---

name: compiler-development description: Expertise in compiler development using LLVM infrastructure including frontend design, IR generation, optimization passes, and code generation. Use this skill when building custom programming languages, implementing DSL compilers, or working on compiler internals.

Compiler Development Skill

This skill provides comprehensive knowledge of building compilers and language implementations using the LLVM infrastructure.

Compiler Architecture Overview

Classic Three-Phase Design

CopySource Code → Frontend → Middle-End (Optimizer) → Backend → Machine Code
                ↓              ↓                      ↓
             AST/IR      LLVM IR Passes          Target Code

Frontend Development

Lexical Analysis

Copy// Token types for a simple language
enum class TokenKind {
    Identifier,
    Number,
    String,
    Keyword,
    Operator,
    Punctuation,
    EndOfFile
};

struct Token {
    TokenKind kind;
    std::string value;
    SourceLocation location;
};

Parser Implementation

• Recursive Descent: Easy to implement, good error messages
• Operator Precedence Parsing: Efficient for expression parsing
• LALR/LR: Use tools like Bison for complex grammars

AST Design

Copyclass Expr {
public:
    virtual ~Expr() = default;
    virtual llvm::Value* codegen() = 0;
};

class BinaryExpr : public Expr {
    std::unique_ptr<Expr> LHS, RHS;
    char Op;
public:
    llvm::Value* codegen() override {
        llvm::Value* L = LHS->codegen();
        llvm::Value* R = RHS->codegen();
        
        switch (Op) {
            case '+': return Builder.CreateFAdd(L, R, "addtmp");
            case '-': return Builder.CreateFSub(L, R, "subtmp");
            case '*': return Builder.CreateFMul(L, R, "multmp");
            case '/': return Builder.CreateFDiv(L, R, "divtmp");
        }
    }
};

LLVM IR Generation

Module and Context Setup

Copy#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/IRBuilder.h"

class CodeGen {
    std::unique_ptr<llvm::LLVMContext> Context;
    std::unique_ptr<llvm::Module> Module;
    std::unique_ptr<llvm::IRBuilder<>> Builder;
    
public:
    CodeGen() {
        Context = std::make_unique<llvm::LLVMContext>();
        Module = std::make_unique<llvm::Module>("my_module", *Context);
        Builder = std::make_unique<llvm::IRBuilder<>>(*Context);
    }
};

Function Generation

Copyllvm::Function* createFunction(const std::string& name, 
                                llvm::Type* returnType,
                                std::vector<llvm::Type*> params) {
    llvm::FunctionType* FT = llvm::FunctionType::get(returnType, params, false);
    llvm::Function* F = llvm::Function::Create(
        FT, llvm::Function::ExternalLinkage, name, Module.get());
    
    llvm::BasicBlock* BB = llvm::BasicBlock::Create(*Context, "entry", F);
    Builder->SetInsertPoint(BB);
    
    return F;
}

JIT Compilation

LLVM ORC JIT

Copy#include "llvm/ExecutionEngine/Orc/LLJIT.h"

auto JIT = llvm::orc::LLJITBuilder().create();
if (!JIT) {
    handleError(JIT.takeError());
}

// Add module
(*JIT)->addIRModule(llvm::orc::ThreadSafeModule(
    std::move(Module), std::move(Context)));

// Look up symbol and execute
auto Sym = (*JIT)->lookup("main");
auto* MainFn = (int(*)())Sym->getAddress();
int result = MainFn();

Optimization Pass Pipeline

New Pass Manager (Recommended)

Copy#include "llvm/Passes/PassBuilder.h"

void optimizeModule(llvm::Module& M) {
    llvm::PassBuilder PB;
    llvm::LoopAnalysisManager LAM;
    llvm::FunctionAnalysisManager FAM;
    llvm::CGSCCAnalysisManager CGAM;
    llvm::ModuleAnalysisManager MAM;
    
    PB.registerModuleAnalyses(MAM);
    PB.registerCGSCCAnalyses(CGAM);
    PB.registerFunctionAnalyses(FAM);
    PB.registerLoopAnalyses(LAM);
    PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
    
    llvm::ModulePassManager MPM = PB.buildPerModuleDefaultPipeline(
        llvm::OptimizationLevel::O2);
    MPM.run(M, MAM);
}

Custom Pass Implementation

Copystruct MyPass : public llvm::PassInfoMixin<MyPass> {
    llvm::PreservedAnalyses run(llvm::Function& F, 
                                 llvm::FunctionAnalysisManager& FAM) {
        for (auto& BB : F) {
            for (auto& I : BB) {
                // Transform instructions
            }
        }
        return llvm::PreservedAnalyses::none();
    }
};

Language Implementation Patterns

Memory-Safe Languages

• Use LLVM's memory sanitizer hooks
• Implement bounds checking with GEP introspection
• Reference counting or garbage collection integration

Type Systems

• Implement type inference during AST construction
• Generate appropriate LLVM types (i32, float, struct, ptr)
• Handle generic types via monomorphization or boxing

Error Handling

• Generate exception handling via LLVM's landingpad/invoke
• Implement Result/Option types as tagged unions
• Use LLVM's personality functions for unwinding

Notable Language Implementations

Systems Languages

• Rust: Complex borrow checker, trait system → LLVM
• Zig: Comptime evaluation, safety features
• Carbon: C++ interop, modern syntax

Scripting Languages

• Julia: JIT-compiled scientific computing
• Crystal: Ruby-like syntax, static typing
• Nim: Python-like, multi-backend

Domain-Specific

• Solidity: Ethereum smart contracts
• MLIR: Multi-level IR for ML/AI workloads
• Halide: Image processing DSL

Development Workflow

1. Start Simple: Begin with Kaleidoscope tutorial
2. Incremental Features: Add one language feature at a time
3. Test Extensively: Unit tests for each compiler phase
4. Use LLVM Tools: opt, llc, llvm-dis for debugging IR
5. Profile and Optimize: Focus on common code patterns

Resources

Official Tutorials

• LLVM Kaleidoscope: Building a language from scratch
• Clang internals: Frontend implementation patterns
• Writing an LLVM Backend: Target code generation

Community Projects

See DIY Compiler section in README.md for 100+ example implementations across different language paradigms.