Mapping Python to LLVM

The type conversion assumptions here are real problematic. "64 bits ought to be enough for anybody"-style statements ignore integers as bitfields, large constants (eg Avogadro's number), any kind of math with large intermediate terms, all kinds of stuff.

Makes me very suspect about the rest of this project when they try to glide past all of these issues with nary a mention.

I don't know how codon does this. But I always supposed that existing optimized pythons like pypy map integer operations to native types and promote them to arbitrary precision when they encounter overflow. It's IMO a similar problem to "but what if someone decided to overwrite Int.__add__ with some other function?" - arguably these are weird/bad things to do but AFAIK permitted by the language semantics. So to fix problems like these you just make it work for the paranoid case and implement optimizations that rely on that not being common. When the weird behavior is detected you fall back to the slower path.

How good is Coden's performance compared to Cyphon and mypyc?

I recall that Google had a project to compile Python to LLVM (Unladen Swallow @ https://code.google.com/archive/p/unladen-swallow/), but work stopped on it a long time ago.

If I recall it really wasn't that much faster than CPython given the overhead, but it's been a long time; if it was faster I assume it wouldn't have been abandoned.

Looks like it does it by not being Python, but rather Python-ish.