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/ErrorHandling.h" 19 #include "llvm/Support/raw_ostream.h" 20 #include <algorithm> 21 #include <cstdlib> 22 #include <vector> 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 37 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 // 52 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
