[llvm] [SDag] Notify listeners when deleting a node (PR #66991)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Hmm - doesn't look great https://llvm-compile-time-tracker.com/compare.php?from=66e1d2c96a194f572be5b373705f493b1a4dc811&to=29fbcd00a16a199cd94533dac76b20ba069527b4&stat=instructions:u

That's a shame but (a) it doesn't look _too_ bad and (b) this does feel like a reasonably serious bug, if running the legalizer does not result in a fully legalized DAG.

Incidentally I understand that the DAG gets fixed up by later combine passes, but I was a bit surprised that all the combine passes are run even at -O0. Was there ever a plan to _not_ run them at -O0? Would that be feasible?

https://github.com/llvm/llvm-project/pull/66991