[llvm] Make a tablegen test match-table.td more robust. (PR #106508)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

I'm not sure I like this approach because it makes the test a lot more annoying to update, and it's easy to drop these patterns by just copy-pasting the new output.  There are no checks upstream to ensure these patterns remain, and I broke them once in the past because of that.

Also if all tests end up like this then a small change to the match table will be 10 min of work and 50 min to update tests.

I think the best solution would be to have some Python script to update these tests easily.
Failing that, maybe a CL opt for TableGen to emit a more testable match-table (for instance, one that omits all of the indexes)  ?

https://github.com/llvm/llvm-project/pull/106508