text: //===- Local.cpp - Functions to perform local transformations -------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This family of functions perform various local transformations to the
  // program.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Transforms/Utils/Local.h"
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/DenseMapInfo.h"
  #include "llvm/ADT/DenseSet.h"
  #include "llvm/ADT/Hashing.h"
  #include "llvm/ADT/None.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/ADT/TinyPtrVector.h"
  #include "llvm/Analysis/AssumeBundleQueries.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/DomTreeUpdater.h"
  #include "llvm/Analysis/EHPersonalities.h"
  #include "llvm/Analysis/InstructionSimplify.h"
  #include "llvm/Analysis/LazyValueInfo.h"
  #include "llvm/Analysis/MemoryBuiltins.h"
  #include "llvm/Analysis/MemorySSAUpdater.h"
  #include "llvm/Analysis/TargetLibraryInfo.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/Analysis/VectorUtils.h"
  #include "llvm/BinaryFormat/Dwarf.h"
  #include "llvm/IR/Argument.h"
  #include "llvm/IR/Attributes.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/CFG.h"
  #include "llvm/IR/Constant.h"
  #include "llvm/IR/ConstantRange.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DIBuilder.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DebugInfoMetadata.h"
  #include "llvm/IR/DebugLoc.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/Dominators.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/GetElementPtrTypeIterator.h"
  #include "llvm/IR/GlobalObject.h"
  #include "llvm/IR/IRBuilder.h"
  #include "llvm/IR/InstrTypes.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/Intrinsics.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/MDBuilder.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/Operator.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Use.h"
  #include "llvm/IR/User.h"
  #include "llvm/IR/Value.h"
  #include "llvm/IR/ValueHandle.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/KnownBits.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/ValueMapper.h"
  #include <algorithm>
  #include <cassert>
  #include <climits>
  #include <cstdint>
  #include <iterator>
  #include <map>
  #include <utility>
  
  using namespace llvm;
  using namespace llvm::PatternMatch;
  
  #define DEBUG_TYPE "local"
  
  STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
  STATISTIC(NumPHICSEs, "Number of PHI's that got CSE'd");
  
  static cl::opt<bool> PHICSEDebugHash(
      "phicse-debug-hash",
  #ifdef EXPENSIVE_CHECKS
      cl::init(true),
  #else
      cl::init(false),
  #endif
      cl::Hidden,
      cl::desc("Perform extra assertion checking to verify that PHINodes's hash "
               "function is well-behaved w.r.t. its isEqual predicate"));
  
  static cl::opt<unsigned> PHICSENumPHISmallSize(
      "phicse-num-phi-smallsize", cl::init(32), cl::Hidden,
      cl::desc(
          "When the basic block contains not more than this number of PHI nodes, "
          "perform a (faster!) exhaustive search instead of set-driven one."));
  
  // Max recursion depth for collectBitParts used when detecting bswap and
  // bitreverse idioms
  static const unsigned BitPartRecursionMaxDepth = 64;
  
  //===----------------------------------------------------------------------===//
  //  Local constant propagation.
  //
  
  /// ConstantFoldTerminator - If a terminator instruction is predicated on a
  /// constant value, convert it into an unconditional branch to the constant
  /// destination.  This is a nontrivial operation because the successors of this
  /// basic block must have their PHI nodes updated.
  /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
  /// conditions and indirectbr addresses this might make dead if
  /// DeleteDeadConditions is true.
  bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
                                    const TargetLibraryInfo *TLI,
                                    DomTreeUpdater *DTU) {
    Instruction *T = BB->getTerminator();
    IRBuilder<> Builder(T);
  
    // Branch - See if we are conditional jumping on constant
    if (auto *BI = dyn_cast<BranchInst>(T)) {
      if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
      BasicBlock *Dest1 = BI->getSuccessor(0);
      BasicBlock *Dest2 = BI->getSuccessor(1);
  
      if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
        // Are we branching on constant?
        // YES.  Change to unconditional branch...
        BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
        BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;
  
        // Let the basic block know that we are letting go of it.  Based on this,
        // it will adjust it's PHI nodes.
        OldDest->removePredecessor(BB);
  
        // Replace the conditional branch with an unconditional one.
        Builder.CreateBr(Destination);
        BI->eraseFromParent();
        if (DTU)
          DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, OldDest}});
        return true;
      }
  
      if (Dest2 == Dest1) {       // Conditional branch to same location?
        // This branch matches something like this:
        //     br bool %cond, label %Dest, label %Dest
        // and changes it into:  br label %Dest
  
        // Let the basic block know that we are letting go of one copy of it.
        assert(BI->getParent() && "Terminator not inserted in block!");
        Dest1->removePredecessor(BI->getParent());
  
        // Replace the conditional branch with an unconditional one.
        Builder.CreateBr(Dest1);
        Value *Cond = BI->getCondition();
        BI->eraseFromParent();
        if (DeleteDeadConditions)
          RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
        return true;
      }
      return false;
    }
  
    if (auto *SI = dyn_cast<SwitchInst>(T)) {
      // If we are switching on a constant, we can convert the switch to an
      // unconditional branch.
      auto *CI = dyn_cast<ConstantInt>(SI->getCondition());
      BasicBlock *DefaultDest = SI->getDefaultDest();
      BasicBlock *TheOnlyDest = DefaultDest;
  
      // If the default is unreachable, ignore it when searching for TheOnlyDest.
      if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
          SI->getNumCases() > 0) {
        TheOnlyDest = SI->case_begin()->getCaseSuccessor();
      }
  
      bool Changed = false;
  
      // Figure out which case it goes to.
      for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
        // Found case matching a constant operand?
        if (i->getCaseValue() == CI) {
          TheOnlyDest = i->getCaseSuccessor();
          break;
        }
  
        // Check to see if this branch is going to the same place as the default
        // dest.  If so, eliminate it as an explicit compare.
        if (i->getCaseSuccessor() == DefaultDest) {
          MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
          unsigned NCases = SI->getNumCases();
          // Fold the case metadata into the default if there will be any branches
          // left, unless the metadata doesn't match the switch.
          if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
            // Collect branch weights into a vector.
            SmallVector<uint32_t, 8> Weights;
            for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
                 ++MD_i) {
              auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
              Weights.push_back(CI->getValue().getZExtValue());
            }
            // Merge weight of this case to the default weight.
            unsigned idx = i->getCaseIndex();
            Weights[0] += Weights[idx+1];
            // Remove weight for this case.
            std::swap(Weights[idx+1], Weights.back());
            Weights.pop_back();
            SI->setMetadata(LLVMContext::MD_prof,
                            MDBuilder(BB->getContext()).
                            createBranchWeights(Weights));
          }
          // Remove this entry.
          BasicBlock *ParentBB = SI->getParent();
          DefaultDest->removePredecessor(ParentBB);
          i = SI->removeCase(i);
          e = SI->case_end();
          Changed = true;
          if (DTU)
            DTU->applyUpdatesPermissive(
                {{DominatorTree::Delete, ParentBB, DefaultDest}});
          continue;
        }
  
        // Otherwise, check to see if the switch only branches to one destination.
        // We do this by reseting "TheOnlyDest" to null when we find two non-equal
        // destinations.
        if (i->getCaseSuccessor() != TheOnlyDest)
          TheOnlyDest = nullptr;
  
        // Increment this iterator as we haven't removed the case.
        ++i;
      }
  
      if (CI && !TheOnlyDest) {
        // Branching on a constant, but not any of the cases, go to the default
        // successor.
        TheOnlyDest = SI->getDefaultDest();
      }
  
      // If we found a single destination that we can fold the switch into, do so
      // now.
      if (TheOnlyDest) {
        // Insert the new branch.
        Builder.CreateBr(TheOnlyDest);
        BasicBlock *BB = SI->getParent();
        std::vector <DominatorTree::UpdateType> Updates;
        if (DTU)
          Updates.reserve(SI->getNumSuccessors() - 1);
  
        // Remove entries from PHI nodes which we no longer branch to...
        for (BasicBlock *Succ : successors(SI)) {
          // Found case matching a constant operand?
          if (Succ == TheOnlyDest) {
            TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
          } else {
            Succ->removePredecessor(BB);
            if (DTU)
              Updates.push_back({DominatorTree::Delete, BB, Succ});
          }
        }
  
        // Delete the old switch.
        Value *Cond = SI->getCondition();
        SI->eraseFromParent();
        if (DeleteDeadConditions)
          RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
        if (DTU)
          DTU->applyUpdatesPermissive(Updates);
        return true;
      }
  
      if (SI->getNumCases() == 1) {
        // Otherwise, we can fold this switch into a conditional branch
        // instruction if it has only one non-default destination.
        auto FirstCase = *SI->case_begin();
        Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
            FirstCase.getCaseValue(), "cond");
  
        // Insert the new branch.
        BranchInst *NewBr = Builder.CreateCondBr(Cond,
                                                 FirstCase.getCaseSuccessor(),
                                                 SI->getDefaultDest());
        MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
        if (MD && MD->getNumOperands() == 3) {
          ConstantInt *SICase =
              mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
          ConstantInt *SIDef =
              mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
          assert(SICase && SIDef);
          // The TrueWeight should be the weight for the single case of SI.
          NewBr->setMetadata(LLVMContext::MD_prof,
                          MDBuilder(BB->getContext()).
                          createBranchWeights(SICase->getValue().getZExtValue(),
                                              SIDef->getValue().getZExtValue()));
        }
  
        // Update make.implicit metadata to the newly-created conditional branch.
        MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
        if (MakeImplicitMD)
          NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
  
        // Delete the old switch.
        SI->eraseFromParent();
        return true;
      }
      return Changed;
    }
  
    if (auto *IBI = dyn_cast<IndirectBrInst>(T)) {
      // indirectbr blockaddress(@F, @BB) -> br label @BB
      if (auto *BA =
            dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
        BasicBlock *TheOnlyDest = BA->getBasicBlock();
        std::vector <DominatorTree::UpdateType> Updates;
        if (DTU)
          Updates.reserve(IBI->getNumDestinations() - 1);
  
        // Insert the new branch.
        Builder.CreateBr(TheOnlyDest);
  
        for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
          if (IBI->getDestination(i) == TheOnlyDest) {
            TheOnlyDest = nullptr;
          } else {
            BasicBlock *ParentBB = IBI->getParent();
            BasicBlock *DestBB = IBI->getDestination(i);
            DestBB->removePredecessor(ParentBB);
            if (DTU)
              Updates.push_back({DominatorTree::Delete, ParentBB, DestBB});
          }
        }
        Value *Address = IBI->getAddress();
        IBI->eraseFromParent();
        if (DeleteDeadConditions)
          // Delete pointer cast instructions.
          RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
  
        // Also zap the blockaddress constant if there are no users remaining,
        // otherwise the destination is still marked as having its address taken.
        if (BA->use_empty())
          BA->destroyConstant();
  
        // If we didn't find our destination in the IBI successor list, then we
        // have undefined behavior.  Replace the unconditional branch with an
        // 'unreachable' instruction.
        if (TheOnlyDest) {
          BB->getTerminator()->eraseFromParent();
          new UnreachableInst(BB->getContext(), BB);
        }
  
        if (DTU)
          DTU->applyUpdatesPermissive(Updates);
        return true;
      }
    }
  
    return false;
  }
  
  //===----------------------------------------------------------------------===//
  //  Local dead code elimination.
  //
  
  /// isInstructionTriviallyDead - Return true if the result produced by the
  /// instruction is not used, and the instruction has no side effects.
  ///
  bool llvm::isInstructionTriviallyDead(Instruction *I,
                                        const TargetLibraryInfo *TLI) {
    if (!I->use_empty())
      return false;
    return wouldInstructionBeTriviallyDead(I, TLI);
  }
  
  bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
                                             const TargetLibraryInfo *TLI) {
    if (I->isTerminator())
      return false;
  
    // We don't want the landingpad-like instructions removed by anything this
    // general.
    if (I->isEHPad())
      return false;
  
    // We don't want debug info removed by anything this general, unless
    // debug info is empty.
    if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
      if (DDI->getAddress())
        return false;
      return true;
    }
    if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
      if (DVI->getValue())
        return false;
      return true;
    }
    if (DbgLabelInst *DLI = dyn_cast<DbgLabelInst>(I)) {
      if (DLI->getLabel())
        return false;
      return true;
    }
  
    if (!I->mayHaveSideEffects())
      return true;
  
    // Special case intrinsics that "may have side effects" but can be deleted
    // when dead.
    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
      // Safe to delete llvm.stacksave and launder.invariant.group if dead.
      if (II->getIntrinsicID() == Intrinsic::stacksave ||
          II->getIntrinsicID() == Intrinsic::launder_invariant_group)
        return true;
  
      if (II->isLifetimeStartOrEnd()) {
        auto *Arg = II->getArgOperand(1);
        // Lifetime intrinsics are dead when their right-hand is undef.
        if (isa<UndefValue>(Arg))
          return true;
        // If the right-hand is an alloc, global, or argument and the only uses
        // are lifetime intrinsics then the intrinsics are dead.
        if (isa<AllocaInst>(Arg) || isa<GlobalValue>(Arg) || isa<Argument>(Arg))
          return llvm::all_of(Arg->uses(), [](Use &Use) {
            if (IntrinsicInst *IntrinsicUse =
                    dyn_cast<IntrinsicInst>(Use.getUser()))
              return IntrinsicUse->isLifetimeStartOrEnd();
            return false;
          });
        return false;
      }
  
      // Assumptions are dead if their condition is trivially true.  Guards on
      // true are operationally no-ops.  In the future we can consider more
      // sophisticated tradeoffs for guards considering potential for check
      // widening, but for now we keep things simple.
      if ((II->getIntrinsicID() == Intrinsic::assume &&
           isAssumeWithEmptyBundle(*II)) ||
          II->getIntrinsicID() == Intrinsic::experimental_guard) {
        if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
          return !Cond->isZero();
  
        return false;
      }
    }
  
    if (isAllocLikeFn(I, TLI))
      return true;
  
    if (CallInst *CI = isFreeCall(I, TLI))
      if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
        return C->isNullValue() || isa<UndefValue>(C);
  
    if (auto *Call = dyn_cast<CallBase>(I))
      if (isMathLibCallNoop(Call, TLI))
        return true;
  
    return false;
  }
  
  /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
  /// trivially dead instruction, delete it.  If that makes any of its operands
  /// trivially dead, delete them too, recursively.  Return true if any
  /// instructions were deleted.
  bool llvm::RecursivelyDeleteTriviallyDeadInstructions(
      Value *V, const TargetLibraryInfo *TLI, MemorySSAUpdater *MSSAU,
      std::function<void(Value *)> AboutToDeleteCallback) {
    Instruction *I = dyn_cast<Instruction>(V);
    if (!I || !isInstructionTriviallyDead(I, TLI))
      return false;
  
