[llvm] [NFC][SBVec] Rename BottomUpVec to SLPTreeVec (PR #213197)

[Anshil Gandhi via llvm-commits]

gandhi56 wrote:

> Thanks for the cleanup patch ! Not so sure about the "SLPTree" part: It's a DAG, not a tree, and then it's not really SLP. The differentiating factor between this and the load-store vectorizer is that it follows use-def/def-use chains and it operates on bundles. So something like ChainVec ? or BundleVec ? Wdyt ?

"SLP" because we are packing scalar values to obtain superword level parallelism. "Tree" because we are forming a tree of bundles. I think BundleVec is more descriptive though. I wil rename.

https://github.com/llvm/llvm-project/pull/213197