[llvm] [DAGCombiner] Lower dynamic insertelt chain more efficiently (PR #162368)

[via llvm-commits]

https://github.com/Chengjunp approved this pull request.

LGTM. Only concern I have is the lowering of non-byte-aligned element types. You may add some tests for this case.

https://github.com/llvm/llvm-project/pull/162368