| //===- InsertDivideCheck.cpp - Add divide by zero checks ------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass adds a check for divide by zero before every integer DIV or REM. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "add-divide-check" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CFG.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Transforms/NaCl.h" |
| |
| using namespace llvm; |
| |
| namespace { |
| class InsertDivideCheck : public FunctionPass { |
| public: |
| static char ID; |
| InsertDivideCheck() : FunctionPass(ID) { |
| initializeInsertDivideCheckPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F); |
| }; |
| } |
| |
| static BasicBlock *CreateTrapBlock(Function &F, DebugLoc dl) { |
| BasicBlock *TrapBlock = BasicBlock::Create(F.getContext(), "divrem.by.zero", |
| &F); |
| Value *TrapFn = Intrinsic::getDeclaration(F.getParent(), Intrinsic::trap); |
| CallInst::Create(TrapFn, "", TrapBlock)->setDebugLoc(dl); |
| (new UnreachableInst(F.getContext(), TrapBlock))->setDebugLoc(dl); |
| return TrapBlock; |
| } |
| |
| bool InsertDivideCheck::runOnFunction(Function &F) { |
| SmallPtrSet<Instruction*, 8> GuardedDivs; |
| // If the pass finds a DIV/REM that needs to be checked for zero denominator, |
| // it will insert a new "trap" block, and split the block that contains the |
| // DIV/REM into two blocks. The new BasicBlocks are added after the current |
| // BasicBlock, so that if there is more than one DIV/REM in the same block, |
| // all are visited. |
| for (Function::iterator I = F.begin(); I != F.end(); I++) { |
| BasicBlock *BB = &*I; |
| |
| for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); |
| BI != BE; BI++) { |
| BinaryOperator *DivInst = dyn_cast<BinaryOperator>(BI); |
| if (!DivInst || (GuardedDivs.count(DivInst) != 0)) |
| continue; |
| unsigned Opcode = DivInst->getOpcode(); |
| if (Opcode != Instruction::SDiv && Opcode != Instruction::UDiv && |
| Opcode != Instruction::SRem && Opcode != Instruction::URem) |
| continue; |
| Value *Denominator = DivInst->getOperand(1); |
| if (!Denominator->getType()->isIntegerTy()) |
| continue; |
| DebugLoc dl = DivInst->getDebugLoc(); |
| if (ConstantInt *DenomConst = dyn_cast<ConstantInt>(Denominator)) { |
| // Divides by constants do not need a denominator test. |
| if (DenomConst->isZero()) { |
| // For explicit divides by zero, insert a trap before DIV/REM |
| Value *TrapFn = Intrinsic::getDeclaration(F.getParent(), |
| Intrinsic::trap); |
| CallInst::Create(TrapFn, "", DivInst)->setDebugLoc(dl); |
| } |
| continue; |
| } |
| // Create a trap block. |
| BasicBlock *TrapBlock = CreateTrapBlock(F, dl); |
| // Move instructions in BB from DivInst to BB's end to a new block. |
| BasicBlock *Successor = BB->splitBasicBlock(BI, "guarded.divrem"); |
| // Remove the unconditional branch inserted by splitBasicBlock. |
| BB->getTerminator()->eraseFromParent(); |
| // Remember that DivInst was already processed, so that when we process |
| // inserted blocks later, we do not attempt to again guard it. |
| GuardedDivs.insert(DivInst); |
| // Compare the denominator with zero. |
| Value *Zero = ConstantInt::get(Denominator->getType(), 0); |
| Value *DenomIsZero = new ICmpInst(*BB, ICmpInst::ICMP_EQ, Denominator, |
| Zero, ""); |
| // Put in a condbranch to the trap block. |
| BranchInst::Create(TrapBlock, Successor, DenomIsZero, BB); |
| // BI is invalidated when we split. Stop the BasicBlock iterator. |
| break; |
| } |
| } |
| |
| return false; |
| } |
| |
| char InsertDivideCheck::ID = 0; |
| INITIALIZE_PASS(InsertDivideCheck, "insert-divide-check", |
| "Insert divide by zero checks", false, false) |
| |
| FunctionPass *llvm::createInsertDivideCheckPass() { |
| return new InsertDivideCheck(); |
| } |