[WIP] Compute At Refactoring 4

[csarofeen]

Start trying to see if we can disentangle concepts with burying more direct mapping concepts in IterDomainGraph. This graph is a highly connected, multi-dimensional map. Also including now concept of mapped expressions. Pulled using replay out of mapping the exact map and propagating within IterDomainGraph across Exprs directly.

[csarofeen]

@zasdfgbnm and @naoyam not urgent but would like your opinion on this PR, specifically removing the need to use transformation replay for building the Exact map. I'm wondering if we should try extend this for Permissive and loop mapping, and start deprecating much of BestEffortReplay since IterDomainGraph could/ maybe should be responsible for building many of the relationships that currently BestEffortReplay is responsible for today.

[naoyam]

I don't see any red flag, but curious why you want to deprecate BestEffortReplay.

[csarofeen]

I'm not sure I want to yet, but I'm considering the option. BestEffortReplay is kind of doing some overloaded things, and understanding what IterDomain's map with what, makes more sense to me in the format IterDomainGraph holds. I believe if we remove BestEffortReplay dependency in IterDomainGraph which should be quite possible, it's easy to get a map like what getReplay returns, but more directly by looking at relationships between two tensor views as described in the IterDomainGraph. To me having more logic about what maps with what in IterDomainGraph makes a lot of sense to try and centralize more of that information, if possible. BestEffortReplay to me just feels quite convoluted with how it's reasoning about mappings with the forwarding maps. I'm somewhat hopeful, but not heavily convinced this may be more straightforward in a fully built out IterDomainGraph.

[naoyam]

Sounds reasonable. I guess the forwarding logic would be one reason that makes BestEffortReplay convoluted. I'm not sure moving it to IterDomainGraph could make it cleaner.

[csarofeen]

It might not make it cleaner, but if it's just as "not clean" but only implemented in one straightforward way I might still be happier.

[naoyam]

Agreed.

[csarofeen]

Closing in favor of #2316