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diff --git a/contrib/llvm/lib/Transforms/Scalar/NaryReassociate.cpp b/contrib/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
new file mode 100644
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+++ b/contrib/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
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+//===- NaryReassociate.cpp - Reassociate n-ary expressions ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass reassociates n-ary add expressions and eliminates the redundancy
+// exposed by the reassociation.
+//
+// A motivating example:
+//
+//   void foo(int a, int b) {
+//     bar(a + b);
+//     bar((a + 2) + b);
+//   }
+//
+// An ideal compiler should reassociate (a + 2) + b to (a + b) + 2 and simplify
+// the above code to
+//
+//   int t = a + b;
+//   bar(t);
+//   bar(t + 2);
+//
+// However, the Reassociate pass is unable to do that because it processes each
+// instruction individually and believes (a + 2) + b is the best form according
+// to its rank system.
+//
+// To address this limitation, NaryReassociate reassociates an expression in a
+// form that reuses existing instructions. As a result, NaryReassociate can
+// reassociate (a + 2) + b in the example to (a + b) + 2 because it detects that
+// (a + b) is computed before.
+//
+// NaryReassociate works as follows. For every instruction in the form of (a +
+// b) + c, it checks whether a + c or b + c is already computed by a dominating
+// instruction. If so, it then reassociates (a + b) + c into (a + c) + b or (b +
+// c) + a and removes the redundancy accordingly. To efficiently look up whether
+// an expression is computed before, we store each instruction seen and its SCEV
+// into an SCEV-to-instruction map.
+//
+// Although the algorithm pattern-matches only ternary additions, it
+// automatically handles many >3-ary expressions by walking through the function
+// in the depth-first order. For example, given
+//
+//   (a + c) + d
+//   ((a + b) + c) + d
+//
+// NaryReassociate first rewrites (a + b) + c to (a + c) + b, and then rewrites
+// ((a + c) + b) + d into ((a + c) + d) + b.
+//
+// Finally, the above dominator-based algorithm may need to be run multiple
+// iterations before emitting optimal code. One source of this need is that we
+// only split an operand when it is used only once. The above algorithm can
+// eliminate an instruction and decrease the usage count of its operands. As a
+// result, an instruction that previously had multiple uses may become a
+// single-use instruction and thus eligible for split consideration. For
+// example,
+//
+//   ac = a + c
+//   ab = a + b
+//   abc = ab + c
+//   ab2 = ab + b
+//   ab2c = ab2 + c
+//
+// In the first iteration, we cannot reassociate abc to ac+b because ab is used
+// twice. However, we can reassociate ab2c to abc+b in the first iteration. As a
+// result, ab2 becomes dead and ab will be used only once in the second
+// iteration.
+//
+// Limitations and TODO items:
+//
+// 1) We only considers n-ary adds for now. This should be extended and
+// generalized.
+//
+// 2) Besides arithmetic operations, similar reassociation can be applied to
+// GEPs. For example, if
+//   X = &arr[a]
+// dominates
+//   Y = &arr[a + b]
+// we may rewrite Y into X + b.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+using namespace llvm;
+using namespace PatternMatch;
+
+#define DEBUG_TYPE "nary-reassociate"
+
+namespace {
+class NaryReassociate : public FunctionPass {
+public:
+  static char ID;
+
+  NaryReassociate(): FunctionPass(ID) {
+    initializeNaryReassociatePass(*PassRegistry::getPassRegistry());
+  }
+
+  bool doInitialization(Module &M) override {
+    DL = &M.getDataLayout();
+    return false;
+  }
+  bool runOnFunction(Function &F) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addPreserved<DominatorTreeWrapperPass>();
+    AU.addPreserved<ScalarEvolution>();
+    AU.addPreserved<TargetLibraryInfoWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addRequired<ScalarEvolution>();
+    AU.addRequired<TargetLibraryInfoWrapperPass>();
+    AU.addRequired<TargetTransformInfoWrapperPass>();
+    AU.setPreservesCFG();
+  }
+
+private:
+  // Runs only one iteration of the dominator-based algorithm. See the header
+  // comments for why we need multiple iterations.
