[llvm] [TableGen] Efficiency improvements for encoding HwMode collection. (PR #82902)

[Jason Eckhardt via llvm-commits]

nvjle wrote:

> LGTM.

Thank you @wangpc-pp , could I also trouble you to merge on my behalf? (will apply for write access soon, almost enough commits).

https://github.com/llvm/llvm-project/pull/82902