67b302c52f
This patch adds a new vector.step operation to the Vector dialect. It
produces a linear sequence of index values from 0 to N, where N is the
number of elements in the result vector, and can be used to create
vectors of indices.
It supports both fixed-width and scalable vectors. For fixed the
canonical representation is `arith.constant dense<[0, .., N]>`. A
scalable step cannot be represented as a constant and is lowered to the
`llvm.experimental.stepvector` intrinsic [1].
This op enables scalable vectorization of linalg.index ops, see #96778. It can
also be used in the SparseVectorizer in-place of lower-level stepvector
intrinsic, see [2] (patch to follow).
[1] https://llvm.org/docs/LangRef.html#llvm-experimental-stepvector-intrinsic
[2] acf675b63f/mlir/lib/Dialect/SparseTensor/Transforms/SparseVectorization.cpp (L385-L388)
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