将IR操作数与LLVM中的常量进行比较

时间:2012-02-14 08:30:09

标签: llvm

我有一个IR,看起来像这样:

%5=icmp eq i32 %4,0

我想检查icmp指令的第二个操作数是否为0或其他。我使用了getOperand(1),它以Value *格式返回结果。如何将它与常数0进行比较?

1 个答案:

答案 0 :(得分:4)

以下是您可以运行的示例传递来找到它:

class DetectZeroValuePass : public FunctionPass {
public:
    static char ID;

    DetectZeroValuePass()
        : FunctionPass(ID)
    {}

    virtual bool runOnFunction(Function &F) {
        for (Function::iterator bb = F.begin(), bb_e = F.end(); bb != bb_e; ++bb) {
            for (BasicBlock::iterator ii = bb->begin(), ii_e = bb->end(); ii != ii_e; ++ii) {
                if (CmpInst *cmpInst = dyn_cast<CmpInst>(&*ii)) {
                    handle_cmp(cmpInst);
                }
            }
        }
    }

    void handle_cmp(CmpInst *cmpInst) {
        // Detect cmp instructions with the second operand being 0
        if (cmpInst->getNumOperands() >= 2) {
            Value *secondOperand = cmpInst->getOperand(1);
            if (ConstantInt *CI = dyn_cast<ConstantInt>(secondOperand))
                if (CI->isZero()) {
                    errs() << "In the following instruction, second operand is 0\n";
                    cmpInst->dump();
                }
        }
    }
};