llvm-project

ddf9b91f - [mlir][Vector] Add `vector.shuffle` tree transformation (#145740)

[mlir][Vector] Add `vector.shuffle` tree transformation (#145740) This PR adds a new transformation that turns sequences of `vector.to_elements` and `vector.from_elements` into a binary tree of `vector.shuffle` operations. (Related RFC: https://discourse.llvm.org/t/rfc-adding-vector-to-elements-op-to-the-vector-dialect/86779). Example: ``` %0:4 = vector.to_elements %a : vector<4xf32> %1:4 = vector.to_elements %b : vector<4xf32> %2:4 = vector.to_elements %c : vector<4xf32> %3 = vector.from_elements %0#0, %0#1, %0#2, %0#3, %1#0, %1#1, %1#2, %1#3, %2#0, %2#1, %2#2, %2#3 : vector<12xf32> ==> %0 = vector.shuffle %a, %b [0, 1, 2, 3, 4, 5, 6, 7] : vector<4xf32>, vector<4xf32> %1 = vector.shuffle %c, %c [0, 1, 2, 3, -1, -1, -1, -1] : vector<4xf32>, vector<4xf32> %2 = vector.shuffle %0, %1 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] : vector<8xf32>, vector<8xf32> ``` The algorithm leverages the structured extraction/insertion information of `vector.to_elements` and `vector.from_elements` operations and builds a set of intervals to determine the vector length that should be used at each level of the tree to combine the level inputs in pairs. There are a few improvements that can be implemented in the future, such as shuffle mask compression to avoid unnecessarily large vector lengths with poison values, but I decided to keep things "simpler" and spend more time documenting the different steps of the algorithm so that people can follow along.