[analyzer] Added custom hashing to the CloneDetector.

[teemperor]

Summary

The CloneDetector consumes in it's current state to much memory to analyze big code bases such as SQLite.

This patch reintroduces the custom hashing functionality which replaces CloneSignature's large data vectors with fixed size hash codes. This includes an additional check for each clone that prevents that the CloneDetector produces false-positives because of collisions in the hash function.

[v.g.vassilev]

Could you add some tests?

[NoQ]

Hmm. Since you're working with FoldingSetNodeIDs, maybe you could avoid numeric hashes completely in your code, and use FoldingSetNodeIDs themselves as your keys? Just organize the whole clone list as a map from FoldingSetNodeIDs to lists of particular code samples. There would be no collisions at all from the beginning (even if internally the map would hash the FoldingSetNodeIDs to a number and there will be collisions in this hashing, but you wouldn't need to know about them - and there's no performance loss at the same time).

[v.g.vassilev]

@teemperor: could you summarize what we discussed at the phone meeting today wrt to this patch.

[teemperor]

This patch is no longer needed because the CloneDetector from patch https://reviews.llvm.org/D20795 no longer uses custom hashing.

[teemperor]

• Rebased the patch to the newest code base.

This patch is live again as it turned out that the CloneDetector can't handle large code bases without it. The simpler approach that we implemented instead consumed too much memory (e.g. at least 15 GB for analyzing SQLite) because the large data vectors and the quadratic space complexity of the sub-sequence search didn't play together very well.

[teemperor]

• Fixed some formatting problems.
• Updated Title/Summary

[NoQ]

Considering the refactoring planned in D23418, i've no more comments on the part of the code that isn't rewritten in the subsequent review. I like how the new hashing system is put to work here.

lib/Analysis/CloneDetection.cpp

620

Hmm. FoldingSetNodeIDWrapper? Because in fact we're wrapping neither a set, nor a node, but only an ID.

631

// end anonymous namespace?

[teemperor]

• Renamed FoldingSetWrapper to FoldingSetNodeIDWrapper
• Added missing // end anonymous namespace

[teemperor]

• As the hash_stream patch will take a while to land upstream, we will change this to use FoldingSetNodeID and change it to hash_stream once that landed.

[v.g.vassilev]

LGTM.

[teemperor]

• Moved from hash_stream to LLVM's MD5 implementation.

[NoQ]

lib/Analysis/CloneDetection.cpp

550

Hmm, this still uses hash_stream.

[teemperor]

• Replaced hash_stream with MD5 in the sub-sequence code.

include/clang/Analysis/CloneDetection.h

 /// This file defines classes for searching and anlyzing source code clones.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_AST_CLONEDETECTION_H
 #define LLVM_CLANG_AST_CLONEDETECTION_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringMap.h"
 
 #include <vector>
 
 namespace clang {
 
 class Stmt;
 class Decl;

 /// are not supported.
 class CloneDetector {
 public:
   typedef unsigned DataPiece;
 
   /// Holds the data about a StmtSequence that is needed during the search for
   /// code clones.
   struct CloneSignature {
-    /// \brief Holds all relevant data of a StmtSequence.
+    /// \brief The hash code of the StmtSequence.
     ///
-    /// If this variable is equal for two different StmtSequences, then they can
-    /// be considered clones of each other.
-    std::vector<DataPiece> Data;
+    /// The initial clone groups that are formed during the search for clones
+    /// consist only of Sequences that share the same hash code. This makes this
+    /// value the central part of this heuristic that is needed to find clones
+    /// in a performant way. For this to work, the type of this variable
+    /// always needs to be small and fast to compare.
+    ///
+    /// Also, StmtSequences that are clones of each others have to share
+    /// the same hash code. StmtSequences that are not clones of each other
+    /// shouldn't share the same hash code, but if they do, it will only
+    /// degrade the performance of the hash search but doesn't influence
+    /// the correctness of the result.
+    size_t Hash;
 
     /// \brief The complexity of the StmtSequence.
     ///
     /// This value gives an approximation on how many direct or indirect child
     /// statements are contained in the related StmtSequence. In general, the
     /// greater this value, the greater the amount of statements. However, this
     /// is only an approximation and the actual amount of statements can be
     /// higher or lower than this value. Statements that are generated by the
     /// compiler (e.g. macro expansions) for example barely influence the
     /// complexity value.
     ///
     /// The main purpose of this value is to filter clones that are too small
     /// and therefore probably not interesting enough for the user.
     unsigned Complexity;
 
