[llvm] [LoopVectorize] Add support for vectorisation of more early exit loops (PR #88385)

[David Sherwood via llvm-commits]

david-arm wrote:

Please note this patch is becoming out of date, since I've been splitting off various parts of this patch and landing them separately. Once enough of those patches have landed I will rebase this and hopefully the diff will be smaller and more concentrated on the vectoriser/vplan code!

https://github.com/llvm/llvm-project/pull/88385