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

[James Y Knight via llvm-commits]

jyknight wrote:

Given the context you've already provided, I don't object to this PR (nor other future ones addressing issues in HwMode support), so, yes, this definitely isn't the right place to continue the discussion.

But, this is what I mean: https://gist.github.com/jyknight/af4c461b7ad7a5f0bcfac6dd5a33d4a1

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