[llvm] [SLP] Ensure TreeCost is scaled for ordered fadd reductions (PR #199388)

[Alexey Bataev via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
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alexey-bataev wrote:

Precommit the test in a separate NFC patch

https://github.com/llvm/llvm-project/pull/199388