9cc is a successor of the 8cc C compiler. It's written in such a way to
be easily understood while generating reasonably efficient assembly.

9cc has more stages than 8cc. Here is an overview of the internals:

* Compiles an input string to abstract syntax trees.
* Runs a semantic analyzer on the trees to add a type to each tree node.
* Converts the trees to intermediate code (IR), which in some degree
resembles x86-64 instructions but has an infinite number of registers.
* Maps an infinite number of registers to a finite number of registers.
* Generates x86-64 instructions from the IR.