[PATCH] D117926: [SLP] Optionally preserve MemorySSA

[Philip Reames via Phabricator via llvm-commits]

reames updated this revision to Diff 413553.
reames added a comment.
Herald added a project: All.

Refresh the patch.

Ok, I'm back to this, and want to strongly argue for this patch being accepted largely as is.  I went ahead and filed an issue with a long form writeup explaining why I think this is the right approach (https://github.com/llvm/llvm-project/issues/54256).

I want to request that we defer *efficiency* of update to separate reviews.  I have investigated the cause of the slowdowns, and have a local patch which is fast on my motivating example.  My local patch is definitely not fully correct as it hacks around several issues, but I'm now reasonable convinced a correct and fast preservation of MSSA is entirely possible.  However, the number of interlocking and subtle changes required is well beyond anything reasonable for a single review.

If we can't unblock incremental review on this, I don't think implementing this is practical at all.  There's too much undocumented assumptions about memory ssa form, and attempting to post the entire series without being able to do cleanups in between would be simply unmanageable and unreviewable.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117926/new/

https://reviews.llvm.org/D117926

Files:
  llvm/include/llvm/Transforms/Vectorize/SLPVectorizer.h
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

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