) {
- DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
- DominanceFrontier::DomSetType S = it->second;
- for (DominanceFrontier::DomSetType::iterator P = S.begin(), PE = S.end();
- P != PE; ++P)
- QueuePhiNode(*P, i);
+
+ if (AST)
+ PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
+
+ // If we haven't computed a numbering for the BB's in the function, do so
+ // now.
+ if (BBNumbers.empty()) {
+ unsigned ID = 0;
+ for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
+ BBNumbers[I] = ID++;
+ }
+
+ // Compute the locations where PhiNodes need to be inserted. Look at the
+ // dominance frontier of EACH basic-block we have a write in.
+ //
+ unsigned CurrentVersion = 0;
+ SmallPtrSet<PHINode*, 16> InsertedPHINodes;
+ std::vector<std::pair<unsigned, BasicBlock*> > DFBlocks;
+ while (!Info.DefiningBlocks.empty()) {
+ BasicBlock *BB = Info.DefiningBlocks.back();
+ Info.DefiningBlocks.pop_back();
+
+ // Look up the DF for this write, add it to PhiNodes
+ DominanceFrontier::const_iterator it = DF.find(BB);
+ if (it != DF.end()) {
+ const DominanceFrontier::DomSetType &S = it->second;
+
+ // In theory we don't need the indirection through the DFBlocks vector.
+ // In practice, the order of calling QueuePhiNode would depend on the
+ // (unspecified) ordering of basic blocks in the dominance frontier,
+ // which would give PHI nodes non-determinstic subscripts. Fix this by
+ // processing blocks in order of the occurance in the function.
+ for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
+ PE = S.end(); P != PE; ++P)
+ DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P));
+
+ // Sort by which the block ordering in the function.
+ std::sort(DFBlocks.begin(), DFBlocks.end());
+
+ for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
+ BasicBlock *BB = DFBlocks[i].second;
+ if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
+ Info.DefiningBlocks.push_back(BB);
+ }
+ DFBlocks.clear();
+ }
}
+
+ // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
+ // of the writes to the variable, scan through the reads of the variable,
+ // marking PHI nodes which are actually necessary as alive (by removing them
+ // from the InsertedPHINodes set). This is not perfect: there may PHI
+ // marked alive because of loads which are dominated by stores, but there
+ // will be no unmarked PHI nodes which are actually used.
+ //
+ for (unsigned i = 0, e = Info.UsingBlocks.size(); i != e; ++i)
+ MarkDominatingPHILive(Info.UsingBlocks[i], AllocaNum, InsertedPHINodes);
+ Info.UsingBlocks.clear();
+
+ // If there are any PHI nodes which are now known to be dead, remove them!
+ for (SmallPtrSet<PHINode*, 16>::iterator I = InsertedPHINodes.begin(),
+ E = InsertedPHINodes.end(); I != E; ++I) {
+ PHINode *PN = *I;
+ bool Erased=NewPhiNodes.erase(std::make_pair(PN->getParent(), AllocaNum));
+ Erased=Erased;
+ assert(Erased && "PHI already removed?");
+
+ if (AST && isa<PointerType>(PN->getType()))
+ AST->deleteValue(PN);
+ PN->eraseFromParent();
+ PhiToAllocaMap.erase(PN);
+ }
+
+ // Keep the reverse mapping of the 'Allocas' array.
+ AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
}
+ // Process all allocas which are only used in a single basic block.
+ for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
+ LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
+ const std::vector<AllocaInst*> &LocAllocas = I->second;
+ assert(!LocAllocas.empty() && "empty alloca list??");
+
+ // It's common for there to only be one alloca in the list. Handle it
+ // efficiently.
+ if (LocAllocas.size() == 1) {
+ // If we can do the quick promotion pass, do so now.
+ if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0]))
+ RetryList.push_back(LocAllocas[0]); // Failed, retry later.
+ } else {
+ // Locally promote anything possible. Note that if this is unable to
+ // promote a particular alloca, it puts the alloca onto the Allocas vector
+ // for global processing.
+ PromoteLocallyUsedAllocas(I->first, LocAllocas);
+ }
+ }
+
+ if (Allocas.empty())
+ return; // All of the allocas must have been trivial!
