I ran the sanitizers again, and found a few more instances of undefined behaviour, mostly around bit-shifting of signed integers and arithmetic with NULL pointers.

export CC="clang"
export ASAN_OPTIONS=detect_leaks=0
configure --with-assertions --with-address-sanitizer --with-trace-refs --with-undefined-behavior-sanitizer --with-pydebug
nice make -j8
make test

I put some asserts to demonstrate the undefined behaviour into pull requests for main (matthiasgoergens#18) and 3.11 (matthiasgoergens#19).

More information about my environment:

$ clang --version
clang version 14.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin