[llvm] [SLPVectorizer] Handle InsertValueInst in getVectorElementSize (PR #215473)

[Tony Varghese via llvm-commits]

https://github.com/tonykuttai requested changes to this pull request.

IIUC, this fix only affects RISCV target and needs only `insert-value-element.ll` test.

https://github.com/llvm/llvm-project/pull/215473