1//===- llvm/Support/DebugCounter.h - Debug counter support ------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9/// \file
10/// \brief This file provides an implementation of debug counters.  Debug
11/// counters are a tool that let you narrow down a miscompilation to a specific
12/// thing happening.
13///
14/// To give a use case: Imagine you have a file, very large, and you
15/// are trying to understand the minimal transformation that breaks it. Bugpoint
16/// and bisection is often helpful here in narrowing it down to a specific pass,
17/// but it's still a very large file, and a very complicated pass to try to
18/// debug.  That is where debug counting steps in.  You can instrument the pass
19/// with a debug counter before it does a certain thing, and depending on the
20/// counts, it will either execute that thing or not.  The debug counter itself
21/// consists of a skip and a count.  Skip is the number of times shouldExecute
22/// needs to be called before it returns true.  Count is the number of times to
23/// return true once Skip is 0.  So a skip=47, count=2 ,would skip the first 47
24/// executions by returning false from shouldExecute, then execute twice, and
25/// then return false again.
26/// Note that a counter set to a negative number will always execute.
27/// For a concrete example, during predicateinfo creation, the renaming pass
28/// replaces each use with a renamed use.
29////
30/// If I use DEBUG_COUNTER to create a counter called "predicateinfo", and
31/// variable name RenameCounter, and then instrument this renaming with a debug
32/// counter, like so:
33///
34/// if (!DebugCounter::shouldExecute(RenameCounter)
35/// <continue or return or whatever not executing looks like>
36///
37/// Now I can, from the command line, make it rename or not rename certain uses
38/// by setting the skip and count.
39/// So for example
40/// bin/opt -debug-counter=predicateinfo-skip=47,predicateinfo-count=1
41/// will skip renaming the first 47 uses, then rename one, then skip the rest.
42//===----------------------------------------------------------------------===//
43
44#ifndef LLVM_SUPPORT_DEBUGCOUNTER_H
45#define LLVM_SUPPORT_DEBUGCOUNTER_H
46
47#include "llvm/ADT/DenseMap.h"
48#include "llvm/ADT/UniqueVector.h"
49#include "llvm/Support/CommandLine.h"
50#include "llvm/Support/Debug.h"
51#include "llvm/Support/raw_ostream.h"
52#include <string>
53
54namespace llvm {
55
56class DebugCounter {
57public:
58  /// \brief Returns a reference to the singleton instance.
59  static DebugCounter &instance();
60
61  // Used by the command line option parser to push a new value it parsed.
62  void push_back(const std::string &);
63
64  // Register a counter with the specified name.
65  //
66  // FIXME: Currently, counter registration is required to happen before command
67  // line option parsing. The main reason to register counters is to produce a
68  // nice list of them on the command line, but i'm not sure this is worth it.
69  static unsigned registerCounter(StringRef Name, StringRef Desc) {
70    return instance().addCounter(Name, Desc);
71  }
72  inline static bool shouldExecute(unsigned CounterName) {
73// Compile to nothing when debugging is off
74#ifdef NDEBUG
75    return true;
76#else
77    auto &Us = instance();
78    auto Result = Us.Counters.find(CounterName);
79    if (Result != Us.Counters.end()) {
80      auto &CounterPair = Result->second;
81      // We only execute while the skip (first) is zero and the count (second)
82      // is non-zero.
83      // Negative counters always execute.
84      if (CounterPair.first < 0)
85        return true;
86      if (CounterPair.first != 0) {
87        --CounterPair.first;
88        return false;
89      }
90      if (CounterPair.second < 0)
91        return true;
92      if (CounterPair.second != 0) {
93        --CounterPair.second;
94        return true;
95      }
96      return false;
97    }
98    // Didn't find the counter, should we warn?
99    return true;
100#endif // NDEBUG
101  }
102
103  // Return true if a given counter had values set (either programatically or on
104  // the command line).  This will return true even if those values are
105  // currently in a state where the counter will always execute.
106  static bool isCounterSet(unsigned ID) {
107    return instance().Counters.count(ID);
108  }
109
110  // Return the skip and count for a counter. This only works for set counters.
111  static std::pair<int, int> getCounterValue(unsigned ID) {
112    auto &Us = instance();
113    auto Result = Us.Counters.find(ID);
114    assert(Result != Us.Counters.end() && "Asking about a non-set counter");
115    return Result->second;
116  }
117
118  // Set a registered counter to a given value.
119  static void setCounterValue(unsigned ID, const std::pair<int, int> &Val) {
120    auto &Us = instance();
121    Us.Counters[ID] = Val;
122  }
123
124  // Dump or print the current counter set.
125  LLVM_DUMP_METHOD void dump() { print(dbgs()); }
126
127  void print(raw_ostream &OS);
128
129  // Get the counter ID for a given named counter, or return 0 if none is found.
130  unsigned getCounterId(const std::string &Name) const {
131    return RegisteredCounters.idFor(Name);
132  }
133
134  // Return the number of registered counters.
135  unsigned int getNumCounters() const { return RegisteredCounters.size(); }
136
137  // Return the name and description of the counter with the given ID.
138  std::pair<std::string, std::string> getCounterInfo(unsigned ID) const {
139    return std::make_pair(RegisteredCounters[ID], CounterDesc.lookup(ID));
140  }
141
142  // Iterate through the registered counters
143  typedef UniqueVector<std::string> CounterVector;
144  CounterVector::const_iterator begin() const {
145    return RegisteredCounters.begin();
146  }
147  CounterVector::const_iterator end() const { return RegisteredCounters.end(); }
148
149private:
150  unsigned addCounter(const std::string &Name, const std::string &Desc) {
151    unsigned Result = RegisteredCounters.insert(Name);
152    CounterDesc[Result] = Desc;
153    return Result;
154  }
155  DenseMap<unsigned, std::pair<long, long>> Counters;
156  DenseMap<unsigned, std::string> CounterDesc;
157  CounterVector RegisteredCounters;
158};
159
160#define DEBUG_COUNTER(VARNAME, COUNTERNAME, DESC)                              \
161  static const unsigned VARNAME =                                              \
162      DebugCounter::registerCounter(COUNTERNAME, DESC);
163
164} // namespace llvm
165#endif
166