Use the space freed up by sparc and zaurus to import LLVM.

ok hackroom@

1 files changed, 993 insertions, 0 deletions

diff --git a/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
new file mode 100644
index 00000000000..c4f9b9f6140
--- /dev/null
+++ b/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -0,0 +1,993 @@
+//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file promotes memory references to be register references.  It promotes
+// alloca instructions which only have loads and stores as uses.  An alloca is
+// transformed by using iterated dominator frontiers to place PHI nodes, then
+// traversing the function in depth-first order to rewrite loads and stores as
+// appropriate.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/PromoteMemToReg.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasSetTracker.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/IteratedDominanceFrontier.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include <algorithm>
+using namespace llvm;
+
+#define DEBUG_TYPE "mem2reg"
+
+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");
+STATISTIC(NumPHIInsert,     "Number of PHI nodes inserted");
+
+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.
+  unsigned AS = AI->getType()->getAddressSpace();
+
+  // Only allow direct and non-volatile loads and stores...
+  for (const User *U : AI->users()) {
+    if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
+      // Note that atomic loads can be transformed; atomic semantics do
+      // not have any meaning for a local alloca.
+      if (LI->isVolatile())
+        return false;
+    } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
+      if (SI->getOperand(0) == AI)
+        return false; // Don't allow a store OF the AI, only INTO the AI.
+      // Note that atomic stores can be transformed; atomic semantics do
+      // not have any meaning for a local alloca.
+      if (SI->isVolatile())
+        return false;
+    } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
+      if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
+          II->getIntrinsicID() != Intrinsic::lifetime_end)
+        return false;
+    } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
+      if (BCI->getType() != Type::getInt8PtrTy(U->getContext(), AS))
+        return false;
+      if (!onlyUsedByLifetimeMarkers(BCI))
+        return false;
+    } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
+      if (GEPI->getType() != Type::getInt8PtrTy(U->getContext(), AS))
+        return false;
+      if (!GEPI->hasAllZeroIndices())
+        return false;
+      if (!onlyUsedByLifetimeMarkers(GEPI))
+        return false;
+    } else {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+namespace {
+
+struct AllocaInfo {
+  SmallVector<BasicBlock *, 32> DefiningBlocks;
+  SmallVector<BasicBlock *, 32> UsingBlocks;
+
+  StoreInst *OnlyStore;
+  BasicBlock *OnlyBlock;
+  bool OnlyUsedInOneBlock;
+
+  Value *AllocaPointerVal;
+  DbgDeclareInst *DbgDeclare;
+
+  void clear() {
+    DefiningBlocks.clear();
+    UsingBlocks.clear();
+    OnlyStore = nullptr;
+    OnlyBlock = nullptr;
+    OnlyUsedInOneBlock = true;
+    AllocaPointerVal = nullptr;
+    DbgDeclare = nullptr;
+  }
+
+  /// Scan the uses of the specified alloca, filling in the AllocaInfo used
+  /// by the rest of the pass to reason about the uses of this alloca.
+  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 (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
+      Instruction *User = cast<Instruction>(*UI++);
+
+      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)
+          OnlyBlock = User->getParent();
+        else if (OnlyBlock != User->getParent())
+          OnlyUsedInOneBlock = false;
+      }
+    }
+
+    DbgDeclare = FindAllocaDbgDeclare(AI);
+  }
+};
+
+// Data package used by RenamePass()
+class RenamePassData {
+public:
+  typedef std::vector<Value *> ValVector;
+
+  RenamePassData() : BB(nullptr), Pred(nullptr), Values() {}
+  RenamePassData(BasicBlock *B, BasicBlock *P, const ValVector &V)
+      : BB(B), Pred(P), Values(V) {}
+  BasicBlock *BB;
+  BasicBlock *Pred;
+  ValVector Values;
+
+  void swap(RenamePassData &RHS) {
+    std::swap(BB, RHS.BB);
+    std::swap(Pred, RHS.Pred);
+    Values.swap(RHS.Values);
+  }
+};
+
+/// \brief This assigns and keeps a per-bb relative ordering of load/store
+/// instructions in the block that directly load or store an alloca.
