[llvm] [Machine-Combiner] Add a pass to reassociate chains of accumulation instructions into a tree (PR #132728)

[David Green via llvm-commits]

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

LGTM. 

It looks like it was updated last week after #131272. It might be good to link back to #126060 in the commit message so there is a reference to the original.

https://github.com/llvm/llvm-project/pull/132728