BasicCompiler-LLVMSwift

A work in progress project to make a basic compiler that takes in some source code(small grammar) and generates an executable.

Goals

1. Learn various stages of the compilation process by making basic versions of the sub-components - Lexer, Parser, Sema, LLVM IR Generator and other optimisations that can be explored.
2. To become more familiar with the LLVM environment.
3. To explore different type inference algorithms - Hindley Milner Inference etc.
4. Better developer diagnostics - how Swift and other languages contribute to making this possible, their relative trade-offs and strengths etc.
5. Prototyping other explorations to see their respective impact and limitations.
6. DSLs.

Installation

1. Install LLVM 11.0+ using your favorite package manager. For example: brew install llvm@11
2. Ensure llvm-config is in your PATH
3. swift run Sources/Utils/make-pkgconfig.swift Once the above is done, the project will build all file hopefully!

What's the grammar of the acceptable language here?

1. It's a pretty basic subset of my favourite language - Swift :).
2. It supports primitive types and doesn't support custom types as of now but can be easily extended to support other types.
3. It supports functions, their call expressions, constants/variables, return values, if-else conditions.
4. The scope is intentionally kept small so that more focus is towards how these layers work and how can they be extended considering the above mentioned goals.

Example

For the followig code,

func main() {
 let a = 10
 print(a)
}

It emits the following LLVM IR:

; ModuleID = 'main'
source_filename = "main"

@PRINTF_INTEGER = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1

define void @main() {
entry:
  %a = alloca i32, align 4
  store i32 10, i32* %a, align 4
  %0 = load i32, i32* %a, align 4
  %1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @PRINTF_INTEGER, i32 0, i32 0), i32 %0)
  ret void
}

declare i32 @printf(i8* %0, ...)

The above can be converted to binary using the following:

$ llc -filetype=obj main.ll -o main.o
$ clang main.o -o main
$ ./main

References

1. https://github.com/llvm-swift/LLVMSwift
2. 2019 LLVM Developers’ Meeting: E. Christopher & J. Doerfert “Introduction to LLVM”
3. Introduction To LLVM
4. Types and Programming Languages - Benjamin C. Pierce