    SmallVector<WeakTrackingVH, 16> DeadInsts;
    DeadInsts.push_back(I);
    RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, TLI, MSSAU,
                                               AboutToDeleteCallback);
  
    return true;
  }
  
  bool llvm::RecursivelyDeleteTriviallyDeadInstructionsPermissive(
      SmallVectorImpl<WeakTrackingVH> &DeadInsts, const TargetLibraryInfo *TLI,
      MemorySSAUpdater *MSSAU,
      std::function<void(Value *)> AboutToDeleteCallback) {
    unsigned S = 0, E = DeadInsts.size(), Alive = 0;
    for (; S != E; ++S) {
      auto *I = cast<Instruction>(DeadInsts[S]);
      if (!isInstructionTriviallyDead(I)) {
        DeadInsts[S] = nullptr;
        ++Alive;
      }
    }
    if (Alive == E)
      return false;
    RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, TLI, MSSAU,
                                               AboutToDeleteCallback);
    return true;
  }
  
  void llvm::RecursivelyDeleteTriviallyDeadInstructions(
      SmallVectorImpl<WeakTrackingVH> &DeadInsts, const TargetLibraryInfo *TLI,
      MemorySSAUpdater *MSSAU,
      std::function<void(Value *)> AboutToDeleteCallback) {
    // Process the dead instruction list until empty.
    while (!DeadInsts.empty()) {
      Value *V = DeadInsts.pop_back_val();
      Instruction *I = cast_or_null<Instruction>(V);
      if (!I)
        continue;
      assert(isInstructionTriviallyDead(I, TLI) &&
             "Live instruction found in dead worklist!");
      assert(I->use_empty() && "Instructions with uses are not dead.");
  
      // Don't lose the debug info while deleting the instructions.
      salvageDebugInfo(*I);
  
      if (AboutToDeleteCallback)
        AboutToDeleteCallback(I);
  
      // Null out all of the instruction's operands to see if any operand becomes
      // dead as we go.
      for (Use &OpU : I->operands()) {
        Value *OpV = OpU.get();
        OpU.set(nullptr);
  
        if (!OpV->use_empty())
          continue;
  
        // If the operand is an instruction that became dead as we nulled out the
        // operand, and if it is 'trivially' dead, delete it in a future loop
        // iteration.
        if (Instruction *OpI = dyn_cast<Instruction>(OpV))
          if (isInstructionTriviallyDead(OpI, TLI))
            DeadInsts.push_back(OpI);
      }
      if (MSSAU)
        MSSAU->removeMemoryAccess(I);
  
      I->eraseFromParent();
    }
  }
  
  bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
    SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
    findDbgUsers(DbgUsers, I);
    for (auto *DII : DbgUsers) {
      Value *Undef = UndefValue::get(I->getType());
      DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
                                              ValueAsMetadata::get(Undef)));
    }
    return !DbgUsers.empty();
  }
  
  /// areAllUsesEqual - Check whether the uses of a value are all the same.
  /// This is similar to Instruction::hasOneUse() except this will also return
  /// true when there are no uses or multiple uses that all refer to the same
  /// value.
  static bool areAllUsesEqual(Instruction *I) {
    Value::user_iterator UI = I->user_begin();
    Value::user_iterator UE = I->user_end();
    if (UI == UE)
      return true;
  
    User *TheUse = *UI;
    for (++UI; UI != UE; ++UI) {
      if (*UI != TheUse)
        return false;
    }
    return true;
  }
  
  /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
  /// dead PHI node, due to being a def-use chain of single-use nodes that
  /// either forms a cycle or is terminated by a trivially dead instruction,
  /// delete it.  If that makes any of its operands trivially dead, delete them
  /// too, recursively.  Return true if a change was made.
  bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
                                          const TargetLibraryInfo *TLI,
                                          llvm::MemorySSAUpdater *MSSAU) {
    SmallPtrSet<Instruction*, 4> Visited;
    for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
         I = cast<Instruction>(*I->user_begin())) {
      if (I->use_empty())
        return RecursivelyDeleteTriviallyDeadInstructions(I, TLI, MSSAU);
  
      // If we find an instruction more than once, we're on a cycle that
      // won't prove fruitful.
      if (!Visited.insert(I).second) {
        // Break the cycle and delete the instruction and its operands.
        I->replaceAllUsesWith(UndefValue::get(I->getType()));
        (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI, MSSAU);
        return true;
      }
    }
    return false;
  }
  
  static bool
  simplifyAndDCEInstruction(Instruction *I,
                            SmallSetVector<Instruction *, 16> &WorkList,
                            const DataLayout &DL,
                            const TargetLibraryInfo *TLI) {
    if (isInstructionTriviallyDead(I, TLI)) {
      salvageDebugInfo(*I);
  
      // Null out all of the instruction's operands to see if any operand becomes
      // dead as we go.
      for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
        Value *OpV = I->getOperand(i);
        I->setOperand(i, nullptr);
  
        if (!OpV->use_empty() || I == OpV)
          continue;
  
        // If the operand is an instruction that became dead as we nulled out the
        // operand, and if it is 'trivially' dead, delete it in a future loop
        // iteration.
        if (Instruction *OpI = dyn_cast<Instruction>(OpV))
          if (isInstructionTriviallyDead(OpI, TLI))
            WorkList.insert(OpI);
      }
  
      I->eraseFromParent();
  
      return true;
    }
  
    if (Value *SimpleV = SimplifyInstruction(I, DL)) {
      // Add the users to the worklist. CAREFUL: an instruction can use itself,
      // in the case of a phi node.
      for (User *U : I->users()) {
        if (U != I) {
          WorkList.insert(cast<Instruction>(U));
        }
      }
  
      // Replace the instruction with its simplified value.
      bool Changed = false;
      if (!I->use_empty()) {
        I->replaceAllUsesWith(SimpleV);
        Changed = true;
      }
      if (isInstructionTriviallyDead(I, TLI)) {
        I->eraseFromParent();
        Changed = true;
      }
      return Changed;
    }
    return false;
  }
  
  /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
  /// simplify any instructions in it and recursively delete dead instructions.
  ///
  /// This returns true if it changed the code, note that it can delete
  /// instructions in other blocks as well in this block.
  bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
                                         const TargetLibraryInfo *TLI) {
    bool MadeChange = false;
    const DataLayout &DL = BB->getModule()->getDataLayout();
  
  #ifndef NDEBUG
    // In debug builds, ensure that the terminator of the block is never replaced
    // or deleted by these simplifications. The idea of simplification is that it
    // cannot introduce new instructions, and there is no way to replace the
    // terminator of a block without introducing a new instruction.
    AssertingVH<Instruction> TerminatorVH(&BB->back());
  #endif
  
    SmallSetVector<Instruction *, 16> WorkList;
    // Iterate over the original function, only adding insts to the worklist
    // if they actually need to be revisited. This avoids having to pre-init
    // the worklist with the entire function's worth of instructions.
    for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end());
         BI != E;) {
      assert(!BI->isTerminator());
      Instruction *I = &*BI;
      ++BI;
  
      // We're visiting this instruction now, so make sure it's not in the
      // worklist from an earlier visit.
      if (!WorkList.count(I))
        MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
    }
  
    while (!WorkList.empty()) {
      Instruction *I = WorkList.pop_back_val();
      MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
    }
    return MadeChange;
  }
  
  //===----------------------------------------------------------------------===//
  //  Control Flow Graph Restructuring.
  //
  
  void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
                                          DomTreeUpdater *DTU) {
    // This only adjusts blocks with PHI nodes.
    if (!isa<PHINode>(BB->begin()))
      return;
  
    // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
    // them down.  This will leave us with single entry phi nodes and other phis
    // that can be removed.
    BB->removePredecessor(Pred, true);
  
    WeakTrackingVH PhiIt = &BB->front();
    while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
      PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
      Value *OldPhiIt = PhiIt;
  
      if (!recursivelySimplifyInstruction(PN))
        continue;
  
      // If recursive simplification ended up deleting the next PHI node we would
      // iterate to, then our iterator is invalid, restart scanning from the top
      // of the block.
      if (PhiIt != OldPhiIt) PhiIt = &BB->front();
    }
    if (DTU)
      DTU->applyUpdatesPermissive({{DominatorTree::Delete, Pred, BB}});
  }
  
  void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB,
                                         DomTreeUpdater *DTU) {
  
    // If BB has single-entry PHI nodes, fold them.
    while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
      Value *NewVal = PN->getIncomingValue(0);
      // Replace self referencing PHI with undef, it must be dead.
      if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
      PN->replaceAllUsesWith(NewVal);
      PN->eraseFromParent();
    }
  
    BasicBlock *PredBB = DestBB->getSinglePredecessor();
    assert(PredBB && "Block doesn't have a single predecessor!");
  
    bool ReplaceEntryBB = false;
    if (PredBB == &DestBB->getParent()->getEntryBlock())
      ReplaceEntryBB = true;
  
    // DTU updates: Collect all the edges that enter
    // PredBB. These dominator edges will be redirected to DestBB.
    SmallVector<DominatorTree::UpdateType, 32> Updates;
  
    if (DTU) {
      Updates.push_back({DominatorTree::Delete, PredBB, DestBB});
      for (auto I = pred_begin(PredBB), E = pred_end(PredBB); I != E; ++I) {
        Updates.push_back({DominatorTree::Delete, *I, PredBB});
        // This predecessor of PredBB may already have DestBB as a successor.
        if (llvm::find(successors(*I), DestBB) == succ_end(*I))
          Updates.push_back({DominatorTree::Insert, *I, DestBB});
      }
    }
  
    // Zap anything that took the address of DestBB.  Not doing this will give the
    // address an invalid value.
    if (DestBB->hasAddressTaken()) {
      BlockAddress *BA = BlockAddress::get(DestBB);
      Constant *Replacement =
        ConstantInt::get(Type::getInt32Ty(BA->getContext()), 1);
      BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
                                                       BA->getType()));
      BA->destroyConstant();
    }
  
    // Anything that branched to PredBB now branches to DestBB.
    PredBB->replaceAllUsesWith(DestBB);
  
    // Splice all the instructions from PredBB to DestBB.
    PredBB->getTerminator()->eraseFromParent();
    DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
    new UnreachableInst(PredBB->getContext(), PredBB);
  
    // If the PredBB is the entry block of the function, move DestBB up to
    // become the entry block after we erase PredBB.
    if (ReplaceEntryBB)
      DestBB->moveAfter(PredBB);
  
    if (DTU) {
      assert(PredBB->getInstList().size() == 1 &&
             isa<UnreachableInst>(PredBB->getTerminator()) &&
             "The successor list of PredBB isn't empty before "
             "applying corresponding DTU updates.");
      DTU->applyUpdatesPermissive(Updates);
      DTU->deleteBB(PredBB);
      // Recalculation of DomTree is needed when updating a forward DomTree and
      // the Entry BB is replaced.
      if (ReplaceEntryBB && DTU->hasDomTree()) {
        // The entry block was removed and there is no external interface for
        // the dominator tree to be notified of this change. In this corner-case
        // we recalculate the entire tree.
        DTU->recalculate(*(DestBB->getParent()));
      }
    }
  
    else {
      PredBB->eraseFromParent(); // Nuke BB if DTU is nullptr.
    }
  }
  
  /// Return true if we can choose one of these values to use in place of the
  /// other. Note that we will always choose the non-undef value to keep.
  static bool CanMergeValues(Value *First, Value *Second) {
    return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
  }
  
  /// Return true if we can fold BB, an almost-empty BB ending in an unconditional
  /// branch to Succ, into Succ.
  ///
  /// Assumption: Succ is the single successor for BB.
  static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
    assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
  
    LLVM_DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
                      << Succ->getName() << "\n");
    // Shortcut, if there is only a single predecessor it must be BB and merging
    // is always safe
    if (Succ->getSinglePredecessor()) return true;
  
    // Make a list of the predecessors of BB
    SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
  
    // Look at all the phi nodes in Succ, to see if they present a conflict when
    // merging these blocks
    for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
      PHINode *PN = cast<PHINode>(I);
  
      // If the incoming value from BB is again a PHINode in
      // BB which has the same incoming value for *PI as PN does, we can
      // merge the phi nodes and then the blocks can still be merged
      PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
      if (BBPN && BBPN->getParent() == BB) {
        for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
          BasicBlock *IBB = PN->getIncomingBlock(PI);
          if (BBPreds.count(IBB) &&
              !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
                              PN->getIncomingValue(PI))) {
            LLVM_DEBUG(dbgs()
                       << "Can't fold, phi node " << PN->getName() << " in "
                       << Succ->getName() << " is conflicting with "
                       << BBPN->getName() << " with regard to common predecessor "
                       << IBB->getName() << "\n");
            return false;
          }
        }
      } else {
        Value* Val = PN->getIncomingValueForBlock(BB);
        for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
          // See if the incoming value for the common predecessor is equal to the
          // one for BB, in which case this phi node will not prevent the merging
          // of the block.
          BasicBlock *IBB = PN->getIncomingBlock(PI);
          if (BBPreds.count(IBB) &&
              !CanMergeValues(Val, PN->getIncomingValue(PI))) {
            LLVM_DEBUG(dbgs() << "Can't fold, phi node " << PN->getName()
                              << " in " << Succ->getName()
                              << " is conflicting with regard to common "
                              << "predecessor " << IBB->getName() << "\n");
            return false;
          }
        }
      }
    }
  
    return true;
  }
  
  using PredBlockVector = SmallVector<BasicBlock *, 16>;
  using IncomingValueMap = DenseMap<BasicBlock *, Value *>;
  
  /// Determines the value to use as the phi node input for a block.
  ///
  /// Select between \p OldVal any value that we know flows from \p BB
  /// to a particular phi on the basis of which one (if either) is not
  /// undef. Update IncomingValues based on the selected value.
  ///
  /// \param OldVal The value we are considering selecting.
  /// \param BB The block that the value flows in from.
  /// \param IncomingValues A map from block-to-value for other phi inputs
  /// that we have examined.
  ///
  /// \returns the selected value.
  static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
                                            IncomingValueMap &IncomingValues) {
    if (!isa<UndefValue>(OldVal)) {
      assert((!IncomingValues.count(BB) ||
              IncomingValues.find(BB)->second == OldVal) &&
             "Expected OldVal to match incoming value from BB!");
  
