lib/Transforms/Utils/LowerSwitch.cpp - llvm - Git at Google

 //===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // The LowerSwitch transformation rewrites switch instructions with a sequence
 // of branches, which allows targets to get away with not implementing the
 // switch instruction until it is convenient.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
 #include <algorithm>
 using namespace llvm;

 #define DEBUG_TYPE "lower-switch"

 namespace {
   struct IntRange {
     int64_t Low, High;
   };
   // Return true iff R is covered by Ranges.
   static bool IsInRanges(const IntRange &R,
                          const std::vector<IntRange> &Ranges) {
     // Note: Ranges must be sorted, non-overlapping and non-adjacent.

     // Find the first range whose High field is >= R.High,
     // then check if the Low field is <= R.Low. If so, we
     // have a Range that covers R.
     auto I = std::lower_bound(
         Ranges.begin(), Ranges.end(), R,
         [](const IntRange &A, const IntRange &B) { return A.High < B.High; });
     return I != Ranges.end() && I->Low <= R.Low;
   }

   /// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
   /// instructions.
   class LowerSwitch : public FunctionPass {
   public:
     static char ID; // Pass identification, replacement for typeid
     LowerSwitch() : FunctionPass(ID) {
       initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
     }

     bool runOnFunction(Function &F) override;

     void getAnalysisUsage(AnalysisUsage &AU) const override {
       // This is a cluster of orthogonal Transforms
       AU.addPreserved<UnifyFunctionExitNodes>();
       AU.addPreservedID(LowerInvokePassID);
     }

     struct CaseRange {
       ConstantInt* Low;
       ConstantInt* High;
       BasicBlock* BB;

       CaseRange(ConstantInt *low, ConstantInt *high, BasicBlock *bb)
           : Low(low), High(high), BB(bb) {}
     };

     typedef std::vector<CaseRange> CaseVector;
     typedef std::vector<CaseRange>::iterator CaseItr;
   private:
     void processSwitchInst(SwitchInst *SI);

     BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
                               ConstantInt *LowerBound, ConstantInt *UpperBound,
                               Value *Val, BasicBlock *Predecessor,
                               BasicBlock *OrigBlock, BasicBlock *Default,
                               const std::vector<IntRange> &UnreachableRanges);
     BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val, BasicBlock *OrigBlock,
                              BasicBlock *Default);
     unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
   };

   /// The comparison function for sorting the switch case values in the vector.
   /// WARNING: Case ranges should be disjoint!
   struct CaseCmp {
     bool operator () (const LowerSwitch::CaseRange& C1,
                       const LowerSwitch::CaseRange& C2) {

       const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
       const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
       return CI1->getValue().slt(CI2->getValue());
     }
   };
 }

 char LowerSwitch::ID = 0;
 INITIALIZE_PASS(LowerSwitch, "lowerswitch",
                 "Lower SwitchInst's to branches", false, false)

 // Publicly exposed interface to pass...
 char &llvm::LowerSwitchID = LowerSwitch::ID;
 // createLowerSwitchPass - Interface to this file...
 FunctionPass *llvm::createLowerSwitchPass() {
   return new LowerSwitch();
 }

 bool LowerSwitch::runOnFunction(Function &F) {
   bool Changed = false;

   for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
     BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks

     if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
       Changed = true;
       processSwitchInst(SI);
     }
   }

   return Changed;
 }

 // operator<< - Used for debugging purposes.
 //
 static raw_ostream& operator<<(raw_ostream &O,
                                const LowerSwitch::CaseVector &C)
     LLVM_ATTRIBUTE_USED;
 static raw_ostream& operator<<(raw_ostream &O,
                                const LowerSwitch::CaseVector &C) {
   O << "[";

   for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
          E = C.end(); B != E; ) {
     O << *B->Low << " -" << *B->High;
     if (++B != E) O << ", ";
   }

   return O << "]";
 }

 // \brief Update the first occurrence of the "switch statement" BB in the PHI
 // node with the "new" BB. The other occurrences will:
 //
 // 1) Be updated by subsequent calls to this function.  Switch statements may
 // have more than one outcoming edge into the same BB if they all have the same
 // value. When the switch statement is converted these incoming edges are now
 // coming from multiple BBs.
 // 2) Removed if subsequent incoming values now share the same case, i.e.,
 // multiple outcome edges are condensed into one. This is necessary to keep the
 // number of phi values equal to the number of branches to SuccBB.
 static void fixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
                     unsigned NumMergedCases) {
   for (BasicBlock::iterator I = SuccBB->begin(), IE = SuccBB->getFirstNonPHI();
        I != IE; ++I) {
     PHINode *PN = cast<PHINode>(I);

