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220 lines
8.4 KiB
C++
220 lines
8.4 KiB
C++
//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Guarantees that all loops with identifiable, linear, induction variables will
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// be transformed to have a single, canonical, induction variable. After this
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// pass runs, it guarantees the the first PHI node of the header block in the
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// loop is the canonical induction variable if there is one.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Analysis/InductionVariable.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/iPHINode.h"
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#include "llvm/iOther.h"
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#include "llvm/Type.h"
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#include "llvm/Constants.h"
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#include "llvm/Support/CFG.h"
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#include "Support/Debug.h"
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#include "Support/Statistic.h"
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#include "Support/STLExtras.h"
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namespace {
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Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
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Statistic<> NumInserted("indvars", "Number of canonical indvars added");
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}
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// InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
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// name...
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//
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static Instruction *InsertCast(Value *Val, const Type *Ty,
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Instruction *InsertBefore) {
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return new CastInst(Val, Ty, Val->getName()+"-casted", InsertBefore);
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}
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static bool TransformLoop(LoopInfo *Loops, Loop *Loop) {
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// Transform all subloops before this loop...
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bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
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Loop->getSubLoops().end(),
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std::bind1st(std::ptr_fun(TransformLoop), Loops));
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// Get the header node for this loop. All of the phi nodes that could be
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// induction variables must live in this basic block.
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//
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BasicBlock *Header = Loop->getHeader();
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// Loop over all of the PHI nodes in the basic block, calculating the
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// induction variables that they represent... stuffing the induction variable
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// info into a vector...
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//
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std::vector<InductionVariable> IndVars; // Induction variables for block
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BasicBlock::iterator AfterPHIIt = Header->begin();
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for (; PHINode *PN = dyn_cast<PHINode>(AfterPHIIt); ++AfterPHIIt)
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IndVars.push_back(InductionVariable(PN, Loops));
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// AfterPHIIt now points to first non-phi instruction...
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// If there are no phi nodes in this basic block, there can't be indvars...
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if (IndVars.empty()) return Changed;
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// Loop over the induction variables, looking for a canonical induction
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// variable, and checking to make sure they are not all unknown induction
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// variables.
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//
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bool FoundIndVars = false;
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InductionVariable *Canonical = 0;
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for (unsigned i = 0; i < IndVars.size(); ++i) {
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if (IndVars[i].InductionType == InductionVariable::Canonical &&
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!isa<PointerType>(IndVars[i].Phi->getType()))
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Canonical = &IndVars[i];
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if (IndVars[i].InductionType != InductionVariable::Unknown)
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FoundIndVars = true;
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}
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// No induction variables, bail early... don't add a canonical indvar
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if (!FoundIndVars) return Changed;
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// Okay, we want to convert other induction variables to use a canonical
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// indvar. If we don't have one, add one now...
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if (!Canonical) {
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// Create the PHI node for the new induction variable, and insert the phi
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// node at the start of the PHI nodes...
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PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar", Header->begin());
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// Create the increment instruction to add one to the counter...
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Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
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ConstantUInt::get(Type::UIntTy,1),
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"add1-indvar", AfterPHIIt);
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// Figure out which block is incoming and which is the backedge for the loop
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BasicBlock *Incoming, *BackEdgeBlock;
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pred_iterator PI = pred_begin(Header);
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assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
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if (Loop->contains(*PI)) { // First pred is back edge...
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BackEdgeBlock = *PI++;
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Incoming = *PI++;
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} else {
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Incoming = *PI++;
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BackEdgeBlock = *PI++;
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}
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assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
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// Add incoming values for the PHI node...
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PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming);
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PN->addIncoming(Add, BackEdgeBlock);
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// Analyze the new induction variable...
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IndVars.push_back(InductionVariable(PN, Loops));
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assert(IndVars.back().InductionType == InductionVariable::Canonical &&
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"Just inserted canonical indvar that is not canonical!");
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Canonical = &IndVars.back();
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++NumInserted;
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Changed = true;
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} else {
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// If we have a canonical induction variable, make sure that it is the first
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// one in the basic block.
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if (&Header->front() != Canonical->Phi)
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Header->getInstList().splice(Header->begin(), Header->getInstList(),
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Canonical->Phi);
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}
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DEBUG(std::cerr << "Induction variables:\n");
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// Get the current loop iteration count, which is always the value of the
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// canonical phi node...
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//
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PHINode *IterCount = Canonical->Phi;
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// Loop through and replace all of the auxiliary induction variables with
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// references to the canonical induction variable...
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//
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for (unsigned i = 0; i < IndVars.size(); ++i) {
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InductionVariable *IV = &IndVars[i];
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DEBUG(IV->print(std::cerr));
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// Don't do math with pointers...
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const Type *IVTy = IV->Phi->getType();
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if (isa<PointerType>(IVTy)) IVTy = Type::ULongTy;
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// Don't modify the canonical indvar or unrecognized indvars...
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if (IV != Canonical && IV->InductionType != InductionVariable::Unknown) {
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Instruction *Val = IterCount;
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if (!isa<ConstantInt>(IV->Step) || // If the step != 1
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!cast<ConstantInt>(IV->Step)->equalsInt(1)) {
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// If the types are not compatible, insert a cast now...
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if (Val->getType() != IVTy)
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Val = InsertCast(Val, IVTy, AfterPHIIt);
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if (IV->Step->getType() != IVTy)
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IV->Step = InsertCast(IV->Step, IVTy, AfterPHIIt);
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Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step,
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IV->Phi->getName()+"-scale", AfterPHIIt);
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}
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// If the start != 0
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if (IV->Start != Constant::getNullValue(IV->Start->getType())) {
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// If the types are not compatible, insert a cast now...
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if (Val->getType() != IVTy)
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Val = InsertCast(Val, IVTy, AfterPHIIt);
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if (IV->Start->getType() != IVTy)
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IV->Start = InsertCast(IV->Start, IVTy, AfterPHIIt);
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// Insert the instruction after the phi nodes...
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Val = BinaryOperator::create(Instruction::Add, Val, IV->Start,
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IV->Phi->getName()+"-offset", AfterPHIIt);
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}
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// If the PHI node has a different type than val is, insert a cast now...
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if (Val->getType() != IV->Phi->getType())
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Val = InsertCast(Val, IV->Phi->getType(), AfterPHIIt);
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// Replace all uses of the old PHI node with the new computed value...
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IV->Phi->replaceAllUsesWith(Val);
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// Move the PHI name to it's new equivalent value...
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std::string OldName = IV->Phi->getName();
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IV->Phi->setName("");
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Val->setName(OldName);
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// Delete the old, now unused, phi node...
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Header->getInstList().erase(IV->Phi);
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Changed = true;
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++NumRemoved;
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}
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}
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return Changed;
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}
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namespace {
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struct InductionVariableSimplify : public FunctionPass {
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virtual bool runOnFunction(Function &) {
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LoopInfo &LI = getAnalysis<LoopInfo>();
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// Induction Variables live in the header nodes of loops
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return reduce_apply_bool(LI.getTopLevelLoops().begin(),
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LI.getTopLevelLoops().end(),
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std::bind1st(std::ptr_fun(TransformLoop), &LI));
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LoopInfo>();
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AU.addRequiredID(LoopSimplifyID);
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AU.setPreservesCFG();
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}
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};
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RegisterOpt<InductionVariableSimplify> X("indvars",
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"Canonicalize Induction Variables");
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}
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Pass *createIndVarSimplifyPass() {
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return new InductionVariableSimplify();
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}
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