XLS: IR Pass Profiling

The XLS Optimization pipeline is quite complex with many passes run repeatedly and in fixed-point loops. This can make pinpointing what parts of optimization are taking time difficult. To improve this situation we have a --passes_profile=<path> flag on most binaries which interact with the pass system. This flag will generate a (uncompressed) pprof profile recording the number of invocations, number of changed runs, and timings of each pass.

Using pprof

There are many pprof visualizers including the go visualizer found at google/pprof.

Known issues

Due to how we structure our pass pipelines some compound passes might appear multiple times in a stack. This is due to the profile recording both the actual compound pass and a wrapper which is used to implement some opt-level behaviors.