[llvm] [SLP]Remove operands upon marking instruction for deletion. (PR #97409)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

More info about the assert in case its helpful:

We typically see this assert when a pass sets an insertion point to the beginning of a block or the first non-phi using an `Instruction *` rather than iterator (which carries a bit that describes whether the insertion point comes before the instruction only or before the instruction and the debug records attached to it). Scanning it I couldn't see anything obvious in this patch that would cause that assertion to fire - it's possible that this patch is just exercising a latent bug in SLP. I also have no clues as to why it's nondeterministic.

DbgRecords and the new iterator bit are documented over [here](https://llvm.org/docs/RemoveDIsDebugInfo.html#api-changes). I'm happy to help with any debug-info questions.

https://github.com/llvm/llvm-project/pull/97409