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

[Stefan Monnier]

> and "side-effect free" is like GCC's "pure." That is, a side-effect
> free function can dereference pointers stored in Lisp_Objects, but a
> pure function can't.

I think it's still not very satisfactory since it's written in terms of
low-level operations in the C code.

I think the current intention of our "pure" goes something along the
lines of: the function will always return the "same" (the sense of `eql`)
value (or signal the same error) when called with `eql` arguments.
IOW "the function preserves `eql`ity".


        Stefan