      IncomingValues.insert(std::make_pair(BB, OldVal));
      return OldVal;
    }
  
    IncomingValueMap::const_iterator It = IncomingValues.find(BB);
    if (It != IncomingValues.end()) return It->second;
  
    return OldVal;
  }
  
  /// Create a map from block to value for the operands of a
  /// given phi.
  ///
  /// Create a map from block to value for each non-undef value flowing
  /// into \p PN.
  ///
  /// \param PN The phi we are collecting the map for.
  /// \param IncomingValues [out] The map from block to value for this phi.
  static void gatherIncomingValuesToPhi(PHINode *PN,
                                        IncomingValueMap &IncomingValues) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *BB = PN->getIncomingBlock(i);
      Value *V = PN->getIncomingValue(i);
  
      if (!isa<UndefValue>(V))
        IncomingValues.insert(std::make_pair(BB, V));
    }
  }
  
  /// Replace the incoming undef values to a phi with the values
  /// from a block-to-value map.
  ///
  /// \param PN The phi we are replacing the undefs in.
  /// \param IncomingValues A map from block to value.
  static void replaceUndefValuesInPhi(PHINode *PN,
                                      const IncomingValueMap &IncomingValues) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      Value *V = PN->getIncomingValue(i);
  
      if (!isa<UndefValue>(V)) continue;
  
      BasicBlock *BB = PN->getIncomingBlock(i);
      IncomingValueMap::const_iterator It = IncomingValues.find(BB);
      if (It == IncomingValues.end()) continue;
  
      PN->setIncomingValue(i, It->second);
    }
  }
  
  /// Replace a value flowing from a block to a phi with
  /// potentially multiple instances of that value flowing from the
  /// block's predecessors to the phi.
  ///
  /// \param BB The block with the value flowing into the phi.
  /// \param BBPreds The predecessors of BB.
  /// \param PN The phi that we are updating.
  static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
                                                  const PredBlockVector &BBPreds,
                                                  PHINode *PN) {
    Value *OldVal = PN->removeIncomingValue(BB, false);
    assert(OldVal && "No entry in PHI for Pred BB!");
  
    IncomingValueMap IncomingValues;
  
    // We are merging two blocks - BB, and the block containing PN - and
    // as a result we need to redirect edges from the predecessors of BB
    // to go to the block containing PN, and update PN
    // accordingly. Since we allow merging blocks in the case where the
    // predecessor and successor blocks both share some predecessors,
    // and where some of those common predecessors might have undef
    // values flowing into PN, we want to rewrite those values to be
    // consistent with the non-undef values.
  
    gatherIncomingValuesToPhi(PN, IncomingValues);
  
    // If this incoming value is one of the PHI nodes in BB, the new entries
    // in the PHI node are the entries from the old PHI.
    if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
      PHINode *OldValPN = cast<PHINode>(OldVal);
      for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
        // Note that, since we are merging phi nodes and BB and Succ might
        // have common predecessors, we could end up with a phi node with
        // identical incoming branches. This will be cleaned up later (and
        // will trigger asserts if we try to clean it up now, without also
        // simplifying the corresponding conditional branch).
        BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
        Value *PredVal = OldValPN->getIncomingValue(i);
        Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
                                                      IncomingValues);
  
        // And add a new incoming value for this predecessor for the
        // newly retargeted branch.
        PN->addIncoming(Selected, PredBB);
      }
    } else {
      for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
        // Update existing incoming values in PN for this
        // predecessor of BB.
        BasicBlock *PredBB = BBPreds[i];
        Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
                                                      IncomingValues);
  
        // And add a new incoming value for this predecessor for the
        // newly retargeted branch.
        PN->addIncoming(Selected, PredBB);
      }
    }
  
    replaceUndefValuesInPhi(PN, IncomingValues);
  }
  
  bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
                                                     DomTreeUpdater *DTU) {
    assert(BB != &BB->getParent()->getEntryBlock() &&
           "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
  
    // We can't eliminate infinite loops.
    BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
    if (BB == Succ) return false;
  
    // Check to see if merging these blocks would cause conflicts for any of the
    // phi nodes in BB or Succ. If not, we can safely merge.
    if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
  
    // Check for cases where Succ has multiple predecessors and a PHI node in BB
    // has uses which will not disappear when the PHI nodes are merged.  It is
    // possible to handle such cases, but difficult: it requires checking whether
    // BB dominates Succ, which is non-trivial to calculate in the case where
    // Succ has multiple predecessors.  Also, it requires checking whether
    // constructing the necessary self-referential PHI node doesn't introduce any
    // conflicts; this isn't too difficult, but the previous code for doing this
    // was incorrect.
    //
    // Note that if this check finds a live use, BB dominates Succ, so BB is
    // something like a loop pre-header (or rarely, a part of an irreducible CFG);
    // folding the branch isn't profitable in that case anyway.
    if (!Succ->getSinglePredecessor()) {
      BasicBlock::iterator BBI = BB->begin();
      while (isa<PHINode>(*BBI)) {
        for (Use &U : BBI->uses()) {
          if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
            if (PN->getIncomingBlock(U) != BB)
              return false;
          } else {
            return false;
          }
        }
        ++BBI;
      }
    }
  
    // We cannot fold the block if it's a branch to an already present callbr
    // successor because that creates duplicate successors.
    for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
      if (auto *CBI = dyn_cast<CallBrInst>((*I)->getTerminator())) {
        if (Succ == CBI->getDefaultDest())
          return false;
        for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
          if (Succ == CBI->getIndirectDest(i))
            return false;
      }
    }
  
    LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
  
    SmallVector<DominatorTree::UpdateType, 32> Updates;
    if (DTU) {
      Updates.push_back({DominatorTree::Delete, BB, Succ});
      // All predecessors of BB will be moved to Succ.
      for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
        Updates.push_back({DominatorTree::Delete, *I, BB});
        // This predecessor of BB may already have Succ as a successor.
        if (llvm::find(successors(*I), Succ) == succ_end(*I))
          Updates.push_back({DominatorTree::Insert, *I, Succ});
      }
    }
  
    if (isa<PHINode>(Succ->begin())) {
      // If there is more than one pred of succ, and there are PHI nodes in
      // the successor, then we need to add incoming edges for the PHI nodes
      //
      const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
  
      // Loop over all of the PHI nodes in the successor of BB.
      for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
        PHINode *PN = cast<PHINode>(I);
  
        redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
      }
    }
  
    if (Succ->getSinglePredecessor()) {
      // BB is the only predecessor of Succ, so Succ will end up with exactly
      // the same predecessors BB had.
  
      // Copy over any phi, debug or lifetime instruction.
      BB->getTerminator()->eraseFromParent();
      Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
                                 BB->getInstList());
    } else {
      while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
        // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
        assert(PN->use_empty() && "There shouldn't be any uses here!");
        PN->eraseFromParent();
      }
    }
  
    // If the unconditional branch we replaced contains llvm.loop metadata, we
    // add the metadata to the branch instructions in the predecessors.
    unsigned LoopMDKind = BB->getContext().getMDKindID("llvm.loop");
    Instruction *TI = BB->getTerminator();
    if (TI)
      if (MDNode *LoopMD = TI->getMetadata(LoopMDKind))
        for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
          BasicBlock *Pred = *PI;
          Pred->getTerminator()->setMetadata(LoopMDKind, LoopMD);
        }
  
    // Everything that jumped to BB now goes to Succ.
    BB->replaceAllUsesWith(Succ);
    if (!Succ->hasName()) Succ->takeName(BB);
  
    // Clear the successor list of BB to match updates applying to DTU later.
    if (BB->getTerminator())
      BB->getInstList().pop_back();
    new UnreachableInst(BB->getContext(), BB);
    assert(succ_empty(BB) && "The successor list of BB isn't empty before "
                             "applying corresponding DTU updates.");
  
    if (DTU) {
      DTU->applyUpdatesPermissive(Updates);
      DTU->deleteBB(BB);
    } else {
      BB->eraseFromParent(); // Delete the old basic block.
    }
    return true;
  }
  
  static bool EliminateDuplicatePHINodesNaiveImpl(BasicBlock *BB) {
    // This implementation doesn't currently consider undef operands
    // specially. Theoretically, two phis which are identical except for
    // one having an undef where the other doesn't could be collapsed.
  
    bool Changed = false;
  
    // Examine each PHI.
    // Note that increment of I must *NOT* be in the iteration_expression, since
    // we don't want to immediately advance when we restart from the beginning.
    for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I);) {
      ++I;
      // Is there an identical PHI node in this basic block?
      // Note that we only look in the upper square's triangle,
      // we already checked that the lower triangle PHI's aren't identical.
      for (auto J = I; PHINode *DuplicatePN = dyn_cast<PHINode>(J); ++J) {
        if (!DuplicatePN->isIdenticalToWhenDefined(PN))
          continue;
        // A duplicate. Replace this PHI with the base PHI.
        ++NumPHICSEs;
        DuplicatePN->replaceAllUsesWith(PN);
        DuplicatePN->eraseFromParent();
        Changed = true;
  
        // The RAUW can change PHIs that we already visited.
        I = BB->begin();
        break; // Start over from the beginning.
      }
    }
    return Changed;
  }
  
  static bool EliminateDuplicatePHINodesSetBasedImpl(BasicBlock *BB) {
    // This implementation doesn't currently consider undef operands
    // specially. Theoretically, two phis which are identical except for
    // one having an undef where the other doesn't could be collapsed.
  
    struct PHIDenseMapInfo {
      static PHINode *getEmptyKey() {
        return DenseMapInfo<PHINode *>::getEmptyKey();
      }
  
      static PHINode *getTombstoneKey() {
        return DenseMapInfo<PHINode *>::getTombstoneKey();
      }
  
      static bool isSentinel(PHINode *PN) {
        return PN == getEmptyKey() || PN == getTombstoneKey();
      }
  
      // WARNING: this logic must be kept in sync with
      //          Instruction::isIdenticalToWhenDefined()!
      static unsigned getHashValueImpl(PHINode *PN) {
        // Compute a hash value on the operands. Instcombine will likely have
        // sorted them, which helps expose duplicates, but we have to check all
        // the operands to be safe in case instcombine hasn't run.
        return static_cast<unsigned>(hash_combine(
            hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
            hash_combine_range(PN->block_begin(), PN->block_end())));
      }
  
      static unsigned getHashValue(PHINode *PN) {
  #ifndef NDEBUG
        // If -phicse-debug-hash was specified, return a constant -- this
        // will force all hashing to collide, so we'll exhaustively search
        // the table for a match, and the assertion in isEqual will fire if
        // there's a bug causing equal keys to hash differently.
        if (PHICSEDebugHash)
          return 0;
  #endif
        return getHashValueImpl(PN);
      }
  
      static bool isEqualImpl(PHINode *LHS, PHINode *RHS) {
        if (isSentinel(LHS) || isSentinel(RHS))
          return LHS == RHS;
        return LHS->isIdenticalTo(RHS);
      }
  
      static bool isEqual(PHINode *LHS, PHINode *RHS) {
        // These comparisons are nontrivial, so assert that equality implies
        // hash equality (DenseMap demands this as an invariant).
        bool Result = isEqualImpl(LHS, RHS);
        assert(!Result || (isSentinel(LHS) && LHS == RHS) ||
               getHashValueImpl(LHS) == getHashValueImpl(RHS));
        return Result;
      }
    };
  
    // Set of unique PHINodes.
    DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
    PHISet.reserve(4 * PHICSENumPHISmallSize);
  
    // Examine each PHI.
    bool Changed = false;
    for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
      auto Inserted = PHISet.insert(PN);
      if (!Inserted.second) {
        // A duplicate. Replace this PHI with its duplicate.
        ++NumPHICSEs;
        PN->replaceAllUsesWith(*Inserted.first);
        PN->eraseFromParent();
        Changed = true;
  
        // The RAUW can change PHIs that we already visited. Start over from the
        // beginning.
        PHISet.clear();
        I = BB->begin();
      }
    }
  
    return Changed;
  }
  
  bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
    if (
  #ifndef NDEBUG
        !PHICSEDebugHash &&
  #endif
        hasNItemsOrLess(BB->phis(), PHICSENumPHISmallSize))
      return EliminateDuplicatePHINodesNaiveImpl(BB);
    return EliminateDuplicatePHINodesSetBasedImpl(BB);
  }
  
  /// If the specified pointer points to an object that we control, try to modify
  /// the object's alignment to PrefAlign. Returns a minimum known alignment of
  /// the value after the operation, which may be lower than PrefAlign.
  ///
  /// Increating value alignment isn't often possible though. If alignment is
  /// important, a more reliable approach is to simply align all global variables
  /// and allocation instructions to their preferred alignment from the beginning.
  static Align tryEnforceAlignment(Value *V, Align PrefAlign,
                                   const DataLayout &DL) {
    V = V->stripPointerCasts();
  
    if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
      // TODO: Ideally, this function would not be called if PrefAlign is smaller
      // than the current alignment, as the known bits calculation should have
      // already taken it into account. However, this is not always the case,
      // as computeKnownBits() has a depth limit, while stripPointerCasts()
      // doesn't.
      Align CurrentAlign = AI->getAlign();
      if (PrefAlign <= CurrentAlign)
        return CurrentAlign;
  
      // If the preferred alignment is greater than the natural stack alignment
      // then don't round up. This avoids dynamic stack realignment.
      if (DL.exceedsNaturalStackAlignment(PrefAlign))
        return CurrentAlign;
      AI->setAlignment(PrefAlign);
      return PrefAlign;
    }
  
    if (auto *GO = dyn_cast<GlobalObject>(V)) {
      // TODO: as above, this shouldn't be necessary.
      Align CurrentAlign = GO->getPointerAlignment(DL);
      if (PrefAlign <= CurrentAlign)
        return CurrentAlign;
  
      // If there is a large requested alignment and we can, bump up the alignment
      // of the global.  If the memory we set aside for the global may not be the
      // memory used by the final program then it is impossible for us to reliably
      // enforce the preferred alignment.
      if (!GO->canIncreaseAlignment())
        return CurrentAlign;
  
      GO->setAlignment(PrefAlign);
      return PrefAlign;
    }
  
    return Align(1);
  }
  
  Align llvm::getOrEnforceKnownAlignment(Value *V, MaybeAlign PrefAlign,
                                         const DataLayout &DL,
                                         const Instruction *CxtI,
                                         AssumptionCache *AC,
                                         const DominatorTree *DT) {
    assert(V->getType()->isPointerTy() &&
           "getOrEnforceKnownAlignment expects a pointer!");
  
