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Lab 6: Compiler

CSCI 341 C
2022-12-07

This is a compiler (written in rust) for an extremely rudimentary programming language targeting the risc-v (RV32IM) instruction set, and RARS in particular. The language itself is somewhat similar to rust in syntax, but much simpler in semantics. For example, it does not have any type system and has no checks for correctness.

The following is a short example:

let num = 0;
print_str("Enter a number: ");
set num = read_int();
if !(num & 1) {
  print_str("even!\n");
} else {
  if num % 3 == 0 {
    print_str("divisible by 3!\n");
  } else {
    print_str("not divisible by 3!\n");
  }
}

Compiling and running

To compile the compiler, you will need a rust toolchain installed. That can be downloaded here: https://www.rust-lang.org/tools/install

At that point, one can simply cargo build --release to compile a release build. A binary will be placed at target/compiler/compiler[.exe] which can be run with a file path to compile:

./target/compiler/compiler tests/while.oh

the resulting assembly will be printed to stdout, while errors will (should?) print to stderr.

Dependencies

besides a rust toolchain, this compiler uses logos to generate a lexer, which is automatically downloaded and compiled.

features

  • expressions
    • operators (precedence similar to C):
    • +, -
    • *, /, %
    • >>, <<, >>_ (logical right shift)
    • &, |, ^
    • <, >, <u (less unsigned)
    • ==
    • unary -, ~, !
  • variables (let, set)
  • calls to standard functions for RARS ecalls
  • C-style strings
  • if(/else) and while

Standard functions

these all wrap RARS ecalls and can be found in resources/stdlib.s.

known issues

  • registers are not saved before function calls
  • the entire standard library is always included, even if it isnt all used
  • variables are only static, not on the stack
  • extremely poor performance - this compiler attempts to generate correct code, but performs no optimizations. this means that the end result tends to be somewhat redundant and overly explicit.
  • there are likely bugs.
  • poor code quality due to rushed development

implementation

  • expr.rs - abstract syntax tree definitions
  • parse.rs - lexer definition and recursive descent parser
  • riscv.rs - compiler implementation
    • noteworthy: compile_stmt and compile_expr
  • main.rs - command line interface