Add an implementation of the delta debugging algorithm.

 - This is a pretty slow / memory intensive implementation, and I will likely
   change it to an iterative model, but it works.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90447 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 89 insertions, 0 deletions

diff --git a/include/llvm/ADT/DeltaAlgorithm.h b/include/llvm/ADT/DeltaAlgorithm.h
new file mode 100644
index 0000000000..0cf7c7c466
--- /dev/null
+++ b/include/llvm/ADT/DeltaAlgorithm.h
@@ -0,0 +1,89 @@
+//===--- DeltaAlgorithm.h - A Set Minimization Algorithm -------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_DELTAALGORITHM_H
+#define LLVM_ADT_DELTAALGORITHM_H
+
+#include <vector>
+#include <set>
+
+namespace llvm {
+
+/// DeltaAlgorithm - Implements the delta debugging algorithm (A. Zeller '99)
+/// for minimizing arbitrary sets using a predicate function.
+///
+/// The result of the algorithm is a subset of the input change set which is
+/// guaranteed to satisfy the predicate, assuming that the input set did. For
+/// well formed predicates, the result set is guaranteed to be such that
+/// removing any single element would falsify the predicate.
+///
+/// For best results the predicate function *should* (but need not) satisfy
+/// certain properties, in particular:
+///  (1) The predicate should return false on an empty set and true on the full
+///  set.
+///  (2) If the predicate returns true for a set of changes, it should return
+///  true for all supersets of that set.
+///
+/// It is not an error to provide a predicate that does not satisfy these
+/// requirements, and the algorithm will generally produce reasonable
+/// results. However, it may run substantially more tests than with a good
+/// predicate.
+class DeltaAlgorithm {
+public:
+  typedef unsigned change_ty;
+  // FIXME: Use a decent data structure.
+  typedef std::set<change_ty> changeset_ty;
+  typedef std::vector<changeset_ty> changesetlist_ty;
+
+private:
+  /// Cache of failed test results. Successful test results are never cached
+  /// since we always reduce following a success.
+  std::set<changeset_ty> FailedTestsCache;
+
+  /// GetTestResult - Get the test result for the \arg Changes from the
+  /// cache, executing the test if necessary.
+  ///
+  /// \param Changes - The change set to test.
+  /// \return - The test result.
+  bool GetTestResult(const changeset_ty &Changes);
+
+  /// Split - Partition a set of changes \arg Sinto one or two subsets.
+  void Split(const changeset_ty &S, changesetlist_ty &Res);
+
+  /// Delta - Minimize a set of \arg Changes which has been partioned into
+  /// smaller sets, by attempting to remove individual subsets.
+  changeset_ty Delta(const changeset_ty &Changes,
+                     const changesetlist_ty &Sets);
+
+  /// Search - Search for a subset (or subsets) in \arg Sets which can be
+  /// removed from \arg Changes while still satisfying the predicate.
+  ///
+  /// \param Res - On success, a subset of Changes which satisfies the
+  /// predicate.
+  /// \return - True on success.
+  bool Search(const changeset_ty &Changes, const changesetlist_ty &Sets,
+              changeset_ty &Res);
+              
+protected:
+  /// UpdatedSearchState - Callback used when the search state changes.
+  virtual void UpdatedSearchState(const changeset_ty &Changes,
+                                  const changesetlist_ty &Sets) {}
+
+  /// ExecuteOneTest - Execute a single test predicate on the change set \arg S.
+  virtual bool ExecuteOneTest(const changeset_ty &S) = 0;
+
+public:
+  /// Run - Minimize the set \arg Changes by executing \see ExecuteOneTest() on
+  /// subsets of changes and returning the smallest set which still satisfies
+  /// the test predicate.
+  changeset_ty Run(const changeset_ty &Changes);
+};
+
+} // end namespace llvm
+
+#endif