    KnownBits Known = computeKnownBits(V, DL, 0, AC, CxtI, DT);
    unsigned TrailZ = Known.countMinTrailingZeros();
  
    // Avoid trouble with ridiculously large TrailZ values, such as
    // those computed from a null pointer.
    // LLVM doesn't support alignments larger than (1 << MaxAlignmentExponent).
    TrailZ = std::min(TrailZ, +Value::MaxAlignmentExponent);
  
    Align Alignment = Align(1ull << std::min(Known.getBitWidth() - 1, TrailZ));
  
    if (PrefAlign && *PrefAlign > Alignment)
      Alignment = std::max(Alignment, tryEnforceAlignment(V, *PrefAlign, DL));
  
    // We don't need to make any adjustment.
    return Alignment;
  }
  
  ///===---------------------------------------------------------------------===//
  ///  Dbg Intrinsic utilities
  ///
  
  /// See if there is a dbg.value intrinsic for DIVar for the PHI node.
  static bool PhiHasDebugValue(DILocalVariable *DIVar,
                               DIExpression *DIExpr,
                               PHINode *APN) {
    // Since we can't guarantee that the original dbg.declare instrinsic
    // is removed by LowerDbgDeclare(), we need to make sure that we are
    // not inserting the same dbg.value intrinsic over and over.
    SmallVector<DbgValueInst *, 1> DbgValues;
    findDbgValues(DbgValues, APN);
    for (auto *DVI : DbgValues) {
      assert(DVI->getValue() == APN);
      if ((DVI->getVariable() == DIVar) && (DVI->getExpression() == DIExpr))
        return true;
    }
    return false;
  }
  
  /// Check if the alloc size of \p ValTy is large enough to cover the variable
  /// (or fragment of the variable) described by \p DII.
  ///
  /// This is primarily intended as a helper for the different
  /// ConvertDebugDeclareToDebugValue functions. The dbg.declare/dbg.addr that is
  /// converted describes an alloca'd variable, so we need to use the
  /// alloc size of the value when doing the comparison. E.g. an i1 value will be
  /// identified as covering an n-bit fragment, if the store size of i1 is at
  /// least n bits.
  static bool valueCoversEntireFragment(Type *ValTy, DbgVariableIntrinsic *DII) {
    const DataLayout &DL = DII->getModule()->getDataLayout();
    uint64_t ValueSize = DL.getTypeAllocSizeInBits(ValTy);
    if (auto FragmentSize = DII->getFragmentSizeInBits())
      return ValueSize >= *FragmentSize;
    // We can't always calculate the size of the DI variable (e.g. if it is a
    // VLA). Try to use the size of the alloca that the dbg intrinsic describes
    // intead.
    if (DII->isAddressOfVariable())
      if (auto *AI = dyn_cast_or_null<AllocaInst>(DII->getVariableLocation()))
        if (auto FragmentSize = AI->getAllocationSizeInBits(DL))
          return ValueSize >= *FragmentSize;
    // Could not determine size of variable. Conservatively return false.
    return false;
  }
  
  /// Produce a DebugLoc to use for each dbg.declare/inst pair that are promoted
  /// to a dbg.value. Because no machine insts can come from debug intrinsics,
  /// only the scope and inlinedAt is significant. Zero line numbers are used in
  /// case this DebugLoc leaks into any adjacent instructions.
  static DebugLoc getDebugValueLoc(DbgVariableIntrinsic *DII, Instruction *Src) {
    // Original dbg.declare must have a location.
    DebugLoc DeclareLoc = DII->getDebugLoc();
    MDNode *Scope = DeclareLoc.getScope();
    DILocation *InlinedAt = DeclareLoc.getInlinedAt();
    // Produce an unknown location with the correct scope / inlinedAt fields.
    return DebugLoc::get(0, 0, Scope, InlinedAt);
  }
  
  /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
  /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
  void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
                                             StoreInst *SI, DIBuilder &Builder) {
    assert(DII->isAddressOfVariable());
    auto *DIVar = DII->getVariable();
    assert(DIVar && "Missing variable");
    auto *DIExpr = DII->getExpression();
    Value *DV = SI->getValueOperand();
  
    DebugLoc NewLoc = getDebugValueLoc(DII, SI);
  
    if (!valueCoversEntireFragment(DV->getType(), DII)) {
      // FIXME: If storing to a part of the variable described by the dbg.declare,
      // then we want to insert a dbg.value for the corresponding fragment.
      LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
                        << *DII << '\n');
      // For now, when there is a store to parts of the variable (but we do not
      // know which part) we insert an dbg.value instrinsic to indicate that we
      // know nothing about the variable's content.
      DV = UndefValue::get(DV->getType());
      Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, NewLoc, SI);
      return;
    }
  
    Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, NewLoc, SI);
  }
  
  /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
  /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
  void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
                                             LoadInst *LI, DIBuilder &Builder) {
    auto *DIVar = DII->getVariable();
    auto *DIExpr = DII->getExpression();
    assert(DIVar && "Missing variable");
  
    if (!valueCoversEntireFragment(LI->getType(), DII)) {
      // FIXME: If only referring to a part of the variable described by the
      // dbg.declare, then we want to insert a dbg.value for the corresponding
      // fragment.
      LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
                        << *DII << '\n');
      return;
    }
  
    DebugLoc NewLoc = getDebugValueLoc(DII, nullptr);
  
    // We are now tracking the loaded value instead of the address. In the
    // future if multi-location support is added to the IR, it might be
    // preferable to keep tracking both the loaded value and the original
    // address in case the alloca can not be elided.
    Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
        LI, DIVar, DIExpr, NewLoc, (Instruction *)nullptr);
    DbgValue->insertAfter(LI);
  }
  
  /// Inserts a llvm.dbg.value intrinsic after a phi that has an associated
  /// llvm.dbg.declare or llvm.dbg.addr intrinsic.
  void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
                                             PHINode *APN, DIBuilder &Builder) {
    auto *DIVar = DII->getVariable();
    auto *DIExpr = DII->getExpression();
    assert(DIVar && "Missing variable");
  
    if (PhiHasDebugValue(DIVar, DIExpr, APN))
      return;
  
    if (!valueCoversEntireFragment(APN->getType(), DII)) {
      // FIXME: If only referring to a part of the variable described by the
      // dbg.declare, then we want to insert a dbg.value for the corresponding
      // fragment.
      LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
                        << *DII << '\n');
      return;
    }
  
    BasicBlock *BB = APN->getParent();
    auto InsertionPt = BB->getFirstInsertionPt();
  
    DebugLoc NewLoc = getDebugValueLoc(DII, nullptr);
  
    // The block may be a catchswitch block, which does not have a valid
    // insertion point.
    // FIXME: Insert dbg.value markers in the successors when appropriate.
    if (InsertionPt != BB->end())
      Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, NewLoc, &*InsertionPt);
  }
  
  /// Determine whether this alloca is either a VLA or an array.
  static bool isArray(AllocaInst *AI) {
    return AI->isArrayAllocation() ||
           (AI->getAllocatedType() && AI->getAllocatedType()->isArrayTy());
  }
  
  /// Determine whether this alloca is a structure.
  static bool isStructure(AllocaInst *AI) {
    return AI->getAllocatedType() && AI->getAllocatedType()->isStructTy();
  }
  
  /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
  /// of llvm.dbg.value intrinsics.
  bool llvm::LowerDbgDeclare(Function &F) {
    bool Changed = false;
    DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
    SmallVector<DbgDeclareInst *, 4> Dbgs;
    for (auto &FI : F)
      for (Instruction &BI : FI)
        if (auto DDI = dyn_cast<DbgDeclareInst>(&BI))
          Dbgs.push_back(DDI);
  
    if (Dbgs.empty())
      return Changed;
  
    for (auto &I : Dbgs) {
      DbgDeclareInst *DDI = I;
      AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
      // If this is an alloca for a scalar variable, insert a dbg.value
      // at each load and store to the alloca and erase the dbg.declare.
      // The dbg.values allow tracking a variable even if it is not
      // stored on the stack, while the dbg.declare can only describe
      // the stack slot (and at a lexical-scope granularity). Later
      // passes will attempt to elide the stack slot.
      if (!AI || isArray(AI) || isStructure(AI))
        continue;
  
      // A volatile load/store means that the alloca can't be elided anyway.
      if (llvm::any_of(AI->users(), [](User *U) -> bool {
            if (LoadInst *LI = dyn_cast<LoadInst>(U))
              return LI->isVolatile();
            if (StoreInst *SI = dyn_cast<StoreInst>(U))
              return SI->isVolatile();
            return false;
          }))
        continue;
  
      SmallVector<const Value *, 8> WorkList;
      WorkList.push_back(AI);
      while (!WorkList.empty()) {
        const Value *V = WorkList.pop_back_val();
        for (auto &AIUse : V->uses()) {
          User *U = AIUse.getUser();
          if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
            if (AIUse.getOperandNo() == 1)
              ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
          } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
            ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
          } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
            // This is a call by-value or some other instruction that takes a
            // pointer to the variable. Insert a *value* intrinsic that describes
            // the variable by dereferencing the alloca.
            if (!CI->isLifetimeStartOrEnd()) {
              DebugLoc NewLoc = getDebugValueLoc(DDI, nullptr);
              auto *DerefExpr =
                  DIExpression::append(DDI->getExpression(), dwarf::DW_OP_deref);
              DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(), DerefExpr,
                                          NewLoc, CI);
            }
          } else if (BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
            if (BI->getType()->isPointerTy())
              WorkList.push_back(BI);
          }
        }
      }
      DDI->eraseFromParent();
      Changed = true;
    }
  
    if (Changed)
    for (BasicBlock &BB : F)
      RemoveRedundantDbgInstrs(&BB);
  
    return Changed;
  }
  
  /// Propagate dbg.value intrinsics through the newly inserted PHIs.
  void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
                                      SmallVectorImpl<PHINode *> &InsertedPHIs) {
    assert(BB && "No BasicBlock to clone dbg.value(s) from.");
    if (InsertedPHIs.size() == 0)
      return;
  
    // Map existing PHI nodes to their dbg.values.
    ValueToValueMapTy DbgValueMap;
    for (auto &I : *BB) {
      if (auto DbgII = dyn_cast<DbgVariableIntrinsic>(&I)) {
        if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
          DbgValueMap.insert({Loc, DbgII});
      }
    }
    if (DbgValueMap.size() == 0)
      return;
  
    // Then iterate through the new PHIs and look to see if they use one of the
    // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
    // propagate the info through the new PHI.
    LLVMContext &C = BB->getContext();
    for (auto PHI : InsertedPHIs) {
      BasicBlock *Parent = PHI->getParent();
      // Avoid inserting an intrinsic into an EH block.
      if (Parent->getFirstNonPHI()->isEHPad())
        continue;
      auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
      for (auto VI : PHI->operand_values()) {
        auto V = DbgValueMap.find(VI);
        if (V != DbgValueMap.end()) {
          auto *DbgII = cast<DbgVariableIntrinsic>(V->second);
          Instruction *NewDbgII = DbgII->clone();
          NewDbgII->setOperand(0, PhiMAV);
          auto InsertionPt = Parent->getFirstInsertionPt();
          assert(InsertionPt != Parent->end() && "Ill-formed basic block");
          NewDbgII->insertBefore(&*InsertionPt);
        }
      }
    }
  }
  
  /// Finds all intrinsics declaring local variables as living in the memory that
  /// 'V' points to. This may include a mix of dbg.declare and
  /// dbg.addr intrinsics.
  TinyPtrVector<DbgVariableIntrinsic *> llvm::FindDbgAddrUses(Value *V) {
    // This function is hot. Check whether the value has any metadata to avoid a
    // DenseMap lookup.
    if (!V->isUsedByMetadata())
      return {};
    auto *L = LocalAsMetadata::getIfExists(V);
    if (!L)
      return {};
    auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L);
    if (!MDV)
      return {};
  
    TinyPtrVector<DbgVariableIntrinsic *> Declares;
    for (User *U : MDV->users()) {
      if (auto *DII = dyn_cast<DbgVariableIntrinsic>(U))
        if (DII->isAddressOfVariable())
          Declares.push_back(DII);
    }
  
    return Declares;
  }
  
  TinyPtrVector<DbgDeclareInst *> llvm::FindDbgDeclareUses(Value *V) {
    TinyPtrVector<DbgDeclareInst *> DDIs;
    for (DbgVariableIntrinsic *DVI : FindDbgAddrUses(V))
      if (auto *DDI = dyn_cast<DbgDeclareInst>(DVI))
        DDIs.push_back(DDI);
    return DDIs;
  }
  
  void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
    // This function is hot. Check whether the value has any metadata to avoid a
    // DenseMap lookup.
    if (!V->isUsedByMetadata())
      return;
    if (auto *L = LocalAsMetadata::getIfExists(V))
      if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
        for (User *U : MDV->users())
          if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
            DbgValues.push_back(DVI);
  }
  
  void llvm::findDbgUsers(SmallVectorImpl<DbgVariableIntrinsic *> &DbgUsers,
                          Value *V) {
    // This function is hot. Check whether the value has any metadata to avoid a
    // DenseMap lookup.
    if (!V->isUsedByMetadata())
      return;
    if (auto *L = LocalAsMetadata::getIfExists(V))
      if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
        for (User *U : MDV->users())
          if (DbgVariableIntrinsic *DII = dyn_cast<DbgVariableIntrinsic>(U))
            DbgUsers.push_back(DII);
  }
  
  bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
                               DIBuilder &Builder, uint8_t DIExprFlags,
                               int Offset) {
    auto DbgAddrs = FindDbgAddrUses(Address);
    for (DbgVariableIntrinsic *DII : DbgAddrs) {
      DebugLoc Loc = DII->getDebugLoc();
      auto *DIVar = DII->getVariable();
      auto *DIExpr = DII->getExpression();
      assert(DIVar && "Missing variable");
      DIExpr = DIExpression::prepend(DIExpr, DIExprFlags, Offset);
      // Insert llvm.dbg.declare immediately before DII, and remove old
      // llvm.dbg.declare.
      Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, DII);
      DII->eraseFromParent();
    }
    return !DbgAddrs.empty();
  }
  
  static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
                                          DIBuilder &Builder, int Offset) {
    DebugLoc Loc = DVI->getDebugLoc();
    auto *DIVar = DVI->getVariable();
    auto *DIExpr = DVI->getExpression();
    assert(DIVar && "Missing variable");
  
