Explanation of scope about wasmtime

[sunfishcode]

Cranelift (formerly Cretonne) is currently focusing on "backend" compilation, however if it is successful, we hope to extend it some day with high-level inter-procedural optimizations.

While Cranelift includes the cranelift-wasm crate for translating wasm, it isn't sufficient for complete wasm compilation. One needs additional support, such as the support now provided by Wasmtime.

It is theoretically possible that Cranelift could output to wasm some day, however it is not set up to do so right now.

Cranelift is indeed meant to be useful in both JIT and AOT configurations. Lucet and rustc_codegen_cranelift are examples of using it in an AOT configuration, and Wasmtime is an example of using it in a JIT configuration.

If you have any further questions, please re-open this issue or file a new one!