     // Only update the first occurence.
     unsigned Idx = 0, E = PN->getNumIncomingValues();
     unsigned LocalNumMergedCases = NumMergedCases;
     for (; Idx != E; ++Idx) {
       if (PN->getIncomingBlock(Idx) == OrigBB) {
         PN->setIncomingBlock(Idx, NewBB);
         break;
       }
     }

     // Remove additional occurences coming from condensed cases and keep the
     // number of incoming values equal to the number of branches to SuccBB.
     SmallVector<unsigned, 8> Indices;
     for (++Idx; LocalNumMergedCases > 0 && Idx < E; ++Idx)
       if (PN->getIncomingBlock(Idx) == OrigBB) {
         Indices.push_back(Idx);
         LocalNumMergedCases--;
       }
     // Remove incoming values in the reverse order to prevent invalidating
     // *successive* index.
     for (auto III = Indices.rbegin(), IIE = Indices.rend(); III != IIE; ++III)
       PN->removeIncomingValue(*III);
   }
 }

 // switchConvert - Convert the switch statement into a binary lookup of
 // the case values. The function recursively builds this tree.
 // LowerBound and UpperBound are used to keep track of the bounds for Val
 // that have already been checked by a block emitted by one of the previous
 // calls to switchConvert in the call stack.
 BasicBlock *
 LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
                            ConstantInt *UpperBound, Value *Val,
                            BasicBlock *Predecessor, BasicBlock *OrigBlock,
                            BasicBlock *Default,
                            const std::vector<IntRange> &UnreachableRanges) {
   unsigned Size = End - Begin;

   if (Size == 1) {
     // Check if the Case Range is perfectly squeezed in between
     // already checked Upper and Lower bounds. If it is then we can avoid
     // emitting the code that checks if the value actually falls in the range
     // because the bounds already tell us so.
     if (Begin->Low == LowerBound && Begin->High == UpperBound) {
       unsigned NumMergedCases = 0;
       if (LowerBound && UpperBound)
         NumMergedCases =
             UpperBound->getSExtValue() - LowerBound->getSExtValue();
       fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
       return Begin->BB;
     }
     return newLeafBlock(*Begin, Val, OrigBlock, Default);
   }

   unsigned Mid = Size / 2;
   std::vector<CaseRange> LHS(Begin, Begin + Mid);
   DEBUG(dbgs() << "LHS: " << LHS << "\n");
   std::vector<CaseRange> RHS(Begin + Mid, End);
   DEBUG(dbgs() << "RHS: " << RHS << "\n");

   CaseRange &Pivot = *(Begin + Mid);
   DEBUG(dbgs() << "Pivot ==> "
                << Pivot.Low->getValue()
                << " -" << Pivot.High->getValue() << "\n");

   // NewLowerBound here should never be the integer minimal value.
   // This is because it is computed from a case range that is never
   // the smallest, so there is always a case range that has at least
   // a smaller value.
   ConstantInt *NewLowerBound = Pivot.Low;

   // Because NewLowerBound is never the smallest representable integer
   // it is safe here to subtract one.
   ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
                                                 NewLowerBound->getValue() - 1);

   if (!UnreachableRanges.empty()) {
     // Check if the gap between LHS's highest and NewLowerBound is unreachable.
     int64_t GapLow = LHS.back().High->getSExtValue() + 1;
     int64_t GapHigh = NewLowerBound->getSExtValue() - 1;
     IntRange Gap = { GapLow, GapHigh };
     if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges))
       NewUpperBound = LHS.back().High;
   }

   DEBUG(dbgs() << "LHS Bounds ==> ";
         if (LowerBound) {
           dbgs() << LowerBound->getSExtValue();
         } else {
           dbgs() << "NONE";
         }
         dbgs() << " - " << NewUpperBound->getSExtValue() << "\n";
         dbgs() << "RHS Bounds ==> ";
         dbgs() << NewLowerBound->getSExtValue() << " - ";
         if (UpperBound) {
           dbgs() << UpperBound->getSExtValue() << "\n";
         } else {
           dbgs() << "NONE\n";
         });