    // This is an alloca-based llvm.dbg.value. The first thing it should do with
    // the alloca pointer is dereference it. Otherwise we don't know how to handle
    // it and give up.
    if (!DIExpr || DIExpr->getNumElements() < 1 ||
        DIExpr->getElement(0) != dwarf::DW_OP_deref)
      return;
  
    // Insert the offset before the first deref.
    // We could just change the offset argument of dbg.value, but it's unsigned...
    if (Offset)
      DIExpr = DIExpression::prepend(DIExpr, 0, Offset);
  
    Builder.insertDbgValueIntrinsic(NewAddress, DIVar, DIExpr, Loc, DVI);
    DVI->eraseFromParent();
  }
  
  void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
                                      DIBuilder &Builder, int Offset) {
    if (auto *L = LocalAsMetadata::getIfExists(AI))
      if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
        for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) {
          Use &U = *UI++;
          if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser()))
            replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset);
        }
  }
  
  /// Wrap \p V in a ValueAsMetadata instance.
  static MetadataAsValue *wrapValueInMetadata(LLVMContext &C, Value *V) {
    return MetadataAsValue::get(C, ValueAsMetadata::get(V));
  }
  
  /// Where possible to salvage debug information for \p I do so
  /// and return True. If not possible mark undef and return False.
  void llvm::salvageDebugInfo(Instruction &I) {
    SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
    findDbgUsers(DbgUsers, &I);
    salvageDebugInfoForDbgValues(I, DbgUsers);
  }
  
  void llvm::salvageDebugInfoForDbgValues(
      Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
    auto &Ctx = I.getContext();
    bool Salvaged = false;
    auto wrapMD = [&](Value *V) { return wrapValueInMetadata(Ctx, V); };
  
    for (auto *DII : DbgUsers) {
      // Do not add DW_OP_stack_value for DbgDeclare and DbgAddr, because they
      // are implicitly pointing out the value as a DWARF memory location
      // description.
      bool StackValue = isa<DbgValueInst>(DII);
  
      DIExpression *DIExpr =
          salvageDebugInfoImpl(I, DII->getExpression(), StackValue);
  
      // salvageDebugInfoImpl should fail on examining the first element of
      // DbgUsers, or none of them.
      if (!DIExpr)
        break;
  
      DII->setOperand(0, wrapMD(I.getOperand(0)));
      DII->setOperand(2, MetadataAsValue::get(Ctx, DIExpr));
      LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
      Salvaged = true;
    }
  
    if (Salvaged)
      return;
  
    for (auto *DII : DbgUsers) {
      Value *Undef = UndefValue::get(I.getType());
      DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
                                              ValueAsMetadata::get(Undef)));
    }
  }
  
  DIExpression *llvm::salvageDebugInfoImpl(Instruction &I,
                                           DIExpression *SrcDIExpr,
                                           bool WithStackValue) {
    auto &M = *I.getModule();
    auto &DL = M.getDataLayout();
  
    // Apply a vector of opcodes to the source DIExpression.
    auto doSalvage = [&](SmallVectorImpl<uint64_t> &Ops) -> DIExpression * {
      DIExpression *DIExpr = SrcDIExpr;
      if (!Ops.empty()) {
        DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
      }
      return DIExpr;
    };
  
    // Apply the given offset to the source DIExpression.
    auto applyOffset = [&](uint64_t Offset) -> DIExpression * {
      SmallVector<uint64_t, 8> Ops;
      DIExpression::appendOffset(Ops, Offset);
      return doSalvage(Ops);
    };
  
    // initializer-list helper for applying operators to the source DIExpression.
    auto applyOps = [&](ArrayRef<uint64_t> Opcodes) -> DIExpression * {
      SmallVector<uint64_t, 8> Ops(Opcodes.begin(), Opcodes.end());
      return doSalvage(Ops);
    };
  
    if (auto *CI = dyn_cast<CastInst>(&I)) {
      // No-op casts are irrelevant for debug info.
      if (CI->isNoopCast(DL))
        return SrcDIExpr;
  
      Type *Type = CI->getType();
      // Casts other than Trunc, SExt, or ZExt to scalar types cannot be salvaged.
      if (Type->isVectorTy() ||
          !(isa<TruncInst>(&I) || isa<SExtInst>(&I) || isa<ZExtInst>(&I)))
        return nullptr;
  
      Value *FromValue = CI->getOperand(0);
      unsigned FromTypeBitSize = FromValue->getType()->getScalarSizeInBits();
      unsigned ToTypeBitSize = Type->getScalarSizeInBits();
  
      return applyOps(DIExpression::getExtOps(FromTypeBitSize, ToTypeBitSize,
                                              isa<SExtInst>(&I)));
    }
  
    if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
      unsigned BitWidth =
          M.getDataLayout().getIndexSizeInBits(GEP->getPointerAddressSpace());
      // Rewrite a constant GEP into a DIExpression.
      APInt Offset(BitWidth, 0);
      if (GEP->accumulateConstantOffset(M.getDataLayout(), Offset)) {
        return applyOffset(Offset.getSExtValue());
      } else {
        return nullptr;
      }
    } else if (auto *BI = dyn_cast<BinaryOperator>(&I)) {
      // Rewrite binary operations with constant integer operands.
      auto *ConstInt = dyn_cast<ConstantInt>(I.getOperand(1));
      if (!ConstInt || ConstInt->getBitWidth() > 64)
        return nullptr;
  
      uint64_t Val = ConstInt->getSExtValue();
      switch (BI->getOpcode()) {
      case Instruction::Add:
        return applyOffset(Val);
      case Instruction::Sub:
        return applyOffset(-int64_t(Val));
      case Instruction::Mul:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_mul});
      case Instruction::SDiv:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_div});
      case Instruction::SRem:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_mod});
      case Instruction::Or:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_or});
      case Instruction::And:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_and});
      case Instruction::Xor:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_xor});
      case Instruction::Shl:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shl});
      case Instruction::LShr:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shr});
      case Instruction::AShr:
        return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shra});
      default:
        // TODO: Salvage constants from each kind of binop we know about.
        return nullptr;
      }
      // *Not* to do: we should not attempt to salvage load instructions,
      // because the validity and lifetime of a dbg.value containing
      // DW_OP_deref becomes difficult to analyze. See PR40628 for examples.
    }
    return nullptr;
  }
  
  /// A replacement for a dbg.value expression.
  using DbgValReplacement = Optional<DIExpression *>;
  
  /// Point debug users of \p From to \p To using exprs given by \p RewriteExpr,
  /// possibly moving/undefing users to prevent use-before-def. Returns true if
  /// changes are made.
  static bool rewriteDebugUsers(
      Instruction &From, Value &To, Instruction &DomPoint, DominatorTree &DT,
      function_ref<DbgValReplacement(DbgVariableIntrinsic &DII)> RewriteExpr) {
    // Find debug users of From.
    SmallVector<DbgVariableIntrinsic *, 1> Users;
    findDbgUsers(Users, &From);
    if (Users.empty())
      return false;
  
    // Prevent use-before-def of To.
    bool Changed = false;
    SmallPtrSet<DbgVariableIntrinsic *, 1> UndefOrSalvage;
    if (isa<Instruction>(&To)) {
      bool DomPointAfterFrom = From.getNextNonDebugInstruction() == &DomPoint;
  
      for (auto *DII : Users) {
        // It's common to see a debug user between From and DomPoint. Move it
        // after DomPoint to preserve the variable update without any reordering.
        if (DomPointAfterFrom && DII->getNextNonDebugInstruction() == &DomPoint) {
          LLVM_DEBUG(dbgs() << "MOVE:  " << *DII << '\n');
          DII->moveAfter(&DomPoint);
          Changed = true;
  
        // Users which otherwise aren't dominated by the replacement value must
        // be salvaged or deleted.
        } else if (!DT.dominates(&DomPoint, DII)) {
          UndefOrSalvage.insert(DII);
        }
      }
    }
  
    // Update debug users without use-before-def risk.
    for (auto *DII : Users) {
      if (UndefOrSalvage.count(DII))
        continue;
  
      LLVMContext &Ctx = DII->getContext();
      DbgValReplacement DVR = RewriteExpr(*DII);
      if (!DVR)
        continue;
  
      DII->setOperand(0, wrapValueInMetadata(Ctx, &To));
      DII->setOperand(2, MetadataAsValue::get(Ctx, *DVR));
      LLVM_DEBUG(dbgs() << "REWRITE:  " << *DII << '\n');
      Changed = true;
    }
  
    if (!UndefOrSalvage.empty()) {
      // Try to salvage the remaining debug users.
      salvageDebugInfo(From);
      Changed = true;
    }
  
    return Changed;
  }
  
  /// Check if a bitcast between a value of type \p FromTy to type \p ToTy would
  /// losslessly preserve the bits and semantics of the value. This predicate is
  /// symmetric, i.e swapping \p FromTy and \p ToTy should give the same result.
  ///
  /// Note that Type::canLosslesslyBitCastTo is not suitable here because it
  /// allows semantically unequivalent bitcasts, such as <2 x i64> -> <4 x i32>,
  /// and also does not allow lossless pointer <-> integer conversions.
  static bool isBitCastSemanticsPreserving(const DataLayout &DL, Type *FromTy,
                                           Type *ToTy) {
    // Trivially compatible types.
    if (FromTy == ToTy)
      return true;
  
    // Handle compatible pointer <-> integer conversions.
    if (FromTy->isIntOrPtrTy() && ToTy->isIntOrPtrTy()) {
      bool SameSize = DL.getTypeSizeInBits(FromTy) == DL.getTypeSizeInBits(ToTy);
      bool LosslessConversion = !DL.isNonIntegralPointerType(FromTy) &&
                                !DL.isNonIntegralPointerType(ToTy);
      return SameSize && LosslessConversion;
    }
  
    // TODO: This is not exhaustive.
    return false;
  }
  
  bool llvm::replaceAllDbgUsesWith(Instruction &From, Value &To,
                                   Instruction &DomPoint, DominatorTree &DT) {
    // Exit early if From has no debug users.
    if (!From.isUsedByMetadata())
      return false;
  
    assert(&From != &To && "Can't replace something with itself");
  
    Type *FromTy = From.getType();
    Type *ToTy = To.getType();
  
    auto Identity = [&](DbgVariableIntrinsic &DII) -> DbgValReplacement {
      return DII.getExpression();
    };
  
    // Handle no-op conversions.
    Module &M = *From.getModule();
    const DataLayout &DL = M.getDataLayout();
    if (isBitCastSemanticsPreserving(DL, FromTy, ToTy))
      return rewriteDebugUsers(From, To, DomPoint, DT, Identity);
  
    // Handle integer-to-integer widening and narrowing.
    // FIXME: Use DW_OP_convert when it's available everywhere.
    if (FromTy->isIntegerTy() && ToTy->isIntegerTy()) {
      uint64_t FromBits = FromTy->getPrimitiveSizeInBits();
      uint64_t ToBits = ToTy->getPrimitiveSizeInBits();
      assert(FromBits != ToBits && "Unexpected no-op conversion");
  
      // When the width of the result grows, assume that a debugger will only
      // access the low `FromBits` bits when inspecting the source variable.
      if (FromBits < ToBits)
        return rewriteDebugUsers(From, To, DomPoint, DT, Identity);
  
      // The width of the result has shrunk. Use sign/zero extension to describe
      // the source variable's high bits.
      auto SignOrZeroExt = [&](DbgVariableIntrinsic &DII) -> DbgValReplacement {
        DILocalVariable *Var = DII.getVariable();
  
        // Without knowing signedness, sign/zero extension isn't possible.
        auto Signedness = Var->getSignedness();
        if (!Signedness)
          return None;
  
        bool Signed = *Signedness == DIBasicType::Signedness::Signed;
        return DIExpression::appendExt(DII.getExpression(), ToBits, FromBits,
                                       Signed);
      };
      return rewriteDebugUsers(From, To, DomPoint, DT, SignOrZeroExt);
    }
  
    // TODO: Floating-point conversions, vectors.
    return false;
  }
  
  std::pair<unsigned, unsigned>
  llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
    unsigned NumDeadInst = 0;
    unsigned NumDeadDbgInst = 0;
    // Delete the instructions backwards, as it has a reduced likelihood of
    // having to update as many def-use and use-def chains.
    Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
    while (EndInst != &BB->front()) {
      // Delete the next to last instruction.
      Instruction *Inst = &*--EndInst->getIterator();
      if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
        Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
      if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
        EndInst = Inst;
        continue;
      }
      if (isa<DbgInfoIntrinsic>(Inst))
        ++NumDeadDbgInst;
      else
        ++NumDeadInst;
      Inst->eraseFromParent();
    }
    return {NumDeadInst, NumDeadDbgInst};
  }
  
  unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap,
                                     bool PreserveLCSSA, DomTreeUpdater *DTU,
                                     MemorySSAUpdater *MSSAU) {
    BasicBlock *BB = I->getParent();
    std::vector <DominatorTree::UpdateType> Updates;
  
    if (MSSAU)
      MSSAU->changeToUnreachable(I);
  
    // Loop over all of the successors, removing BB's entry from any PHI
    // nodes.
    if (DTU)
      Updates.reserve(BB->getTerminator()->getNumSuccessors());
    for (BasicBlock *Successor : successors(BB)) {
      Successor->removePredecessor(BB, PreserveLCSSA);
      if (DTU)
        Updates.push_back({DominatorTree::Delete, BB, Successor});
    }
    // Insert a call to llvm.trap right before this.  This turns the undefined
    // behavior into a hard fail instead of falling through into random code.
    if (UseLLVMTrap) {
      Function *TrapFn =
        Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
      CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
      CallTrap->setDebugLoc(I->getDebugLoc());
    }
    auto *UI = new UnreachableInst(I->getContext(), I);
    UI->setDebugLoc(I->getDebugLoc());
  
    // All instructions after this are dead.
    unsigned NumInstrsRemoved = 0;
    BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end();
    while (BBI != BBE) {
      if (!BBI->use_empty())
        BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
      BB->getInstList().erase(BBI++);
      ++NumInstrsRemoved;
    }
    if (DTU)
      DTU->applyUpdatesPermissive(Updates);
    return NumInstrsRemoved;
  }
  
