ru-compiler (Control Flow) 🎛️

Rust-Based Compiler for a Mini-Language with Control Flow and LLVM Trivial SSA Generation

PROJECT OVERVIEW

This project is a Rust command-line compiler that tokenizes, parses, and lowers a small imperative language into LLVM IR using trivial SSA (alloca, store, load). It extends a recursive-descent parser to support full control flow (if–then–else, while) and produces executable LLVM IR that can be compiled and run with clang.

KEY FEATURES 🔑

• Recursive-Descent Parser implementing a top-down grammar with left-recursion removed:

        EXPR → TERM EXPRDASH

        EXPRDASH → + TERM EXPRDASH | ε

        TERM → FACTOR TERMDASH

        TERMDASH → * FACTOR TERMDASH | ε

        FACTOR → IDENTIFIER | NUMBER | ( EXPR ) 

• Scanner recognizes identifiers ([A-Za-z]+), numbers ([0-9]+), +, *, (, ), and skips whitespace.

• Control-Flow Codegen:

  • Lowers if into LLVM blocks:

      br i1 %cond, label %if.then, label %if.else
  

  • Lowers while into canonical loop form:

     br label %while.cond
     while.cond:
          %cmp = icmp ...
          br i1 %cmp, label %while.body, label %while.end
  
  

• LLVM IR Generation (Trivial SSA):

  • Allocates stack slots for all variables:

      %x.alloc = alloca i64
  
  

  • Loads and stores using typed instructions:

     store i64 %t1, ptr %x.alloc
      %t2 = load i64, ptr %x.alloc
  

  • Always emits valid i64 IR compatible with clang.

TECHNICAL STACK 🧱

• Programming Languages/Technologies: Rust, Cargo, C, Makefile

• Compiler Backend: LLVM IR code generation

• Build Automation: Makefile (multi-test automation + SDK detection)

• Key Modules:

      scanner.rs → Lexical analysis
  
      parser.rs → Recursive-descent parsing
  
      ast.rs → AST data structure + BFS printer
  
      llvm_codegen.rs → LLVM IR emitter
  
      main.rs  → Entry point
  
  

🚀 BUILD & RUN

    # Build compiler
    cargo build

    # Run a program
    make exec PROG=programs/pdf_example.rucomp DRIVER=c_driver/driver1.c


    # Check IR structure (sanity checks)
    make check-ir PROG=programs/pdf_example.rucomp

WHAT'S NEXT?

• Add constant folding

• Add SSA optimization pass (extra credit)

Contributors

• Kelvin Ihezue