+///
+/// This functionality is important because it avoids scanning large basic
+/// blocks multiple times when promoting many allocas in the same block.
+class LargeBlockInfo {
+  /// \brief For each instruction that we track, keep the index of the
+  /// instruction.
+  ///
+  /// The index starts out as the number of the instruction from the start of
+  /// the block.
+  DenseMap<const Instruction *, unsigned> InstNumbers;
+
+public:
+
+  /// This code only looks at accesses to allocas.
+  static bool isInterestingInstruction(const Instruction *I) {
+    return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
+           (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
+  }
+
+  /// Get or calculate the index of the specified instruction.
+  unsigned getInstructionIndex(const Instruction *I) {
+    assert(isInterestingInstruction(I) &&
+           "Not a load/store to/from an alloca?");
+
+    // If we already have this instruction number, return it.
+    DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I);
+    if (It != InstNumbers.end())
+      return It->second;
+
+    // Scan the whole block to get the instruction.  This accumulates
+    // information for every interesting instruction in the block, in order to
+    // avoid gratuitus rescans.
+    const BasicBlock *BB = I->getParent();
+    unsigned InstNo = 0;
+    for (const Instruction &BBI : *BB)
+      if (isInterestingInstruction(&BBI))
+        InstNumbers[&BBI] = InstNo++;
+    It = InstNumbers.find(I);
+
+    assert(It != InstNumbers.end() && "Didn't insert instruction?");
+    return It->second;
+  }
+
+  void deleteValue(const Instruction *I) { InstNumbers.erase(I); }
+
+  void clear() { InstNumbers.clear(); }
+};
+
+struct PromoteMem2Reg {
+  /// The alloca instructions being promoted.
+  std::vector<AllocaInst *> Allocas;
+  DominatorTree &DT;
+  DIBuilder DIB;
+
+  /// An AliasSetTracker object to update.  If null, don't update it.
+  AliasSetTracker *AST;
+
+  /// A cache of @llvm.assume intrinsics used by SimplifyInstruction.
+  AssumptionCache *AC;
+
+  /// Reverse mapping of Allocas.
+  DenseMap<AllocaInst *, unsigned> AllocaLookup;
+
+  /// \brief The PhiNodes we're adding.
+  ///
+  /// That map is used to simplify some Phi nodes as we iterate over it, so
+  /// it should have deterministic iterators.  We could use a MapVector, but
+  /// since we already maintain a map from BasicBlock* to a stable numbering
+  /// (BBNumbers), the DenseMap is more efficient (also supports removal).
+  DenseMap<std::pair<unsigned, unsigned>, PHINode *> NewPhiNodes;
+
+  /// For each PHI node, keep track of which entry in Allocas it corresponds
+  /// to.
+  DenseMap<PHINode *, unsigned> PhiToAllocaMap;
+
+  /// 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;
+
+  /// For each alloca, we keep track of the dbg.declare intrinsic that
+  /// describes it, if any, so that we can convert it to a dbg.value
+  /// intrinsic if the alloca gets promoted.
+  SmallVector<DbgDeclareInst *, 8> AllocaDbgDeclares;
+
+  /// The set of basic blocks the renamer has already visited.
+  ///
+  SmallPtrSet<BasicBlock *, 16> Visited;
+
+  /// Contains a stable numbering of basic blocks to avoid non-determinstic
+  /// behavior.
+  DenseMap<BasicBlock *, unsigned> BBNumbers;
+
+  /// Lazily compute the number of predecessors a block has.
