From this comment: it would be great to have an optimization such that

if a table's default funcref is null, don't do lazy-init, and make the 0 bit-pattern mean null rather than non-initialized-pointer-to-anyfunc.

This comes from a circumstance where we know we'll initialize a table slot manually before calling it (not doing so is a program error that should lead to a trap), possibly because we already have a branch for the case where it is null at the program-logic level (e.g. fallback IC). We still must trap on null somehow but #8159 can do that implicitly by detecting a segfault in a load from a NULL anyfunc pointer. The above optimization then means that we do not need the lengthy lazy-init-check sequence on loads from such tables, and we can do so without requiring any initialization at instantiation time either.

cc @alexcrichton @jameysharp