RCC-Legacy

An optimizing compiler for SysY (a C subset) targeting RISC-V 64GC.

This is the first generation of rcc, built as a C++ compiler project inspired by QBE's SSA-based architecture. It is kept here as a frozen reference; note that active development has moved to a new implementation in a separate directory, and this directory will no longer be maintained.

Pipeline

SysY source
  → frontend         lexer / parser / AST
  → IRGen            SSA construction (Braun et al.), QBE-style IR
  → mid-end          SSA optimization passes
  → rv64 backend     instruction selection → register allocation → emit
  → RISC-V assembly

Per-function processing is decoupled from global mutable state via an explicit Ctx / SubPool model, allowing functions to be compiled independently.

Mid-end passes

mem2reg / promote, load forwarding, constant folding, copy propagation, GVN, GCM, LICM, SCCP, reassociation, strength reduction (div / mul), loop strength reduction, loop idiom recognition (memset / memcpy), inlining, and DCE.

Backend (RISC-V 64)

ABI lowering, instruction selection (with cmp+branch fusion and address-offset folding), liveness, spilling, register allocation, peephole, and ELF assembly emission.

Build

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j

The compiler binary is build/rcc. Use --emit-il to dump the intermediate representation and -d <flags> for per-pass debug output.

Test

Test cases are stored in tests/.

./tests/run_rv64_e2e.sh
./tests/run_perf.sh

You may need to edit the shell scripts in tests/ to adapt to your local environment.

Competition

This compiler was built for the 2026 compiler design competition @ RUC.

Thanks

• QBE
• TrivialCompiler
• indigo
• sysy-testsuit-collection
• lava-test

License

rcc-legacy is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.