+  bool doOneIteration(Function &F);
+
+  // Reassociates I for better CSE.
+  Instruction *tryReassociate(Instruction *I);
+
+  // Reassociate GEP for better CSE.
+  Instruction *tryReassociateGEP(GetElementPtrInst *GEP);
+  // Try splitting GEP at the I-th index and see whether either part can be
+  // CSE'ed. This is a helper function for tryReassociateGEP.
+  //
+  // \p IndexedType The element type indexed by GEP's I-th index. This is
+  //                equivalent to
+  //                  GEP->getIndexedType(GEP->getPointerOperand(), 0-th index,
+  //                                      ..., i-th index).
+  GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
+                                              unsigned I, Type *IndexedType);
+  // Given GEP's I-th index = LHS + RHS, see whether &Base[..][LHS][..] or
+  // &Base[..][RHS][..] can be CSE'ed and rewrite GEP accordingly.
+  GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
+                                              unsigned I, Value *LHS,
+                                              Value *RHS, Type *IndexedType);
+
+  // Reassociate Add for better CSE.
+  Instruction *tryReassociateAdd(BinaryOperator *I);
+  // A helper function for tryReassociateAdd. LHS and RHS are explicitly passed.
+  Instruction *tryReassociateAdd(Value *LHS, Value *RHS, Instruction *I);
+  // Rewrites I to LHS + RHS if LHS is computed already.
+  Instruction *tryReassociatedAdd(const SCEV *LHS, Value *RHS, Instruction *I);
+
+  // Returns the closest dominator of \c Dominatee that computes
+  // \c CandidateExpr. Returns null if not found.
+  Instruction *findClosestMatchingDominator(const SCEV *CandidateExpr,
+                                            Instruction *Dominatee);
+  // GetElementPtrInst implicitly sign-extends an index if the index is shorter
+  // than the pointer size. This function returns whether Index is shorter than
+  // GEP's pointer size, i.e., whether Index needs to be sign-extended in order
+  // to be an index of GEP.
+  bool requiresSignExtension(Value *Index, GetElementPtrInst *GEP);
+
+  DominatorTree *DT;
+  ScalarEvolution *SE;
+  TargetLibraryInfo *TLI;
+  TargetTransformInfo *TTI;
+  const DataLayout *DL;
+  // A lookup table quickly telling which instructions compute the given SCEV.
+  // Note that there can be multiple instructions at different locations
+  // computing to the same SCEV, so we map a SCEV to an instruction list.  For
+  // example,
+  //
+  //   if (p1)
+  //     foo(a + b);
+  //   if (p2)
+  //     bar(a + b);
+  DenseMap<const SCEV *, SmallVector<Instruction *, 2>> SeenExprs;
+};
+} // anonymous namespace
+
+char NaryReassociate::ID = 0;
+INITIALIZE_PASS_BEGIN(NaryReassociate, "nary-reassociate", "Nary reassociation",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_END(NaryReassociate, "nary-reassociate", "Nary reassociation",
+                    false, false)
+
+FunctionPass *llvm::createNaryReassociatePass() {
+  return new NaryReassociate();
+}
+
+bool NaryReassociate::runOnFunction(Function &F) {
+  if (skipOptnoneFunction(F))
+    return false;
+
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  SE = &getAnalysis<ScalarEvolution>();
+  TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+  TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+
+  bool Changed = false, ChangedInThisIteration;
+  do {
+    ChangedInThisIteration = doOneIteration(F);
+    Changed |= ChangedInThisIteration;
+  } while (ChangedInThisIteration);
+  return Changed;
+}
+
+// Whitelist the instruction types NaryReassociate handles for now.
+static bool isPotentiallyNaryReassociable(Instruction *I) {
+  switch (I->getOpcode()) {
+  case Instruction::Add:
+  case Instruction::GetElementPtr:
+    return true;
+  default:
+    return false;
+  }
+}
+
+bool NaryReassociate::doOneIteration(Function &F) {
+  bool Changed = false;
+  SeenExprs.clear();
+  // Process the basic blocks in pre-order of the dominator tree. This order
+  // ensures that all bases of a candidate are in Candidates when we process it.
+  for (auto Node = GraphTraits<DominatorTree *>::nodes_begin(DT);
+       Node != GraphTraits<DominatorTree *>::nodes_end(DT); ++Node) {
+    BasicBlock *BB = Node->getBlock();
+    for (auto I = BB->begin(); I != BB->end(); ++I) {
+      if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
+        const SCEV *OldSCEV = SE->getSCEV(I);
+        if (Instruction *NewI = tryReassociate(I)) {
+          Changed = true;
+          SE->forgetValue(I);
+          I->replaceAllUsesWith(NewI);
+          RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
+          I = NewI;
+        }
+        // Add the rewritten instruction to SeenExprs; the original instruction
+        // is deleted.
+        const SCEV *NewSCEV = SE->getSCEV(I);
+        SeenExprs[NewSCEV].push_back(I);
+        // Ideally, NewSCEV should equal OldSCEV because tryReassociate(I)
+        // is equivalent to I. However, ScalarEvolution::getSCEV may
+        // weaken nsw causing NewSCEV not to equal OldSCEV. For example, suppose
+        // we reassociate
+        //   I = &a[sext(i +nsw j)] // assuming sizeof(a[0]) = 4
+        // to
+        //   NewI = &a[sext(i)] + sext(j).
+        //
+        // ScalarEvolution computes
+        //   getSCEV(I)    = a + 4 * sext(i + j)
+        //   getSCEV(newI) = a + 4 * sext(i) + 4 * sext(j)
+        // which are different SCEVs.
+        //
+        // To alleviate this issue of ScalarEvolution not always capturing
+        // equivalence, we add I to SeenExprs[OldSCEV] as well so that we can
+        // map both SCEV before and after tryReassociate(I) to I.
+        //
+        // This improvement is exercised in @reassociate_gep_nsw in nary-gep.ll.
+        if (NewSCEV != OldSCEV)
+          SeenExprs[OldSCEV].push_back(I);
+      }
+    }
+  }
+  return Changed;
+}
+
+Instruction *NaryReassociate::tryReassociate(Instruction *I) {
+  switch (I->getOpcode()) {
+  case Instruction::Add:
+    return tryReassociateAdd(cast<BinaryOperator>(I));
+  case Instruction::GetElementPtr:
+    return tryReassociateGEP(cast<GetElementPtrInst>(I));
+  default:
+    llvm_unreachable("should be filtered out by isPotentiallyNaryReassociable");
+  }
+}
+
+// FIXME: extract this method into TTI->getGEPCost.
+static bool isGEPFoldable(GetElementPtrInst *GEP,
+                          const TargetTransformInfo *TTI,
+                          const DataLayout *DL) {
+  GlobalVariable *BaseGV = nullptr;
+  int64_t BaseOffset = 0;
+  bool HasBaseReg = false;
+  int64_t Scale = 0;
+
+  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getPointerOperand()))
+    BaseGV = GV;
+  else
+    HasBaseReg = true;
+
+  gep_type_iterator GTI = gep_type_begin(GEP);
+  for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I, ++GTI) {
+    if (isa<SequentialType>(*GTI)) {
+      int64_t ElementSize = DL->getTypeAllocSize(GTI.getIndexedType());
+      if (ConstantInt *ConstIdx = dyn_cast<ConstantInt>(*I)) {
+        BaseOffset += ConstIdx->getSExtValue() * ElementSize;
+      } else {
+        // Needs scale register.
+        if (Scale != 0) {
+          // No addressing mode takes two scale registers.
+          return false;
+        }
+        Scale = ElementSize;
+      }
+    } else {
+      StructType *STy = cast<StructType>(*GTI);
+      uint64_t Field = cast<ConstantInt>(*I)->getZExtValue();
+      BaseOffset += DL->getStructLayout(STy)->getElementOffset(Field);
+    }
+  }
+
+  unsigned AddrSpace = GEP->getPointerAddressSpace();
+  return TTI->isLegalAddressingMode(GEP->getType()->getElementType(), BaseGV,
+                                    BaseOffset, HasBaseReg, Scale, AddrSpace);
+}
+
+Instruction *NaryReassociate::tryReassociateGEP(GetElementPtrInst *GEP) {
+  // Not worth reassociating GEP if it is foldable.
+  if (isGEPFoldable(GEP, TTI, DL))
+    return nullptr;
+
+  gep_type_iterator GTI = gep_type_begin(*GEP);
+  for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I) {
+    if (isa<SequentialType>(*GTI++)) {
+      if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I - 1, *GTI)) {
+        return NewGEP;
+      }
+    }
+  }
+  return nullptr;
+}
+
+bool NaryReassociate::requiresSignExtension(Value *Index,
+                                            GetElementPtrInst *GEP) {
+  unsigned PointerSizeInBits =
+      DL->getPointerSizeInBits(GEP->getType()->getPointerAddressSpace());
+  return cast<IntegerType>(Index->getType())->getBitWidth() < PointerSizeInBits;
+}
+
+GetElementPtrInst *
+NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
+                                          Type *IndexedType) {
+  Value *IndexToSplit = GEP->getOperand(I + 1);
+  if (SExtInst *SExt = dyn_cast<SExtInst>(IndexToSplit))
+    IndexToSplit = SExt->getOperand(0);
+
+  if (AddOperator *AO = dyn_cast<AddOperator>(IndexToSplit)) {
+    // If the I-th index needs sext and the underlying add is not equipped with
+    // nsw, we cannot split the add because
+    //   sext(LHS + RHS) != sext(LHS) + sext(RHS).
+    if (requiresSignExtension(IndexToSplit, GEP) && !AO->hasNoSignedWrap())
+      return nullptr;
+    Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
+    // IndexToSplit = LHS + RHS.
+    if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I, LHS, RHS, IndexedType))
+      return NewGEP;
+    // Symmetrically, try IndexToSplit = RHS + LHS.
+    if (LHS != RHS) {
+      if (auto *NewGEP =
+              tryReassociateGEPAtIndex(GEP, I, RHS, LHS, IndexedType))
+        return NewGEP;
+    }
+  }
+  return nullptr;
+}
+
+GetElementPtrInst *
+NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
+                                          Value *LHS, Value *RHS,
+                                          Type *IndexedType) {
+  // Look for GEP's closest dominator that has the same SCEV as GEP except that
+  // the I-th index is replaced with LHS.
+  SmallVector<const SCEV *, 4> IndexExprs;
+  for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index)
+    IndexExprs.push_back(SE->getSCEV(*Index));
+  // Replace the I-th index with LHS.
+  IndexExprs[I] = SE->getSCEV(LHS);
+  const SCEV *CandidateExpr = SE->getGEPExpr(
+      GEP->getSourceElementType(), SE->getSCEV(GEP->getPointerOperand()),
+      IndexExprs, GEP->isInBounds());
+
+  auto *Candidate = findClosestMatchingDominator(CandidateExpr, GEP);
+  if (Candidate == nullptr)
+    return nullptr;
+
+  PointerType *TypeOfCandidate = dyn_cast<PointerType>(Candidate->getType());
+  // Pretty rare but theoretically possible when a numeric value happens to
+  // share CandidateExpr.
+  if (TypeOfCandidate == nullptr)
+    return nullptr;
+
+  // NewGEP = (char *)Candidate + RHS * sizeof(IndexedType)
+  uint64_t IndexedSize = DL->getTypeAllocSize(IndexedType);
+  Type *ElementType = TypeOfCandidate->getElementType();
+  uint64_t ElementSize = DL->getTypeAllocSize(ElementType);
+  // Another less rare case: because I is not necessarily the last index of the
+  // GEP, the size of the type at the I-th index (IndexedSize) is not
+  // necessarily divisible by ElementSize. For example,
+  //
+  // #pragma pack(1)
+  // struct S {
+  //   int a[3];
+  //   int64 b[8];
+  // };
+  // #pragma pack()
+  //
+  // sizeof(S) = 100 is indivisible by sizeof(int64) = 8.
