Iterating Function, Basicblock, and Instruction with LLVM

As we discussed previous post, LLVM Structure consists of Modules, functions, basicblocks, and instructions. Therefore, we can search for one of them through its super set. For example, if you are looking for an add instruction, you can find it by investigating BasicBlocks.

Learning Objectives

  • Learn how to iterate LLVM structures(Module, Function, BasicBlock, Instruction)

LLVM

Iterating over Functions

Iterating over Basicblocks

llvm/IR/BasicBlock.h header is deprecated. So you may include Function.h or Module.h when you iterate BasicBlocks.

You can iterate BasicBlocks in a function F.

for(BasicBlock &BB: F){
    errs() << "Start BB: " << BB.getName() << ' ' << BB.size() << '\n';
}

Iterating over Instructions

You can iterate instructions in a BasicBlocks BB.

for(Instruction &I: BB){
    errs() << "Start Inst: " << I << '\n';
}

#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Instructions.h"

#include "llvm/Support/raw_ostream.h"

using namespace llvm;

namespace {
    struct YJ00003BB : public FunctionPass{
        static char ID;
        YJ00003BB() : FunctionPass(ID){}

        bool runOnFunction(Function &F) override{
            // Function
            errs() << "Start Function: " << F.getName() << '\n';

            for(BasicBlock &BB: F){
                errs() << "Start BB: " << BB.getName() << ' ' << BB.size() << '\n';

                for(Instruction & I : BB){
                    errs() << "Start Inst: " << I << '\n';
                }
            }

            return false;
        }
    };
}

char YJ00003BB::ID = 0;
static RegisterPass<YJ00003BB> X("BasicBlock", "Print basic block", false, false);
Pass Type
Writing HelloLLVM Pass analysis
Iterating over Module, Function, Basic block analysis
Count the number of insts, func calls analysis
Insert func call transformation
Change Insts (obfuscation) transformation
Control flow graph transformation

Reference

[1] Andrzej Warzyński. llvm-tutor. github
[2] Adrian Sampson. LLVM for Grad Students. blog
[3] Keshav Pingali. CS 380C: Advanced Topics in Compilers. blog