forked from OSchip/llvm-project
210 lines
7.1 KiB
C++
210 lines
7.1 KiB
C++
//===- BoundsChecking.cpp - Instrumentation for run-time bounds checking --===//
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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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// This file implements a pass that instruments the code to perform run-time
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// bounds checking on loads, stores, and other memory intrinsics.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "bounds-checking"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/IRBuilder.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/Support/TargetFolder.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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static cl::opt<bool> SingleTrapBB("bounds-checking-single-trap",
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cl::desc("Use one trap block per function"));
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STATISTIC(ChecksAdded, "Bounds checks added");
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STATISTIC(ChecksSkipped, "Bounds checks skipped");
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STATISTIC(ChecksUnable, "Bounds checks unable to add");
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typedef IRBuilder<true, TargetFolder> BuilderTy;
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namespace {
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struct BoundsChecking : public FunctionPass {
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static char ID;
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BoundsChecking(unsigned _Penalty = 5) : FunctionPass(ID), Penalty(_Penalty){
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initializeBoundsCheckingPass(*PassRegistry::getPassRegistry());
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}
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virtual bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<TargetData>();
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}
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private:
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const TargetData *TD;
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ObjectSizeOffsetEvaluator *ObjSizeEval;
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BuilderTy *Builder;
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Instruction *Inst;
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BasicBlock *TrapBB;
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unsigned Penalty;
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BasicBlock *getTrapBB();
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void emitBranchToTrap(Value *Cmp = 0);
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bool computeAllocSize(Value *Ptr, APInt &Offset, Value* &OffsetValue,
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APInt &Size, Value* &SizeValue);
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bool instrument(Value *Ptr, Value *Val);
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};
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}
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char BoundsChecking::ID = 0;
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INITIALIZE_PASS(BoundsChecking, "bounds-checking", "Run-time bounds checking",
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false, false)
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/// getTrapBB - create a basic block that traps. All overflowing conditions
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/// branch to this block. There's only one trap block per function.
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BasicBlock *BoundsChecking::getTrapBB() {
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if (TrapBB && SingleTrapBB)
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return TrapBB;
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Function *Fn = Inst->getParent()->getParent();
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BasicBlock::iterator PrevInsertPoint = Builder->GetInsertPoint();
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TrapBB = BasicBlock::Create(Fn->getContext(), "trap", Fn);
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Builder->SetInsertPoint(TrapBB);
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llvm::Value *F = Intrinsic::getDeclaration(Fn->getParent(), Intrinsic::trap);
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CallInst *TrapCall = Builder->CreateCall(F);
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TrapCall->setDoesNotReturn();
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TrapCall->setDoesNotThrow();
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TrapCall->setDebugLoc(Inst->getDebugLoc());
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Builder->CreateUnreachable();
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Builder->SetInsertPoint(PrevInsertPoint);
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return TrapBB;
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}
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/// emitBranchToTrap - emit a branch instruction to a trap block.
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/// If Cmp is non-null, perform a jump only if its value evaluates to true.
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void BoundsChecking::emitBranchToTrap(Value *Cmp) {
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// check if the comparison is always false
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ConstantInt *C = dyn_cast_or_null<ConstantInt>(Cmp);
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if (C) {
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++ChecksSkipped;
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if (!C->getZExtValue())
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return;
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else
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Cmp = 0; // unconditional branch
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}
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Instruction *Inst = Builder->GetInsertPoint();
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BasicBlock *OldBB = Inst->getParent();
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BasicBlock *Cont = OldBB->splitBasicBlock(Inst);
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OldBB->getTerminator()->eraseFromParent();
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if (Cmp)
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BranchInst::Create(getTrapBB(), Cont, Cmp, OldBB);
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else
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BranchInst::Create(getTrapBB(), OldBB);
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}
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/// instrument - adds run-time bounds checks to memory accessing instructions.
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/// Ptr is the pointer that will be read/written, and InstVal is either the
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/// result from the load or the value being stored. It is used to determine the
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/// size of memory block that is touched.
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/// Returns true if any change was made to the IR, false otherwise.
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bool BoundsChecking::instrument(Value *Ptr, Value *InstVal) {
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uint64_t NeededSize = TD->getTypeStoreSize(InstVal->getType());
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DEBUG(dbgs() << "Instrument " << *Ptr << " for " << Twine(NeededSize)
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<< " bytes\n");
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SizeOffsetEvalType SizeOffset = ObjSizeEval->compute(Ptr);
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if (!ObjSizeEval->bothKnown(SizeOffset)) {
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++ChecksUnable;
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return false;
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}
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Value *Size = SizeOffset.first;
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Value *Offset = SizeOffset.second;
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ConstantInt *SizeCI = dyn_cast<ConstantInt>(Size);
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IntegerType *IntTy = TD->getIntPtrType(Inst->getContext());
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Value *NeededSizeVal = ConstantInt::get(IntTy, NeededSize);
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// three checks are required to ensure safety:
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// . Offset >= 0 (since the offset is given from the base ptr)
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// . Size >= Offset (unsigned)
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// . Size - Offset >= NeededSize (unsigned)
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//
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// optimization: if Size >= 0 (signed), skip 1st check
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// FIXME: add NSW/NUW here? -- we dont care if the subtraction overflows
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Value *ObjSize = Builder->CreateSub(Size, Offset);
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Value *Cmp2 = Builder->CreateICmpULT(Size, Offset);
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Value *Cmp3 = Builder->CreateICmpULT(ObjSize, NeededSizeVal);
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Value *Or = Builder->CreateOr(Cmp2, Cmp3);
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if (!SizeCI || SizeCI->getValue().slt(0)) {
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Value *Cmp1 = Builder->CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
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Or = Builder->CreateOr(Cmp1, Or);
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}
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emitBranchToTrap(Or);
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++ChecksAdded;
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return true;
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}
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bool BoundsChecking::runOnFunction(Function &F) {
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TD = &getAnalysis<TargetData>();
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TrapBB = 0;
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BuilderTy TheBuilder(F.getContext(), TargetFolder(TD));
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Builder = &TheBuilder;
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ObjectSizeOffsetEvaluator TheObjSizeEval(TD, F.getContext());
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ObjSizeEval = &TheObjSizeEval;
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// check HANDLE_MEMORY_INST in include/llvm/Instruction.def for memory
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// touching instructions
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std::vector<Instruction*> WorkList;
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for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
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Instruction *I = &*i;
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if (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<AtomicCmpXchgInst>(I) ||
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isa<AtomicRMWInst>(I))
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WorkList.push_back(I);
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}
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bool MadeChange = false;
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for (std::vector<Instruction*>::iterator i = WorkList.begin(),
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e = WorkList.end(); i != e; ++i) {
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Inst = *i;
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Builder->SetInsertPoint(Inst);
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
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MadeChange |= instrument(LI->getPointerOperand(), LI);
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} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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MadeChange |= instrument(SI->getPointerOperand(), SI->getValueOperand());
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} else if (AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(Inst)) {
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MadeChange |= instrument(AI->getPointerOperand(),AI->getCompareOperand());
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} else if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(Inst)) {
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MadeChange |= instrument(AI->getPointerOperand(), AI->getValOperand());
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} else {
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llvm_unreachable("unknown Instruction type");
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}
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}
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return MadeChange;
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}
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FunctionPass *llvm::createBoundsCheckingPass(unsigned Penalty) {
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return new BoundsChecking(Penalty);
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}
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