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, 110 insertions, 0 deletions

diff --git a/lib/Support/DeltaAlgorithm.cpp b/lib/Support/DeltaAlgorithm.cpp
new file mode 100644
index 0000000000..9aabd8d1a0
--- /dev/null
+++ b/lib/Support/DeltaAlgorithm.cpp
@@ -0,0 +1,110 @@
+//===--- 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.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DeltaAlgorithm.h"
+#include <algorithm>
+using namespace llvm;
+
+bool DeltaAlgorithm::GetTestResult(const changeset_ty &Changes) {
+  if (FailedTestsCache.count(Changes))
+    return false;
+
+  bool Result = ExecuteOneTest(Changes);
+  if (!Result)
+    FailedTestsCache.insert(Changes);
+
+  return Result;
+}
+
+void DeltaAlgorithm::Split(const changeset_ty &S, changesetlist_ty &Res) {
+  // FIXME: Allow clients to provide heuristics for improved splitting.
+
+  // FIXME: This is really slow.
+  changeset_ty LHS, RHS;
+  unsigned idx = 0;
+  for (changeset_ty::const_iterator it = S.begin(),
+         ie = S.end(); it != ie; ++it, ++idx)
+    ((idx & 1) ? LHS : RHS).insert(*it);
+  if (!LHS.empty())
+    Res.push_back(LHS);
+  if (!RHS.empty())
+    Res.push_back(RHS);
+}
+
+DeltaAlgorithm::changeset_ty
+DeltaAlgorithm::Delta(const changeset_ty &Changes,
+                      const changesetlist_ty &Sets) {
+  // Invariant: union(Res) == Changes
+  UpdatedSearchState(Changes, Sets);
+
+  // If there is nothing left we can remove, we are done.
+  if (Sets.size() <= 1)
+    return Changes;
+
+  // Look for a passing subset.
+  changeset_ty Res;
+  if (Search(Changes, Sets, Res))
+    return Res;
+
+  // Otherwise, partition the sets if possible; if not we are done.
+  changesetlist_ty SplitSets;
+  for (changesetlist_ty::const_iterator it = Sets.begin(),
+         ie = Sets.end(); it != ie; ++it)
+    Split(*it, SplitSets);
+  if (SplitSets.size() == Sets.size())
+    return Changes;
+
+  return Delta(Changes, SplitSets);
+}
+
+bool DeltaAlgorithm::Search(const changeset_ty &Changes,
+                            const changesetlist_ty &Sets,
+                            changeset_ty &Res) {
+  // FIXME: Parallelize.
+  for (changesetlist_ty::const_iterator it = Sets.begin(),
+         ie = Sets.end(); it != ie; ++it) {
+    // If the test passes on this subset alone, recurse.
+    if (GetTestResult(*it)) {
+      changesetlist_ty Sets;
+      Split(*it, Sets);
+      Res = Delta(*it, Sets);
+      return true;
+    }
+
+    // Otherwise, if we have more than two sets, see if test passes on the
+    // complement.
+    if (Sets.size() > 2) {
+      // FIXME: This is really slow.
+      changeset_ty Complement;
+      std::set_difference(
+        Changes.begin(), Changes.end(), it->begin(), it->end(),
+        std::insert_iterator<changeset_ty>(Complement, Complement.begin()));
+      if (GetTestResult(Complement)) {
+        changesetlist_ty ComplementSets;
+        ComplementSets.insert(ComplementSets.end(), Sets.begin(), it);
+        ComplementSets.insert(ComplementSets.end(), it + 1, Sets.end());
+        Res = Delta(Complement, ComplementSets);
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+DeltaAlgorithm::changeset_ty DeltaAlgorithm::Run(const changeset_ty &Changes) {
+  // Check empty set first to quickly find poor test functions.
+  if (GetTestResult(changeset_ty()))
+    return changeset_ty();
+
+  // Otherwise run the real delta algorithm.
+  changesetlist_ty Sets;
+  Split(Changes, Sets);
+
+  return Delta(Changes, Sets);
+}