[PATCH] D102834: [SLP] Implement initial memory versioning.

Thu Dec 16 01:56:37 PST 2021

fhahn added a comment.

In D102834#3175761 <https://reviews.llvm.org/D102834#3175761>, @SjoerdMeijer wrote:

> Yeah okay, sure, fair enough. Just wanted to double check, and you haven't seen any performance disasters in Spec or the test suite?
> I am thinking if we should not just start with this enabled:
>
>   static cl::opt<bool> EnableMemoryVersioning(
>       "slp-memory-versioning", cl::init(false), cl::Hidden,
>
> If we get perf regression reports, this can be kept in tree but with this flag off, then at least we directly know what to fix.

I agree it would be good to start with this enabled by default! My main concern at the moment is compile-time impact. I need to re-measure, but from last time I remember that there were a few CTMark cases that had noticeable increases.

I think the rate of when versioning leads to actually vectorizing the versioned block at the moment is ~15%. I think for it to be enabled by default it would be good to increase this rate first. At the moment the reason this rate is so low is that we consider a block for versioning once we found an aliasing access and effectively stop analyzing further. So even if there are other problems preventing vectorization, we still try to version it.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102834/new/

https://reviews.llvm.org/D102834