[PATCH] D117926: [SLP] Optionally preserve MemorySSA

Philip Reames via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Mon Mar 14 12:02:36 PDT 2022


reames added a comment.

In D117926#3379735 <https://reviews.llvm.org/D117926#3379735>, @asbirlea wrote:

> Reading the details in your post and looking at the SLPVectorizer code I think there's the potential for the pass to benefit from using MemorySSA.  However I do not understand enough of the SLPVectorizer mechanics to guess if this will work out or not.
> In this context, I think it makes sense to have incremental changes while keeping building and updating MSSA off by default; as you mentioned in the post, all changes can (and should) be reverted if a later decision is to pursue something else.
>
> @nikic Thoughts?

Was this meant to be an LGTM?  It sort of sounds like it, but you never say that explicitly.

> Regarding this patch, seeing MSSA used in a dependent patch would help.
> Is there a benefit from the existance of an `insertAccesses() `/`insertDefs() `/`insertUses` API in MSSA (i.e. bulk add update, perhaps limited to within the same BB)? Does doing lazy updates during the vectorizeTree() call make sense or will MSSA need to be queried?

I explicitly don't want to try to answer this until future patches.  That's the whole point of being incremental; we can discuss each one in the appropriate context, and I can avoid repeating myself and speculating about hypothetical situations which don't match the code structure as it evolves.


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