jcc

JCC is designed to be a pure C11 (no dependencies) C11/C18/C23 compiler.

Is it sound?

No, it is text based

Support

It currently supports AArch64 almost fully, with partial WIP RISC-V support.

Design

• Preprocessor
  • Has two modes
    • Self-contained - when invoked with the -E flag, will run the preprocessor and output the result
    • Streaming - in normal compilation, tokens from the preprocessor are consumed and fed to the lexer
  • Code is preproc.h and preproc.c
• Frontend - Lexer + Parser
  • These work in lockstep (tokens are provided on-demand by the lexer), and build the AST
  • It is a very loose and untyped AST, to try and parse as many programs as possible, with little verification
  • Lexing code is lex.h and lex.c
    • Lexer takes preproc tokens
  • Parsing code is parse.h and parse.c
• Semantic analysis - Typecheck
  • Builds a typed AST from the parser output
  • Performs most validation (are types correct, do variables exist, etc)
  • Parsing code is typechk.h and typechk.c
• Intermediate Representations and passes
  • All code located in the ir folder
  • IR representation structs and helper methods are in ir/ir.h and ir/ir.c
  • Pretty-printing functionality is in ir/prettyprint.h and ir/prettyprint.c
    • This also includes graph-building functionality with graphviz
  • IR building
    • This stage converts the AST into an SSA IR form
    • It assumes the AST is entirely valid and well-typed
    • Code is ir/build.h and ir/build.c
  • Lowering
    • Firstly, global lowering is performed. This lowers certain operations that are lowered on all platforms
      • E.g br.switchs are converted into a series of if-elses, and loadglb/storeglb operations are transformed to loadaddr/storeaddr
    • This converts the IR into the platform-native form
    • Then, per-target lowering occurs
      • For example, AArch64 has no % instr, so x = a % b is converted to c = a / b; x = a - (c * b)
    • The code for lowering is within the appropriate backend folders
  • Register allocation
    • Simple LSRA, done seperately across floating-point & general-purpose registers
  • Eliminate phi
    • Splits critical edges and inserts moves to preserve semantics of phi ops
• Code Generation
  • Converts the IR into a list of 1:1 machine code instructions
  • These are all target specific
  • Currently codegen does too much - in the future I would like to move lots of its responsibilities (e.g ABI) into IR passes
• Emitting
  • Actually emits the instructions from code generation into memory
• Object file building
  • Writes the object file to disk
  • Currently only macOS Mach-O format supported
  • Code is macos/mach-o.h and macos/mach-o.c
• Linking
  • Links using the platform linker
  • Effectively just runs the linker as one would from the command line
  • Code is link.h and link.c