I set myself a challenge: write a self-hosting C compiler in 10 hours. This is the result, plus lots of cleanup (check "releases" for the 10 hour version).

Implementation:

• Generates 32-bit x86 assembly, which is then assembled and linked by GCC.
• It is all implemented in a single pass. Code generation is mixed with parsing. This requires some creativity.
• The parser peeks at the next token to decide whether to generate an lvalue.

Language:

• Local and global variables, parameters.
• Functions, if, while, do``while, return.
• =, ?: (ternary), ||, &&, ==, !=, <, >=, +, -, *, ++, -- (post-ops), !, - (unary), [], ()
• Integer, character, true and false literals. String literals, with automatic concatenation.
• The language it implements is typeless. Everything is a 4 byte signed integer.
• Pointer indexing works in increments of 4 bytes, pointer arithmetic is byte-by-byte.

The general philosophy was: only include a feature if it reduces the total code size. This is taken to its extreme in the insane branch.

git clone http://github.com/Fedjmike/mini-c
cd mini-c
make selftest

This will first produce cc by compiling mini-c with GCC. Then it makes ccself by compiling mini-c with cc. Finally it makes test/triangular using ccself, and checks the result. You should get something like this:

$ make selftest
gcc -std=c11 -Werror -Wall cc.c -o cc
cc cc.c
gcc -m32 a.s -o ccself
ccself tests/triangular.c
gcc -m32 a.s -o triangular; triangular 5; [ $? -eq 15 ]

If you are on Windows, you will need to checkout the windows branch. On 64 bit Linux, you may need to sudo apt-get install gcc-multilib to be able to compile and run the 32 bit code.

Another microscopic C compiler is c4 by rswier. He implemented more C, but I'd say mine is simpler :). Also, c4 generates code for its own VM, whereas mine has the significant difficulty of working with x86 assembly and cdecl.

I wrote another, much more advanced C compiler. Check it out. It too is self-hosting, but with a much more complete feature set, and even some experimental additions like lambdas.

Copyright (c) 2015 Sam Nipps

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