Design Compiler with LLVM

A custom compiler implementation built using LLVM infrastructure. This project demonstrates the design and implementation of a compiler pipeline including lexical analysis, parsing, semantic analysis, intermediate representation (IR) generation, and native code generation using LLVM.

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Overview

This project implements a full compiler for a custom-designed programming language. The compiler translates high-level source code into LLVM Intermediate Representation (IR), which can then be optimized and compiled into machine code using LLVM tools.

The purpose of this project is to:

• Understand compiler construction principles
• Implement a full compilation pipeline
• Integrate LLVM for backend code generation
• Produce executable machine code from custom language programs

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Compiler Architecture

The compiler follows a traditional multi-stage architecture:

Source Code
→ Lexical Analysis
→ Parsing
→ AST Construction
→ Semantic Analysis
→ LLVM IR Generation
→ Optimization
→ Machine Code Generation

Each stage is modular and separated logically in the codebase.

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Compilation Pipeline

1. Lexical Analysis

The lexer converts raw source code into tokens such as:

• Keywords
• Identifiers
• Literals
• Operators
• Delimiters

2. Parsing

The parser processes tokens and builds an Abstract Syntax Tree (AST) according to the language grammar.

Supported constructs typically include:

• Variable declarations
• Arithmetic expressions
• Conditional statements
• Loops
• Function definitions
• Function calls
• Return statements

3. Semantic Analysis

This stage ensures:

• Type correctness
• Scope validation
• Symbol table consistency
• Function signature matching
• Proper variable usage

4. LLVM IR Generation

The AST is translated into LLVM IR using LLVM APIs such as:

• LLVMContext
• Module
• IRBuilder
• Function
• BasicBlock

The generated IR can be:

• Printed as .ll file
• JIT executed
• Compiled into object code

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Language Features

The custom language includes:

Data Types

• int
• float
• bool
• void

Operators

• Arithmetic: +, -, *, /
• Comparison: ==, !=, <, >, <=, >=
• Logical: &&, ||

Control Flow

• if / else
• while / for

Functions

• User-defined functions
• Parameters
• Return values

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Project Structure

Example structure:

src/
  lexer/
  parser/
  ast/
  semantic/
  codegen/
main.cpp
CMakeLists.txt
README.md

Module descriptions:

• lexer/ → Token generation
• parser/ → Syntax analysis
• ast/ → AST node definitions
• semantic/ → Symbol tables and type checking
• codegen/ → LLVM IR generation
• main.cpp → Compiler entry point

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Build Instructions

Requirements

• LLVM (version 14+ recommended)
• CMake
• C++17 compatible compiler (clang++ or g++)

Install LLVM (Linux)

sudo apt install llvm clang

Build Steps

mkdir build
cd build
cmake ..
make

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Running the Compiler

Compile a source file:

./compiler input.my

Generate LLVM IR:

./compiler input.my -emit-llvm

Execute using LLVM interpreter:

lli output.ll

Compile to native executable:

llc output.ll -filetype=obj
clang output.o -o program
./program

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Example

Example source program:

int main() {
    int a = 5;
    int b = 10;
    return a + b;
}

The compiler generates LLVM IR including:

• Function definition
• Alloca instructions
• Load/store instructions
• Add instruction
• Return instruction

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Optimization

LLVM allows multiple optimization passes such as:

• Constant propagation
• Dead code elimination
• Loop optimizations
• Instruction combining

Optimization example:

opt -O2 output.ll -o optimized.ll

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Error Handling

The compiler includes:

• Syntax error reporting with line numbers
• Type mismatch detection
• Undeclared variable errors
• Function signature mismatch errors

These diagnostics help users debug source programs effectively.

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Future Improvements

• Add arrays and structs
• Add object-oriented features
• Improve error recovery
• Add unit testing framework
• Implement REPL mode
• Improve optimization pipeline
• Add JIT execution mode

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Author

Mahan Baneshi _ Compiler Design Project implemented using LLVM infrastructure.