+
// Set the incoming values for the basic block to be null values for all of
// the alloca's. We do this in case there is a load of a value that has not
// been stored yet. In this case, it will get this null value.
//
- vector<Value *> Values(Allocas.size());
+ RenamePassData::ValVector Values(Allocas.size());
for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
- Values[i] = Constant::getNullValue(Allocas[i]->getAllocatedType());
+ Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
// Walks all basic blocks in the function performing the SSA rename algorithm
// and inserting the phi nodes we marked as necessary
//
- set<BasicBlock*> Visited; // The basic blocks we've already visited
- Traverse(F.begin(), 0, Values, Visited);
+ std::vector<RenamePassData> RenamePassWorkList;
+ RenamePassWorkList.push_back(RenamePassData(F.begin(), 0, Values));
+ while (!RenamePassWorkList.empty()) {
+ RenamePassData RPD;
+ RPD.swap(RenamePassWorkList.back());
+ RenamePassWorkList.pop_back();
+ // RenamePass may add new worklist entries.
+ RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
+ }
+
+ // The renamer uses the Visited set to avoid infinite loops. Clear it now.
+ Visited.clear();
- // Remove all instructions marked by being placed in the KillList...
- //
- while (!KillList.empty()) {
- Instruction *I = KillList.back();
- KillList.pop_back();
+ // Remove the allocas themselves from the function.
+ for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
+ Instruction *A = Allocas[i];
- I->getParent()->getInstList().erase(I);
+ // If there are any uses of the alloca instructions left, they must be in
+ // sections of dead code that were not processed on the dominance frontier.
+ // Just delete the users now.
+ //
+ if (!A->use_empty())
+ A->replaceAllUsesWith(UndefValue::get(A->getType()));
+ if (AST) AST->deleteValue(A);
+ A->eraseFromParent();
}
- NumPromoted += Allocas.size();
+
+ // Loop over all of the PHI nodes and see if there are any that we can get
+ // rid of because they merge all of the same incoming values. This can
+ // happen due to undef values coming into the PHI nodes. This process is
+ // iterative, because eliminating one PHI node can cause others to be removed.
+ bool EliminatedAPHI = true;
+ while (EliminatedAPHI) {
+ EliminatedAPHI = false;
+
+ for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
+ NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) {
+ PHINode *PN = I->second;
+
+ // If this PHI node merges one value and/or undefs, get the value.
+ if (Value *V = PN->hasConstantValue(true)) {
+ if (!isa<Instruction>(V) ||
+ properlyDominates(cast<Instruction>(V), PN)) {
+ if (AST && isa<PointerType>(PN->getType()))
+ AST->deleteValue(PN);
+ PN->replaceAllUsesWith(V);
+ PN->eraseFromParent();
+ NewPhiNodes.erase(I++);
+ EliminatedAPHI = true;
+ continue;
+ }
+ }
+ ++I;
+ }
+ }
+
+ // At this point, the renamer has added entries to PHI nodes for all reachable
+ // code. Unfortunately, there may be unreachable blocks which the renamer
+ // hasn't traversed. If this is the case, the PHI nodes may not
+ // have incoming values for all predecessors. Loop over all PHI nodes we have
+ // created, inserting undef values if they are missing any incoming values.
+ //
+ for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
+ NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
+ // We want to do this once per basic block. As such, only process a block
+ // when we find the PHI that is the first entry in the block.
+ PHINode *SomePHI = I->second;
+ BasicBlock *BB = SomePHI->getParent();
+ if (&BB->front() != SomePHI)
+ continue;
+
+ // Count the number of preds for BB.
+ SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
+
+ // Only do work here if there the PHI nodes are missing incoming values. We
+ // know that all PHI nodes that were inserted in a block will have the same
+ // number of incoming values, so we can just check any of them.
+ if (SomePHI->getNumIncomingValues() == Preds.size())
+ continue;
+
+ // Ok, now we know that all of the PHI nodes are missing entries for some
+ // basic blocks. Start by sorting the incoming predecessors for efficient
+ // access.
+ std::sort(Preds.begin(), Preds.end());
+
+ // Now we loop through all BB's which have entries in SomePHI and remove
+ // them from the Preds list.
+ for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
+ // Do a log(n) search of the Preds list for the entry we want.
