> Ah-ha! The generated instructions were ever so slightly different. This would be great news, if it wasn't for me forgetting about one little detail: I have zero knowledge of x86 assembly.

Lol'd at this. I've been there: "ah hah! I found you. hrm, now what does this mean..."

TFA makes me thankful my work doesn't involve C / C++. Learning it earlier in life was enough.

If I were the author, I would skip the part about using the compiler explorer and reading the assembly. When I write C code, I need to satisfy the rules of the C language. Unless I’m debugging the compiler or dealing with performance issues, my experience is that reading the generated assembler and understanding it is usually a slow way of debugging. The author eventually did compile with -fsanitize=undefined but I would honestly do that first. It prints a nice error message about the exact issue as the author has shown.

> Option 1) seemed like the easiest one, but it also felt a bit like kicking the can down the road – plus, it introduced the question of which standard to use.

Arguably, that's the sanest one: you can't expect the old C code to follow the rules of the new versions of the language. In a better world, each source file would start with something like

    #pragma lang_ver stdc89

On the topic of the article, yeah, sticking anything other than 0 or 1 into C99 bool type is UB. Use ints.