  CallInst *llvm::createCallMatchingInvoke(InvokeInst *II) {
    SmallVector<Value *, 8> Args(II->arg_begin(), II->arg_end());
    SmallVector<OperandBundleDef, 1> OpBundles;
    II->getOperandBundlesAsDefs(OpBundles);
    CallInst *NewCall = CallInst::Create(II->getFunctionType(),
                                         II->getCalledOperand(), Args, OpBundles);
    NewCall->setCallingConv(II->getCallingConv());
    NewCall->setAttributes(II->getAttributes());
    NewCall->setDebugLoc(II->getDebugLoc());
    NewCall->copyMetadata(*II);
  
    // If the invoke had profile metadata, try converting them for CallInst.
    uint64_t TotalWeight;
    if (NewCall->extractProfTotalWeight(TotalWeight)) {
      // Set the total weight if it fits into i32, otherwise reset.
      MDBuilder MDB(NewCall->getContext());
      auto NewWeights = uint32_t(TotalWeight) != TotalWeight
                            ? nullptr
                            : MDB.createBranchWeights({uint32_t(TotalWeight)});
      NewCall->setMetadata(LLVMContext::MD_prof, NewWeights);
    }
  
    return NewCall;
  }
  
  /// changeToCall - Convert the specified invoke into a normal call.
  void llvm::changeToCall(InvokeInst *II, DomTreeUpdater *DTU) {
    CallInst *NewCall = createCallMatchingInvoke(II);
    NewCall->takeName(II);
    NewCall->insertBefore(II);
    II->replaceAllUsesWith(NewCall);
  
    // Follow the call by a branch to the normal destination.
    BasicBlock *NormalDestBB = II->getNormalDest();
    BranchInst::Create(NormalDestBB, II);
  
    // Update PHI nodes in the unwind destination
    BasicBlock *BB = II->getParent();
    BasicBlock *UnwindDestBB = II->getUnwindDest();
    UnwindDestBB->removePredecessor(BB);
    II->eraseFromParent();
    if (DTU)
      DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, UnwindDestBB}});
  }
  
  BasicBlock *llvm::changeToInvokeAndSplitBasicBlock(CallInst *CI,
                                                     BasicBlock *UnwindEdge) {
    BasicBlock *BB = CI->getParent();
  
    // Convert this function call into an invoke instruction.  First, split the
    // basic block.
    BasicBlock *Split =
        BB->splitBasicBlock(CI->getIterator(), CI->getName() + ".noexc");
  
    // Delete the unconditional branch inserted by splitBasicBlock
    BB->getInstList().pop_back();
  
    // Create the new invoke instruction.
    SmallVector<Value *, 8> InvokeArgs(CI->arg_begin(), CI->arg_end());
    SmallVector<OperandBundleDef, 1> OpBundles;
  
    CI->getOperandBundlesAsDefs(OpBundles);
  
    // Note: we're round tripping operand bundles through memory here, and that
    // can potentially be avoided with a cleverer API design that we do not have
    // as of this time.
  
    InvokeInst *II =
        InvokeInst::Create(CI->getFunctionType(), CI->getCalledOperand(), Split,
                           UnwindEdge, InvokeArgs, OpBundles, CI->getName(), BB);
    II->setDebugLoc(CI->getDebugLoc());
    II->setCallingConv(CI->getCallingConv());
    II->setAttributes(CI->getAttributes());
  
    // Make sure that anything using the call now uses the invoke!  This also
    // updates the CallGraph if present, because it uses a WeakTrackingVH.
    CI->replaceAllUsesWith(II);
  
    // Delete the original call
    Split->getInstList().pop_front();
    return Split;
  }
  
  static bool markAliveBlocks(Function &F,
                              SmallPtrSetImpl<BasicBlock *> &Reachable,
                              DomTreeUpdater *DTU = nullptr) {
    SmallVector<BasicBlock*, 128> Worklist;
    BasicBlock *BB = &F.front();
    Worklist.push_back(BB);
    Reachable.insert(BB);
    bool Changed = false;
    do {
      BB = Worklist.pop_back_val();
  
      // Do a quick scan of the basic block, turning any obviously unreachable
      // instructions into LLVM unreachable insts.  The instruction combining pass
      // canonicalizes unreachable insts into stores to null or undef.
      for (Instruction &I : *BB) {
        if (auto *CI = dyn_cast<CallInst>(&I)) {
          Value *Callee = CI->getCalledOperand();
          // Handle intrinsic calls.
          if (Function *F = dyn_cast<Function>(Callee)) {
            auto IntrinsicID = F->getIntrinsicID();
            // Assumptions that are known to be false are equivalent to
            // unreachable. Also, if the condition is undefined, then we make the
            // choice most beneficial to the optimizer, and choose that to also be
            // unreachable.
            if (IntrinsicID == Intrinsic::assume) {
              if (match(CI->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) {
                // Don't insert a call to llvm.trap right before the unreachable.
                changeToUnreachable(CI, false, false, DTU);
                Changed = true;
                break;
              }
            } else if (IntrinsicID == Intrinsic::experimental_guard) {
              // A call to the guard intrinsic bails out of the current
              // compilation unit if the predicate passed to it is false. If the
              // predicate is a constant false, then we know the guard will bail
              // out of the current compile unconditionally, so all code following
              // it is dead.
              //
              // Note: unlike in llvm.assume, it is not "obviously profitable" for
              // guards to treat `undef` as `false` since a guard on `undef` can
              // still be useful for widening.
              if (match(CI->getArgOperand(0), m_Zero()))
                if (!isa<UnreachableInst>(CI->getNextNode())) {
                  changeToUnreachable(CI->getNextNode(), /*UseLLVMTrap=*/false,
                                      false, DTU);
                  Changed = true;
                  break;
                }
            }
          } else if ((isa<ConstantPointerNull>(Callee) &&
                      !NullPointerIsDefined(CI->getFunction())) ||
                     isa<UndefValue>(Callee)) {
            changeToUnreachable(CI, /*UseLLVMTrap=*/false, false, DTU);
            Changed = true;
            break;
          }
          if (CI->doesNotReturn() && !CI->isMustTailCall()) {
            // If we found a call to a no-return function, insert an unreachable
            // instruction after it.  Make sure there isn't *already* one there
            // though.
            if (!isa<UnreachableInst>(CI->getNextNode())) {
              // Don't insert a call to llvm.trap right before the unreachable.
              changeToUnreachable(CI->getNextNode(), false, false, DTU);
              Changed = true;
            }
            break;
          }
        } else if (auto *SI = dyn_cast<StoreInst>(&I)) {
          // Store to undef and store to null are undefined and used to signal
          // that they should be changed to unreachable by passes that can't
          // modify the CFG.
  
          // Don't touch volatile stores.
          if (SI->isVolatile()) continue;
  
          Value *Ptr = SI->getOperand(1);
  
          if (isa<UndefValue>(Ptr) ||
              (isa<ConstantPointerNull>(Ptr) &&
               !NullPointerIsDefined(SI->getFunction(),
                                     SI->getPointerAddressSpace()))) {
            changeToUnreachable(SI, true, false, DTU);
            Changed = true;
            break;
          }
        }
      }
  
      Instruction *Terminator = BB->getTerminator();
      if (auto *II = dyn_cast<InvokeInst>(Terminator)) {
        // Turn invokes that call 'nounwind' functions into ordinary calls.
        Value *Callee = II->getCalledOperand();
        if ((isa<ConstantPointerNull>(Callee) &&
             !NullPointerIsDefined(BB->getParent())) ||
            isa<UndefValue>(Callee)) {
          changeToUnreachable(II, true, false, DTU);
          Changed = true;
        } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
          if (II->use_empty() && II->onlyReadsMemory()) {
            // jump to the normal destination branch.
            BasicBlock *NormalDestBB = II->getNormalDest();
            BasicBlock *UnwindDestBB = II->getUnwindDest();
            BranchInst::Create(NormalDestBB, II);
            UnwindDestBB->removePredecessor(II->getParent());
            II->eraseFromParent();
            if (DTU)
              DTU->applyUpdatesPermissive(
                  {{DominatorTree::Delete, BB, UnwindDestBB}});
          } else
            changeToCall(II, DTU);
          Changed = true;
        }
      } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
        // Remove catchpads which cannot be reached.
        struct CatchPadDenseMapInfo {
          static CatchPadInst *getEmptyKey() {
            return DenseMapInfo<CatchPadInst *>::getEmptyKey();
          }
  
          static CatchPadInst *getTombstoneKey() {
            return DenseMapInfo<CatchPadInst *>::getTombstoneKey();
          }
  
          static unsigned getHashValue(CatchPadInst *CatchPad) {
            return static_cast<unsigned>(hash_combine_range(
                CatchPad->value_op_begin(), CatchPad->value_op_end()));
          }
  
          static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) {
            if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
                RHS == getEmptyKey() || RHS == getTombstoneKey())
              return LHS == RHS;
            return LHS->isIdenticalTo(RHS);
          }
        };
  
        // Set of unique CatchPads.
        SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
                      CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
            HandlerSet;
        detail::DenseSetEmpty Empty;
        for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(),
                                               E = CatchSwitch->handler_end();
             I != E; ++I) {
          BasicBlock *HandlerBB = *I;
          auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
          if (!HandlerSet.insert({CatchPad, Empty}).second) {
            CatchSwitch->removeHandler(I);
            --I;
            --E;
            Changed = true;
          }
        }
      }
  
      Changed |= ConstantFoldTerminator(BB, true, nullptr, DTU);
      for (BasicBlock *Successor : successors(BB))
        if (Reachable.insert(Successor).second)
          Worklist.push_back(Successor);
    } while (!Worklist.empty());
    return Changed;
  }
  
  void llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
    Instruction *TI = BB->getTerminator();
  
    if (auto *II = dyn_cast<InvokeInst>(TI)) {
      changeToCall(II, DTU);
      return;
    }
  
    Instruction *NewTI;
    BasicBlock *UnwindDest;
  
    if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
      NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
      UnwindDest = CRI->getUnwindDest();
    } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
      auto *NewCatchSwitch = CatchSwitchInst::Create(
          CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
          CatchSwitch->getName(), CatchSwitch);
      for (BasicBlock *PadBB : CatchSwitch->handlers())
        NewCatchSwitch->addHandler(PadBB);
  
      NewTI = NewCatchSwitch;
      UnwindDest = CatchSwitch->getUnwindDest();
    } else {
      llvm_unreachable("Could not find unwind successor");
    }
  
    NewTI->takeName(TI);
    NewTI->setDebugLoc(TI->getDebugLoc());
    UnwindDest->removePredecessor(BB);
    TI->replaceAllUsesWith(NewTI);
    TI->eraseFromParent();
    if (DTU)
      DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, UnwindDest}});
  }
  
  /// removeUnreachableBlocks - Remove blocks that are not reachable, even
  /// if they are in a dead cycle.  Return true if a change was made, false
  /// otherwise.
  bool llvm::removeUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
                                     MemorySSAUpdater *MSSAU) {
    SmallPtrSet<BasicBlock *, 16> Reachable;
    bool Changed = markAliveBlocks(F, Reachable, DTU);
  
    // If there are unreachable blocks in the CFG...
    if (Reachable.size() == F.size())
      return Changed;
  
    assert(Reachable.size() < F.size());
    NumRemoved += F.size() - Reachable.size();
  
    SmallSetVector<BasicBlock *, 8> DeadBlockSet;
    for (BasicBlock &BB : F) {
      // Skip reachable basic blocks
      if (Reachable.count(&BB))
        continue;
      DeadBlockSet.insert(&BB);
    }
  
    if (MSSAU)
      MSSAU->removeBlocks(DeadBlockSet);
  
    // Loop over all of the basic blocks that are not reachable, dropping all of
    // their internal references. Update DTU if available.
    std::vector<DominatorTree::UpdateType> Updates;
    for (auto *BB : DeadBlockSet) {
      for (BasicBlock *Successor : successors(BB)) {
        if (!DeadBlockSet.count(Successor))
          Successor->removePredecessor(BB);
        if (DTU)
          Updates.push_back({DominatorTree::Delete, BB, Successor});
      }
      BB->dropAllReferences();
      if (DTU) {
        Instruction *TI = BB->getTerminator();
        assert(TI && "Basic block should have a terminator");
        // Terminators like invoke can have users. We have to replace their users,
        // before removing them.
        if (!TI->use_empty())
          TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
        TI->eraseFromParent();
        new UnreachableInst(BB->getContext(), BB);
        assert(succ_empty(BB) && "The successor list of BB isn't empty before "
                                 "applying corresponding DTU updates.");
      }
    }
  
    if (DTU) {
      DTU->applyUpdatesPermissive(Updates);
      bool Deleted = false;
      for (auto *BB : DeadBlockSet) {
        if (DTU->isBBPendingDeletion(BB))
          --NumRemoved;
        else
          Deleted = true;
        DTU->deleteBB(BB);
      }
      if (!Deleted)
        return false;
    } else {
      for (auto *BB : DeadBlockSet)
        BB->eraseFromParent();
    }
  
    return true;
  }
  
  void llvm::combineMetadata(Instruction *K, const Instruction *J,
                             ArrayRef<unsigned> KnownIDs, bool DoesKMove) {
    SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
    K->dropUnknownNonDebugMetadata(KnownIDs);
    K->getAllMetadataOtherThanDebugLoc(Metadata);
    for (const auto &MD : Metadata) {
      unsigned Kind = MD.first;
      MDNode *JMD = J->getMetadata(Kind);
      MDNode *KMD = MD.second;
  
      switch (Kind) {
        default:
          K->setMetadata(Kind, nullptr); // Remove unknown metadata
          break;
        case LLVMContext::MD_dbg:
          llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
        case LLVMContext::MD_tbaa:
          K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
          break;
        case LLVMContext::MD_alias_scope:
          K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
          break;
        case LLVMContext::MD_noalias:
        case LLVMContext::MD_mem_parallel_loop_access:
          K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
          break;
        case LLVMContext::MD_access_group:
          K->setMetadata(LLVMContext::MD_access_group,
                         intersectAccessGroups(K, J));
          break;
        case LLVMContext::MD_range:
  