+ SmallVector<BasicBlock*, 16>::iterator EntIt =
+ std::lower_bound(Preds.begin(), Preds.end(),
+ SomePHI->getIncomingBlock(i));
+ assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
+ "PHI node has entry for a block which is not a predecessor!");
+
+ // Remove the entry
+ Preds.erase(EntIt);
+ }
- // Purge data structurse so they are available the next iteration...
- Allocas.clear();
- AllocaLookup.clear();
- PhiNodes.clear();
+ // At this point, the blocks left in the preds list must have dummy
+ // entries inserted into every PHI nodes for the block. Update all the phi
+ // nodes in this block that we are inserting (there could be phis before
+ // mem2reg runs).
+ unsigned NumBadPreds = SomePHI->getNumIncomingValues();
+ BasicBlock::iterator BBI = BB->begin();
+ while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
+ SomePHI->getNumIncomingValues() == NumBadPreds) {
+ Value *UndefVal = UndefValue::get(SomePHI->getType());
+ for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
+ SomePHI->addIncoming(UndefVal, Preds[pred]);
+ }
+ }
+
NewPhiNodes.clear();
- return true;
}
+/// RewriteSingleStoreAlloca - If there is only a single store to this value,
+/// replace any loads of it that are directly dominated by the definition with
+/// the value stored.
+void PromoteMem2Reg::RewriteSingleStoreAlloca(AllocaInst *AI,
+ AllocaInfo &Info) {
+ // Be aware of loads before the store.
+ std::set<BasicBlock*> ProcessedBlocks;
+ for (unsigned i = 0, e = Info.UsingBlocks.size(); i != e; ++i) {
+ // If the store dominates the block and if we haven't processed it yet,
+ // do so now.
+ if (!dominates(Info.OnlyStore->getParent(), Info.UsingBlocks[i]))
+ continue;
+
+ if (!ProcessedBlocks.insert(Info.UsingBlocks[i]).second)
+ continue;
+
+ BasicBlock *UseBlock = Info.UsingBlocks[i];
+
+ // If the use and store are in the same block, do a quick scan to
+ // verify that there are no uses before the store.
+ if (UseBlock == Info.OnlyStore->getParent()) {
+ BasicBlock::iterator I = UseBlock->begin();
+ for (; &*I != Info.OnlyStore; ++I) { // scan block for store.
+ if (isa<LoadInst>(I) && I->getOperand(0) == AI)
+ break;
+ }
+ if (&*I != Info.OnlyStore) break; // Do not handle this case.
+ }
+
+ // Otherwise, if this is a different block or if all uses happen
+ // after the store, do a simple linear scan to replace loads with
+ // the stored value.
+ for (BasicBlock::iterator I = UseBlock->begin(),E = UseBlock->end();
+ I != E; ) {
+ if (LoadInst *LI = dyn_cast<LoadInst>(I++)) {
+ if (LI->getOperand(0) == AI) {
+ LI->replaceAllUsesWith(Info.OnlyStore->getOperand(0));
+ if (AST && isa<PointerType>(LI->getType()))
+ AST->deleteValue(LI);
+ LI->eraseFromParent();
+ }
+ }
+ }
+
+ // Finally, remove this block from the UsingBlock set.
+ Info.UsingBlocks[i] = Info.UsingBlocks.back();
+ --i; --e;
+ }
+}
+
+
+// MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
+// "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
+// as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
+// each read of the variable. For each block that reads the variable, this
+// function is called, which removes used PHI nodes from the DeadPHINodes set.
+// After all of the reads have been processed, any PHI nodes left in the
+// DeadPHINodes set are removed.
+//
+void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
+ SmallPtrSet<PHINode*, 16> &DeadPHINodes) {
+ // Scan the immediate dominators of this block looking for a block which has a
+ // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
+ DomTreeNode *IDomNode = DT.getNode(BB);
+ for (DomTreeNode *IDom = IDomNode; IDom; IDom = IDom->getIDom()) {
+ BasicBlock *DomBB = IDom->getBlock();
+ DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator
+ I = NewPhiNodes.find(std::make_pair(DomBB, AllocaNum));
+ if (I != NewPhiNodes.end()) {
+ // Ok, we found an inserted PHI node which dominates this value.
