LLVM  6.0.0svn
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DebugCounter.h File Reference

This file provides an implementation of debug counters. More...

#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/UniqueVector.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <string>
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Classes

class  llvm::DebugCounter
 

Namespaces

 llvm
 Compute iterated dominance frontiers using a linear time algorithm.
 

Macros

#define DEBUG_COUNTER(VARNAME, COUNTERNAME, DESC)
 

Detailed Description

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 skip and a count. Skip is the number of times shouldExecute needs to be called before it returns true. Count is the number of times to return true once Skip is 0. So a skip=47, count=2 ,would skip the first 47 executions by returning false from shouldExecute, then execute twice, and then return false again. 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) <continue or="" return="" or="" whatever="" not="" executing="" looks="" like>="">

Now I can, from the command line, make it rename or not rename certain uses by setting the skip and count. So for example bin/opt -debug-counter=predicateinfo-skip=47,predicateinfo-count=1 will skip renaming the first 47 uses, then rename one, then skip the rest.

Definition in file DebugCounter.h.

Macro Definition Documentation

◆ DEBUG_COUNTER

#define DEBUG_COUNTER (   VARNAME,
  COUNTERNAME,
  DESC 
)
Value:
static const unsigned VARNAME = \
DebugCounter::registerCounter(COUNTERNAME, DESC)

Definition at line 160 of file DebugCounter.h.