+  DenseMap<const BasicBlock *, unsigned> BBNumPreds;
+
+public:
+  PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
+                 AliasSetTracker *AST, AssumptionCache *AC)
+      : Allocas(Allocas.begin(), Allocas.end()), DT(DT),
+        DIB(*DT.getRoot()->getParent()->getParent(), /*AllowUnresolved*/ false),
+        AST(AST), AC(AC) {}
+
+  void run();
+
+private:
+  void RemoveFromAllocasList(unsigned &AllocaIdx) {
+    Allocas[AllocaIdx] = Allocas.back();
+    Allocas.pop_back();
+    --AllocaIdx;
+  }
+
+  unsigned getNumPreds(const BasicBlock *BB) {
+    unsigned &NP = BBNumPreds[BB];
+    if (NP == 0)
+      NP = std::distance(pred_begin(BB), pred_end(BB)) + 1;
+    return NP - 1;
+  }
+
+  void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
+                           const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
+                           SmallPtrSetImpl<BasicBlock *> &LiveInBlocks);
+  void RenamePass(BasicBlock *BB, BasicBlock *Pred,
+                  RenamePassData::ValVector &IncVals,
+                  std::vector<RenamePassData> &Worklist);
+  bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
+};
+
+} // end of anonymous namespace
+
+static void removeLifetimeIntrinsicUsers(AllocaInst *AI) {
+  // Knowing that this alloca is promotable, we know that it's safe to kill all
+  // instructions except for load and store.
+
+  for (auto UI = AI->user_begin(), UE = AI->user_end(); UI != UE;) {
+    Instruction *I = cast<Instruction>(*UI);
+    ++UI;
+    if (isa<LoadInst>(I) || isa<StoreInst>(I))
+      continue;
+
+    if (!I->getType()->isVoidTy()) {
+      // The only users of this bitcast/GEP instruction are lifetime intrinsics.
+      // Follow the use/def chain to erase them now instead of leaving it for
+      // dead code elimination later.
+      for (auto UUI = I->user_begin(), UUE = I->user_end(); UUI != UUE;) {
+        Instruction *Inst = cast<Instruction>(*UUI);
+        ++UUI;
+        Inst->eraseFromParent();
+      }
+    }
+    I->eraseFromParent();
+  }
+}
+
+/// \brief Rewrite as many loads as possible given a single store.
+///
+/// When there is only a single store, we can use the domtree to trivially
+/// replace all of the dominated loads with the stored value. Do so, and return
+/// true if this has successfully promoted the alloca entirely. If this returns
+/// false there were some loads which were not dominated by the single store
+/// and thus must be phi-ed with undef. We fall back to the standard alloca
+/// promotion algorithm in that case.
+static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
+                                     LargeBlockInfo &LBI,
+                                     DominatorTree &DT,
+                                     AliasSetTracker *AST) {
+  StoreInst *OnlyStore = Info.OnlyStore;
+  bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
+  BasicBlock *StoreBB = OnlyStore->getParent();
+  int StoreIndex = -1;
+
+  // Clear out UsingBlocks.  We will reconstruct it here if needed.
+  Info.UsingBlocks.clear();
+
+  for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
+    Instruction *UserInst = cast<Instruction>(*UI++);
+    if (!isa<LoadInst>(UserInst)) {
+      assert(UserInst == OnlyStore && "Should only have load/stores");
+      continue;
+    }
+    LoadInst *LI = cast<LoadInst>(UserInst);
+
+    // Okay, if we have a load from the alloca, we want to replace it with the
+    // only value stored to the alloca.  We can do this if the value is
+    // dominated by the store.  If not, we use the rest of the mem2reg machinery
+    // to insert the phi nodes as needed.
+    if (!StoringGlobalVal) { // Non-instructions are always dominated.
+      if (LI->getParent() == StoreBB) {
+        // If we have a use that is in the same block as the store, compare the
+        // indices of the two instructions to see which one came first.  If the
+        // load came before the store, we can't handle it.
+        if (StoreIndex == -1)
+          StoreIndex = LBI.getInstructionIndex(OnlyStore);
+
+        if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
+          // Can't handle this load, bail out.
+          Info.UsingBlocks.push_back(StoreBB);
+          continue;
+        }
+
+      } else if (LI->getParent() != StoreBB &&
+                 !DT.dominates(StoreBB, LI->getParent())) {
+        // If the load and store are in different blocks, use BB dominance to
+        // check their relationships.  If the store doesn't dom the use, bail
+        // out.
+        Info.UsingBlocks.push_back(LI->getParent());
+        continue;
+      }
+    }
+
+    // Otherwise, we *can* safely rewrite this load.