   // Create a new node that checks if the value is < pivot. Go to the
   // left branch if it is and right branch if not.
   Function* F = OrigBlock->getParent();
   BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");

   ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
                                 Val, Pivot.Low, "Pivot");

   BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
                                       NewUpperBound, Val, NewNode, OrigBlock,
                                       Default, UnreachableRanges);
   BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
                                       UpperBound, Val, NewNode, OrigBlock,
                                       Default, UnreachableRanges);

   Function::iterator FI = OrigBlock;
   F->getBasicBlockList().insert(++FI, NewNode);
   NewNode->getInstList().push_back(Comp);

   BranchInst::Create(LBranch, RBranch, Comp, NewNode);
   return NewNode;
 }

 // newLeafBlock - Create a new leaf block for the binary lookup tree. It
 // checks if the switch's value == the case's value. If not, then it
 // jumps to the default branch. At this point in the tree, the value
 // can't be another valid case value, so the jump to the "default" branch
 // is warranted.
 //
 BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
                                       BasicBlock* OrigBlock,
                                       BasicBlock* Default)
 {
   Function* F = OrigBlock->getParent();
   BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
   Function::iterator FI = OrigBlock;
   F->getBasicBlockList().insert(++FI, NewLeaf);

   // Emit comparison
   ICmpInst* Comp = nullptr;
   if (Leaf.Low == Leaf.High) {
     // Make the seteq instruction...
     Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
                         Leaf.Low, "SwitchLeaf");
   } else {
     // Make range comparison
     if (Leaf.Low->isMinValue(true /*isSigned*/)) {
       // Val >= Min && Val <= Hi --> Val <= Hi
       Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
                           "SwitchLeaf");
     } else if (Leaf.Low->isZero()) {
       // Val >= 0 && Val <= Hi --> Val <=u Hi
       Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
                           "SwitchLeaf");
     } else {
       // Emit V-Lo <=u Hi-Lo
       Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
       Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
                                                    Val->getName()+".off",
                                                    NewLeaf);
       Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
       Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
                           "SwitchLeaf");
     }
   }

   // Make the conditional branch...
   BasicBlock* Succ = Leaf.BB;
   BranchInst::Create(Succ, Default, Comp, NewLeaf);

   // If there were any PHI nodes in this successor, rewrite one entry
   // from OrigBlock to come from NewLeaf.
   for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
     PHINode* PN = cast<PHINode>(I);
     // Remove all but one incoming entries from the cluster
     uint64_t Range = Leaf.High->getSExtValue() -
                      Leaf.Low->getSExtValue();
     for (uint64_t j = 0; j < Range; ++j) {
       PN->removeIncomingValue(OrigBlock);
     }

     int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
     assert(BlockIdx != -1 && "Switch didn't go to this successor??");
     PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
   }

   return NewLeaf;
 }

 // Clusterify - Transform simple list of Cases into list of CaseRange's
 unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
   unsigned numCmps = 0;

   // Start with "simple" cases
   for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
     Cases.push_back(CaseRange(i.getCaseValue(), i.getCaseValue(),
                               i.getCaseSuccessor()));

   std::sort(Cases.begin(), Cases.end(), CaseCmp());

   // Merge case into clusters
   if (Cases.size() >= 2) {
     CaseItr I = Cases.begin();
     for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) {
       int64_t nextValue = J->Low->getSExtValue();
       int64_t currentValue = I->High->getSExtValue();
       BasicBlock* nextBB = J->BB;
       BasicBlock* currentBB = I->BB;

       // If the two neighboring cases go to the same destination, merge them
       // into a single case.
       assert(nextValue > currentValue && "Cases should be strictly ascending");
       if ((nextValue == currentValue + 1) && (currentBB == nextBB)) {
         I->High = J->High;
         // FIXME: Combine branch weights.
       } else if (++I != J) {
         *I = *J;
       }
     }
     Cases.erase(std::next(I), Cases.end());
   }

   for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
     if (I->Low != I->High)
       // A range counts double, since it requires two compares.
       ++numCmps;
   }

   return numCmps;
 }

 // processSwitchInst - Replace the specified switch instruction with a sequence
 // of chained if-then insts in a balanced binary search.
 //
 void LowerSwitch::processSwitchInst(SwitchInst *SI) {
   BasicBlock *CurBlock = SI->getParent();
   BasicBlock *OrigBlock = CurBlock;
   Function *F = CurBlock->getParent();
   Value *Val = SI->getCondition();  // The value we are switching on...
   BasicBlock* Default = SI->getDefaultDest();

