[llvm] [AArch64] Eliminate Common SUBS by Reassociating Non-Constants (PR #123344)

[David Sherwood via llvm-commits]

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david-arm wrote:

I noticed the only tests affected by this patch are i32 variants. Should this also work for i64 and is it worth adding at least one test for it?

Also, I realise that i8 and i16 types will get promoted during legalisation and so the DAG may look different, but perhaps it's still worth having at least one i8 and i16 variant of `test_eq_nonconst_sub_add_i32` or something like that?

https://github.com/llvm/llvm-project/pull/123344