[llvm] [RISCV] Check only demanded VTYPE fields in needVSETVLIPHI (PR #90168)

[Philip Reames via llvm-commits]

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

This is unsound because the CurInfo state during rewriting will differ from the CurInfo computed during the forward data flow.  The first instruction may not care, but later ones in the block (or following blocks!) may depend on the other fields.  

There is a correct variant of this, but you end of with different states flowing through the block during emission, and the need to compensate.  Not sure if it's worth the complexity?

https://github.com/llvm/llvm-project/pull/90168