[PATCH] D29998: Add initial support for debug counting

[Daniel Berlin via Phabricator via llvm-commits]

dberlin created this revision.
Herald added a subscriber: mgorny.

(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
"skip" again.

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
parameters).


https://reviews.llvm.org/D29998

Files:
  include/llvm/Support/DebugCounter.h
  lib/Support/CMakeLists.txt
  lib/Support/DebugCounter.cpp

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