Auto merge of #2378 - RalfJung:sb, r=RalfJung
Auto merge of #2378 - RalfJung:sb, r=RalfJung

use PlaceTy visitor and dedup sime retagging code

I benchmarked this and as far as I can see the difference to the old code is totally within noise. And this makes the code a lot simpler and removes duplication so yay. :)

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri