1 files changed, 86 insertions, 0 deletions
diff --git a/tools/bugpoint/ListReducer.h b/tools/bugpoint/ListReducer.h
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+//===- ListReducer.h - Trim down list while retaining property --*- C++ -*-===//
+//
+// This class is to be used as a base class for operations that want to zero in
+// on a subset of the input which still causes the bug we are tracking.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef BUGPOINT_LIST_REDUCER_H
+#define BUGPOINT_LIST_REDUCER_H
+
+#include <vector>
+
+template<typename ElTy>
+struct ListReducer {
+  enum TestResult {
+    NoFailure,         // No failure of the predicate was detected
+    KeepSuffix,        // The suffix alone satisfies the predicate
+    KeepPrefix,        // The prefix alone satisfies the predicate
+  };
+
+  // doTest - This virtual function should be overriden by subclasses to
+  // implement the test desired.  The testcase is only required to test to see
+  // if the Kept list still satisfies the property, but if it is going to check
+  // the prefix anyway, it can.
+  //
+  virtual TestResult doTest(const std::vector<ElTy> &Prefix,
+                            const std::vector<ElTy> &Kept) = 0;
+
+  // reduceList - This function attempts to reduce the length of the specified
+  // list while still maintaining the "test" property.  This is the core of the
+  // "work" that bugpoint does.
+  //
+  void reduceList(std::vector<ElTy> &TheList) {
+    unsigned MidTop = TheList.size();
+    while (MidTop > 1) {
+      unsigned Mid = MidTop / 2;
+      std::vector<ElTy> Prefix(TheList.begin()+Mid, TheList.end());
+      std::vector<ElTy> Kept  (TheList.begin(), TheList.begin()+Mid);
+
+      switch (doTest(Prefix, Kept)) {
+      case KeepSuffix:
+        // The property still holds.  We can just drop the prefix elements, and
+        // shorten the list to the "kept" elements.
+        TheList.swap(Kept);
+        MidTop = TheList.size();
+        break;
+      case KeepPrefix:
+        // The predicate still holds, shorten the list to the prefix elements.
+        TheList.swap(Prefix);
+        MidTop = TheList.size();
+        break;
+      case NoFailure:
+        // Otherwise the property doesn't hold.  Some of the elements we removed
+        // must be neccesary to maintain the property.
+        MidTop = Mid;
+        break;
+      }
+    }
+
+    // Okay, we trimmed as much off the top and the bottom of the list as we
+    // could.  If there is more two elements in the list, try deleting interior
+    // elements and testing that.
+    //
+    if (TheList.size() > 2) {
+      bool Changed = true;
+      std::vector<ElTy> EmptyList;
+      while (Changed) {
+        Changed = false;
+        std::vector<ElTy> TrimmedList;
+        for (unsigned i = 1; i < TheList.size()-1; ++i) { // Check interior elts
+          std::vector<ElTy> TestList(TheList);
+          TestList.erase(TestList.begin()+i);
+
+          if (doTest(EmptyList, TestList) == KeepSuffix) {
+            // We can trim down the list!
+            TheList.swap(TestList);
+            --i;  // Don't skip an element of the list
+            Changed = true;
+          }
+        }
+      }
+    }
+  }
+};
+
+#endif