[llvm] [SLP]Initial support for copyable elements (non-schedulable only) (PR #140279)

[Hans Wennborg via llvm-commits]

zmodem wrote:

A reduced C++ repro: [reduced.ii.gz](https://github.com/user-attachments/files/22383908/reduced.ii.gz)

```
$ build/bin/clang -cc1 -triple thumbv7-unknown-linux-android29 -Os -emit-obj -fprofile-instrument=llvm -vectorize-slp /tmp/reduced.ii
```

An IR reproducer based on the above: [reduced.ll.gz](https://github.com/user-attachments/files/22383919/reduced.ll.gz)

```
$ build/bin/opt -passes='default<O3>,slp-vectorizer' /tmp/reduced.ll -o - | build/bin/llc -filetype=asm -o -
```

Could you take a look?

https://github.com/llvm/llvm-project/pull/140279