This is a fork of Rui Ueyama's chibicc with fixes and enhancements, including:

C99 features: VLA parameters, VLA de-allocation, K&R old-style functions.
C11 features: _Static_assert(), over-aligned locals, _Generic with qualifiers.
C23 features: constexpr, enum:T, #embed, auto, _BitInt, nullptr, ={}
C2Y features: named loops, if declarations, _Countof.
defer/_Defer: enable un-uglified form with -fdefer-ts option or #include <stddefer.h>.
WG14 proposals: __VA_TAIL__, #def #enddef.
GNU features: inline assembly, commonly used __attribute__'s.
MSVC features: #pragma pack, anonymous struct.
Basic codegen optimizations (close to GCC/Clang at -O0).

What can it build?

Compiling real C projects with slimcc has been a major focus, the CI workflow now regularly build-test a healthy collection of familiar names, for bragging rights:

Core system commands (GNU utils, busybox, toybox, bash, zsh)
Command-line tools (curl, git, jq, wget, rsync, apk, pacman)
Programming languages (Python, Go, Lua, Perl, Ruby, PHP, Ocaml, Erlang, C3, Zig)
Gamedev/graphics libraries (SDL3, glfw, stb, raylib, sokol)
Critical infrastructure software (Redis, Valkey, Nginx, PostgreSQL)

slimcc-musl-bootstrap is a minimal statically-linked chroot environment with musl, binutils, toybox entirely compiled with slimcc.

Building and Using

Recent GNU binutils is required.
Find a relevant preset in platform/, copy/symlink to platform.c or create one, hit make.
On recent glibc Linux, this should just work:

ln -s platform/linux-glibc-generic.c platform.c
make

For simplicity, built-in headers are searched relative to the binary, it's intended to be executed in-tree like:

~/slimcc/slimcc *.c
CC=~/slimcc/slimcc ./configure
cmake -DCMAKE_C_COMPILER=/home/username/slimcc/slimcc

For installing/symlinking/packaging, please edit platform.c with absolute paths.
cc scripts/amalgamation.c builds the project as a single translation unit.
make slimcc-asan/test-asan build and run tests with address sanitizer, recommended if you are hacking the source.
make slimcc-filc/test-filc build and run tests with Fil-C, env FILC is used.

Compatibility

Autoconf based projects might fail to build due to -fPIC or -Wl not being passed. If there is a block in ./configure that looks like below, append -Wl,, -fPIC, -static respectively and re-configure:

  lt_prog_compiler_wl=
lt_prog_compiler_pic=
lt_prog_compiler_static=

CMake: these extra flags might be helpful:
- -DCMAKE_PREFIX_PATH: help find_package() find installed libraries.
- -DCMAKE_C_COMPILE_OPTIONS_PIC=-fPIC
- -DCMAKE_C_COMPILE_OPTIONS_PIE=-fPIE
Meson: see https://github.com/mesonbuild/meson/issues/5406. Try Muon.
Muon: slimcc works ok under Muon's posix cc mode, for better compatibility, register slimcc in Muon's src/script/runtime/toolchains.meson with:

toolchain.register_compiler(
    'slimcc',
    inherit: 'posix',
    linker: 'ld',
    detect: func(out str) -> int
        return 'slimcc' in out ? 100 : 0
    endfunc,
    handlers: {
        'print_search_dirs': ['-print-search-dirs'],
    },
)

Projects with deep GCC assumptions might actually work if you carefully opt in/out of #if __GNUC__ blocks, see the CI test scripts for a taste of hacks that can be done.

Compatibility options

-fms-anon-struct: Enable declaring anonymous struct member with tags like GCC's -fms-extensions or -fplan9-extensions.
-fdisable-visibility: Some projects adopt an idiom that globally set -fvisibility=hidden then selectively export public API with __attribute__((visibility("default"))). slimcc support both, yet a problem arises when the former is probed by build system while the latter hardcoded in #if __GNUC__ blocks regardless of the build system's decision. The option simply disable both features to prevent the conflict.
-ffake-always-inline: slimcc currently don't inline functions, but some projects' usage of GCC always_inline on non-static inline functions would cause missing definition at link time. This option turns these definitions into static inline's to work around compile error.

How optimized is the compiler?

The coding style is highly influenced by chibicc, which means in the eyes of C veterans there might be all kinds of inefficiencies in the name of readability. While micro-optimizing is fun, I only commit changes that noticeably improve fully-optimized builds.

As such, optimization flags and custom allocators have great impact on its performance, make slimcc-(lto/lto-mi/lto-je) is provided for optimized builds. It's usually faster than Clang/GCC for common tasks, but only by doing less internally.

How portable is the compiler?

It's written in C99 with several POSIX 2008 functions.
Host is assumed to be little-endian.
For compilers with more restricted feature set, preprocessor flags are provided to enable bootstrapping stage1 with unneeded features crippled, please don't use them outside of self-hosting.
- BOOTSTRAP_NO_LDOUBLE aliases long double to double.
- BOOTSTRAP_NO_VLA makes VLA-using functions no-op (only _BitInt evaluation affected).
As proof of portability and reproducibility, the following compilers are known to bootstrap identical stage2 of slimcc:
- gcc, clang, tcc, kefir, fil-c
- chibicc with backported patches, widcc
- pcc with -std=c99
- antcc with -DBOOTSTRAP_NO_VLA
- cproc with -DBOOTSTRAP_NO_LDOUBLE -U__has_builtin
- cparser with -DBOOTSTRAP_NO_LDOUBLE
- compcert with -DBOOTSTRAP_NO_LDOUBLE -DBOOTSTRAP_NO_VLA -U__has_builtin -fstruct-passing
- dmd with -P=-DBOOTSTRAP_NO_VLA -P=-U__has_builtin, without -O, after patching out file scope compound literals with perl -i -pe 's|^([\w ]+) \*(\S+) = &$\S+$({.*};)$|\1 _\2 = \3\n\1 *\2 = &_\2;|g' *.c
- If using platform/linux-glibc-generic.c, remember to pass -fno-pie -no-pie when building stage2 to avoid host deterministic behavior.
- In case you're wondering — no, "Claude's C compiler" doesn't work, worse still, the cli option that could help bypass the miscompilation also wasn't implemented properly.

Slimcc

Install / Use

README