d8bf3fd584
reachable computation: extend explanation of what this does, and why Follow-up to https://github.com/rust-lang/rust/pull/122769. I had the time to think about this some more, in particular in the context of https://github.com/rust-lang/rust/issues/119214, so I felt it was worth extending these comments some more. I also gave up on the context of "externally reachable" as it is not called that way anywhere else in the compiler. Cc `@tmiasko` `@saethlin`