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Wednesday, October 17 • 11:30am - 12:00pm
Outer Loop Vectorization in LLVM: Current Status and Future Plans

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We recently proposed adding an alternative VPlan native path in Loop Vectorizer (LV) to implement support for outer loop vectorization. In this presentation, we first give a status update and discuss progress made since our initial proposal. We briefly talk about the addition of a VPlan-native code path in LV, initial explicit outer loop vectorization support, cost modelling and vector code generation in the VPlan-native path. We also summarize the current limitations.

Next, we introduce VPlan-to-VPlan transformations, which highlight a major strength of VPlan infrastructure. Different vectorization strategies can be modelled using the VPlan representation which allows reuse of VPlan-based cost modelling and code generation infrastructure. Starting from an initial VPlan, a set of VPlan-to-VPlan transformations can be applied, resulting in a set of plans representing different optimization strategies (e.g. interleaving of memory accesses, using SLP opportunities, predication). These plans can then be evaluated against each other and code generated for the most profitable one. We present VPlan-based SLP and predication as concrete examples of VPlan-to-VPlan transformation.

We end this talk with a discussion of the next steps in the VPlan roadmap. In particular, we discuss plans to achieve convergence of the inner loop and VPlan-native vectorization paths. We present opportunities to get involved with VPlan development and possibilities for collaboration. Furthermore, we discuss how vectorization for scalable vector architectures could fit into VPlan. We also plan to organize a VPlan focused hacker’s table after the talk, to provide a space for more in-depth discussions relating to VPlan.


Satish Guggilla

Intel Corporation

Wednesday October 17, 2018 11:30am - 12:00pm PDT
2 - Technical Talk (Rm LL21AB)