CCC

Cimple C Compiler Flex, Bison, and LLVM compiler for a subset of the C language. Generates LLVM IR.

Keywords

The compiler supports the following C keywords:

• if
• while
• for
• break
• continue
• return

It supports the following types:

• int
• float
• bool (built-in true and false)
• void

It supports the following operations:

• Comparisons (!=, ==, <, >, <=, >=)
• Addition (+, +=)
• Subtraction (-, -=)
• Multiplication (*, *=)
• Division (/, /=)
• Modulo (%)
• Logical and (&&), logical or (||)
• Ternary expression (condition ? true expression : false expression)
• Bitwise operators and(&), or(|), xor(^), and not(~)
• Shift operators << and >>

ccc consists of the following components:

• Preprocessor

  • Removes comments from the original source code

• Lexer

  • Uses Flex to parse the preprocessed file into lexemes

• Parser

  • Uses Bison to parse the lexems following our grammar rules
  • Generates an Abstract Synta Tree that we can use for further analysis and transformations

• Verification

  • Traverses our AST and performs semantic analysis of the program to ensure correctness
  • Errors checked:
    • Existence of main function
    • Redeclaration of variables in the same scope
    • Type mismatch in variable assignment or function returns
    • Type mismatch in binary, logical, or relational operation
    • Use of undeclared variables or functions
    • Missing return value in non-void functions
    • Redefinition of function (Multiple declaration are OK!)
    • Type returned from function doesn't match declared type
    • If, for, while, and ternary conditions must evaluate to boolean
    • Can only cast between int and float

• Optimization

  • Any binary, unary, or relational operation whose operands are strictly constant will be simplified as much as possible
  • If statements with constant predicates will either be removed entirely if it always evaluates to false, or always executed if the condition always evaluates to true.
  • Ternary operations with a constant predicate will be replaced with either their true expression or false expression.
  • While statements with a constantly false conditions will be removed entirely.

• Code generation

  • Traverse the AST and emit the appropriate LLVM IR

• Command line options

  • --print-lex or -l, display the tokens generated by flex
  • --print-ir or -i, display the IR code generated by LLVM
  • --print-ast or -a, display the asbtract syntax tree generated by
  • --optimization-level NUM or -o NUM, NUM is 0 or 1 where 0 is no optimization, 1 is default
  • --keep-preprocessed or -e, don't erase preprocessed file upon completion
  • --help or -h, display help message
  • --version or -v, display version information

• Requirements:

  • Bison 3.6.4
  • Cmake 3.18.2
  • gcc 10.2.0
  • flex 2.6.4
  • llvm 10.0.1

• Installation
  Create folder, clone repo, make sure you have above requirements installed, and run Make in ccc/src