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       1             : //===- DeltaAlgorithm.h - A Set Minimization Algorithm ---------*- 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             : #ifndef LLVM_ADT_DELTAALGORITHM_H
      10             : #define LLVM_ADT_DELTAALGORITHM_H
      11             : 
      12             : #include <set>
      13             : #include <vector>
      14             : 
      15             : namespace llvm {
      16             : 
      17             : /// DeltaAlgorithm - Implements the delta debugging algorithm (A. Zeller '99)
      18             : /// for minimizing arbitrary sets using a predicate function.
      19             : ///
      20             : /// The result of the algorithm is a subset of the input change set which is
      21             : /// guaranteed to satisfy the predicate, assuming that the input set did. For
      22             : /// well formed predicates, the result set is guaranteed to be such that
      23             : /// removing any single element would falsify the predicate.
      24             : ///
      25             : /// For best results the predicate function *should* (but need not) satisfy
      26             : /// certain properties, in particular:
      27             : ///  (1) The predicate should return false on an empty set and true on the full
      28             : ///  set.
      29             : ///  (2) If the predicate returns true for a set of changes, it should return
      30             : ///  true for all supersets of that set.
      31             : ///
      32             : /// It is not an error to provide a predicate that does not satisfy these
      33             : /// requirements, and the algorithm will generally produce reasonable
      34             : /// results. However, it may run substantially more tests than with a good
      35             : /// predicate.
      36             : class DeltaAlgorithm {
      37             : public:
      38             :   using change_ty = unsigned;
      39             :   // FIXME: Use a decent data structure.
      40             :   using changeset_ty = std::set<change_ty>;
      41             :   using changesetlist_ty = std::vector<changeset_ty>;
      42             : 
      43             : private:
      44             :   /// Cache of failed test results. Successful test results are never cached
      45             :   /// since we always reduce following a success.
      46             :   std::set<changeset_ty> FailedTestsCache;
      47             : 
      48             :   /// GetTestResult - Get the test result for the \p Changes from the
      49             :   /// cache, executing the test if necessary.
      50             :   ///
      51             :   /// \param Changes - The change set to test.
      52             :   /// \return - The test result.
      53             :   bool GetTestResult(const changeset_ty &Changes);
      54             : 
      55             :   /// Split - Partition a set of changes \p S into one or two subsets.
      56             :   void Split(const changeset_ty &S, changesetlist_ty &Res);
      57             : 
      58             :   /// Delta - Minimize a set of \p Changes which has been partioned into
      59             :   /// smaller sets, by attempting to remove individual subsets.
      60             :   changeset_ty Delta(const changeset_ty &Changes,
      61             :                      const changesetlist_ty &Sets);
      62             : 
      63             :   /// Search - Search for a subset (or subsets) in \p Sets which can be
      64             :   /// removed from \p Changes while still satisfying the predicate.
      65             :   ///
      66             :   /// \param Res - On success, a subset of Changes which satisfies the
      67             :   /// predicate.
      68             :   /// \return - True on success.
      69             :   bool Search(const changeset_ty &Changes, const changesetlist_ty &Sets,
      70             :               changeset_ty &Res);
      71             : 
      72             : protected:
      73             :   /// UpdatedSearchState - Callback used when the search state changes.
      74          16 :   virtual void UpdatedSearchState(const changeset_ty &Changes,
      75          16 :                                   const changesetlist_ty &Sets) {}
      76             : 
      77             :   /// ExecuteOneTest - Execute a single test predicate on the change set \p S.
      78             :   virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
      79             : 
      80             :   DeltaAlgorithm& operator=(const DeltaAlgorithm&) = default;
      81             : 
      82             : public:
      83             :   virtual ~DeltaAlgorithm();
      84             : 
      85             :   /// Run - Minimize the set \p Changes by executing \see ExecuteOneTest() on
      86             :   /// subsets of changes and returning the smallest set which still satisfies
      87             :   /// the test predicate.
      88             :   changeset_ty Run(const changeset_ty &Changes);
      89             : };
      90             : 
      91             : } // end namespace llvm
      92             : 
      93             : #endif // LLVM_ADT_DELTAALGORITHM_H