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1 //===- ListReducer.h - Trim down list while retaining property --*- 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 //
10 // This class is to be used as a base class for operations that want to zero in
11 // on a subset of the input which still causes the bug we are tracking.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef BUGPOINT_LIST_REDUCER_H
16 #define BUGPOINT_LIST_REDUCER_H
17 
18 #include "llvm/Support/raw_ostream.h"
19 #include "llvm/Support/ErrorHandling.h"
20 #include <vector>
21 #include <cstdlib>
22 #include <algorithm>
23 
24 namespace llvm {
25 
26   extern bool BugpointIsInterrupted;
27 
28 template<typename ElTy>
29 struct ListReducer {
30   enum TestResult {
31     NoFailure,         // No failure of the predicate was detected
32     KeepSuffix,        // The suffix alone satisfies the predicate
33     KeepPrefix,        // The prefix alone satisfies the predicate
34     InternalError      // Encountered an error trying to run the predicate
35   };
36 
~ListReducerListReducer37   virtual ~ListReducer() {}
38 
39   // doTest - This virtual function should be overriden by subclasses to
40   // implement the test desired.  The testcase is only required to test to see
41   // if the Kept list still satisfies the property, but if it is going to check
42   // the prefix anyway, it can.
43   //
44   virtual TestResult doTest(std::vector<ElTy> &Prefix,
45                             std::vector<ElTy> &Kept,
46                             std::string &Error) = 0;
47 
48   // reduceList - This function attempts to reduce the length of the specified
49   // list while still maintaining the "test" property.  This is the core of the
50   // "work" that bugpoint does.
51   //
reduceListListReducer52   bool reduceList(std::vector<ElTy> &TheList, std::string &Error) {
53     std::vector<ElTy> empty;
54     std::srand(0x6e5ea738); // Seed the random number generator
55     switch (doTest(TheList, empty, Error)) {
56     case KeepPrefix:
57       if (TheList.size() == 1) // we are done, it's the base case and it fails
58         return true;
59       else
60         break; // there's definitely an error, but we need to narrow it down
61 
62     case KeepSuffix:
63       // cannot be reached!
64       llvm_unreachable("bugpoint ListReducer internal error: "
65                        "selected empty set.");
66 
67     case NoFailure:
68       return false; // there is no failure with the full set of passes/funcs!
69 
70     case InternalError:
71       assert(!Error.empty());
72       return true;
73     }
74 
75     // Maximal number of allowed splitting iterations,
76     // before the elements are randomly shuffled.
77     const unsigned MaxIterationsWithoutProgress = 3;
78     bool ShufflingEnabled = true;
79 
80 Backjump:
81     unsigned MidTop = TheList.size();
82     unsigned MaxIterations = MaxIterationsWithoutProgress;
83     unsigned NumOfIterationsWithoutProgress = 0;
84     while (MidTop > 1) { // Binary split reduction loop
85       // Halt if the user presses ctrl-c.
86       if (BugpointIsInterrupted) {
87         errs() << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
88         return true;
89       }
90 
91       // If the loop doesn't make satisfying progress, try shuffling.
92       // The purpose of shuffling is to avoid the heavy tails of the
93       // distribution (improving the speed of convergence).
94       if (ShufflingEnabled &&
95           NumOfIterationsWithoutProgress > MaxIterations) {
96         std::vector<ElTy> ShuffledList(TheList);
97         std::random_shuffle(ShuffledList.begin(), ShuffledList.end());
98         errs() << "\n\n*** Testing shuffled set...\n\n";
99         // Check that random shuffle doesn't loose the bug
100         if (doTest(ShuffledList, empty, Error) == KeepPrefix) {
101           // If the bug is still here, use the shuffled list.
102           TheList.swap(ShuffledList);
103           MidTop = TheList.size();
104           // Must increase the shuffling treshold to avoid the small
105           // probability of inifinite looping without making progress.
106           MaxIterations += 2;
107           errs() << "\n\n*** Shuffling does not hide the bug...\n\n";
108         } else {
109           ShufflingEnabled = false; // Disable shuffling further on
110           errs() << "\n\n*** Shuffling hides the bug...\n\n";
111         }
112         NumOfIterationsWithoutProgress = 0;
113       }
114 
115       unsigned Mid = MidTop / 2;
116       std::vector<ElTy> Prefix(TheList.begin(), TheList.begin()+Mid);
117       std::vector<ElTy> Suffix(TheList.begin()+Mid, TheList.end());
118 
119       switch (doTest(Prefix, Suffix, Error)) {
120       case KeepSuffix:
121         // The property still holds.  We can just drop the prefix elements, and
122         // shorten the list to the "kept" elements.
123         TheList.swap(Suffix);
124         MidTop = TheList.size();
125         // Reset progress treshold and progress counter
126         MaxIterations = MaxIterationsWithoutProgress;
127         NumOfIterationsWithoutProgress = 0;
128         break;
129       case KeepPrefix:
130         // The predicate still holds, shorten the list to the prefix elements.
131         TheList.swap(Prefix);
132         MidTop = TheList.size();
133         // Reset progress treshold and progress counter
134         MaxIterations = MaxIterationsWithoutProgress;
135         NumOfIterationsWithoutProgress = 0;
136         break;
137       case NoFailure:
138         // Otherwise the property doesn't hold.  Some of the elements we removed
139         // must be necessary to maintain the property.
140         MidTop = Mid;
141         NumOfIterationsWithoutProgress++;
142         break;
143       case InternalError:
144         return true;  // Error was set by doTest.
145       }
146       assert(Error.empty() && "doTest did not return InternalError for error");
147     }
148 
149     // Probability of backjumping from the trimming loop back to the binary
150     // split reduction loop.
151     const int BackjumpProbability = 10;
152 
153     // Okay, we trimmed as much off the top and the bottom of the list as we
154     // could.  If there is more than two elements in the list, try deleting
155     // interior elements and testing that.
156     //
157     if (TheList.size() > 2) {
158       bool Changed = true;
159       std::vector<ElTy> EmptyList;
160       while (Changed) {  // Trimming loop.
161         Changed = false;
162 
163         // If the binary split reduction loop made an unfortunate sequence of
164         // splits, the trimming loop might be left off with a huge number of
165         // remaining elements (large search space). Backjumping out of that
166         // search space and attempting a different split can significantly
167         // improve the convergence speed.
168         if (std::rand() % 100 < BackjumpProbability)
169           goto Backjump;
170 
171         for (unsigned i = 1; i < TheList.size()-1; ++i) { // Check interior elts
172           if (BugpointIsInterrupted) {
173             errs() << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
174             return true;
175           }
176 
177           std::vector<ElTy> TestList(TheList);
178           TestList.erase(TestList.begin()+i);
179 
180           if (doTest(EmptyList, TestList, Error) == KeepSuffix) {
181             // We can trim down the list!
182             TheList.swap(TestList);
183             --i;  // Don't skip an element of the list
184             Changed = true;
185           }
186           if (!Error.empty())
187             return true;
188         }
189         // This can take a long time if left uncontrolled.  For now, don't
190         // iterate.
191         break;
192       }
193     }
194 
195     return true; // there are some failure and we've narrowed them down
196   }
197 };
198 
199 } // End llvm namespace
200 
201 #endif
202