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1c8a23c440
constructors. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80049 91177308-0d34-0410-b5e6-96231b3b80d8
324 lines
12 KiB
C++
324 lines
12 KiB
C++
//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// The LowerSwitch transformation rewrites switch instructions with a sequence
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// of branches, which allows targets to get away with not implementing the
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// switch instruction until it is convenient.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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using namespace llvm;
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namespace {
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/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
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/// instructions. Note that this cannot be a BasicBlock pass because it
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/// modifies the CFG!
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class VISIBILITY_HIDDEN LowerSwitch : public FunctionPass {
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public:
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static char ID; // Pass identification, replacement for typeid
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LowerSwitch() : FunctionPass(&ID) {}
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virtual bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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// This is a cluster of orthogonal Transforms
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AU.addPreserved<UnifyFunctionExitNodes>();
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AU.addPreservedID(PromoteMemoryToRegisterID);
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AU.addPreservedID(LowerInvokePassID);
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AU.addPreservedID(LowerAllocationsID);
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}
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struct CaseRange {
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Constant* Low;
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Constant* High;
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BasicBlock* BB;
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CaseRange() : Low(0), High(0), BB(0) { }
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CaseRange(Constant* low, Constant* high, BasicBlock* bb) :
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Low(low), High(high), BB(bb) { }
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};
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typedef std::vector<CaseRange> CaseVector;
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typedef std::vector<CaseRange>::iterator CaseItr;
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private:
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void processSwitchInst(SwitchInst *SI);
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BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
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BasicBlock* OrigBlock, BasicBlock* Default);
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BasicBlock* newLeafBlock(CaseRange& Leaf, Value* Val,
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BasicBlock* OrigBlock, BasicBlock* Default);
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unsigned Clusterify(CaseVector& Cases, SwitchInst *SI);
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};
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/// The comparison function for sorting the switch case values in the vector.
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/// WARNING: Case ranges should be disjoint!
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struct CaseCmp {
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bool operator () (const LowerSwitch::CaseRange& C1,
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const LowerSwitch::CaseRange& C2) {
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const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
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const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
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return CI1->getValue().slt(CI2->getValue());
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}
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};
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}
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char LowerSwitch::ID = 0;
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static RegisterPass<LowerSwitch>
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X("lowerswitch", "Lower SwitchInst's to branches");
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// Publically exposed interface to pass...
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const PassInfo *const llvm::LowerSwitchID = &X;
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// createLowerSwitchPass - Interface to this file...
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FunctionPass *llvm::createLowerSwitchPass() {
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return new LowerSwitch();
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}
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bool LowerSwitch::runOnFunction(Function &F) {
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bool Changed = false;
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
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BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks
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if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
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Changed = true;
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processSwitchInst(SI);
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}
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}
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return Changed;
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}
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// operator<< - Used for debugging purposes.
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//
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static raw_ostream& operator<<(raw_ostream &O,
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const LowerSwitch::CaseVector &C) ATTRIBUTE_USED;
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static raw_ostream& operator<<(raw_ostream &O,
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const LowerSwitch::CaseVector &C) {
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O << "[";
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for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
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E = C.end(); B != E; ) {
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O << *B->Low << " -" << *B->High;
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if (++B != E) O << ", ";
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}
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return O << "]";
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}
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// switchConvert - Convert the switch statement into a binary lookup of
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// the case values. The function recursively builds this tree.
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//
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BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
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Value* Val, BasicBlock* OrigBlock,
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BasicBlock* Default)
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{
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unsigned Size = End - Begin;
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if (Size == 1)
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return newLeafBlock(*Begin, Val, OrigBlock, Default);
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unsigned Mid = Size / 2;
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std::vector<CaseRange> LHS(Begin, Begin + Mid);
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DEBUG(errs() << "LHS: " << LHS << "\n");
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std::vector<CaseRange> RHS(Begin + Mid, End);
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DEBUG(errs() << "RHS: " << RHS << "\n");
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CaseRange& Pivot = *(Begin + Mid);
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DEBUG(errs() << "Pivot ==> "
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<< cast<ConstantInt>(Pivot.Low)->getValue() << " -"
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<< cast<ConstantInt>(Pivot.High)->getValue() << "\n");
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BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
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OrigBlock, Default);
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BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
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OrigBlock, Default);
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// Create a new node that checks if the value is < pivot. Go to the
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// left branch if it is and right branch if not.
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Function* F = OrigBlock->getParent();
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BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");
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Function::iterator FI = OrigBlock;
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F->getBasicBlockList().insert(++FI, NewNode);
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ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
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Val, Pivot.Low, "Pivot");
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NewNode->getInstList().push_back(Comp);
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BranchInst::Create(LBranch, RBranch, Comp, NewNode);
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return NewNode;
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}
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// newLeafBlock - Create a new leaf block for the binary lookup tree. It
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// checks if the switch's value == the case's value. If not, then it
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// jumps to the default branch. At this point in the tree, the value
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// can't be another valid case value, so the jump to the "default" branch
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// is warranted.
