[llvm] [TableGen] Add support for sparse direct-lookup tables (PR #201158)

[Jay Foad via llvm-commits]

jayfoad wrote:

> The `GenericTable` only generate a direct look-up for continues tables, defaulting to binary search for non-contngious spaces.

"continuous"? "contiguous"?

> This patch adds a `SparseLookupTable` that allows to trade-off table size with look up speed by generating spare tables.

"sparse"

https://github.com/llvm/llvm-project/pull/201158