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IIRC Cranelift doesn't use copy-and-patch. It uses e-graphs [0] as part of its optimization pipeline, though.

Closest thing in (relatively) recent news that uses copy-and-patch I can think of is CPython's new JIT.

[0]: https://github.com/bytecodealliance/rfcs/pull/27

My understanding is that e-graphs take care of selecting the best patch (by examining many options in parallel) but fundamentally it is still copy-and-patch.

Could you elaborate more on "fundamentally it is still copy-and-patch"? From what I can recall when I had first read about copy-and-patch a not-uncommon comparison was against Cranelift, which to me would imply that different approaches were taken. I don't recall any discussion about Cranelift's use of the technique, either, so your claim that it's at the heart of Cranelift is new information to me. Has Cranelift adopted copy-and-patch (maybe for a specific compilation stage?) in the meantime?

You are right. Somehow I had in my mind that e-graphs worked with pre-compiled snippets of code but it seems Cranelift does not do that.

Indeed, the original copy-and-patch paper explicitly compares against Cranelift: https://fredrikbk.com/publications/copy-and-patch.pdf

But not that is conceptually related, only that the copy-and-patch is faster than cranelift in that particular scenario.

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