[PATCH] D57779: [SLP] Add support for throttling.

[Dinar Temirbulatov via Phabricator via llvm-commits]

dtemirbulatov marked an inline comment as done.
dtemirbulatov added inline comments.


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:645
+  /// Save seed instructions to try partially vectorize later.
+  void recordSeeds(ArrayRef<Value *> Ops);
+
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dtemirbulatov wrote:
> dtemirbulatov wrote:
> > vporpo wrote:
> > > dtemirbulatov wrote:
> > > > vporpo wrote:
> > > > > Why are we collecting the seeds specifically for partial vectorization? Is this really needed? Why don't you just call tryPartialVectorization(Seeds) within vectorizeStorChain() etc. ?
> > > > Ok, Imagine that we could do partial vectorization with vector size 4 for 30% of the tree, but for the same tree, we could have full vectorization with vector size 2. I think that it would be serious regression if we could do it with just 30%. Or for example, for the same tree, we could do reduction later for the whole tree.
> > > Yes, but this problem is not specific to throttling. As it is now, SLP will greedily accept 4-wide vectorization if profitable, without comparing it against 2x 2-wide. I think this problem should be addressed separately.
> > Let's change that behavior separately or this change grows even further. BTW, I measured the SLP run-time change on SPEC2k6 compilation and it is about ~10% on average.
> and It is not clear to me how to compare the benefit of one vectorization against another, the same example we achieved 50% of tree 4 wide vectorization with still profitable cost, let's say,  -1. But, for the same tree, we have 90% of vectorization with vector size 2 with for example the same cost. We could not say let's pick one with the highest score, we are interesting to vectorize while it is profitable.
Maybe we could have a subjective score based upon a vectorized tree-hight and vector widening.


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  https://reviews.llvm.org/D57779/new/

https://reviews.llvm.org/D57779