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Optimizing "Scrap Your Boilerplate" with HERMIT

Michael D. Adams, Andrew Farmer and José Pedro Magalhães

GHC has a flexible system for adding new optimizations to the compiler pipeline. However, the traditional workflow for developing these optimizations is still batch oriented, which slows down the development of new optimizations. The HERMIT system addresses this by extending GHC and allowing compiler developers to experiment with optimizations interactively and thus more easily explore various optimization designs. Such an optimization can then be converted to a traditional, batch optimization for practical use by compiler users.

In this talk, we present a case study in this methodology by using HERMIT to develop an optimization for the Scrap Your Boilerplate library. Code written with Scrap Your Boilerplate is often an order of magnitude or more slower than equivalent handwritten code, and previous attempts at optimizing Scrap Your Boilerplate have met with little success. Nevertheless, by using the interactive style of optimization development enabled by HERMIT, we can create an optimization that completely eliminates the runtime overhead of Scrap Your Boilerplate programs and produces code that is as fast as handwritten code.