[llvm] SCEV: return std::nullopt for invalid TC (NFC) (PR #94162)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> The PR description (but especially the title) are confused. On wrap, the TC is treated as unknown, which is represented as a 0 value. There was no "conflation" here.

Yes, sorry. Title fixed.

> > Improvements are planned for future patches.
> 
> What improvements are you planning?

The patch was motivated by LV printing a "Found TC: 0".

https://github.com/llvm/llvm-project/pull/94162