     /// \brief Creates an empty CloneSignature without any data.
     CloneSignature() : Complexity(1) {}
 
-    CloneSignature(const std::vector<unsigned> &Data, unsigned Complexity)
-        : Data(Data), Complexity(Complexity) {}
-
-    /// \brief Adds the data from the given CloneSignature to this one.
-    void add(const CloneSignature &Other) {
-      Data.insert(Data.end(), Other.Data.begin(), Other.Data.end());
-      Complexity += Other.Complexity;
-    }
+    CloneSignature(llvm::hash_code Hash, unsigned Complexity)
+        : Hash(Hash), Complexity(Complexity) {}
   };
 
   /// Holds group of StmtSequences that are clones of each other and the
   /// complexity value (see CloneSignature::Complexity) that all stored
   /// StmtSequences have in common.
   struct CloneGroup {
     std::vector<StmtSequence> Sequences;
-    unsigned Complexity;
+    CloneSignature Signature;
+
+    CloneGroup() {}
 
-    CloneGroup(const StmtSequence &Seq, unsigned Complexity)
-        : Complexity(Complexity) {
+    CloneGroup(const StmtSequence &Seq, CloneSignature Signature)
+        : Signature(Signature) {
       Sequences.push_back(Seq);
     }
 
     /// \brief Returns false if and only if this group should be skipped when
     ///        searching for clones.
     bool isValid() const {
       // A clone group with only one member makes no sense, so we skip them.
       return Sequences.size() > 1;
public:
   ///        follow the same pattern when referencing variables.
   /// \param Result Output parameter that will contain the clone pairs.
   /// \param MinGroupComplexity Only clone pairs in which the clones have at
   ///                           least this complexity value.
   void findSuspiciousClones(std::vector<SuspiciousClonePair> &Result,
                             unsigned MinGroupComplexity);
 
 private:
-  /// Stores all found clone groups including invalid groups with only a single
-  /// statement.
-  std::vector<CloneGroup> CloneGroups;
-  /// Maps search data to its related index in the \p CloneGroups vector.
-  llvm::StringMap<std::size_t> CloneGroupIndexes;
+  /// Stores all encountered StmtSequences alongside their CloneSignature.
+  std::vector<std::pair<CloneSignature, StmtSequence>> Sequences;
 };
 
 } // end namespace clang
 
 #endif // LLVM_CLANG_AST_CLONEDETECTION_H

lib/Analysis/CloneDetection.cpp

 #include "clang/Analysis/CloneDetection.h"
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/Stmt.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Lex/Lexer.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/MD5.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace clang;
 
 StmtSequence::StmtSequence(const CompoundStmt *Stmt, ASTContext &Context,
                            unsigned StartIndex, unsigned EndIndex)
     : S(Stmt), Context(&Context), StartIndex(StartIndex), EndIndex(EndIndex) {
   assert(Stmt && "Stmt must not be a nullptr");

 }
 
 namespace {
 /// \brief Collects the data of a single Stmt.
 ///
 /// This class defines what a code clone is: If it collects for two statements
 /// the same data, then those two statements are considered to be clones of each
 /// other.
-class StmtDataCollector : public ConstStmtVisitor<StmtDataCollector> {
+///
+/// All collected data is forwarded to the given data consumer of the type T.
+/// The data consumer class needs to provide a member method with the signature:
+///   update(StringRef Str)
+template <typename T>
+class StmtDataCollector : public ConstStmtVisitor<StmtDataCollector<T>> {
 
   ASTContext &Context;
-  std::vector<CloneDetector::DataPiece> &CollectedData;
+  /// \brief The data sink to which all data is forwarded.
+  T &DataConsumer;
 
 public:
   /// \brief Collects data of the given Stmt.
   /// \param S The given statement.
   /// \param Context The ASTContext of S.
-  /// \param D The given data vector to which all collected data is appended.
-  StmtDataCollector(const Stmt *S, ASTContext &Context,
-                    std::vector<CloneDetector::DataPiece> &D)
-      : Context(Context), CollectedData(D) {
-    Visit(S);
+  /// \param D The data sink to which all data is forwarded.
+  StmtDataCollector(const Stmt *S, ASTContext &Context, T &DataConsumer)
+      : Context(Context), DataConsumer(DataConsumer) {
+    this->Visit(S);
   }
 
   // Below are utility methods for appending different data to the vector.
 
   void addData(CloneDetector::DataPiece Integer) {
-    CollectedData.push_back(Integer);
+    DataConsumer.update(
+        StringRef(reinterpret_cast<char *>(&Integer), sizeof(Integer)));
   }
 
-  // FIXME: The functions below add long strings to the data vector which are
-  // probably not good for performance. Replace the strings with pointer values
-  // or a some other unique integer.
-
-  void addData(llvm::StringRef Str) {
-    if (Str.empty())
-      return;
-
-    const size_t OldSize = CollectedData.size();
-
-    const size_t PieceSize = sizeof(CloneDetector::DataPiece);
-    // Calculate how many vector units we need to accomodate all string bytes.
-    size_t RoundedUpPieceNumber = (Str.size() + PieceSize - 1) / PieceSize;
-    // Allocate space for the string in the data vector.
-    CollectedData.resize(CollectedData.size() + RoundedUpPieceNumber);
-
-    // Copy the string to the allocated space at the end of the vector.
-    std::memcpy(CollectedData.data() + OldSize, Str.data(), Str.size());
-  }
+  void addData(llvm::StringRef Str) { DataConsumer.update(Str); }
 
   void addData(const QualType &QT) { addData(QT.getAsString()); }
 
 // The functions below collect the class specific data of each Stmt subclass.
 
 // Utility macro for defining a visit method for a given class. This method
 // calls back to the ConstStmtVisitor to visit all parent classes.
 #define DEF_ADD_DATA(CLASS, CODE)                                              \
class CloneSignatureGenerator {
   ///                         macros generated the parent statement.
   ///                         See getMacroStack() for generating such a string.
   /// \return The CloneSignature of the root statement.
   CloneDetector::CloneSignature
   generateSignatures(const Stmt *S, const std::string &ParentMacroStack) {
     // Create an empty signature that will be filled in this method.
     CloneDetector::CloneSignature Signature;
 
-    // Collect all relevant data from S and put it into the empty signature.
-    StmtDataCollector(S, Context, Signature.Data);
+    llvm::MD5 Hash;
+
+    // Collect all relevant data from S and hash it.
+    StmtDataCollector<llvm::MD5>(S, Context, Hash);
 
     // Look up what macros expanded into the current statement.
     std::string StartMacroStack = getMacroStack(S->getLocStart(), Context);
     std::string EndMacroStack = getMacroStack(S->getLocEnd(), Context);
 
     // First, check if ParentMaroStack is not empty which means we are currently
     // dealing with a parent statement which was expanded from a macro.
     // If this parent statement was expanded from the same macros as this
for (const Stmt *Child : S->children()) {
         continue;
 
       // Recursive call to create the signature of the child statement. This
       // will also create and store all clone groups in this child statement.
       // We pass only the StartMacroStack along to keep things simple.
       auto ChildSignature = generateSignatures(Child, StartMacroStack);
 
       // Add the collected data to the signature of the current statement.
-      Signature.add(ChildSignature);
+      Signature.Complexity += ChildSignature.Complexity;
+      Hash.update(StringRef(reinterpret_cast<char *>(&ChildSignature.Hash),
+                            sizeof(ChildSignature.Hash)));
 
       // If the current statement is a CompoundStatement, we need to store the
       // signature for the generation of the sub-sequences.
       if (CS)
         ChildSignatures.push_back(ChildSignature);
     }
 
     // If the current statement is a CompoundStmt, we also need to create the
     // clone groups from the sub-sequences inside the children.
     if (CS)
       handleSubSequences(CS, ChildSignatures);
 
+    // Create the final hash code for the current signature.
+    llvm::MD5::MD5Result HashResult;
+    Hash.final(HashResult);
+
+    // Copy as much of the generated hash code to the signature's hash code.
+    std::memcpy(&Signature.Hash, &HashResult,
+                std::min(sizeof(Signature.Hash), sizeof(HashResult)));
+
     // Save the signature for the current statement in the CloneDetector object.
     CD.add(StmtSequence(S, Context), Signature);
 
     return Signature;
   }
 
   /// \brief Adds all possible sub-sequences in the child array of the given
   ///        CompoundStmt to the CloneDetector.
void handleSubSequences(
     for (unsigned Length = 2; Length <= CS->size(); ++Length) {
       // The start index in the body of the CompoundStmt. We increase the
       // position until the end of the sub-sequence reaches the end of the
       // CompoundStmt body.
       for (unsigned Pos = 0; Pos <= CS->size() - Length; ++Pos) {
         // Create an empty signature and add the signatures of all selected
         // child statements to it.
         CloneDetector::CloneSignature SubSignature;
+        llvm::hash_stream SubHash;
 
         for (unsigned i = Pos; i < Pos + Length; ++i) {
-          SubSignature.add(ChildSignatures[i]);
+          SubSignature.Complexity += ChildSignatures[i].Complexity;
+          SubHash << static_cast<size_t>(ChildSignatures[i].Hash);
         }
 