+    Value *ReplVal = OnlyStore->getOperand(0);
+    // If the replacement value is the load, this must occur in unreachable
+    // code.
+    if (ReplVal == LI)
+      ReplVal = UndefValue::get(LI->getType());
+    LI->replaceAllUsesWith(ReplVal);
+    if (AST && LI->getType()->isPointerTy())
+      AST->deleteValue(LI);
+    LI->eraseFromParent();
+    LBI.deleteValue(LI);
+  }
+
+  // Finally, after the scan, check to see if the store is all that is left.
+  if (!Info.UsingBlocks.empty())
+    return false; // If not, we'll have to fall back for the remainder.
+
+  // Record debuginfo for the store and remove the declaration's
+  // debuginfo.
+  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+    DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
+    ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
+    DDI->eraseFromParent();
+    LBI.deleteValue(DDI);
+  }
+  // Remove the (now dead) store and alloca.
+  Info.OnlyStore->eraseFromParent();
+  LBI.deleteValue(Info.OnlyStore);
+
+  if (AST)
+    AST->deleteValue(AI);
+  AI->eraseFromParent();
+  LBI.deleteValue(AI);
+  return true;
+}
+
+/// 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 false.  This is necessary in cases where, due to control flow, the
+/// alloca is undefined only on some control flow paths.  e.g. code like
+/// this is correct in LLVM IR:
+///  // A is an alloca with no stores so far
+///  for (...) {
+///    int t = *A;
+///    if (!first_iteration)
+///      use(t);
+///    *A = 42;
+///  }
+static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
+                                     LargeBlockInfo &LBI,
+                                     AliasSetTracker *AST) {
+  // The trickiest case to handle is when we have large blocks. Because of this,
+  // this code is optimized assuming that large blocks happen.  This does not
+  // significantly pessimize the small block case.  This uses LargeBlockInfo to
+  // make it efficient to get the index of various operations in the block.
+
+  // Walk the use-def list of the alloca, getting the locations of all stores.
+  typedef SmallVector<std::pair<unsigned, StoreInst *>, 64> StoresByIndexTy;
+  StoresByIndexTy StoresByIndex;
+
+  for (User *U : AI->users())
+    if (StoreInst *SI = dyn_cast<StoreInst>(U))
+      StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
+
+  // Sort the stores by their index, making it efficient to do a lookup with a
+  // binary search.
+  std::sort(StoresByIndex.begin(), StoresByIndex.end(), less_first());
+
+  // Walk all of the loads from this alloca, replacing them with the nearest
+  // store above them, if any.
+  for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
+    LoadInst *LI = dyn_cast<LoadInst>(*UI++);
+    if (!LI)
+      continue;
+
+    unsigned LoadIdx = LBI.getInstructionIndex(LI);
+
+    // Find the nearest store that has a lower index than this load.
+    StoresByIndexTy::iterator I =
+        std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(),
+                         std::make_pair(LoadIdx,
+                                        static_cast<StoreInst *>(nullptr)),
+                         less_first());
+    if (I == StoresByIndex.begin()) {
+      if (StoresByIndex.empty())
+        // If there are no stores, the load takes the undef value.
+        LI->replaceAllUsesWith(UndefValue::get(LI->getType()));
+      else
+        // There is no store before this load, bail out (load may be affected
+        // by the following stores - see main comment).
+        return false;
+    }
+    else
+      // Otherwise, there was a store before this load, the load takes its value.
+      LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0));
+
+    if (AST && LI->getType()->isPointerTy())
+      AST->deleteValue(LI);
+    LI->eraseFromParent();
+    LBI.deleteValue(LI);
+  }
+
+  // Remove the (now dead) stores and alloca.
+  while (!AI->use_empty()) {
+    StoreInst *SI = cast<StoreInst>(AI->user_back());
+    // Record debuginfo for the store before removing it.
+    if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+      DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
+      ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+    }
+    SI->eraseFromParent();
+    LBI.deleteValue(SI);
+  }
+
+  if (AST)
+    AST->deleteValue(AI);
+  AI->eraseFromParent();
+  LBI.deleteValue(AI);
+
+  // The alloca's debuginfo can be removed as well.