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//
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BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
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BasicBlock* OrigBlock,
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BasicBlock* Default)
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{
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Function* F = OrigBlock->getParent();
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BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
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Function::iterator FI = OrigBlock;
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F->getBasicBlockList().insert(++FI, NewLeaf);
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// Emit comparison
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ICmpInst* Comp = NULL;
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if (Leaf.Low == Leaf.High) {
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// Make the seteq instruction...
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Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
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Leaf.Low, "SwitchLeaf");
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} else {
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// Make range comparison
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if (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
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// Val >= Min && Val <= Hi --> Val <= Hi
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Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
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"SwitchLeaf");
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} else if (cast<ConstantInt>(Leaf.Low)->isZero()) {
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// Val >= 0 && Val <= Hi --> Val <=u Hi
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Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
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"SwitchLeaf");
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} else {
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// Emit V-Lo <=u Hi-Lo
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Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
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Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
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Val->getName()+".off",
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NewLeaf);
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Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
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Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
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"SwitchLeaf");
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}
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}
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// Make the conditional branch...
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BasicBlock* Succ = Leaf.BB;
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BranchInst::Create(Succ, Default, Comp, NewLeaf);
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// If there were any PHI nodes in this successor, rewrite one entry
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// from OrigBlock to come from NewLeaf.
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for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
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PHINode* PN = cast<PHINode>(I);
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// Remove all but one incoming entries from the cluster
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uint64_t Range = cast<ConstantInt>(Leaf.High)->getSExtValue() -
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cast<ConstantInt>(Leaf.Low)->getSExtValue();
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for (uint64_t j = 0; j < Range; ++j) {
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PN->removeIncomingValue(OrigBlock);
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}
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int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
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assert(BlockIdx != -1 && "Switch didn't go to this successor??");
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PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
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}
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return NewLeaf;
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}
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// Clusterify - Transform simple list of Cases into list of CaseRange's
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unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
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unsigned numCmps = 0;
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// Start with "simple" cases
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for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
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Cases.push_back(CaseRange(SI->getSuccessorValue(i),
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SI->getSuccessorValue(i),
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SI->getSuccessor(i)));
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std::sort(Cases.begin(), Cases.end(), CaseCmp());
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// Merge case into clusters
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if (Cases.size()>=2)
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for (CaseItr I=Cases.begin(), J=next(Cases.begin()); J!=Cases.end(); ) {
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int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
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int64_t currentValue = cast<ConstantInt>(I->High)->getSExtValue();
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BasicBlock* nextBB = J->BB;
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BasicBlock* currentBB = I->BB;
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// If the two neighboring cases go to the same destination, merge them
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// into a single case.
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if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
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I->High = J->High;
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J = Cases.erase(J);
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} else {
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I = J++;
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}
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}
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for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
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if (I->Low != I->High)
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// A range counts double, since it requires two compares.
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++numCmps;
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}
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return numCmps;
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}
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// processSwitchInst - Replace the specified switch instruction with a sequence
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// of chained if-then insts in a balanced binary search.
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//
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void LowerSwitch::processSwitchInst(SwitchInst *SI) {
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BasicBlock *CurBlock = SI->getParent();
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BasicBlock *OrigBlock = CurBlock;
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Function *F = CurBlock->getParent();
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Value *Val = SI->getOperand(0); // The value we are switching on...
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BasicBlock* Default = SI->getDefaultDest();
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// If there is only the default destination, don't bother with the code below.
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if (SI->getNumOperands() == 2) {
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BranchInst::Create(SI->getDefaultDest(), CurBlock);
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CurBlock->getInstList().erase(SI);
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return;
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}
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// Create a new, empty default block so that the new hierarchy of
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// if-then statements go to this and the PHI nodes are happy.
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BasicBlock* NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
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F->getBasicBlockList().insert(Default, NewDefault);
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BranchInst::Create(Default, NewDefault);
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// If there is an entry in any PHI nodes for the default edge, make sure
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// to update them as well.
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for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
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assert(BlockIdx != -1 && "Switch didn't go to this successor??");
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PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
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}
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// Prepare cases vector.
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CaseVector Cases;
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unsigned numCmps = Clusterify(Cases, SI);
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DEBUG(errs() << "Clusterify finished. Total clusters: " << Cases.size()
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<< ". Total compares: " << numCmps << "\n");
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DEBUG(errs() << "Cases: " << Cases << "\n");
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(void)numCmps;
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BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
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OrigBlock, NewDefault);
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// Branch to our shiny new if-then stuff...
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BranchInst::Create(SwitchBlock, OrigBlock);
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// We are now done with the switch instruction, delete it.
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CurBlock->getInstList().erase(SI);
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}
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