[llvm] [LV] Reuse IRBuilder with InsertPointGuard (NFC) (PR #141236)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> IIUC this is pending the further direction for [#141225 (comment)](https://github.com/llvm/llvm-project/pull/141225#issuecomment-2906888056)?

I think it's going to take some time to craft out the exact direction, but maybe this patch is just a good-to-have cleanup independently of that?

https://github.com/llvm/llvm-project/pull/141236