[PATCH] D65649: [RISCV] Add MC encodings and tests of the Bit Manipulation extension

[Alex Bradbury via Phabricator via llvm-commits]

asb added a comment.

In D65649#1943856 <https://reviews.llvm.org/D65649#1943856>, @simoncook wrote:

> I agree, it seems more like a sketch of what they should be, but the mentioning of the size improvements suggested to me perhaps they should be, since evaluating the potential "what the final B extension should look like" it probably should be included. There is the question of where this should be enabled, my first thought (which this patch implements) is Zbb because it seemed the most logical, but maybe given the instructions stated state does another subextension make sense for its evaluation? These are all experimental so I think there's some leeway to some option, but I think it would be good to land it if we think people may be using it/want to evaluate it. I suspect there's many valid routes with this being experimental, we just need to choose one we have concensus around making sense. Perhaps a topic for today's call?


Yes, let's discuss today. I agree there's value in making it easy to evaluate the compressed instructions too. My concern would be that people implementing experimental support in simulators or CPUs might skip over the section as more speculative, meaning that if we emitted those encodings those users might have a bad experience.


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