   // If there is only the default destination, just branch.
   if (!SI->getNumCases()) {
     BranchInst::Create(Default, CurBlock);
     SI->eraseFromParent();
     return;
   }

   // Prepare cases vector.
   CaseVector Cases;
   unsigned numCmps = Clusterify(Cases, SI);
   DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
                << ". Total compares: " << numCmps << "\n");
   DEBUG(dbgs() << "Cases: " << Cases << "\n");
   (void)numCmps;

   ConstantInt *LowerBound = nullptr;
   ConstantInt *UpperBound = nullptr;
   std::vector<IntRange> UnreachableRanges;

   if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
     // Make the bounds tightly fitted around the case value range, becase we
     // know that the value passed to the switch must be exactly one of the case
     // values.
     assert(!Cases.empty());
     LowerBound = Cases.front().Low;
     UpperBound = Cases.back().High;

     DenseMap<BasicBlock *, unsigned> Popularity;
     unsigned MaxPop = 0;
     BasicBlock *PopSucc = nullptr;

     IntRange R = { INT64_MIN, INT64_MAX };
     UnreachableRanges.push_back(R);
     for (const auto &I : Cases) {
       int64_t Low = I.Low->getSExtValue();
       int64_t High = I.High->getSExtValue();

       IntRange &LastRange = UnreachableRanges.back();
       if (LastRange.Low == Low) {
         // There is nothing left of the previous range.
         UnreachableRanges.pop_back();
       } else {
         // Terminate the previous range.
         assert(Low > LastRange.Low);
         LastRange.High = Low - 1;
       }
       if (High != INT64_MAX) {
         IntRange R = { High + 1, INT64_MAX };
         UnreachableRanges.push_back(R);
       }

       // Count popularity.
       int64_t N = High - Low + 1;
       unsigned &Pop = Popularity[I.BB];
       if ((Pop += N) > MaxPop) {
         MaxPop = Pop;
         PopSucc = I.BB;
       }
     }
 #ifndef NDEBUG
     /* UnreachableRanges should be sorted and the ranges non-adjacent. */
     for (auto I = UnreachableRanges.begin(), E = UnreachableRanges.end();
          I != E; ++I) {
       assert(I->Low <= I->High);
       auto Next = I + 1;
       if (Next != E) {
         assert(Next->Low > I->High);
       }
     }
 #endif

     // Use the most popular block as the new default, reducing the number of
     // cases.
     assert(MaxPop > 0 && PopSucc);
     Default = PopSucc;
     Cases.erase(std::remove_if(
                     Cases.begin(), Cases.end(),
                     [PopSucc](const CaseRange &R) { return R.BB == PopSucc; }),
                 Cases.end());

     // If there are no cases left, just branch.
     if (Cases.empty()) {
       BranchInst::Create(Default, CurBlock);
       SI->eraseFromParent();
       return;
     }
   }

   // Create a new, empty default block so that the new hierarchy of
   // if-then statements go to this and the PHI nodes are happy.
   BasicBlock *NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
   F->getBasicBlockList().insert(Default, NewDefault);
   BranchInst::Create(Default, NewDefault);

   // If there is an entry in any PHI nodes for the default edge, make sure
   // to update them as well.
   for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
     PHINode *PN = cast<PHINode>(I);
     int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
     assert(BlockIdx != -1 && "Switch didn't go to this successor??");
     PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
   }

   BasicBlock *SwitchBlock =
       switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
                     OrigBlock, OrigBlock, NewDefault, UnreachableRanges);

   // Branch to our shiny new if-then stuff...
   BranchInst::Create(SwitchBlock, OrigBlock);

   // We are now done with the switch instruction, delete it.
   BasicBlock *OldDefault = SI->getDefaultDest();
   CurBlock->getInstList().erase(SI);

