[llvm] Add support for single reductions in ComplexDeinterleavingPass (PR #112875)

[Nicholas Guy via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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NickGuy-Arm wrote:

I've removed as much of the loop as I can, however we need the IR to at least resemble a loop in order for the reduction to be valid and recognised.

https://github.com/llvm/llvm-project/pull/112875