Feature

Use Uimm64 for UnaryImm::imm instead of Imm64, since UnaryImm::imm is now always encoding an unsigned integer; following #6850 & #3059.

Benefit

Make it clear that UnaryImm::imm must be interpreted as an unsigned integer; or that it should be reinterpreted as a signed integer with respect to the actual bit-length of the encoded value. For example, since #6850, the immediate of iconst.i32 -2 is encoded in UnaryImm::imm as 0xffff_fffe, and not -2, despite being stored in a signed 64-bit integer.

Implementation

Change the type, listen to the complaints of the type checker, and address tests breakage.

I would like to try to address this issue, if it's suitable for a compiler beginner with limited time resource.

Alternatives

Keep using Imm64 since the verifier is already rejecting incorrect encodings.