evm_llvm VS lcc

Those aren’t necessarily written as people would do that today, but you may try Knuth’s literate sources for TeX[1] and METAFONT. That category also includes LCC[3], but A retargetable C compiler is a book that you’d need to buy; and PBRT[4], but Physically based rendering is more exposition than program (even though the program is perfectly usable). The source for Unix V6[5] with the accompanying commentary by Lions is probably as much of a classic as it gets. And as an eccentric choice in a similar format, may I suggest cmForth[6], perhaps accompanied by Footsteps in an empty valley[7]?

Also, though this is not precisely what you’re asking for, The architecture of open-source applications and its sequels[8] have

[1] http://mirrors.ctan.org/info/knuth-pdf/tex/tex.pdf

[2] http://mirrors.ctan.org/info/knuth-pdf/mf/mf.pdf

[3] https://github.com/drh/lcc

[4] https://pbr-book.org/

[5] http://v6.cuzuco.com/

[6] https://github.com/ForthHub/cmFORTH/blob/combined/cmforth.ft...

[7] http://forth.org/OffeteStore/4001-footstepsFinal.pdf

[8] https://aoasbook.org/

In my first encounter with Dennis Ritchie, I contacted him about using an early CPP from the LCC project (https://github.com/drh/lcc), which I wanted to use for a Bell Labs project, despite some excessive corporate concerns about open source licensing (in the end it was not an issue since Dennis wrote it). That code is still not heavily commented, and 30 years ago there were almost no comments at all, yet even the handcrafted lexer and parser were completely understandable. Not that were they bug-free, I actually found and fixed a few bugs, which even better reflects about how fundamentally understandable they were.

Beware of lcc licensing --- it's got some awkward clauses about forbidding distribution for profit which means it's forbidden in most Linux distributions. https://github.com/drh/lcc/blob/master/CPYRIGHT