include/llvm/ADT/DeltaAlgorithm.h

   1 //===- DeltaAlgorithm.h - A Set Minimization Algorithm ---------*- C++ -*--===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //===----------------------------------------------------------------------===//
   7
   8 #ifndef LLVM_ADT_DELTAALGORITHM_H
   9 #define LLVM_ADT_DELTAALGORITHM_H
  10
  11 #include <set>
  12 #include <vector>
  13
  14 namespace llvm {
  15
  16 /// DeltaAlgorithm - Implements the delta debugging algorithm (A. Zeller '99)
  17 /// for minimizing arbitrary sets using a predicate function.
  18 ///
  19 /// The result of the algorithm is a subset of the input change set which is
  20 /// guaranteed to satisfy the predicate, assuming that the input set did. For
  21 /// well formed predicates, the result set is guaranteed to be such that
  22 /// removing any single element would falsify the predicate.
  23 ///
  24 /// For best results the predicate function *should* (but need not) satisfy
  25 /// certain properties, in particular:
  26 ///  (1) The predicate should return false on an empty set and true on the full
  27 ///  set.
  28 ///  (2) If the predicate returns true for a set of changes, it should return
  29 ///  true for all supersets of that set.
  30 ///
  31 /// It is not an error to provide a predicate that does not satisfy these
  32 /// requirements, and the algorithm will generally produce reasonable
  33 /// results. However, it may run substantially more tests than with a good
  34 /// predicate.
  35 class DeltaAlgorithm {
  36 public:
  37   using change_ty = unsigned;
  38   // FIXME: Use a decent data structure.
  39   using changeset_ty = std::set<change_ty>;
  40   using changesetlist_ty = std::vector<changeset_ty>;
  41
  42 private:
  43   /// Cache of failed test results. Successful test results are never cached
  44   /// since we always reduce following a success.
  45   std::set<changeset_ty> FailedTestsCache;
  46
  47   /// GetTestResult - Get the test result for the \p Changes from the
  48   /// cache, executing the test if necessary.
  49   ///
  50   /// \param Changes - The change set to test.
  51   /// \return - The test result.
  52   bool GetTestResult(const changeset_ty &Changes);
  53
  54   /// Split - Partition a set of changes \p S into one or two subsets.
  55   void Split(const changeset_ty &S, changesetlist_ty &Res);
  56
  57   /// Delta - Minimize a set of \p Changes which has been partioned into
  58   /// smaller sets, by attempting to remove individual subsets.
  59   changeset_ty Delta(const changeset_ty &Changes,
  60                      const changesetlist_ty &Sets);
  61
  62   /// Search - Search for a subset (or subsets) in \p Sets which can be
  63   /// removed from \p Changes while still satisfying the predicate.
  64   ///
  65   /// \param Res - On success, a subset of Changes which satisfies the
  66   /// predicate.
  67   /// \return - True on success.
  68   bool Search(const changeset_ty &Changes, const changesetlist_ty &Sets,
  69               changeset_ty &Res);
  70
  71 protected:
  72   /// UpdatedSearchState - Callback used when the search state changes.
  73   virtual void UpdatedSearchState(const changeset_ty &Changes,
  74                                   const changesetlist_ty &Sets) {}
  75
  76   /// ExecuteOneTest - Execute a single test predicate on the change set \p S.
  77   virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
  78
  79   DeltaAlgorithm& operator=(const DeltaAlgorithm&) = default;
  80
  81 public:
  82   virtual ~DeltaAlgorithm();
  83
  84   /// Run - Minimize the set \p Changes by executing \see ExecuteOneTest() on
  85   /// subsets of changes and returning the smallest set which still satisfies
  86   /// the test predicate.
  87   changeset_ty Run(const changeset_ty &Changes);
  88 };
  89
  90 } // end namespace llvm
  91
  92 #endif // LLVM_ADT_DELTAALGORITHM_H