2014 LLVM Developers’ Meeting: “The LLVM Pass Manager, Part 2 ”

—
The LLVM Pass Manager, Part 2 - Chandler Carruth - Google

—
I will present a new design and implementation of the LLVM pass manager that is currently being developed in the tree. I will cover how it differs from the previous implementation and how those differences allow it to solve many of the long-standing limitations of the current implementation. I will discuss in depth how the new system supports richer analysis dependencies, flexible composition of function-level analyses and module- or call-graph-level transformations. The new pass manager also introduces a caching-based scheduling model which is substantially different from the prior ones and critical to understanding the impact of transitioning. And as I go through these topics I will introduce how to write a pass suitable for the new infrastructure and how to port an existing pass to live happily in both.
Finally, I will show a specific new call-graph analysis used by the new pass manager and discuss how these two components can be used to parallelize the entire LLVM compilation pipeline. I will mention some of the basic correctness and efficiency challenges faced when running in parallel and detail the specific challenges and constraints pursuing this path would impose on analysis and optimization passes.
—