[llvm] [SelectionDAG] Improve isGuaranteedNotToBeUndefOrPoison (PR #147019)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

Is the peekThroughInsertVectorElt code necessary for the test changes? I'm not opposed to adding handling for many opcodes without much test coverage but the INSERT_VECTOR_ELT code looks to be a very special case.

https://github.com/llvm/llvm-project/pull/147019