[llvm] [LoopVectorize] Add llvm.loop.vectorize.fp_reordering.{enable,disable} metadata (PR #219167)

[Karthika Devi C via llvm-commits]

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+; RUN: opt -passes='loop-vectorize' -force-vector-width=4 -S < %s 2>&1 | FileCheck %s
+
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kartcq wrote:

On metadata vs flags: vectorize.enable was redundant since -force-vector-width=4 on the RUN line already enables reordering. I've dropped it. The only metadata left is fp_reordering.{enable,disable}.

On UTC: Since the checks here are specifically targeting the vector reduction instruction, I felt focused checks were cleaner than full UTC output. Please let me know if you still think it's better to prefer UTC!

https://github.com/llvm/llvm-project/pull/219167