          // If K does move, use most generic range. Otherwise keep the range of
          // K.
          if (DoesKMove)
            // FIXME: If K does move, we should drop the range info and nonnull.
            //        Currently this function is used with DoesKMove in passes
            //        doing hoisting/sinking and the current behavior of using the
            //        most generic range is correct in those cases.
            K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
          break;
        case LLVMContext::MD_fpmath:
          K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
          break;
        case LLVMContext::MD_invariant_load:
          // Only set the !invariant.load if it is present in both instructions.
          K->setMetadata(Kind, JMD);
          break;
        case LLVMContext::MD_nonnull:
          // If K does move, keep nonull if it is present in both instructions.
          if (DoesKMove)
            K->setMetadata(Kind, JMD);
          break;
        case LLVMContext::MD_invariant_group:
          // Preserve !invariant.group in K.
          break;
        case LLVMContext::MD_align:
          K->setMetadata(Kind,
            MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
          break;
        case LLVMContext::MD_dereferenceable:
        case LLVMContext::MD_dereferenceable_or_null:
          K->setMetadata(Kind,
            MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
          break;
        case LLVMContext::MD_preserve_access_index:
          // Preserve !preserve.access.index in K.
          break;
      }
    }
    // Set !invariant.group from J if J has it. If both instructions have it
    // then we will just pick it from J - even when they are different.
    // Also make sure that K is load or store - f.e. combining bitcast with load
    // could produce bitcast with invariant.group metadata, which is invalid.
    // FIXME: we should try to preserve both invariant.group md if they are
    // different, but right now instruction can only have one invariant.group.
    if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
      if (isa<LoadInst>(K) || isa<StoreInst>(K))
        K->setMetadata(LLVMContext::MD_invariant_group, JMD);
  }
  
  void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
                                   bool KDominatesJ) {
    unsigned KnownIDs[] = {
        LLVMContext::MD_tbaa,            LLVMContext::MD_alias_scope,
        LLVMContext::MD_noalias,         LLVMContext::MD_range,
        LLVMContext::MD_invariant_load,  LLVMContext::MD_nonnull,
        LLVMContext::MD_invariant_group, LLVMContext::MD_align,
        LLVMContext::MD_dereferenceable,
        LLVMContext::MD_dereferenceable_or_null,
        LLVMContext::MD_access_group,    LLVMContext::MD_preserve_access_index};
    combineMetadata(K, J, KnownIDs, KDominatesJ);
  }
  
  void llvm::copyMetadataForLoad(LoadInst &Dest, const LoadInst &Source) {
    SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
    Source.getAllMetadata(MD);
    MDBuilder MDB(Dest.getContext());
    Type *NewType = Dest.getType();
    const DataLayout &DL = Source.getModule()->getDataLayout();
    for (const auto &MDPair : MD) {
      unsigned ID = MDPair.first;
      MDNode *N = MDPair.second;
      // Note, essentially every kind of metadata should be preserved here! This
      // routine is supposed to clone a load instruction changing *only its type*.
      // The only metadata it makes sense to drop is metadata which is invalidated
      // when the pointer type changes. This should essentially never be the case
      // in LLVM, but we explicitly switch over only known metadata to be
      // conservatively correct. If you are adding metadata to LLVM which pertains
      // to loads, you almost certainly want to add it here.
      switch (ID) {
      case LLVMContext::MD_dbg:
      case LLVMContext::MD_tbaa:
      case LLVMContext::MD_prof:
      case LLVMContext::MD_fpmath:
      case LLVMContext::MD_tbaa_struct:
      case LLVMContext::MD_invariant_load:
      case LLVMContext::MD_alias_scope:
      case LLVMContext::MD_noalias:
      case LLVMContext::MD_nontemporal:
      case LLVMContext::MD_mem_parallel_loop_access:
      case LLVMContext::MD_access_group:
        // All of these directly apply.
        Dest.setMetadata(ID, N);
        break;
  
      case LLVMContext::MD_nonnull:
        copyNonnullMetadata(Source, N, Dest);
        break;
  
      case LLVMContext::MD_align:
      case LLVMContext::MD_dereferenceable:
      case LLVMContext::MD_dereferenceable_or_null:
        // These only directly apply if the new type is also a pointer.
        if (NewType->isPointerTy())
          Dest.setMetadata(ID, N);
        break;
  
      case LLVMContext::MD_range:
        copyRangeMetadata(DL, Source, N, Dest);
        break;
      }
    }
  }
  
  void llvm::patchReplacementInstruction(Instruction *I, Value *Repl) {
    auto *ReplInst = dyn_cast<Instruction>(Repl);
    if (!ReplInst)
      return;
  
    // Patch the replacement so that it is not more restrictive than the value
    // being replaced.
    // Note that if 'I' is a load being replaced by some operation,
    // for example, by an arithmetic operation, then andIRFlags()
    // would just erase all math flags from the original arithmetic
    // operation, which is clearly not wanted and not needed.
    if (!isa<LoadInst>(I))
      ReplInst->andIRFlags(I);
  
    // FIXME: If both the original and replacement value are part of the
    // same control-flow region (meaning that the execution of one
    // guarantees the execution of the other), then we can combine the
    // noalias scopes here and do better than the general conservative
    // answer used in combineMetadata().
  
    // In general, GVN unifies expressions over different control-flow
    // regions, and so we need a conservative combination of the noalias
    // scopes.
    static const unsigned KnownIDs[] = {
        LLVMContext::MD_tbaa,            LLVMContext::MD_alias_scope,
        LLVMContext::MD_noalias,         LLVMContext::MD_range,
        LLVMContext::MD_fpmath,          LLVMContext::MD_invariant_load,
        LLVMContext::MD_invariant_group, LLVMContext::MD_nonnull,
        LLVMContext::MD_access_group,    LLVMContext::MD_preserve_access_index};
    combineMetadata(ReplInst, I, KnownIDs, false);
  }
  
  template <typename RootType, typename DominatesFn>
  static unsigned replaceDominatedUsesWith(Value *From, Value *To,
                                           const RootType &Root,
                                           const DominatesFn &Dominates) {
    assert(From->getType() == To->getType());
  
    unsigned Count = 0;
    for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
         UI != UE;) {
      Use &U = *UI++;
      if (!Dominates(Root, U))
        continue;
      U.set(To);
      LLVM_DEBUG(dbgs() << "Replace dominated use of '" << From->getName()
                        << "' as " << *To << " in " << *U << "\n");
      ++Count;
    }
    return Count;
  }
  
  unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) {
     assert(From->getType() == To->getType());
     auto *BB = From->getParent();
     unsigned Count = 0;
  
    for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
         UI != UE;) {
      Use &U = *UI++;
      auto *I = cast<Instruction>(U.getUser());
      if (I->getParent() == BB)
        continue;
      U.set(To);
      ++Count;
    }
    return Count;
  }
  
  unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
                                          DominatorTree &DT,
                                          const BasicBlockEdge &Root) {
    auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) {
      return DT.dominates(Root, U);
    };
    return ::replaceDominatedUsesWith(From, To, Root, Dominates);
  }
  
  unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
                                          DominatorTree &DT,
                                          const BasicBlock *BB) {
    auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
      auto *I = cast<Instruction>(U.getUser())->getParent();
      return DT.properlyDominates(BB, I);
    };
    return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
  }
  
  bool llvm::callsGCLeafFunction(const CallBase *Call,
                                 const TargetLibraryInfo &TLI) {
    // Check if the function is specifically marked as a gc leaf function.
    if (Call->hasFnAttr("gc-leaf-function"))
      return true;
    if (const Function *F = Call->getCalledFunction()) {
      if (F->hasFnAttribute("gc-leaf-function"))
        return true;
  
      if (auto IID = F->getIntrinsicID()) {
        // Most LLVM intrinsics do not take safepoints.
        return IID != Intrinsic::experimental_gc_statepoint &&
               IID != Intrinsic::experimental_deoptimize &&
               IID != Intrinsic::memcpy_element_unordered_atomic &&
               IID != Intrinsic::memmove_element_unordered_atomic;
      }
    }
  
    // Lib calls can be materialized by some passes, and won't be
    // marked as 'gc-leaf-function.' All available Libcalls are
    // GC-leaf.
    LibFunc LF;
    if (TLI.getLibFunc(*Call, LF)) {
      return TLI.has(LF);
    }
  
    return false;
  }
  
  void llvm::copyNonnullMetadata(const LoadInst &OldLI, MDNode *N,
                                 LoadInst &NewLI) {
    auto *NewTy = NewLI.getType();
  
    // This only directly applies if the new type is also a pointer.
    if (NewTy->isPointerTy()) {
      NewLI.setMetadata(LLVMContext::MD_nonnull, N);
      return;
    }
  
    // The only other translation we can do is to integral loads with !range
    // metadata.
    if (!NewTy->isIntegerTy())
      return;
  
    MDBuilder MDB(NewLI.getContext());
    const Value *Ptr = OldLI.getPointerOperand();
    auto *ITy = cast<IntegerType>(NewTy);
    auto *NullInt = ConstantExpr::getPtrToInt(
        ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
    auto *NonNullInt = ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
    NewLI.setMetadata(LLVMContext::MD_range,
                      MDB.createRange(NonNullInt, NullInt));
  }
  
  void llvm::copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI,
                               MDNode *N, LoadInst &NewLI) {
    auto *NewTy = NewLI.getType();
  
    // Give up unless it is converted to a pointer where there is a single very
    // valuable mapping we can do reliably.
    // FIXME: It would be nice to propagate this in more ways, but the type
    // conversions make it hard.
    if (!NewTy->isPointerTy())
      return;
  
    unsigned BitWidth = DL.getPointerTypeSizeInBits(NewTy);
    if (!getConstantRangeFromMetadata(*N).contains(APInt(BitWidth, 0))) {
      MDNode *NN = MDNode::get(OldLI.getContext(), None);
      NewLI.setMetadata(LLVMContext::MD_nonnull, NN);
    }
  }
  
  void llvm::dropDebugUsers(Instruction &I) {
    SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
    findDbgUsers(DbgUsers, &I);
    for (auto *DII : DbgUsers)
      DII->eraseFromParent();
  }
  
  void llvm::hoistAllInstructionsInto(BasicBlock *DomBlock, Instruction *InsertPt,
                                      BasicBlock *BB) {
    // Since we are moving the instructions out of its basic block, we do not
    // retain their original debug locations (DILocations) and debug intrinsic
    // instructions.
    //
    // Doing so would degrade the debugging experience and adversely affect the
    // accuracy of profiling information.
    //
    // Currently, when hoisting the instructions, we take the following actions:
    // - Remove their debug intrinsic instructions.
    // - Set their debug locations to the values from the insertion point.
    //
    // As per PR39141 (comment #8), the more fundamental reason why the dbg.values
    // need to be deleted, is because there will not be any instructions with a
    // DILocation in either branch left after performing the transformation. We
    // can only insert a dbg.value after the two branches are joined again.
    //
    // See PR38762, PR39243 for more details.
    //
    // TODO: Extend llvm.dbg.value to take more than one SSA Value (PR39141) to
    // encode predicated DIExpressions that yield different results on different
    // code paths.
    for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE;) {
      Instruction *I = &*II;
      I->dropUnknownNonDebugMetadata();
      if (I->isUsedByMetadata())
        dropDebugUsers(*I);
      if (isa<DbgInfoIntrinsic>(I)) {
        // Remove DbgInfo Intrinsics.
        II = I->eraseFromParent();
        continue;
      }
      I->setDebugLoc(InsertPt->getDebugLoc());
      ++II;
    }
    DomBlock->getInstList().splice(InsertPt->getIterator(), BB->getInstList(),
                                   BB->begin(),
                                   BB->getTerminator()->getIterator());
  }
  
  namespace {
  
  /// A potential constituent of a bitreverse or bswap expression. See
  /// collectBitParts for a fuller explanation.
  struct BitPart {
    BitPart(Value *P, unsigned BW) : Provider(P) {
      Provenance.resize(BW);
    }
  
    /// The Value that this is a bitreverse/bswap of.
    Value *Provider;
  
    /// The "provenance" of each bit. Provenance[A] = B means that bit A
    /// in Provider becomes bit B in the result of this expression.
    SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128.
  
    enum { Unset = -1 };
  };
  
  } // end anonymous namespace
  
  /// Analyze the specified subexpression and see if it is capable of providing
  /// pieces of a bswap or bitreverse. The subexpression provides a potential
  /// piece of a bswap or bitreverse if it can be proved that each non-zero bit in
  /// the output of the expression came from a corresponding bit in some other
  /// value. This function is recursive, and the end result is a mapping of
  /// bitnumber to bitnumber. It is the caller's responsibility to validate that
  /// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse.
  ///
  /// For example, if the current subexpression if "(shl i32 %X, 24)" then we know
  /// that the expression deposits the low byte of %X into the high byte of the
  /// result and that all other bits are zero. This expression is accepted and a
  /// BitPart is returned with Provider set to %X and Provenance[24-31] set to
  /// [0-7].
  ///
  /// For vector types, all analysis is performed at the per-element level. No
  /// cross-element analysis is supported (shuffle/insertion/reduction), and all
  /// constant masks must be splatted across all elements.
  ///
  /// To avoid revisiting values, the BitPart results are memoized into the
  /// provided map. To avoid unnecessary copying of BitParts, BitParts are
  /// constructed in-place in the \c BPS map. Because of this \c BPS needs to
  /// store BitParts objects, not pointers. As we need the concept of a nullptr
  /// BitParts (Value has been analyzed and the analysis failed), we an Optional
  /// type instead to provide the same functionality.
  ///
  /// Because we pass around references into \c BPS, we must use a container that
  /// does not invalidate internal references (std::map instead of DenseMap).
  static const Optional<BitPart> &
  collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals,
                  std::map<Value *, Optional<BitPart>> &BPS, int Depth) {
    auto I = BPS.find(V);
    if (I != BPS.end())
      return I->second;
  
    auto &Result = BPS[V] = None;
    auto BitWidth = V->getType()->getScalarSizeInBits();
  
    // Prevent stack overflow by limiting the recursion depth
    if (Depth == BitPartRecursionMaxDepth) {
      LLVM_DEBUG(dbgs() << "collectBitParts max recursion depth reached.\n");
      return Result;
    }
  
    if (auto *I = dyn_cast<Instruction>(V)) {
      Value *X, *Y;
      const APInt *C;
  
      // If this is an or instruction, it may be an inner node of the bswap.
      if (match(V, m_Or(m_Value(X), m_Value(Y)))) {
        const auto &A =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        const auto &B =
            collectBitParts(Y, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        if (!A || !B)
          return Result;
  
        // Try and merge the two together.
        if (!A->Provider || A->Provider != B->Provider)
          return Result;
  
