[all-commits] [llvm/llvm-project] cfe043: [mlir][linalg] Restrict scalable vectorisation (#9...

[Andrzej Warzyński via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cfe043cf99f76980ff91dc1cd4026e852556fba1
      https://github.com/llvm/llvm-project/commit/cfe043cf99f76980ff91dc1cd4026e852556fba1
  Author: Andrzej Warzyński <andrzej.warzynski at arm.com>
  Date:   2024-07-19 (Fri, 19 Jul 2024)

  Changed paths:
    M mlir/lib/Dialect/Linalg/Transforms/Vectorization.cpp
    M mlir/test/Dialect/Linalg/vectorization-unsupported.mlir

  Log Message:
  -----------
  [mlir][linalg] Restrict scalable vectorisation (#98639)

Updates `vectorizeScalableVectorPrecondition` so that scalable
vectorisation is only applied in well understood and tested scenarios.

It's unlikely that we would ever want an arbitrary dimension to be
scalable. While the Linalg vectoriser should be flexible enough to
handle all possibilities:
  * in more "exotic" cases, we are likely to struggle with lowerings
    further down the compilation stack,
  * it would be impractical given the limitations of LLVM (which usually
    reflect the limitations of actual hardware) - e.g. no support for
    "scalable" arrays of scalable or fixed width vectors (*).

Ultimately, the goal of this patch is to better document what's
currently supported. While this PR adds some new restrictions, no
existing tests are affected.

(*) At MLIR vector level that would correspond to e.g.
`vector<[4]x8xf32>`.



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