+ PHINode *DominatingPHI = I->second;
+
+ // Find out if we previously thought it was dead. If so, mark it as being
+ // live by removing it from the DeadPHINodes set.
+ if (DeadPHINodes.erase(DominatingPHI)) {
+ // Now that we have marked the PHI node alive, also mark any PHI nodes
+ // which it might use as being alive as well.
+ for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
+ PI != PE; ++PI)
+ MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
+ }
+ }
+ }
+}
+
+/// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
+/// block. If this is the case, avoid traversing the CFG and inserting a lot of
+/// potentially useless PHI nodes by just performing a single linear pass over
+/// the basic block using the Alloca.
+///
+/// If we cannot promote this alloca (because it is read before it is written),
+/// return true. This is necessary in cases where, due to control flow, the
+/// alloca is potentially undefined on some control flow paths. e.g. code like
+/// this is potentially correct:
+///
+/// for (...) { if (c) { A = undef; undef = B; } }
+///
+/// ... so long as A is not used before undef is set.
+///
+bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
+ assert(!AI->use_empty() && "There are no uses of the alloca!");
+
+ // Handle degenerate cases quickly.
+ if (AI->hasOneUse()) {
+ Instruction *U = cast<Instruction>(AI->use_back());
+ if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
+ // Must be a load of uninitialized value.
+ LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType()));
+ if (AST && isa<PointerType>(LI->getType()))
+ AST->deleteValue(LI);
+ } else {
+ // Otherwise it must be a store which is never read.
+ assert(isa<StoreInst>(U));
+ }
+ BB->getInstList().erase(U);
+ } else {
+ // Uses of the uninitialized memory location shall get undef.
+ Value *CurVal = 0;
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ Instruction *Inst = I++;
+ if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
+ if (LI->getOperand(0) == AI) {
+ if (!CurVal) return true; // Could not locally promote!
+
+ // Loads just returns the "current value"...
+ LI->replaceAllUsesWith(CurVal);
+ if (AST && isa<PointerType>(LI->getType()))
+ AST->deleteValue(LI);
+ BB->getInstList().erase(LI);
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (SI->getOperand(1) == AI) {
+ // Store updates the "current value"...
+ CurVal = SI->getOperand(0);
+ BB->getInstList().erase(SI);
+ }
+ }
+ }
+ }
+
+ // After traversing the basic block, there should be no more uses of the
+ // alloca, remove it now.
+ assert(AI->use_empty() && "Uses of alloca from more than one BB??");
+ if (AST) AST->deleteValue(AI);
+ AI->getParent()->getInstList().erase(AI);
+
+ ++NumLocalPromoted;
+ return false;
+}
+
+/// PromoteLocallyUsedAllocas - This method is just like
+/// PromoteLocallyUsedAlloca, except that it processes multiple alloca
+/// instructions in parallel. This is important in cases where we have large
+/// basic blocks, as we don't want to rescan the entire basic block for each
+/// alloca which is locally used in it (which might be a lot).
+void PromoteMem2Reg::
+PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
+ std::map<AllocaInst*, Value*> CurValues;
+ for (unsigned i = 0, e = AIs.size(); i != e; ++i)
+ CurValues[AIs[i]] = 0; // Insert with null value
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ Instruction *Inst = I++;
+ if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
+ // Is this a load of an alloca we are tracking?
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
+ std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
+ if (AIt != CurValues.end()) {
+ // If loading an uninitialized value, allow the inter-block case to
+ // handle it. Due to control flow, this might actually be ok.
+ if (AIt->second == 0) { // Use of locally uninitialized value??
+ RetryList.push_back(AI); // Retry elsewhere.
+ CurValues.erase(AIt); // Stop tracking this here.
+ if (CurValues.empty()) return;
+ } else {
+ // Loads just returns the "current value"...
+ LI->replaceAllUsesWith(AIt->second);
+ if (AST && isa<PointerType>(LI->getType()))
+ AST->deleteValue(LI);
+ BB->getInstList().erase(LI);
+ }
+ }
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
+ std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
+ if (AIt != CurValues.end()) {
+ // Store updates the "current value"...
