[llvm-dev] Difficulty in understanding loop analysis code

Fatima Ahmed via llvm-dev llvm-dev at lists.llvm.org
Wed Dec 19 09:47:24 PST 2018

Hey all!
I'm new to LLVM and advance C++.
 I came across this piece of code and found it difficult to understand.

Can anyone please explain how is it working ? I want to get loop count, sub loop count etc printed as output.Thanks.
//Iteration on loops            for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i)
                Loop *L = *i;
                int subloop = 1;
                static LLVMContext Context;
                BasicBlock *parentLoopPred = L->getLoopPredecessor();
                BasicBlock *parentLoopHead = L->getHeader();
                std::vector<Loop*> subLoopAll = L->getSubLoops();
                Loop::iterator j, f;
                //Parent Loop Calculation
                //Counter = 0 instruction insertion
                // You must declare a constant Int like so instead of using it directly in a AllocaInst instantiation.
                ConstantInt *IntVal4 = ConstantInt::get(Type::getInt32Ty(Context), 4); // counter = 4
                Value *one1 = ConstantInt::get(Type::getInt32Ty(Context), -1, true);
                Instruction *ACounter1 = new AllocaInst(Type::getInt32Ty(Context), 0, IntVal4, "counter");  //(IntegerType::get(mContext, 32), one,    "counter", loopPredecessor);  //(IntegerType::get(mContext, 32), IR.getInt32(0), "counter");
                parentLoopPred->getInstList().insert(parentLoopPred->getFirstInsertionPt(), ACounter1);

                Instruction *SCounter1 = new StoreInst(one1, ACounter1);
                //Counter++ instruction insertion
                Value *IValue1 = ConstantInt::get(Type::getInt32Ty(Context), 1, true);
                Instruction *CValue1 = new LoadInst(ACounter1, "midCount");
                parentLoopHead->getInstList().insert(parentLoopHead->getFirstInsertionPt(), CValue1);
                Instruction *NValue1 = BinaryOperator::CreateNSWAdd(CValue1, IValue1, "incremented");//  Instruction::Add, CValue, IValue, "");
                Instruction *SNValue1 = new StoreInst(NValue1, ACounter1);
                Value *PValue1 = SNValue1->getOperand(0);
                std::vector<Value *> printArrayRef1;
                Value *PValue12 = ConstantInt::get(Type::getInt32Ty(Context), subLoopAll.size(), true);
                std::vector<Value *> printArrayRef12;
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