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

[Sjoerd Meijer via llvm-commits]

https://github.com/sjoerdmeijer approved this pull request.

This patch basically contains two parts: the LAA/SCEV and the vectorisation part.

I have only looked at the vectorisation part and that looks good to me:
- thanks for taking the cost-model remarks into account, the added logic seems like a good first step,
- the option to vectorise loops with early breaks is off by default. This allows us to experiment more with this, possibly refine the cost-model, without creating a lot of turbulence. 
- It's a shame we can't look at final codegen for these sort of patches, but that is not a problem of this patch. I like the idea of some microbenchmarks for this, but given that this is off by default I don't think that this needs to hold up this patch.

So, LGTM, but I haven't looked at the LAA part, perhaps @nikic or @nikolaypanchenko can sign off on that part. 


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