+ AIt->second = SI->getOperand(0);
+ BB->getInstList().erase(SI);
+ }
+ }
+ }
+ }
+}
+
+
+
// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
// Alloca returns true if there wasn't already a phi-node for that variable
//
-bool PromotePass::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo) {
- // Look up the basic-block in question
- vector<PHINode*> &BBPNs = NewPhiNodes[BB];
- if (BBPNs.empty()) BBPNs.resize(Allocas.size());
+bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
+ unsigned &Version,
+ SmallPtrSet<PHINode*, 16> &InsertedPHINodes) {
+ // Look up the basic-block in question.
+ PHINode *&PN = NewPhiNodes[std::make_pair(BB, AllocaNo)];
// If the BB already has a phi node added for the i'th alloca then we're done!
- if (BBPNs[AllocaNo]) return false;
-
- // Create a PhiNode using the dereferenced type...
- PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
- Allocas[AllocaNo]->getName()+".mem2reg");
- BBPNs[AllocaNo] = PN;
+ if (PN) return false;
+
+ // Create a PhiNode using the dereferenced type... and add the phi-node to the
+ // BasicBlock.
+ PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
+ Allocas[AllocaNo]->getName() + "." +
+ utostr(Version++), BB->begin());
+ PhiToAllocaMap[PN] = AllocaNo;
+
+ InsertedPHINodes.insert(PN);
- // Add the phi-node to the basic-block
- BB->getInstList().push_front(PN);
+ if (AST && isa<PointerType>(PN->getType()))
+ AST->copyValue(PointerAllocaValues[AllocaNo], PN);
- PhiNodes[AllocaNo].push_back(BB);
return true;
}
-void PromotePass::Traverse(BasicBlock *BB, BasicBlock *Pred,
- vector<Value*> &IncomingVals,
- set<BasicBlock*> &Visited) {
- // If this is a BB needing a phi node, lookup/create the phinode for each
- // variable we need phinodes for.
- vector<PHINode *> &BBPNs = NewPhiNodes[BB];
- for (unsigned k = 0; k != BBPNs.size(); ++k)
- if (PHINode *PN = BBPNs[k]) {
- // at this point we can assume that the array has phi nodes.. let's add
- // the incoming data
- PN->addIncoming(IncomingVals[k], Pred);
-
- // also note that the active variable IS designated by the phi node
- IncomingVals[k] = PN;
- }
- // don't revisit nodes
- if (Visited.count(BB)) return;
+// RenamePass - Recursively traverse the CFG of the function, renaming loads and
+// stores to the allocas which we are promoting. IncomingVals indicates what
+// value each Alloca contains on exit from the predecessor block Pred.
+//
+void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
+ RenamePassData::ValVector &IncomingVals,
+ std::vector<RenamePassData> &Worklist) {
+ // If we are inserting any phi nodes into this BB, they will already be in the
+ // block.
+ if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
+ // Pred may have multiple edges to BB. If so, we want to add N incoming
+ // values to each PHI we are inserting on the first time we see the edge.
+ // Check to see if APN already has incoming values from Pred. This also
+ // prevents us from modifying PHI nodes that are not currently being
+ // inserted.
+ bool HasPredEntries = false;
+ for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
+ if (APN->getIncomingBlock(i) == Pred) {
+ HasPredEntries = true;
+ break;
+ }
+ }
+
+ // If we have PHI nodes to update, compute the number of edges from Pred to
+ // BB.
+ if (!HasPredEntries) {
+ TerminatorInst *PredTerm = Pred->getTerminator();
+ unsigned NumEdges = 0;
+ for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) {
+ if (PredTerm->getSuccessor(i) == BB)
+ ++NumEdges;
+ }
+ assert(NumEdges && "Must be at least one edge from Pred to BB!");
+
+ // Add entries for all the phis.
+ BasicBlock::iterator PNI = BB->begin();
+ do {
+ unsigned AllocaNo = PhiToAllocaMap[APN];
+
+ // Add N incoming values to the PHI node.
+ for (unsigned i = 0; i != NumEdges; ++i)
+ APN->addIncoming(IncomingVals[AllocaNo], Pred);
+
+ // The currently active variable for this block is now the PHI.
+ IncomingVals[AllocaNo] = APN;
+
+ // Get the next phi node.
