[llvm] [LoopVectorize] Enable vectorisation of early exit loops with live-outs (PR #120567)

[David Sherwood via llvm-commits]

david-arm wrote:

Hi @fhahn, I've managed to rewrite the patch so that it doesn't depend upon #112147 although it does leave the IR in an unoptimised state. I think this is fine for now, and strangely enough for one of the `std::find` loops I care about it doesn't seem to affect performance that much. The recipes can be optimised in a later patch in a similar way to how you plan to deal with normal live-outs in #112147. I've had to change `fixupIVUsers` so that it doesn't crash when vectorising early exit loops, but this won't last very long since #112147 will be removing this code. I don't think this patch will cause any issues for #112147.

I've also updated the documentation to represent the new VPlan structure.

https://github.com/llvm/llvm-project/pull/120567