[clang] [CodeGen] Refactor accumulateBitFields into two passes (PR #182814)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> I feel like you could have pretty easily achieved your stated goals of removing the goto and reduced nesting by just extracting helper functions in a few places, like `getLimitOffset`, instead of rewriting the entire algorithm.

Thanks for the review. The original single-loop structure inherently needed extra variables due to interleaving span detection and merging. The complexity could only be avoided by switching to an explicit two-pass structure.

>  You've also removed a bunch of comments. It's hard for me to call this a clear improvement.

 This was a real oversight. I've now restored them.

https://github.com/llvm/llvm-project/pull/182814