+ ++PNI;
+ APN = dyn_cast<PHINode>(PNI);
+ if (APN == 0) break;
+
+ // Verify it doesn't already have entries for Pred. If it does, it is
+ // not being inserted by this mem2reg invocation.
+ HasPredEntries = false;
+ for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
+ if (APN->getIncomingBlock(i) == Pred) {
+ HasPredEntries = true;
+ break;
+ }
+ }
+ } while (!HasPredEntries);
+ }
+ }
- // mark as visited
- Visited.insert(BB);
+ // Don't revisit blocks.
+ if (!Visited.insert(BB)) return;
- // keep track of the value of each variable we're watching.. how?
- for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II) {
- Instruction *I = II; // get the instruction
+ for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
+ Instruction *I = II++; // get the instruction, increment iterator
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
- Value *Ptr = LI->getPointerOperand();
-
- if (AllocaInst *Src = dyn_cast<AllocaInst>(Ptr)) {
- map<Instruction*, unsigned>::iterator AI = AllocaLookup.find(Src);
+ if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
+ std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
if (AI != AllocaLookup.end()) {
Value *V = IncomingVals[AI->second];
// walk the use list of this load and replace all uses with r
LI->replaceAllUsesWith(V);
- KillList.push_back(LI); // Mark the load to be deleted
+ if (AST && isa<PointerType>(LI->getType()))
+ AST->deleteValue(LI);
+ BB->getInstList().erase(LI);
}
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
- // delete this instruction and mark the name as the current holder of the
+ // Delete this instruction and mark the name as the current holder of the
// value
- Value *Ptr = SI->getPointerOperand();
- if (AllocaInst *Dest = dyn_cast<AllocaInst>(Ptr)) {
- map<Instruction *, unsigned>::iterator ai = AllocaLookup.find(Dest);
+ if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
+ std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
if (ai != AllocaLookup.end()) {
// what value were we writing?
IncomingVals[ai->second] = SI->getOperand(0);
- KillList.push_back(SI); // Mark the store to be deleted
+ BB->getInstList().erase(SI);
}
}
-
- } else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
- // Recurse across our successors
- for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
- vector<Value*> OutgoingVals(IncomingVals);
- Traverse(TI->getSuccessor(i), BB, OutgoingVals, Visited);
- }
}
}
+
+ // Recurse to our successors.
+ TerminatorInst *TI = BB->getTerminator();
+ for (unsigned i = 0; i != TI->getNumSuccessors(); i++)
+ Worklist.push_back(RenamePassData(TI->getSuccessor(i), BB, IncomingVals));
}
+/// PromoteMemToReg - Promote the specified list of alloca instructions into
+/// scalar registers, inserting PHI nodes as appropriate. This function makes
+/// use of DominanceFrontier information. This function does not modify the CFG
+/// of the function at all. All allocas must be from the same function.
+///
+/// If AST is specified, the specified tracker is updated to reflect changes
+/// made to the IR.
+///
+void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
+ DominatorTree &DT, DominanceFrontier &DF,
+ AliasSetTracker *AST) {
+ // If there is nothing to do, bail out...
+ if (Allocas.empty()) return;
+
+ SmallVector<AllocaInst*, 16> RetryList;
+ PromoteMem2Reg(Allocas, RetryList, DT, DF, AST).run();
+
+ // PromoteMem2Reg may not have been able to promote all of the allocas in one
+ // pass, run it again if needed.
+ std::vector<AllocaInst*> NewAllocas;
+ while (!RetryList.empty()) {
+ // If we need to retry some allocas, this is due to there being no store
+ // before a read in a local block. To counteract this, insert a store of
+ // undef into the alloca right after the alloca itself.
+ for (unsigned i = 0, e = RetryList.size(); i != e; ++i) {
+ BasicBlock::iterator BBI = RetryList[i];
+
+ new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()),
+ RetryList[i], ++BBI);
+ }
-// createPromoteMemoryToRegister - Provide an entry point to create this pass.
-//
-Pass *createPromoteMemoryToRegister() {
- return new PromotePass();
+ NewAllocas.assign(RetryList.begin(), RetryList.end());
+ RetryList.clear();
+ PromoteMem2Reg(NewAllocas, RetryList, DT, DF, AST).run();
+ NewAllocas.clear();
+ }
}
projects / oota-llvm.git / blobdiff