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

Tutorial February 12, 2025 

#include "DSL/Lexer.h"
#include "DSL/Parser.h"
#include "DSL/AST.h"
#include <llvm/IR/LLVMContext.h>
#include <llvm/IR/Module.h>
#include <llvm/Support/TargetSelect.h>
#include <iostream>
#include <memory>

extern llvm::Function* generateFunction(llvm::LLVMContext& context, llvm::Module& module, ASTNode* root);
extern void optimizeModule(llvm::Module& module);

int main() {
    // Initialize LLVM.
    llvm::InitializeNativeTarget();
    llvm::InitializeNativeTargetAsmPrinter();
    llvm::LLVMContext context;
    llvm::Module module("MyDSLModule", context);

    std::string input;
    std::cout << "Enter an expression: ";
    std::getline(std::cin, input);

    Lexer lexer(input);
    Parser parser(lexer);
    std::unique_ptr<ASTNode> astRoot;
    try {
        astRoot = parser.parseExpression();
    } catch (const std::exception& ex) {
        std::cerr << "Parsing error: " << ex.what() << std::endl;
        return 1;
    }

    llvm::Function* func = generateFunction(context, module, astRoot.get());
    if (!func) {
        std::cerr << "Failed to generate LLVM function." << std::endl;
        return 1;
    }

    optimizeModule(module);

    // For demonstration, print the LLVM IR.
    module.print(llvm::outs(), nullptr);

    // In a full implementation, you could now JIT compile and execute the function.
    return 0;
}

This basic runtime lets you enter a mathematical expression, compiles it into LLVM IR, optimizes the code, and prints the IR. Expanding this further, you can use LLVM’s JIT compilation APIs to execute the code on the fly, integrate debugging information, or even embed the DSL into larger systems.

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