+  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+    DDI->eraseFromParent();
+    LBI.deleteValue(DDI);
+  }
+
+  ++NumLocalPromoted;
+  return true;
+}
+
+void PromoteMem2Reg::run() {
+  Function &F = *DT.getRoot()->getParent();
+
+  if (AST)
+    PointerAllocaValues.resize(Allocas.size());
+  AllocaDbgDeclares.resize(Allocas.size());
+
+  AllocaInfo Info;
+  LargeBlockInfo LBI;
+  IDFCalculator IDF(DT);
+
+  for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
+    AllocaInst *AI = Allocas[AllocaNum];
+
+    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!");
+
+    removeLifetimeIntrinsicUsers(AI);
+
+    if (AI->use_empty()) {
+      // If there are no uses of the alloca, just delete it now.
+      if (AST)
+        AST->deleteValue(AI);
+      AI->eraseFromParent();
+
+      // 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 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) {
+      if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) {
+        // The alloca has been processed, move on.
+        RemoveFromAllocasList(AllocaNum);
+        ++NumSingleStore;
+        continue;
+      }
+    }
+
+    // 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 &&
+        promoteSingleBlockAlloca(AI, Info, LBI, AST)) {
+      // The alloca has been processed, move on.
+      RemoveFromAllocasList(AllocaNum);
+      continue;
+    }
+
+    // If we haven't computed a numbering for the BB's in the function, do so
+    // now.
+    if (BBNumbers.empty()) {
+      unsigned ID = 0;
+      for (auto &BB : F)
+        BBNumbers[&BB] = ID++;
+    }
+
+    // If we have an AST to keep updated, remember some pointer value that is
+    // stored into the alloca.
+    if (AST)
+      PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
+
+    // Remember the dbg.declare intrinsic describing this alloca, if any.
+    if (Info.DbgDeclare)
+      AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
+
+    // Keep the reverse mapping of the 'Allocas' array for the rename pass.
+    AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
+
+    // At this point, we're committed to promoting the alloca using IDF's, and
+    // the standard SSA construction algorithm.  Determine which blocks need PHI
+    // nodes and see if we can optimize out some work by avoiding insertion of
+    // dead phi nodes.
+
+
+    // Unique the set of defining blocks for efficient lookup.
+    SmallPtrSet<BasicBlock *, 32> DefBlocks;
+    DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
+
+    // Determine which blocks the value is live in.  These are blocks which lead
+    // to uses.
+    SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
+    ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
+
+    // At this point, we're committed to promoting the alloca using IDF's, and
+    // the standard SSA construction algorithm.  Determine which blocks need phi
+    // nodes and see if we can optimize out some work by avoiding insertion of
+    // dead phi nodes.
+    IDF.setLiveInBlocks(LiveInBlocks);
+    IDF.setDefiningBlocks(DefBlocks);
+    SmallVector<BasicBlock *, 32> PHIBlocks;
+    IDF.calculate(PHIBlocks);
+    if (PHIBlocks.size() > 1)
+      std::sort(PHIBlocks.begin(), PHIBlocks.end(),
+                [this](BasicBlock *A, BasicBlock *B) {
+                  return BBNumbers.lookup(A) < BBNumbers.lookup(B);
+                });
+
+    unsigned CurrentVersion = 0;
+    for (unsigned i = 0, e = PHIBlocks.size(); i != e; ++i)
+      QueuePhiNode(PHIBlocks[i], AllocaNum, CurrentVersion);
+  }
+
+  if (Allocas.empty())
+    return; // All of the allocas must have been trivial!
+
+  LBI.clear();
+
+  // 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.
+  //
+  RenamePassData::ValVector Values(Allocas.size());
+  for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
+    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
+  //
+  std::vector<RenamePassData> RenamePassWorkList;
+  RenamePassWorkList.emplace_back(&F.front(), nullptr, std::move(Values));
+  do {
+    RenamePassData RPD;
+    RPD.swap(RenamePassWorkList.back());
+    RenamePassWorkList.pop_back();
+    // RenamePass may add new worklist entries.
