[llvm] [LAA] Rework getStrideFromPointer, speculate more (PR #212816)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon commented:

There was a serious thinko in the patch, leading to bad test changes: hopefully, all of them should be fixed now.

> What's the point of "speculate more" in LAA?

Not sure how to answer the question of "why improve something that's in use?" -- obviously so we can have improvements?

https://github.com/llvm/llvm-project/pull/212816