[llvm] [TableGen] Use bitwise operations to access HwMode ID. (PR #88377)

[Jason Eckhardt via llvm-commits]

nvjle wrote:

> Hi @nvjle , I'm really sorry for the delay in addressing your review feedback. This update includes the following five main changes:
> 
>     1. Fixed the issue with improper HwMode retrieval during Encoding generation process (the most critical issue).
> 
>     2. Used encoding '0' to represent instructions with mismatched HwMode in the encoding table.
> 
>     3. Added testcase to assess instruction encoding under APInt mode (128-bit length) and introduced more HwModes to validate performance under multiple HwMode scenarios.
> 
>     4. Discovered and resolved a potential issue (not introduced by my patch) where the existing 'getOperandBitOffset' interface was checking HwMode ID without first retrieving it.
> 
>     5. Made some modifications related to Clean Code and also fixed the comments.
> 
> 
> Could you please review these changes again and verify them in your backend? Thank you very much!

Please give me a few days to re-review this iteration and incorporate into our repo to verify failures are gone.

https://github.com/llvm/llvm-project/pull/88377