+        SubSignature.Hash = SubHash.compute_hash();
+
         // Save the signature together with the information about what children
         // sequence we selected.
         CD.add(StmtSequence(CS, Context, Pos, Pos + Length), SubSignature);
       }
     }
   }
 
 public:
void CloneDetector::analyzeCodeBody(const Decl *D) {
   assert(D);
   assert(D->hasBody());
   CloneSignatureGenerator Generator(*this, D->getASTContext());
   Generator.consumeCodeBody(D->getBody());
 }
 
 void CloneDetector::add(const StmtSequence &S,
                         const CloneSignature &Signature) {
-  // StringMap only works with StringRefs, so we create one for our data vector.
-  auto &Data = Signature.Data;
-  StringRef DataRef = StringRef(reinterpret_cast<const char *>(Data.data()),
-                                Data.size() * sizeof(unsigned));
-
-  // Search with the help of the signature if we already have encountered a
-  // clone of the given StmtSequence.
-  auto I = CloneGroupIndexes.find(DataRef);
-  if (I == CloneGroupIndexes.end()) {
-    // We haven't found an existing clone group, so we create a new clone group
-    // for this StmtSequence and store the index of it in our search map.
-    CloneGroupIndexes[DataRef] = CloneGroups.size();
-    CloneGroups.emplace_back(S, Signature.Complexity);
-    return;
-  }
-
-  // We have found an existing clone group and can expand it with the given
-  // StmtSequence.
-  CloneGroups[I->getValue()].Sequences.push_back(S);
+  Sequences.push_back(std::make_pair(Signature, S));
 }
 
 namespace {
 /// \brief Returns true if and only if \p Stmt contains at least one other
 /// sequence in the \p Group.
 bool containsAnyInGroup(StmtSequence &Stmt, CloneDetector::CloneGroup &Group) {
   for (StmtSequence &GroupStmt : Group.Sequences) {
     if (Stmt.contains(GroupStmt))
bool containsGroup(CloneDetector::CloneGroup &Group,
   for (StmtSequence &Stmt : Group.Sequences) {
     if (!containsAnyInGroup(Stmt, OtherGroup))
       return false;
   }
   return true;
 }
 } // end anonymous namespace
 
+namespace {
+/// \brief Wrapper around FoldingSetNodeID that it can be used as the template
+///        argument of the StmtDataCollector.
+class FoldingSetNodeIDWrapper {
+
+  llvm::FoldingSetNodeID &FS;
+
+public:
+  FoldingSetNodeIDWrapper(llvm::FoldingSetNodeID &FS) : FS(FS) {}
+
+  void update(StringRef Str) { FS.AddString(Str); }
+};
+} // end anonymous namespace
+
+/// \brief Writes the relevant data from all statements and child statements
+///        in the given StmtSequence into the given FoldingSetNodeID.
+static void CollectStmtSequenceData(const StmtSequence &Sequence,
+                                    FoldingSetNodeIDWrapper &OutputData) {
+  for (const Stmt *S : Sequence) {
+    StmtDataCollector<FoldingSetNodeIDWrapper>(S, Sequence.getASTContext(),
+                                               OutputData);
+
+    for (const Stmt *Child : S->children()) {
+      if (!Child)
+        continue;
+
+      CollectStmtSequenceData(StmtSequence(Child, Sequence.getASTContext()),
+                              OutputData);
+    }
+  }
+}
+
+/// \brief Returns true if both sequences are clones of each other.
+static bool areSequencesClones(const StmtSequence &LHS,
+                               const StmtSequence &RHS) {
+  // We collect the data from all statements in the sequence as we did before
+  // when generating a hash value for each sequence. But this time we don't
+  // hash the collected data and compare the whole data set instead. This
+  // prevents any false-positives due to hash code collisions.
+  llvm::FoldingSetNodeID DataLHS, DataRHS;
+  FoldingSetNodeIDWrapper LHSWrapper(DataLHS);
+  FoldingSetNodeIDWrapper RHSWrapper(DataRHS);
+
+  CollectStmtSequenceData(LHS, LHSWrapper);
+  CollectStmtSequenceData(RHS, RHSWrapper);
+
+  return DataLHS == DataRHS;
+}
+
 /// \brief Finds all actual clone groups in a single group of presumed clones.
-/// \param Result Output parameter to which all found groups are added. Every
-///               clone in a group that was added this way follows the same
-///               variable pattern as the other clones in its group.
-/// \param Group A group of clones. The clones are allowed to have a different
-///              variable pattern.
+/// \param Result Output parameter to which all found groups are added.
+/// \param Group A group of presumed clones. The clones are allowed to have a
+///              different variable pattern and may not be actual clones of each
+///              other.
+/// \param CheckVariablePatterns If true, every clone in a group that was added
+///              to the output follows the same variable pattern as the other
+///              clones in its group.
 static void createCloneGroups(std::vector<CloneDetector::CloneGroup> &Result,
-                              const CloneDetector::CloneGroup &Group) {
+                              const CloneDetector::CloneGroup &Group,
+                              bool CheckVariablePattern) {
   // We remove the Sequences one by one, so a list is more appropriate.
   std::list<StmtSequence> UnassignedSequences(Group.Sequences.begin(),
                                               Group.Sequences.end());
 
