DebugCounter.h File Reference (original) (raw)

This file provides an implementation of debug counters.

Debug counters are a tool that let you narrow down a miscompilation to a specific thing happening.

To give a use case: Imagine you have a file, very large, and you are trying to understand the minimal transformation that breaks it. Bugpoint and bisection is often helpful here in narrowing it down to a specific pass, but it's still a very large file, and a very complicated pass to try to debug. That is where debug counting steps in. You can instrument the pass with a debug counter before it does a certain thing, and depending on the counts, it will either execute that thing or not. The debug counter itself consists of a list of chunks (inclusive numeric ranges). shouldExecute returns true iff the list is empty or the current count is in one of the chunks.

Note that a counter set to a negative number will always execute. For a concrete example, during predicateinfo creation, the renaming pass replaces each use with a renamed use.

If I use DEBUG_COUNTER to create a counter called "predicateinfo", and variable name RenameCounter, and then instrument this renaming with a debug counter, like so:

if (!DebugCounter::shouldExecute(RenameCounter)

Now I can, from the command line, make it rename or not rename certain uses by setting the chunk list. So for example bin/opt -debug-counter=predicateinfo=47 will skip renaming the first 47 uses, then rename one, then skip the rest.

Definition in file DebugCounter.h.