third_party/LLVM/lib/Transforms/Utils/LowerSwitch.cpp - SwiftShader - 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/Transforms/Utils/UnifyFunctionExitNodes.h"
 #include "llvm/Constants.h"
 #include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Pass.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 using namespace llvm;

 namespace {
   /// 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());
     }

     virtual bool runOnFunction(Function &F);

     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       // This is a cluster of orthogonal Transforms
       AU.addPreserved<UnifyFunctionExitNodes>();
       AU.addPreserved("mem2reg");
       AU.addPreservedID(LowerInvokePassID);
     }

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

       CaseRange(Constant *low = 0, Constant *high = 0, BasicBlock *bb = 0) :
         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, Value* Val,
                               BasicBlock* OrigBlock, BasicBlock* Default);
     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 << "]";
 }

 // switchConvert - Convert the switch statement into a binary lookup of
 // the case values. The function recursively builds this tree.
 //
 BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
                                        Value* Val, BasicBlock* OrigBlock,
                                        BasicBlock* Default)
 {
   unsigned Size = End - Begin;

   if (Size == 1)
     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 ==> "
                << cast<ConstantInt>(Pivot.Low)->getValue() << " -"
                << cast<ConstantInt>(Pivot.High)->getValue() << "\n");

   BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
                                       OrigBlock, Default);
   BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
                                       OrigBlock, Default);

   // 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");
   Function::iterator FI = OrigBlock;
   F->getBasicBlockList().insert(++FI, NewNode);

   ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
                                 Val, Pivot.Low, "Pivot");
   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 = NULL;
   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 (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
       // Val >= Min && Val <= Hi --> Val <= Hi
       Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
                           "SwitchLeaf");
     } else if (cast<ConstantInt>(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 = cast<ConstantInt>(Leaf.High)->getSExtValue() -
                      cast<ConstantInt>(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 (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
     Cases.push_back(CaseRange(SI->getSuccessorValue(i),
                               SI->getSuccessorValue(i),
                               SI->getSuccessor(i)));
   std::sort(Cases.begin(), Cases.end(), CaseCmp());

   // Merge case into clusters
   if (Cases.size()>=2)
     for (CaseItr I=Cases.begin(), J=llvm::next(Cases.begin()); J!=Cases.end(); ) {
       int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
       int64_t currentValue = cast<ConstantInt>(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.
       if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
         I->High = J->High;
         J = Cases.erase(J);
       } else {
         I = J++;
       }
     }

   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, don't bother with the code below.
   if (SI->getNumCases() == 1) {
     BranchInst::Create(SI->getDefaultDest(), CurBlock);
     CurBlock->getInstList().erase(SI);
     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);
   }

   // 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;

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

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

   // We are now done with the switch instruction, delete it.
   CurBlock->getInstList().erase(SI);
 }
	//===- 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/Transforms/Utils/UnifyFunctionExitNodes.h"
	#include "llvm/Constants.h"
	#include "llvm/Function.h"
	#include "llvm/Instructions.h"
	#include "llvm/LLVMContext.h"
	#include "llvm/Pass.h"
	#include "llvm/ADT/STLExtras.h"
	#include "llvm/Support/Compiler.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	#include <algorithm>
	using namespace llvm;

	namespace {
	/// 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());
	}

	virtual bool runOnFunction(Function &F);

	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	// This is a cluster of orthogonal Transforms
	AU.addPreserved<UnifyFunctionExitNodes>();
	AU.addPreserved("mem2reg");
	AU.addPreservedID(LowerInvokePassID);
	}

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

	CaseRange(Constant low = 0, Constant high = 0, BasicBlock *bb = 0) :
	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, Value* Val,
	BasicBlock* OrigBlock, BasicBlock* Default);
	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 << "]";
	}

	// switchConvert - Convert the switch statement into a binary lookup of
	// the case values. The function recursively builds this tree.
	//
	BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
	Value* Val, BasicBlock* OrigBlock,
	BasicBlock* Default)
	{
	unsigned Size = End - Begin;

	if (Size == 1)
	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 ==> "
	<< cast<ConstantInt>(Pivot.Low)->getValue() << " -"
	<< cast<ConstantInt>(Pivot.High)->getValue() << "\n");

	BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
	OrigBlock, Default);
	BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
	OrigBlock, Default);

	// 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");
	Function::iterator FI = OrigBlock;
	F->getBasicBlockList().insert(++FI, NewNode);

	ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
	Val, Pivot.Low, "Pivot");
	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 = NULL;
	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 (cast<ConstantInt>(Leaf.Low)->isMinValue(true /isSigned/)) {
	// Val >= Min && Val <= Hi --> Val <= Hi
	Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
	"SwitchLeaf");
	} else if (cast<ConstantInt>(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 = cast<ConstantInt>(Leaf.High)->getSExtValue() -
	cast<ConstantInt>(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 (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
	Cases.push_back(CaseRange(SI->getSuccessorValue(i),
	SI->getSuccessorValue(i),
	SI->getSuccessor(i)));
	std::sort(Cases.begin(), Cases.end(), CaseCmp());

	// Merge case into clusters
	if (Cases.size()>=2)
	for (CaseItr I=Cases.begin(), J=llvm::next(Cases.begin()); J!=Cases.end(); ) {
	int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
	int64_t currentValue = cast<ConstantInt>(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.
	if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
	I->High = J->High;
	J = Cases.erase(J);
	} else {
	I = J++;
	}
	}

	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, don't bother with the code below.
	if (SI->getNumCases() == 1) {
	BranchInst::Create(SI->getDefaultDest(), CurBlock);
	CurBlock->getInstList().erase(SI);
	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);
	}

	// 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;

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

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

	// We are now done with the switch instruction, delete it.
	CurBlock->getInstList().erase(SI);
	}