[llvm] [DAGCombiner] Add support for scalarising extracts of a vector setcc (PR #118823)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

> I thought this already landed?

The patch was reverted because it exposed a bug within legalisation (expansion) of i128 based setcc operations.

https://github.com/llvm/llvm-project/pull/118823