   // If the Default block has no more predecessors just remove it.
   if (pred_begin(OldDefault) == pred_end(OldDefault))
     DeleteDeadBlock(OldDefault);
 }
	//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// The LowerSwitch transformation rewrites switch instructions with a sequence
	// of branches, which allows targets to get away with not implementing the
	// switch instruction until it is convenient.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Transforms/Scalar.h"
	#include "llvm/ADT/STLExtras.h"
	#include "llvm/IR/CFG.h"
	#include "llvm/IR/Constants.h"
	#include "llvm/IR/Function.h"
	#include "llvm/IR/Instructions.h"
	#include "llvm/IR/LLVMContext.h"
	#include "llvm/Pass.h"
	#include "llvm/Support/Compiler.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	#include "llvm/Transforms/Utils/BasicBlockUtils.h"
	#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
	#include <algorithm>
	using namespace llvm;

	#define DEBUG_TYPE "lower-switch"

	namespace {
	struct IntRange {
	int64_t Low, High;
	};
	// Return true iff R is covered by Ranges.
	static bool IsInRanges(const IntRange &R,
	const std::vector<IntRange> &Ranges) {
	// Note: Ranges must be sorted, non-overlapping and non-adjacent.

	// Find the first range whose High field is >= R.High,
	// then check if the Low field is <= R.Low. If so, we
	// have a Range that covers R.
	auto I = std::lower_bound(
	Ranges.begin(), Ranges.end(), R,
	[](const IntRange &A, const IntRange &B) { return A.High < B.High; });
	return I != Ranges.end() && I->Low <= R.Low;
	}

	/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
	/// instructions.
	class LowerSwitch : public FunctionPass {
	public:
	static char ID; // Pass identification, replacement for typeid
	LowerSwitch() : FunctionPass(ID) {
	initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
	}

	bool runOnFunction(Function &F) override;

	void getAnalysisUsage(AnalysisUsage &AU) const override {
	// This is a cluster of orthogonal Transforms
	AU.addPreserved<UnifyFunctionExitNodes>();
	AU.addPreservedID(LowerInvokePassID);
	}

	struct CaseRange {
	ConstantInt* Low;
	ConstantInt* High;
	BasicBlock* BB;

	CaseRange(ConstantInt low, ConstantInt high, BasicBlock *bb)
	: Low(low), High(high), BB(bb) {}
	};

	typedef std::vector<CaseRange> CaseVector;
	typedef std::vector<CaseRange>::iterator CaseItr;
	private:
	void processSwitchInst(SwitchInst *SI);

	BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
	ConstantInt LowerBound, ConstantInt UpperBound,
	Value Val, BasicBlock Predecessor,
	BasicBlock OrigBlock, BasicBlock Default,
	const std::vector<IntRange> &UnreachableRanges);
	BasicBlock newLeafBlock(CaseRange &Leaf, Value Val, BasicBlock *OrigBlock,
	BasicBlock *Default);
	unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
	};

	/// The comparison function for sorting the switch case values in the vector.
	/// WARNING: Case ranges should be disjoint!
	struct CaseCmp {
	bool operator () (const LowerSwitch::CaseRange& C1,
	const LowerSwitch::CaseRange& C2) {

	const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
	const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
	return CI1->getValue().slt(CI2->getValue());
	}
	};
	}

	char LowerSwitch::ID = 0;
	INITIALIZE_PASS(LowerSwitch, "lowerswitch",
	"Lower SwitchInst's to branches", false, false)

	// Publicly exposed interface to pass...
	char &llvm::LowerSwitchID = LowerSwitch::ID;
	// createLowerSwitchPass - Interface to this file...
	FunctionPass *llvm::createLowerSwitchPass() {
	return new LowerSwitch();
	}

	bool LowerSwitch::runOnFunction(Function &F) {
	bool Changed = false;

	for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
	BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks

	if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
	Changed = true;
	processSwitchInst(SI);
	}
	}

	return Changed;
	}

	// operator<< - Used for debugging purposes.
	//
	static raw_ostream& operator<<(raw_ostream &O,
	const LowerSwitch::CaseVector &C)
	LLVM_ATTRIBUTE_USED;
	static raw_ostream& operator<<(raw_ostream &O,
	const LowerSwitch::CaseVector &C) {
	O << "[";

	for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
	E = C.end(); B != E; ) {
	O << B->Low << " -" << B->High;
	if (++B != E) O << ", ";
	}

	return O << "]";
	}

	// \brief Update the first occurrence of the "switch statement" BB in the PHI
	// node with the "new" BB. The other occurrences will:
	//
	// 1) Be updated by subsequent calls to this function. Switch statements may
	// have more than one outcoming edge into the same BB if they all have the same
	// value. When the switch statement is converted these incoming edges are now
	// coming from multiple BBs.
	// 2) Removed if subsequent incoming values now share the same case, i.e.,
	// multiple outcome edges are condensed into one. This is necessary to keep the
	// number of phi values equal to the number of branches to SuccBB.
	static void fixPhis(BasicBlock SuccBB, BasicBlock OrigBB, BasicBlock *NewBB,
	unsigned NumMergedCases) {
	for (BasicBlock::iterator I = SuccBB->begin(), IE = SuccBB->getFirstNonPHI();
	I != IE; ++I) {
	PHINode *PN = cast<PHINode>(I);

