LLVM Helloworld

llvm-helloworld.cpp

#include <llvm/IR/Function.h>
#include <llvm/IR/IRBuilder.h>
#include <llvm/IR/LLVMContext.h>
#include <llvm/IR/Module.h>
#include <llvm/IR/Value.h>
#include <llvm/Support/raw_os_ostream.h>

#include <memory>


int main() {
    /*
        #include <cstdio>
        int main() {
            printf("hello world");
            return 0;
        }
    */

    auto theContext = std::make_unique<llvm::LLVMContext>();
    auto theModule = std::make_unique<llvm::Module>("helloworld", *theContext);
    auto theBuilder = std::make_unique<llvm::IRBuilder<>>(*theContext);

    // prepare int
    const auto int32Type = llvm::Type::getInt32Ty(*theContext);

    // prepare char*
    const auto int8PtrType = llvm::Type::getInt8PtrTy(*theContext);

    // ----------- codegen ----------

    // create main
    auto mainFuncType = llvm::FunctionType::get(int32Type, false);

    auto mainFunc = llvm::Function::Create(
        mainFuncType, llvm::GlobalValue::ExternalLinkage, "main", *theModule);

    // create printf
    std::vector<llvm::Type*> printfFuncArgs{int8PtrType};

    auto printfFuncType =
        llvm::FunctionType::get(int32Type, printfFuncArgs, true);

    auto printfFunc = llvm::Function::Create(printfFuncType,
                                             llvm::GlobalValue::ExternalLinkage,
                                             "printf", *theModule);

    // create main block
    auto mainBlock = llvm::BasicBlock::Create(*theContext, "entry",
                                              theModule->getFunction("main"));
    theBuilder->SetInsertPoint(mainBlock);

    // create string

    // call printf
    auto helloStr = theBuilder->CreateGlobalStringPtr("hello world\n");
    std::vector<llvm::Value*> callArgs{helloStr};
    theBuilder->CreateCall(printfFunc, callArgs);

    // return 0
    theBuilder->CreateRet(llvm::Constant::getNullValue(int32Type));

    // ------------------------------

    std::error_code errorcode;
    llvm::raw_fd_ostream stream("helloworld.ll", errorcode);

    theModule->print(stream, nullptr);

    return 0;
}