Use a polyhedral model to represent and transform the iteration space

I think this is the simplest (and most disciplined) solution to issues such as:
https://github.com/chriselrod/LoopVectorization.jl/issues/77
https://github.com/chriselrod/LoopVectorization.jl/issues/122
Lots of helpful literature, e.g.:
https://dl.acm.org/doi/pdf/10.1145/1379022.1375594

Start by reviewing issues 77 and 122 in LoopVectorization.jl, then read the linked polyhedral-model literature. The issue names no files, tests, entry points, or concrete acceptance criteria; a completed solution would need to define how iteration spaces are represented and transformed.

Rédigé par le modèle d'indexation à partir du texte de l'issue.