Add documentation on how VN numbers memory

[SingleAccretion]

For the past few days I've been looking into various issues related to #58312 and in the process enhancing my own understanding of VN. It took me quite the long time to fully untangle how the "map-based" numbering actually works, so I decided it would be useful to leave a (rather large) note to future readers of this code.

@dotnet/jit-contrib

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT
See info in area-owners.md if you want to be subscribed.

Issue Details

---

For the past few days I've been looking into various issues related to #58312 and in the process enhancing my own understanding of VN. It took me quite the long time to fully untangle how the "map-based" numbering actually works, so I decided it would be useful to leave a (rather large) note to future readers of this code.

@dotnet/jit-contrib

Author:	SingleAccretion
Assignees:	-
Labels:	area-CodeGen-coreclr, community-contribution
Milestone:	-

[AndyAyersMS]

I did some digging to see if we could refer to any papers here. The "functional" model for the store is similar to what one sees in various abstract program analyses. But I didn't find any exact matches.

@BruceForstall seems like you originally reviewed some of Dave Detlefs' work here, do you happen to recall if there was any theoretical writeup? The changesets (circa 2012) do not mention any.

[AndyAyersMS]

Looks like we do indeed have some detailed docs written when VN was first being developed, though no links to journal or conference papers.

Hopefully we can share these soon.

[AndyAyersMS]

This looks like a good start. I will try to find some time to translate the internal doc we have into markdown so we can share it.

@jakobbotsch PTAL

[jakobbotsch]

Looks great, thanks for writing documentation.