+  //
+  // TODO: bail out on this case for now. We could emit uglygep.
+  if (IndexedSize % ElementSize != 0)
+    return nullptr;
+
+  // NewGEP = &Candidate[RHS * (sizeof(IndexedType) / sizeof(Candidate[0])));
+  IRBuilder<> Builder(GEP);
+  Type *IntPtrTy = DL->getIntPtrType(TypeOfCandidate);
+  if (RHS->getType() != IntPtrTy)
+    RHS = Builder.CreateSExtOrTrunc(RHS, IntPtrTy);
+  if (IndexedSize != ElementSize) {
+    RHS = Builder.CreateMul(
+        RHS, ConstantInt::get(IntPtrTy, IndexedSize / ElementSize));
+  }
+  GetElementPtrInst *NewGEP =
+      cast<GetElementPtrInst>(Builder.CreateGEP(Candidate, RHS));
+  NewGEP->setIsInBounds(GEP->isInBounds());
+  NewGEP->takeName(GEP);
+  return NewGEP;
+}
+
+Instruction *NaryReassociate::tryReassociateAdd(BinaryOperator *I) {
+  Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
+  if (auto *NewI = tryReassociateAdd(LHS, RHS, I))
+    return NewI;
+  if (auto *NewI = tryReassociateAdd(RHS, LHS, I))
+    return NewI;
+  return nullptr;
+}
+
+Instruction *NaryReassociate::tryReassociateAdd(Value *LHS, Value *RHS,
+                                                Instruction *I) {
+  Value *A = nullptr, *B = nullptr;
+  // To be conservative, we reassociate I only when it is the only user of A+B.
+  if (LHS->hasOneUse() && match(LHS, m_Add(m_Value(A), m_Value(B)))) {
+    // I = (A + B) + RHS
+    //   = (A + RHS) + B or (B + RHS) + A
+    const SCEV *AExpr = SE->getSCEV(A), *BExpr = SE->getSCEV(B);
+    const SCEV *RHSExpr = SE->getSCEV(RHS);
+    if (BExpr != RHSExpr) {
+      if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
+        return NewI;
+    }
+    if (AExpr != RHSExpr) {
+      if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
+        return NewI;
+    }
+  }
+  return nullptr;
+}
+
+Instruction *NaryReassociate::tryReassociatedAdd(const SCEV *LHSExpr,
+                                                 Value *RHS, Instruction *I) {
+  auto Pos = SeenExprs.find(LHSExpr);
+  // Bail out if LHSExpr is not previously seen.
+  if (Pos == SeenExprs.end())
+    return nullptr;
+
+  // Look for the closest dominator LHS of I that computes LHSExpr, and replace
+  // I with LHS + RHS.
+  auto *LHS = findClosestMatchingDominator(LHSExpr, I);
+  if (LHS == nullptr)
+    return nullptr;
+
+  Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
+  NewI->takeName(I);
+  return NewI;
+}
+
+Instruction *
+NaryReassociate::findClosestMatchingDominator(const SCEV *CandidateExpr,
+                                              Instruction *Dominatee) {
+  auto Pos = SeenExprs.find(CandidateExpr);
+  if (Pos == SeenExprs.end())
+    return nullptr;
+
+  auto &Candidates = Pos->second;
+  // Because we process the basic blocks in pre-order of the dominator tree, a
+  // candidate that doesn't dominate the current instruction won't dominate any
+  // future instruction either. Therefore, we pop it out of the stack. This
+  // optimization makes the algorithm O(n).
+  while (!Candidates.empty()) {
+    Instruction *Candidate = Candidates.back();
+    if (DT->dominates(Candidate, Dominatee))
+      return Candidate;
+    Candidates.pop_back();
+  }
+  return nullptr;
+}