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Implementing a Domain-Specific Language (DSL) with LLVM and C++

Tutorial February 12, 2025

Implementation: CodeGen.cpp

#include "DSL/AST.h"
#include <llvm/IR/Module.h>
#include <llvm/IR/Verifier.h>
#include <llvm/IR/LegacyPassManager.h>
#include <llvm/IR/Function.h>
#include <llvm/Support/TargetSelect.h>
#include <llvm/IR/IRBuilder.h>
#include <memory>
#include <iostream>

llvm::Function* generateFunction(llvm::LLVMContext& context, llvm::Module& module, ASTNode* root) {
    // Create function type: double ().
    llvm::FunctionType* funcType = llvm::FunctionType::get(llvm::Type::getDoubleTy(context), false);
    llvm::Function* function = llvm::Function::Create(funcType, llvm::Function::ExternalLinkage, "main_expr", module);

    llvm::BasicBlock* block = llvm::BasicBlock::Create(context, "entry", function);
    llvm::IRBuilder<> builder(block);

    llvm::Value* retVal = root->codegen(builder);
    if (!retVal) {
        std::cerr << "Error generating code for the expression." << std::endl;
        return nullptr;
    }

    builder.CreateRet(retVal);
    if (llvm::verifyFunction(*function, &llvm::errs())) {
        function->eraseFromParent();
        return nullptr;
    }

    return function;
}

void optimizeModule(llvm::Module& module) {
    llvm::legacy::PassManager passManager;
    // Add some basic optimization passes.
    // In a production compiler, you'd add many more!
    passManager.add(llvm::createInstructionCombiningPass());
    passManager.add(llvm::createReassociatePass());
    passManager.add(llvm::createGVNPass());
    passManager.add(llvm::createCFGSimplificationPass());
    passManager.run(module);
}

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