llvm-project

a2942d47 - [VectorCombine] foldShuffleChainsToReduce - add support for partial vector reductions (#195119)

[VectorCombine] foldShuffleChainsToReduce - add support for partial vector reductions (#195119) Extend foldShuffleChainsToReduce to recognize partial reduction patterns where only a subvector of the full vector is being reduced. For example, a <16 x i16> vector where the shuffle chain only reduces the lower 8 elements can now be folded into: shufflevector (extract lower <8 x i16>) + vector.reduce.smax The detection works by noticing when the bottom-up walk through the shuffle/op chain ends before consuming the full vector. The number of levels visited determines the subvector size (2^levels), and an extract_subvector + scalar reduction replaces the original chain when profitable. Fixes #194617