[llvm] [SCEV,LAA] Introduce scoped SCEV, use in LAA computations (WIP). (PR #90742)

[Florian Hahn via llvm-commits]

fhahn wrote:

> > The general approach I would consider is to replace our current `const SCEV *` pointers with `SCEVUse`, where the low bits are used to store no-wrap flags for a specific use of the expression.
> 
> Yeah that should also cover my use case here. I'll try to sketch a prototype

Sketched in https://github.com/llvm/llvm-project/pull/91961 with 2 additional linked PRs to use SCEVUse. @nikic Is that along the lines of what you had in mind?

https://github.com/llvm/llvm-project/pull/90742