[llvm] [NFC][AArch64] Refactor AArch64LoopIdiomTransform in preparation for more idioms (PR #78471)

[David Sherwood via llvm-commits]

david-arm wrote:

> Hi, I'm interested in this pattern too, and I wonder that when would you plan to finish this pattern match? Would you just recognize this pattern and transform it to the original while loop IR and do the following transform reusing the original code, or would you like to write something new for this pattern?

I already have a second patch waiting to upstream once this patch lands. This patch just makes it a lot easier to recognise different forms of the same idiom and transform the loop using the same generation code. There are a surprisingly large number of variations of the same idiom out there in SPEC and other benchmarks!

https://github.com/llvm/llvm-project/pull/78471