The main changes needed to make this migration besides a few method call tweaks were:

1. Adapt FunctionCtx to cache information about the StableMIR version of instance and its body.
   • I also cleaned up how we were handling basic blocks which were unnecessary.
2. Created a new ty_stable module that provide stable versions to retrieve type information from StableMIR.
   • I decided to keep these separate so it is cleaner for now. I foresee that the type module will still rely on internal APIs for the next little while, so separating them here made sense to me.
3. Since Place when retrieved from StableMIR body already comes monomorphized, I modified the existing codegen_place to preemptively monomorphize Place before converting it to a Stable version and invoking codegen_place_stable.

Call-outs

Leaving this as a draft for now since this still depends on the following PRs to be merged into the Rust compiler:

• Add more information to StableMIR Instance rust-lang/rust#118524
• Add ADT variant infomation to StableMIR and finish implementing TyKind::internal() rust-lang/rust#118516

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