bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?

[Mattias Engdegård]

2 juli 2020 kl. 22.09 skrev Paul Eggert <eggert@cs.ucla.edu>:

>> Note that it can also be done without slowing down `eq` (by
>> hash-consing the bignums).
> 
> Yes, that's a better way to go. I wrote a patch to do that a while ago but 
> never
> got around to the laborious part, which was benchmarking.

Hash-consing bignums may be a good idea (I'm neutral on the idea), but there 
could be a reason why it isn't very commonly seen in other runtimes; perhaps 
they have more efficient GCs (generational and/or incremental), but Emacs would 
benefit (a lot) from that, too.

In any case, it's a one-way decision: once we guarantee eq to provide numerical 
equality (whether by hash-consing or otherwise), there is no way back.