[PATCH] D42447: [LV][VPlan] Detect outer loops for explicit vectorization.

[Hideki Saito via Phabricator via llvm-commits]

hsaito added a comment.





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Comment at: lib/Transforms/Vectorize/LoopVectorize.cpp:8642
+
+     // TODO: It will be set to true when we introduce codegen support.
+     return false;
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dcaballe wrote:
> rengolin wrote:
> > I'm really uncomfortable with all these temporary code blocks that don't do anything...
> > 
> > They're really just hijacking the existing infrastructure without implementing as a VPlan.
> > 
> > I really thought the whole point of VPlans was that you wouldn't need to hack-it-up like we used to in the old vectoriser...
> This is the entrance to the VPlan-native vectorization path. It's not doing anything yet because we are trying to follow an incremental approach by releasing relatively small patches that are easy to digest. This code will be functional (generating vector code) soon.
> 
> The code block is temporary as long as both vectorization paths co-exist but the final goal is to converge into a single one. This approach will allow us to incrementally and easily extend all the current inner loop vectorization functionality to support outer loops and, most importantly, doing so without destabilizing inner loop vectorization. We are really concerned about the latter and we think that this approach is a reasonable trade-off between safety and temporary code blocks.
> 
> If you want to discuss this further, I would recommend to move the discussion to the RFC thread so that everybody is aware of it: http://lists.llvm.org/pipermail/llvm-dev/2017-December/119523.html
> 
I'm working on the "converge into a singe one" side. At this point, I'm taking care of the ground work of moving the right things to the right places such that I don't have to include those "almost NFC" things as part of "expand VPlan's participation into innermost loop vectorization". Thank you for helping me do that with your reviews. We need to be able to build VPlan for the innermost loop vectorization right after Legal, for example, before we can remove the diverged code path at the beginning. In the meantime, the outer loop vectorization patch series will help people realize how much common things are there between innermost loop vectorization and outer loop vectorization, and more importantly, help people think how to write code that can work in both ways. 
That's as much as I want to write about the approach we are taking, within this patch review. The rest of the discussions should happen on the above mentioned RFC. Thanks.


https://reviews.llvm.org/D42447