	// Only update the first occurence.
	unsigned Idx = 0, E = PN->getNumIncomingValues();
	unsigned LocalNumMergedCases = NumMergedCases;
	for (; Idx != E; ++Idx) {
	if (PN->getIncomingBlock(Idx) == OrigBB) {
	PN->setIncomingBlock(Idx, NewBB);
	break;
	}
	}

	// Remove additional occurences coming from condensed cases and keep the
	// number of incoming values equal to the number of branches to SuccBB.
	SmallVector<unsigned, 8> Indices;
	for (++Idx; LocalNumMergedCases > 0 && Idx < E; ++Idx)
	if (PN->getIncomingBlock(Idx) == OrigBB) {
	Indices.push_back(Idx);
	LocalNumMergedCases--;
	}
	// Remove incoming values in the reverse order to prevent invalidating
	// successive index.
	for (auto III = Indices.rbegin(), IIE = Indices.rend(); III != IIE; ++III)
	PN->removeIncomingValue(*III);
	}
	}

	// switchConvert - Convert the switch statement into a binary lookup of
	// the case values. The function recursively builds this tree.
	// LowerBound and UpperBound are used to keep track of the bounds for Val
	// that have already been checked by a block emitted by one of the previous
	// calls to switchConvert in the call stack.
	BasicBlock *
	LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
	ConstantInt UpperBound, Value Val,
	BasicBlock Predecessor, BasicBlock OrigBlock,
	BasicBlock *Default,
	const std::vector<IntRange> &UnreachableRanges) {
	unsigned Size = End - Begin;

	if (Size == 1) {
	// Check if the Case Range is perfectly squeezed in between
	// already checked Upper and Lower bounds. If it is then we can avoid
	// emitting the code that checks if the value actually falls in the range
	// because the bounds already tell us so.
	if (Begin->Low == LowerBound && Begin->High == UpperBound) {
	unsigned NumMergedCases = 0;
	if (LowerBound && UpperBound)
	NumMergedCases =
	UpperBound->getSExtValue() - LowerBound->getSExtValue();
	fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
	return Begin->BB;
	}
	return newLeafBlock(*Begin, Val, OrigBlock, Default);
	}

	unsigned Mid = Size / 2;
	std::vector<CaseRange> LHS(Begin, Begin + Mid);
	DEBUG(dbgs() << "LHS: " << LHS << "\n");
	std::vector<CaseRange> RHS(Begin + Mid, End);
	DEBUG(dbgs() << "RHS: " << RHS << "\n");

	CaseRange &Pivot = *(Begin + Mid);
	DEBUG(dbgs() << "Pivot ==> "
	<< Pivot.Low->getValue()
	<< " -" << Pivot.High->getValue() << "\n");

	// NewLowerBound here should never be the integer minimal value.
	// This is because it is computed from a case range that is never
	// the smallest, so there is always a case range that has at least
	// a smaller value.
	ConstantInt *NewLowerBound = Pivot.Low;

	// Because NewLowerBound is never the smallest representable integer
	// it is safe here to subtract one.
	ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
	NewLowerBound->getValue() - 1);

	if (!UnreachableRanges.empty()) {
	// Check if the gap between LHS's highest and NewLowerBound is unreachable.
	int64_t GapLow = LHS.back().High->getSExtValue() + 1;
	int64_t GapHigh = NewLowerBound->getSExtValue() - 1;
	IntRange Gap = { GapLow, GapHigh };
	if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges))
	NewUpperBound = LHS.back().High;
	}

