[all-commits] [llvm/llvm-project] efa846: [VectorCombine] Add free concats to shuffleToIdent...

[David Green via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: efa8463ab90147aacd4647eb7715763978235890
      https://github.com/llvm/llvm-project/commit/efa8463ab90147aacd4647eb7715763978235890
  Author: David Green <david.green at arm.com>
  Date:   2024-06-25 (Tue, 25 Jun 2024)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VectorCombine.cpp
    M llvm/test/Transforms/PhaseOrdering/AArch64/interleavevectorization.ll
    M llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity-concat.ll
    M llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll

  Log Message:
  -----------
  [VectorCombine] Add free concats to shuffleToIdentity. (#94954)

This is another relatively small adjustment to shuffleToIdentity, which
has had a few knock-one effects to need a few more changes. It attempts
to detect free concats, that will be legalized to multiple vector
operations. For example if the lanes are '[a[0], a[1], b[0], b[1]]' and
a and b are v2f64 under aarch64.

In order to do this:
- isFreeConcat detects whether the input has piece-wise identities from
multiple inputs that can become a concat.
- A tree of concat shuffles is created to concatenate the input values
into a single vector. This is a little different to most other inputs as
there are created from multiple values that are being combined together,
and we cannot rely on the Lane0 insert location always being valid.
- The insert location is changed to the original location instead of
updating per item, which ensure it is valid due to the order that we
visit and create items.



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