[llvm] [llvm][ARM]Add widen strings pass (PR #107120)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Would it be possible to try and make the size a little more generic, not just 4? It could possibly have a cost-model based of the expected expansion of memcpy's, but that might not save much on many architectures other than the cost of an unaligned load/store.

Maybe the target could return the size to align to for a given array size, as opposed to the boolean useWidenGlobalStrings. So 4 for Arm (for ldm).

https://github.com/llvm/llvm-project/pull/107120