27e5e21bfe
This PR changes how sparse case expressions represent the none-of-the-above information. Instead of of many `x.ctorIdx ≠ i` hypotheses, it introduces a single `Nat.hasNotBit mask x.ctorIdx` hypothesis which compresses that information into a bitmask. This avoids a quadratic overhead during splitter generation, where all n assumptions would be refined through `.subst` and `.cases` constructions for all n assumption of the splitter alternative. The definition of `Nat.hasNotBit` uses `Nat.rightShift` which is fiddly to get to reduce well, especially on open terms and with `Meta.whnf`. Some experimentation was needed to find proof terms that work, these are all put together in the `Lean.Meta.HasNotBit` module. Fixes #11183 --------- Co-authored-by: Rob23oba <152706811+Rob23oba@users.noreply.github.com> |
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