> The original DOHASH's comment indeed said it didn't support that
> operation, yet the code used DOHASH to implement `maphash`, which *does*
> support such operations, and it used DOHASH in places which perform such
> operations, so I think it's clear we do want to support `puthash` there.

Sorry, my fault -- indeed maphash 'supports' irregular mutation in the sense that it shouldn't crash or corrupt Emacs if the rules are violated. I can't reproduce the reported crash(es) on my platform but is my understanding correct that no other uses of DOHASH caused any trouble?

This patch reverts my last change to Fmaphash and yours to DOHASH. It's perfectly fine to forego DOHASH in Fmaphash, it's chums with the hash-table implementation. Assuming that the problems were confined to Fmaphash, this should be safe to apply.

What I certainly would accept is an assertion in DOHASH that verifies the assumptions but doesn't result in any code at all with checking disabled. I'll add that if you think it's warranted (and maybe even if you don't).