+    RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
+  } while (!RenamePassWorkList.empty());
+
+  // The renamer uses the Visited set to avoid infinite loops.  Clear it now.
+  Visited.clear();
+
+  // Remove the allocas themselves from the function.
+  for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
+    Instruction *A = Allocas[i];
+
+    // If there are any uses of the alloca instructions left, they must be in
+    // unreachable basic blocks that were not processed by walking the dominator
+    // tree. Just delete the users now.
+    if (!A->use_empty())
+      A->replaceAllUsesWith(UndefValue::get(A->getType()));
+    if (AST)
+      AST->deleteValue(A);
+    A->eraseFromParent();
+  }
+
+  const DataLayout &DL = F.getParent()->getDataLayout();
+
+  // Remove alloca's dbg.declare instrinsics from the function.
+  for (unsigned i = 0, e = AllocaDbgDeclares.size(); i != e; ++i)
+    if (DbgDeclareInst *DDI = AllocaDbgDeclares[i])
+      DDI->eraseFromParent();
+
+  // 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;
+
+    // Iterating over NewPhiNodes is deterministic, so it is safe to try to
+    // simplify and RAUW them as we go.  If it was not, we could add uses to
+    // the values we replace with in a non-deterministic order, thus creating
+    // non-deterministic def->use chains.
+    for (DenseMap<std::pair<unsigned, 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 = SimplifyInstruction(PN, DL, nullptr, &DT, AC)) {
+        if (AST && PN->getType()->isPointerTy())
+          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<unsigned, 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;
+
+    // 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() == getNumPreds(BB))
+      continue;
+
+    // Get the preds for BB.
+    SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
+
+    // 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.
+      SmallVectorImpl<BasicBlock *>::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);
+    }
+
+    // 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();
+}
+
+/// \brief Determine which blocks the value is live in.
+///
+/// These are blocks which lead to uses.  Knowing this allows us to avoid
+/// inserting PHI nodes into blocks which don't lead to uses (thus, the
+/// inserted phi nodes would be dead).
+void PromoteMem2Reg::ComputeLiveInBlocks(
+    AllocaInst *AI, AllocaInfo &Info,
+    const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
+    SmallPtrSetImpl<BasicBlock *> &LiveInBlocks) {
+
+  // To determine liveness, we must iterate through the predecessors of blocks
+  // where the def is live.  Blocks are added to the worklist if we need to
+  // check their predecessors.  Start with all the using blocks.
+  SmallVector<BasicBlock *, 64> LiveInBlockWorklist(Info.UsingBlocks.begin(),
+                                                    Info.UsingBlocks.end());
+
+  // If any of the using blocks is also a definition block, check to see if the
+  // definition occurs before or after the use.  If it happens before the use,
+  // the value isn't really live-in.
+  for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) {
+    BasicBlock *BB = LiveInBlockWorklist[i];
+    if (!DefBlocks.count(BB))
+      continue;
+
+    // Okay, this is a block that both uses and defines the value.  If the first
+    // reference to the alloca is a def (store), then we know it isn't live-in.
+    for (BasicBlock::iterator I = BB->begin();; ++I) {
+      if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+        if (SI->getOperand(1) != AI)
+          continue;
+
+        // We found a store to the alloca before a load.  The alloca is not
+        // actually live-in here.
+        LiveInBlockWorklist[i] = LiveInBlockWorklist.back();
+        LiveInBlockWorklist.pop_back();
+        --i, --e;
+        break;
+      }
+
+      if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+        if (LI->getOperand(0) != AI)
+          continue;
+
+        // Okay, we found a load before a store to the alloca.  It is actually
+        // live into this block.
+        break;
+      }
+    }
+  }
+
+  // Now that we have a set of blocks where the phi is live-in, recursively add
+  // their predecessors until we find the full region the value is live.
+  while (!LiveInBlockWorklist.empty()) {
+    BasicBlock *BB = LiveInBlockWorklist.pop_back_val();
+
+    // The block really is live in here, insert it into the set.  If already in
+    // the set, then it has already been processed.
