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

[Nikita Popov via llvm-commits]

nikic wrote:

> When absent, allowReordering() retains its existing behaviour: vectorize.enable or an explicit vector width > 1 grants FP reordering. When present, the hint takes precedence over that default.

TIL

I think given that this already introduces new metadata to control this separately, it would be a good idea to also change the vectorize.enable metadata to not imply this.

Also I found this additional code: https://github.com/llvm/llvm-project/blob/a945adae2eb9236392fbbfe1ab5181f8c073d6f8/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h#L178-L185 Don't you need to change it as well? (Possibly making this just about "fp_reordering" is not quite right in that case.)

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