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

[Stefan Monnier]

> That sounds like a very reasonable definition. Do you think it's
> equivalent to my hypothesis and/or to the current behavior of the byte
> optimizer?

Probably not exactly: there might be functions which don't always
"preserve `eql`" but for which we decide nevertheless that it's OK to
precompute them at compile time for pragmatic reasons.

E.g. `concat`.


        Stefan