	DEBUG(dbgs() << "LHS Bounds ==> ";
	if (LowerBound) {
	dbgs() << LowerBound->getSExtValue();
	} else {
	dbgs() << "NONE";
	}
	dbgs() << " - " << NewUpperBound->getSExtValue() << "\n";
	dbgs() << "RHS Bounds ==> ";
	dbgs() << NewLowerBound->getSExtValue() << " - ";
	if (UpperBound) {
	dbgs() << UpperBound->getSExtValue() << "\n";
	} else {
	dbgs() << "NONE\n";
	});

	// Create a new node that checks if the value is < pivot. Go to the
	// left branch if it is and right branch if not.
	Function* F = OrigBlock->getParent();
	BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");

	ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
	Val, Pivot.Low, "Pivot");

	BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
	NewUpperBound, Val, NewNode, OrigBlock,
	Default, UnreachableRanges);
	BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
	UpperBound, Val, NewNode, OrigBlock,
	Default, UnreachableRanges);

	Function::iterator FI = OrigBlock;
	F->getBasicBlockList().insert(++FI, NewNode);
	NewNode->getInstList().push_back(Comp);

	BranchInst::Create(LBranch, RBranch, Comp, NewNode);
	return NewNode;
	}

	// newLeafBlock - Create a new leaf block for the binary lookup tree. It
	// checks if the switch's value == the case's value. If not, then it
	// jumps to the default branch. At this point in the tree, the value
	// can't be another valid case value, so the jump to the "default" branch
	// is warranted.
	//
	BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
	BasicBlock* OrigBlock,
	BasicBlock* Default)
	{
	Function* F = OrigBlock->getParent();
	BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
	Function::iterator FI = OrigBlock;
	F->getBasicBlockList().insert(++FI, NewLeaf);

	// Emit comparison
	ICmpInst* Comp = nullptr;
	if (Leaf.Low == Leaf.High) {
	// Make the seteq instruction...
	Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
	Leaf.Low, "SwitchLeaf");
	} else {
	// Make range comparison
	if (Leaf.Low->isMinValue(true /isSigned/)) {
	// Val >= Min && Val <= Hi --> Val <= Hi
	Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
	"SwitchLeaf");
	} else if (Leaf.Low->isZero()) {
	// Val >= 0 && Val <= Hi --> Val <=u Hi
	Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
	"SwitchLeaf");
	} else {
	// Emit V-Lo <=u Hi-Lo
	Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
	Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
	Val->getName()+".off",
	NewLeaf);
	Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
	Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
	"SwitchLeaf");
	}
	}

	// Make the conditional branch...
	BasicBlock* Succ = Leaf.BB;
	BranchInst::Create(Succ, Default, Comp, NewLeaf);

	// If there were any PHI nodes in this successor, rewrite one entry
	// from OrigBlock to come from NewLeaf.
	for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
	PHINode* PN = cast<PHINode>(I);
	// Remove all but one incoming entries from the cluster
	uint64_t Range = Leaf.High->getSExtValue() -
	Leaf.Low->getSExtValue();
	for (uint64_t j = 0; j < Range; ++j) {
	PN->removeIncomingValue(OrigBlock);
	}

	int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
	assert(BlockIdx != -1 && "Switch didn't go to this successor??");
	PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
	}

	return NewLeaf;
	}

	// Clusterify - Transform simple list of Cases into list of CaseRange's
	unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
	unsigned numCmps = 0;

	// Start with "simple" cases
	for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
	Cases.push_back(CaseRange(i.getCaseValue(), i.getCaseValue(),
	i.getCaseSuccessor()));

	std::sort(Cases.begin(), Cases.end(), CaseCmp());

	// Merge case into clusters
	if (Cases.size() >= 2) {
	CaseItr I = Cases.begin();
	for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) {
	int64_t nextValue = J->Low->getSExtValue();
	int64_t currentValue = I->High->getSExtValue();
	BasicBlock* nextBB = J->BB;
	BasicBlock* currentBB = I->BB;

	// If the two neighboring cases go to the same destination, merge them
	// into a single case.
	assert(nextValue > currentValue && "Cases should be strictly ascending");
	if ((nextValue == currentValue + 1) && (currentBB == nextBB)) {
	I->High = J->High;
	// FIXME: Combine branch weights.
	} else if (++I != J) {
	I = J;
	}
	}
	Cases.erase(std::next(I), Cases.end());
	}

	for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
	if (I->Low != I->High)
	// A range counts double, since it requires two compares.
	++numCmps;
	}

	return numCmps;
	}

	// processSwitchInst - Replace the specified switch instruction with a sequence
	// of chained if-then insts in a balanced binary search.
	//
	void LowerSwitch::processSwitchInst(SwitchInst *SI) {
	BasicBlock *CurBlock = SI->getParent();
	BasicBlock *OrigBlock = CurBlock;
	Function *F = CurBlock->getParent();
	Value *Val = SI->getCondition(); // The value we are switching on...
	BasicBlock* Default = SI->getDefaultDest();

