[llvm] [LV] Add initial support for vectorizing literal struct return values (PR #109833)

[Benjamin Maxwell via llvm-commits]

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+; RUN: opt < %s -passes=loop-vectorize,dce,instcombine -force-vector-interleave=1 -S | FileCheck %s --check-prefixes=NEON
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MacDue wrote:

> Does this test need to be specific to SVE? 

Not really, but I find convincing the vectorizer to use scalable vectors without `+sve` quite finicky... I was playing with `-force-target-supports-scalable-vectors=true`, but it seems not to try scalable VFs unless I force the vector width too, and then it's hit or miss. I'm probably doing something wrong, so I'll play around with it a bit more.

https://github.com/llvm/llvm-project/pull/109833