        Result = BitPart(A->Provider, BitWidth);
        for (unsigned BitIdx = 0; BitIdx < BitWidth; ++BitIdx) {
          if (A->Provenance[BitIdx] != BitPart::Unset &&
              B->Provenance[BitIdx] != BitPart::Unset &&
              A->Provenance[BitIdx] != B->Provenance[BitIdx])
            return Result = None;
  
          if (A->Provenance[BitIdx] == BitPart::Unset)
            Result->Provenance[BitIdx] = B->Provenance[BitIdx];
          else
            Result->Provenance[BitIdx] = A->Provenance[BitIdx];
        }
  
        return Result;
      }
  
      // If this is a logical shift by a constant, recurse then shift the result.
      if (match(V, m_LogicalShift(m_Value(X), m_APInt(C)))) {
        const APInt &BitShift = *C;
  
        // Ensure the shift amount is defined.
        if (BitShift.uge(BitWidth))
          return Result;
  
        const auto &Res =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        if (!Res)
          return Result;
        Result = Res;
  
        // Perform the "shift" on BitProvenance.
        auto &P = Result->Provenance;
        if (I->getOpcode() == Instruction::Shl) {
          P.erase(std::prev(P.end(), BitShift.getZExtValue()), P.end());
          P.insert(P.begin(), BitShift.getZExtValue(), BitPart::Unset);
        } else {
          P.erase(P.begin(), std::next(P.begin(), BitShift.getZExtValue()));
          P.insert(P.end(), BitShift.getZExtValue(), BitPart::Unset);
        }
  
        return Result;
      }
  
      // If this is a logical 'and' with a mask that clears bits, recurse then
      // unset the appropriate bits.
      if (match(V, m_And(m_Value(X), m_APInt(C)))) {
        const APInt &AndMask = *C;
  
        // Check that the mask allows a multiple of 8 bits for a bswap, for an
        // early exit.
        unsigned NumMaskedBits = AndMask.countPopulation();
        if (!MatchBitReversals && (NumMaskedBits % 8) != 0)
          return Result;
  
        const auto &Res =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        if (!Res)
          return Result;
        Result = Res;
  
        for (unsigned BitIdx = 0; BitIdx < BitWidth; ++BitIdx)
          // If the AndMask is zero for this bit, clear the bit.
          if (AndMask[BitIdx] == 0)
            Result->Provenance[BitIdx] = BitPart::Unset;
        return Result;
      }
  
      // If this is a zext instruction zero extend the result.
      if (match(V, m_ZExt(m_Value(X)))) {
        const auto &Res =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        if (!Res)
          return Result;
  
        Result = BitPart(Res->Provider, BitWidth);
        auto NarrowBitWidth = X->getType()->getScalarSizeInBits();
        for (unsigned BitIdx = 0; BitIdx < NarrowBitWidth; ++BitIdx)
          Result->Provenance[BitIdx] = Res->Provenance[BitIdx];
        for (unsigned BitIdx = NarrowBitWidth; BitIdx < BitWidth; ++BitIdx)
          Result->Provenance[BitIdx] = BitPart::Unset;
        return Result;
      }
  
      // BSWAP - most likely due to us previous matching a partial bswap.
      if (match(V, m_BSwap(m_Value(X)))) {
        const auto &Res =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        if (!Res)
          return Result;
  
        unsigned ByteWidth = BitWidth / 8;
        Result = BitPart(Res->Provider, BitWidth);
        for (unsigned ByteIdx = 0; ByteIdx < ByteWidth; ++ByteIdx) {
          unsigned ByteBitOfs = ByteIdx * 8;
          for (unsigned BitIdx = 0; BitIdx < 8; ++BitIdx)
            Result->Provenance[(BitWidth - 8 - ByteBitOfs) + BitIdx] =
                Res->Provenance[ByteBitOfs + BitIdx];
        }
        return Result;
      }
  
      // Funnel 'double' shifts take 3 operands, 2 inputs and the shift
      // amount (modulo).
      // fshl(X,Y,Z): (X << (Z % BW)) | (Y >> (BW - (Z % BW)))
      // fshr(X,Y,Z): (X << (BW - (Z % BW))) | (Y >> (Z % BW))
      if (match(V, m_FShl(m_Value(X), m_Value(Y), m_APInt(C))) ||
          match(V, m_FShr(m_Value(X), m_Value(Y), m_APInt(C)))) {
        // We can treat fshr as a fshl by flipping the modulo amount.
        unsigned ModAmt = C->urem(BitWidth);
        if (cast<IntrinsicInst>(I)->getIntrinsicID() == Intrinsic::fshr)
          ModAmt = BitWidth - ModAmt;
  
        const auto &LHS =
            collectBitParts(X, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
        const auto &RHS =
            collectBitParts(Y, MatchBSwaps, MatchBitReversals, BPS, Depth + 1);
  
        // Check we have both sources and they are from the same provider.
        if (!LHS || !RHS || !LHS->Provider || LHS->Provider != RHS->Provider)
          return Result;
  
        unsigned StartBitRHS = BitWidth - ModAmt;
        Result = BitPart(LHS->Provider, BitWidth);
        for (unsigned BitIdx = 0; BitIdx < StartBitRHS; ++BitIdx)
          Result->Provenance[BitIdx + ModAmt] = LHS->Provenance[BitIdx];
        for (unsigned BitIdx = 0; BitIdx < ModAmt; ++BitIdx)
          Result->Provenance[BitIdx] = RHS->Provenance[BitIdx + StartBitRHS];
        return Result;
      }
    }
  
    // Okay, we got to something that isn't a shift, 'or' or 'and'.  This must be
    // the input value to the bswap/bitreverse.
    Result = BitPart(V, BitWidth);
    for (unsigned BitIdx = 0; BitIdx < BitWidth; ++BitIdx)
      Result->Provenance[BitIdx] = BitIdx;
    return Result;
  }
  
  static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To,
                                            unsigned BitWidth) {
    if (From % 8 != To % 8)
      return false;
    // Convert from bit indices to byte indices and check for a byte reversal.
    From >>= 3;
    To >>= 3;
    BitWidth >>= 3;
    return From == BitWidth - To - 1;
  }
  
  static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To,
                                                 unsigned BitWidth) {
    return From == BitWidth - To - 1;
  }
  
  bool llvm::recognizeBSwapOrBitReverseIdiom(
      Instruction *I, bool MatchBSwaps, bool MatchBitReversals,
      SmallVectorImpl<Instruction *> &InsertedInsts) {
    if (Operator::getOpcode(I) != Instruction::Or)
      return false;
    if (!MatchBSwaps && !MatchBitReversals)
      return false;
    Type *ITy = I->getType();
    if (!ITy->isIntOrIntVectorTy() || ITy->getScalarSizeInBits() > 128)
      return false;  // Can't do integer/elements > 128 bits.
  
    Type *DemandedTy = ITy;
    if (I->hasOneUse())
      if (auto *Trunc = dyn_cast<TruncInst>(I->user_back()))
        DemandedTy = Trunc->getType();
  
    // Try to find all the pieces corresponding to the bswap.
    std::map<Value *, Optional<BitPart>> BPS;
    auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS, 0);
    if (!Res)
      return false;
    ArrayRef<int8_t> BitProvenance = Res->Provenance;
    assert(all_of(BitProvenance,
                  [](int8_t I) { return I == BitPart::Unset || 0 <= I; }) &&
           "Illegal bit provenance index");
  
    // If the upper bits are zero, then attempt to perform as a truncated op.
    if (BitProvenance.back() == BitPart::Unset) {
      while (!BitProvenance.empty() && BitProvenance.back() == BitPart::Unset)
        BitProvenance = BitProvenance.drop_back();
      if (BitProvenance.empty())
        return false; // TODO - handle null value?
      DemandedTy = Type::getIntNTy(I->getContext(), BitProvenance.size());
      if (auto *IVecTy = dyn_cast<VectorType>(ITy))
        DemandedTy = VectorType::get(DemandedTy, IVecTy);
    }
  
    // Check BitProvenance hasn't found a source larger than the result type.
    unsigned DemandedBW = DemandedTy->getScalarSizeInBits();
    if (DemandedBW > ITy->getScalarSizeInBits())
      return false;
  
    // Now, is the bit permutation correct for a bswap or a bitreverse? We can
    // only byteswap values with an even number of bytes.
    APInt DemandedMask = APInt::getAllOnesValue(DemandedBW);
    bool OKForBSwap = MatchBSwaps && (DemandedBW % 16) == 0;
    bool OKForBitReverse = MatchBitReversals;
    for (unsigned BitIdx = 0;
         (BitIdx < DemandedBW) && (OKForBSwap || OKForBitReverse); ++BitIdx) {
      if (BitProvenance[BitIdx] == BitPart::Unset) {
        DemandedMask.clearBit(BitIdx);
        continue;
      }
      OKForBSwap &= bitTransformIsCorrectForBSwap(BitProvenance[BitIdx], BitIdx,
                                                  DemandedBW);
      OKForBitReverse &= bitTransformIsCorrectForBitReverse(BitProvenance[BitIdx],
                                                            BitIdx, DemandedBW);
    }
  
    Intrinsic::ID Intrin;
    if (OKForBSwap)
      Intrin = Intrinsic::bswap;
    else if (OKForBitReverse)
      Intrin = Intrinsic::bitreverse;
    else
      return false;
  
    Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, DemandedTy);
    Value *Provider = Res->Provider;
  
    // We may need to truncate the provider.
    if (DemandedTy != Provider->getType()) {
      auto *Trunc =
          CastInst::CreateIntegerCast(Provider, DemandedTy, false, "trunc", I);
      InsertedInsts.push_back(Trunc);
      Provider = Trunc;
    }
  
    Instruction *Result = CallInst::Create(F, Provider, "rev", I);
    InsertedInsts.push_back(Result);
  
    if (!DemandedMask.isAllOnesValue()) {
      auto *Mask = ConstantInt::get(DemandedTy, DemandedMask);
      Result = BinaryOperator::Create(Instruction::And, Result, Mask, "mask", I);
      InsertedInsts.push_back(Result);
    }
  
    // We may need to zeroextend back to the result type.
    if (ITy != Result->getType()) {
      auto *ExtInst = CastInst::CreateIntegerCast(Result, ITy, false, "zext", I);
      InsertedInsts.push_back(ExtInst);
    }
  
    return true;
  }
  
  // CodeGen has special handling for some string functions that may replace
  // them with target-specific intrinsics.  Since that'd skip our interceptors
  // in ASan/MSan/TSan/DFSan, and thus make us miss some memory accesses,
  // we mark affected calls as NoBuiltin, which will disable optimization
  // in CodeGen.
  void llvm::maybeMarkSanitizerLibraryCallNoBuiltin(
      CallInst *CI, const TargetLibraryInfo *TLI) {
    Function *F = CI->getCalledFunction();
    LibFunc Func;
    if (F && !F->hasLocalLinkage() && F->hasName() &&
        TLI->getLibFunc(F->getName(), Func) && TLI->hasOptimizedCodeGen(Func) &&
        !F->doesNotAccessMemory())
      CI->addAttribute(AttributeList::FunctionIndex, Attribute::NoBuiltin);
  }
  
  bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
    // We can't have a PHI with a metadata type.
    if (I->getOperand(OpIdx)->getType()->isMetadataTy())
      return false;
  
    // Early exit.
    if (!isa<Constant>(I->getOperand(OpIdx)))
      return true;
  
    switch (I->getOpcode()) {
    default:
      return true;
    case Instruction::Call:
    case Instruction::Invoke: {
      const auto &CB = cast<CallBase>(*I);
  
      // Can't handle inline asm. Skip it.
      if (CB.isInlineAsm())
        return false;
  
      // Constant bundle operands may need to retain their constant-ness for
      // correctness.
      if (CB.isBundleOperand(OpIdx))
        return false;
  
      if (OpIdx < CB.getNumArgOperands()) {
        // Some variadic intrinsics require constants in the variadic arguments,
        // which currently aren't markable as immarg.
        if (isa<IntrinsicInst>(CB) &&
            OpIdx >= CB.getFunctionType()->getNumParams()) {
          // This is known to be OK for stackmap.
          return CB.getIntrinsicID() == Intrinsic::experimental_stackmap;
        }
  
        // gcroot is a special case, since it requires a constant argument which
        // isn't also required to be a simple ConstantInt.
        if (CB.getIntrinsicID() == Intrinsic::gcroot)
          return false;
  
        // Some intrinsic operands are required to be immediates.
        return !CB.paramHasAttr(OpIdx, Attribute::ImmArg);
      }
  
      // It is never allowed to replace the call argument to an intrinsic, but it
      // may be possible for a call.
      return !isa<IntrinsicInst>(CB);
    }
    case Instruction::ShuffleVector:
      // Shufflevector masks are constant.
      return OpIdx != 2;
    case Instruction::Switch:
    case Instruction::ExtractValue:
      // All operands apart from the first are constant.
      return OpIdx == 0;
    case Instruction::InsertValue:
      // All operands apart from the first and the second are constant.
      return OpIdx < 2;
    case Instruction::Alloca:
      // Static allocas (constant size in the entry block) are handled by
      // prologue/epilogue insertion so they're free anyway. We definitely don't
      // want to make them non-constant.
      return !cast<AllocaInst>(I)->isStaticAlloca();
    case Instruction::GetElementPtr:
      if (OpIdx == 0)
        return true;
      gep_type_iterator It = gep_type_begin(I);
      for (auto E = std::next(It, OpIdx); It != E; ++It)
        if (It.isStruct())
          return false;
      return true;
    }
  }
  
  Value *llvm::invertCondition(Value *Condition) {
    // First: Check if it's a constant
    if (Constant *C = dyn_cast<Constant>(Condition))
      return ConstantExpr::getNot(C);
  
    // Second: If the condition is already inverted, return the original value
    Value *NotCondition;
    if (match(Condition, m_Not(m_Value(NotCondition))))
      return NotCondition;
  
    BasicBlock *Parent = nullptr;
    Instruction *Inst = dyn_cast<Instruction>(Condition);
    if (Inst)
      Parent = Inst->getParent();
    else if (Argument *Arg = dyn_cast<Argument>(Condition))
      Parent = &Arg->getParent()->getEntryBlock();
    assert(Parent && "Unsupported condition to invert");
  
    // Third: Check all the users for an invert
    for (User *U : Condition->users())
      if (Instruction *I = dyn_cast<Instruction>(U))
        if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
          return I;
  
    // Last option: Create a new instruction
    auto *Inverted =
        BinaryOperator::CreateNot(Condition, Condition->getName() + ".inv");
    if (Inst && !isa<PHINode>(Inst))
      Inverted->insertAfter(Inst);
    else
      Inverted->insertBefore(&*Parent->getFirstInsertionPt());
    return Inverted;
  }
  