	// If there is only the default destination, just branch.
	if (!SI->getNumCases()) {
	BranchInst::Create(Default, CurBlock);
	SI->eraseFromParent();
	return;
	}

	// Prepare cases vector.
	CaseVector Cases;
	unsigned numCmps = Clusterify(Cases, SI);
	DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
	<< ". Total compares: " << numCmps << "\n");
	DEBUG(dbgs() << "Cases: " << Cases << "\n");
	(void)numCmps;

	ConstantInt *LowerBound = nullptr;
	ConstantInt *UpperBound = nullptr;
	std::vector<IntRange> UnreachableRanges;

	if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
	// Make the bounds tightly fitted around the case value range, becase we
	// know that the value passed to the switch must be exactly one of the case
	// values.
	assert(!Cases.empty());
	LowerBound = Cases.front().Low;
	UpperBound = Cases.back().High;

	DenseMap<BasicBlock *, unsigned> Popularity;
	unsigned MaxPop = 0;
	BasicBlock *PopSucc = nullptr;

	IntRange R = { INT64_MIN, INT64_MAX };
	UnreachableRanges.push_back(R);
	for (const auto &I : Cases) {
	int64_t Low = I.Low->getSExtValue();
	int64_t High = I.High->getSExtValue();

	IntRange &LastRange = UnreachableRanges.back();
	if (LastRange.Low == Low) {
	// There is nothing left of the previous range.
	UnreachableRanges.pop_back();
	} else {
	// Terminate the previous range.
	assert(Low > LastRange.Low);
	LastRange.High = Low - 1;
	}
	if (High != INT64_MAX) {
	IntRange R = { High + 1, INT64_MAX };
	UnreachableRanges.push_back(R);
	}

	// Count popularity.
	int64_t N = High - Low + 1;
	unsigned &Pop = Popularity[I.BB];
	if ((Pop += N) > MaxPop) {
	MaxPop = Pop;
	PopSucc = I.BB;
	}
	}
	#ifndef NDEBUG
	/* UnreachableRanges should be sorted and the ranges non-adjacent. */
	for (auto I = UnreachableRanges.begin(), E = UnreachableRanges.end();
	I != E; ++I) {
	assert(I->Low <= I->High);
	auto Next = I + 1;
	if (Next != E) {
	assert(Next->Low > I->High);
	}
	}
	#endif

	// Use the most popular block as the new default, reducing the number of
	// cases.
	assert(MaxPop > 0 && PopSucc);
	Default = PopSucc;
	Cases.erase(std::remove_if(
	Cases.begin(), Cases.end(),
	[PopSucc](const CaseRange &R) { return R.BB == PopSucc; }),
	Cases.end());

	// If there are no cases left, just branch.
	if (Cases.empty()) {
	BranchInst::Create(Default, CurBlock);
	SI->eraseFromParent();
	return;
	}
	}

	// Create a new, empty default block so that the new hierarchy of
	// if-then statements go to this and the PHI nodes are happy.
	BasicBlock *NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
	F->getBasicBlockList().insert(Default, NewDefault);
	BranchInst::Create(Default, NewDefault);

	// If there is an entry in any PHI nodes for the default edge, make sure
	// to update them as well.
	for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
	PHINode *PN = cast<PHINode>(I);
	int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
	assert(BlockIdx != -1 && "Switch didn't go to this successor??");
	PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
	}

	BasicBlock *SwitchBlock =
	switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
	OrigBlock, OrigBlock, NewDefault, UnreachableRanges);

	// Branch to our shiny new if-then stuff...
	BranchInst::Create(SwitchBlock, OrigBlock);

	// We are now done with the switch instruction, delete it.
	BasicBlock *OldDefault = SI->getDefaultDest();
	CurBlock->getInstList().erase(SI);

	// If the Default block has no more predecessors just remove it.
	if (pred_begin(OldDefault) == pred_end(OldDefault))
	DeleteDeadBlock(OldDefault);
	}