+    if (!LiveInBlocks.insert(BB).second)
+      continue;
+
+    // Since the value is live into BB, it is either defined in a predecessor or
+    // live into it to.  Add the preds to the worklist unless they are a
+    // defining block.
+    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+      BasicBlock *P = *PI;
+
+      // The value is not live into a predecessor if it defines the value.
+      if (DefBlocks.count(P))
+        continue;
+
+      // Otherwise it is, add to the worklist.
+      LiveInBlockWorklist.push_back(P);
+    }
+  }
+}
+
+/// \brief Queue 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 PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
+                                  unsigned &Version) {
+  // Look up the basic-block in question.
+  PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)];
+
+  // If the BB already has a phi node added for the i'th alloca then we're done!
+  if (PN)
+    return false;
+
+  // Create a PhiNode using the dereferenced type... and add the phi-node to the
+  // BasicBlock.
+  PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB),
+                       Allocas[AllocaNo]->getName() + "." + Twine(Version++),
+                       &BB->front());
+  ++NumPHIInsert;
+  PhiToAllocaMap[PN] = AllocaNo;
+
+  if (AST && PN->getType()->isPointerTy())
+    AST->copyValue(PointerAllocaValues[AllocaNo], PN);
+
+  return true;
+}
+
+/// \brief 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) {
+NextIteration:
+  // 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())) {
+    // If we have PHI nodes to update, compute the number of edges from Pred to
+    // BB.
+    if (PhiToAllocaMap.count(APN)) {
+      // We want to be able to distinguish between PHI nodes being inserted by
+      // this invocation of mem2reg from those phi nodes that already existed in
+      // the IR before mem2reg was run.  We determine that APN is being inserted
+      // because it is missing incoming edges.  All other PHI nodes being
+      // inserted by this pass of mem2reg will have the same number of incoming
+      // operands so far.  Remember this count.
+      unsigned NewPHINumOperands = APN->getNumOperands();
+
+      unsigned NumEdges = std::count(succ_begin(Pred), succ_end(Pred), BB);
+      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)
+          break;
+
+        // Verify that it is missing entries.  If not, it is not being inserted
+        // by this mem2reg invocation so we want to ignore it.
+      } while (APN->getNumOperands() == NewPHINumOperands);
+    }
+  }
+
+  // Don't revisit blocks.
+  if (!Visited.insert(BB).second)
+    return;
+
+  for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II);) {
+    Instruction *I = &*II++; // get the instruction, increment iterator
+
+    if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+      AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand());
+      if (!Src)
+        continue;
+
+      DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src);
+      if (AI == AllocaLookup.end())
+        continue;
+
+      Value *V = IncomingVals[AI->second];
+
+      // Anything using the load now uses the current value.
+      LI->replaceAllUsesWith(V);
+      if (AST && LI->getType()->isPointerTy())
+        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
+      // value
+      AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand());
+      if (!Dest)
+        continue;
+
+      DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
+      if (ai == AllocaLookup.end())
+        continue;
+
+      // what value were we writing?
+      IncomingVals[ai->second] = SI->getOperand(0);
+      // Record debuginfo for the store before removing it.
+      if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second])
+        ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+      BB->getInstList().erase(SI);
+    }
+  }
+
+  // 'Recurse' to our successors.
+  succ_iterator I = succ_begin(BB), E = succ_end(BB);
+  if (I == E)
+    return;
+
+  // Keep track of the successors so we don't visit the same successor twice
+  SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
+
+  // Handle the first successor without using the worklist.
+  VisitedSuccs.insert(*I);
+  Pred = BB;
+  BB = *I;
+  ++I;
+
+  for (; I != E; ++I)
+    if (VisitedSuccs.insert(*I).second)
+      Worklist.emplace_back(*I, Pred, IncomingVals);
+
+  goto NextIteration;
+}
+
+void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
+                           AliasSetTracker *AST, AssumptionCache *AC) {
+  // If there is nothing to do, bail out...
+  if (Allocas.empty())
+    return;
+
+  PromoteMem2Reg(Allocas, DT, AST, AC).run();
+}