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widcc is a stable branch of slimcc that

  • does not attempt to optimize codegen
  • does not introduce new features (unless I really want certain projects to build)
  • would rather remove a feature than to support it incorrectly (not a motto but to avoid giving autoconf the wrong idea)

slimcc has accomplished a fairly good collection of real world projects it can build and 100% pass tests. widcc in turn is to maintain that status while being simpler-to-port and easier-to-modify.

The following C11 features are removed: _Alignof _Atomic _Generic. These are not seen commonly in use, therefore widcc still declare itself a C11 compiler.

wid stands for "When in doubt" from the famous quote.

widcc is based on Rui Ueyama's chibicc, if you are familiar with chibicc and would like to know what's different here, refer below.

Building & Running

  • Should just work on recent glibc-based (2.28+) x86-64 Linux.
  • Test script needs bash; depending on the distro, file and/or glibc-static packages may be required.
git clone --depth 1 https://github.com/fuhsnn/widcc
cd widcc
make test-stage2 -j

Run it in base directory like CC=~/widcc/widcc

Building real-world projects

(package dependencies are assumed to be present)

curl 8.9.1

git clone --depth 1 https://github.com/curl/curl --branch curl-8_9_1
mkdir curl/cmakebuild
cd curl/cmakebuild
cmake ../ -DCMAKE_C_COMPILER=/full/path/to/widcc -DCMAKE_C_FLAGS=-fPIC
make -j
make quiet-test -j

gcc 4.7.4

mkdir gccbuild gccinstall
wget https://ftp.gnu.org/gnu/gcc/gcc-4.7.4/gcc-4.7.4.tar.bz2
tar -xf gcc-4.7.4.tar.bz2
cd gcc-4.7.4
find . -name 'configure' -exec sh ~/widcc/add_wl_pic.sh {} \;
sed -i 's/^\s*struct ucontext/ucontext_t/g' ./libgcc/config/i386/linux-unwind.h
cd ../gccbuild
CC=~/widcc/widcc MAKEINFO=missing ../gcc-4.7.4/configure --prefix=$HOME/gccinstall/ --enable-languages=c,c++ --disable-multilib --disable-bootstrap
make -j
make install

git 2.46.0

git clone --depth 1 https://github.com/git/git --branch v2.46.0
cd git
make CC=~/widcc/widcc V=1 test -j

Perl 5.41.2

git clone --depth 1 https://github.com/perl/perl5 --branch v5.41.2
cd perl5
sed -i -e 's/1.38/1.39/g' ext/Errno/Errno_pm.PL
sed -i "187i push(@file, '/usr/include/asm-generic/errno-base.h');" ext/Errno/Errno_pm.PL
sed -i "188i push(@file, '/usr/include/asm-generic/errno.h');" ext/Errno/Errno_pm.PL
./Configure -des -Dcc=$HOME/widcc/widcc -Dusedevel -Accflags=-fPIC
make test -j

PHP 8.1.29

git clone --depth 1 https://github.com/php/php-src/ --branch php-8.1.29
cd php-src
sh ~/widcc/add_wl_pic.sh ./configure
CC=~/widcc/widcc CFLAGS=-std=c99 ./configure --without-pcre-jit --disable-opcache --without-valgrind
make NO_INTERACTION=1 test -j

PostgreSQL 17.0

git clone --depth 1 https://github.com/postgres/postgres --branch REL_17_BETA3
cd postgres
sed -i 's/^\#if (defined(__x86_64__) || defined(_M_AMD64))/#if 0/g' src/include/port/simd.h
CC=~/widcc/widcc ./configure --disable-spinlocks --disable-atomics
make check -j

Python 3.12.5

git clone --depth 1 https://github.com/python/cpython --branch v3.12.5
cd cpython
CC=~/widcc/widcc ./configure
make test -j

sqlite 3.46.1

git clone --depth 1 https://github.com/sqlite/sqlite/ --branch version-3.46.1
cd sqlite
sh ~/widcc/add_wl_pic.sh ./configure
CC=~/widcc/widcc CFLAGS=-D_GNU_SOURCE ./configure
make testrunner

TinyCC mob branch

git clone --depth 1 https://repo.or.cz/tinycc.git
cd tinycc
CC=~/widcc/widcc ./configure
make -j
cd tests/tests2/
make

toybox 0.8.11

git clone --depth 1 https://github.com/landley/toybox --branch 0.8.11
cd toybox
sed -i 's/^\#define printf_format$/#define QUIET\n#define printf_format/g' lib/portability.h
make CC=~/widcc/widcc defconfig
make CC=~/widcc/widcc V=1
make CC=~/widcc/widcc tests

vim trunk

git clone --depth 1 https://github.com/vim/vim
cd vim
CC=~/widcc/widcc ./configure
make -j
make testtiny

Changes over chibicc

  • A stack manager for temporaries is introduced to avoid clobbering when setjmp/longjmp happen between pairs of push-pop, by translating push-pop's into mov's. slimcc took this further and added register allocation on top of the manager.
  • Local variables of parallel scopes are folded into the same stack space, this dramatically eliminated segfaults in projects that do recursive calls a lot, and is about the only optimization worth mentioning in widcc.
  • chibicc's preprocessor hideset algorithm had issues with some obscure macro expansion tricks, I moved to a simple-but-dirtier design that avoid building hidesets altogether, but apparently n0tknowing's chibicc fork worked that out.
  • chibicc had a tricky implementation of function call procedure, by interleaving argument-pushing with evaluation, then popping only the pass-by-reg ones off. I simplified the process by storing evaluated arguments to temporary variables, then copy into the right spots; it's inefficient, but the reduction in conceptual load worth it.
  • The evaluation order of binary arithmetic operators are enforced left-right. Although it's implementation-defined behavior in C, I decided to reduce future surprises after encountering a test failing since git 2.43 because certain message output expressions are made on both sides of | and the validation script expect left-right behavior.