(Note: I named it debug counting because that's what we called it in
GCC. I'm also mostly leaving this here until i get back to it because
i promised some folks who wanted to use it. I'll ping the review when
it's cleaned up a bit).
We have support for bisection, and bugpoint can reduce testcases
often to a single pass. But that doesn't help reduce it to a single
transform by a single pass. Which debug counting lets us do.
Debug counting lets you instrument a pass so that it only executes a
certain thing (rwhatever you want) after skipping it a certain time of
times, and then only does a certain number of executions before saying
To make it concrete, for predicateinfo, if i instrument use renaming,
i can make it so it skips renaming the first N uses, renames the next
N, and then skips the rest.
This lets you narrow down a miscompilation to, often, a single
transformation, and then also debug it (by using the same command line