[llvm] [TableGen] Add support for DefaultMode in per-HwMode encode/decode. (PR #83029)

[James Y Knight via llvm-commits]

jyknight wrote:

That's great context, thanks -- and I don't want to cause you any grief. :)

But I also know of a private backend that _tried_ to use this feature, but ran into real trouble due to the inability to set constant values in the usual way. Hearing that you're using this feature extensively makes me think that maybe you have figured out good ways to workaround (or fix?) this issue?

https://github.com/llvm/llvm-project/pull/83029