Author: Larken Barnes
Date: 4/25/2023
Course: CS541
Assignment: Program 4: LLVM Code-Generator

Requires: flex bison llvm
To build: run make
To run: ./c2ll < filename.in

Description:
    The goal of this program is to generate LLVM IR from a subset of the CLUKCS language. The program uses flex to generate a lexer, and bison to generate a parser. LLVM is not required unless you want to compile the output from LLVM IR into an executable. This time around I decided to deal with type errors different than the last project. When an error occurs, I now create variables of type Unknown that slowly spreads throughout the remainder of the generated code. This means that generated code with type errors is not guranteed to be valid, but allows the compiler to attempt to check for multiple errors. The two key functions for this code can be found at the top of parser.y. The functions are named 'cast_to_lhs_type' and 'cast_for_binop'. These are used to implicitly cast variables when needed. I also chose to enforce the LHS of assignments to be variables by changing the rule for these expressions to only accept identifiers as the first arg. This approach made it easier to deal with such issues because it prevents things like '10 = 5' from reaching the parser. There is also a folder with a few tools in the form of shell scripts. 'compile.sh' compiles the program fully from a source file to an executable. It does so by just using the c2ll program from the directory above it, so make sure to run make in the parent directory. The other script, 'test.sh' just runs the program compiled by 'compile.sh' and spits out the exit code - this was the easiest way to test that arithmetic was being generated correctly.

Bugs:
- All known bugs have been fixed as of 4/25/2023 
- (Not really a bug, just an admission of guilt) I am not happy with the way that I determine if the last instruction was a return statement or not. Currently I just read the last line of the generated code and check to see if it begins with 'ret i32'. This works fine in practice, it just feels sloppy.