   // Search for clones as long as there could be clones in UnassignedSequences.
   while (UnassignedSequences.size() > 1) {
 
     // Pick the first Sequence as a protoype for a new clone group.
     StmtSequence Prototype = UnassignedSequences.front();
     UnassignedSequences.pop_front();
 
-    CloneDetector::CloneGroup FilteredGroup(Prototype, Group.Complexity);
+    CloneDetector::CloneGroup FilteredGroup(Prototype, Group.Signature);
 
     // Analyze the variable pattern of the prototype. Every other StmtSequence
     // needs to have the same pattern to get into the new clone group.
     VariablePattern PrototypeFeatures(Prototype);
 
     // Search all remaining StmtSequences for an identical variable pattern
     // and assign them to our new clone group.
     auto I = UnassignedSequences.begin(), E = UnassignedSequences.end();
     while (I != E) {
+      // If the sequence doesn't fit to the prototype, we have encountered
+      // an unintended hash code collision and we skip it.
+      if (!areSequencesClones(Prototype, *I)) {
+        ++I;
+        continue;
+      }
 
-      if (VariablePattern(*I).countPatternDifferences(PrototypeFeatures) == 0) {
+      // If we weren't asked to check for a matching variable pattern in clone
+      // groups we can add the sequence now to the new clone group.
+      // If we were asked to check for matching variable pattern, we first have
+      // to check that there are no differences between the two patterns and
+      // only proceed if they match.
+      if (!CheckVariablePattern ||
+          VariablePattern(*I).countPatternDifferences(PrototypeFeatures) == 0) {
         FilteredGroup.Sequences.push_back(*I);
         I = UnassignedSequences.erase(I);
         continue;
       }
+
+      // We didn't found a matching variable pattern, so we continue with the
+      // next sequence.
       ++I;
     }
 
     // Add a valid clone group to the list of found clone groups.
     if (!FilteredGroup.isValid())
       continue;
 
     Result.push_back(FilteredGroup);
   }
 }
 
 void CloneDetector::findClones(std::vector<CloneGroup> &Result,
                                unsigned MinGroupComplexity,
                                bool CheckPatterns) {
+  // A shortcut (and necessary for the for-loop later in this function).
+  if (Sequences.empty())
+    return;
+
+  // We need to search for groups of StmtSequences with the same hash code to
+  // create our initial clone groups. By sorting all known StmtSequences by
+  // their hash value we make sure that StmtSequences with the same hash code
+  // are grouped together in the Sequences vector.
+  // Note: We stable sort here because the StmtSequences are added in the order
+  // in which they appear in the source file. We want to preserve that order
+  // because we also want to report them in that order in the CloneChecker.
+  std::stable_sort(Sequences.begin(), Sequences.end(),
+                   [](std::pair<CloneSignature, StmtSequence> LHS,
+                      std::pair<CloneSignature, StmtSequence> RHS) {
+                     return LHS.first.Hash < RHS.first.Hash;
+                   });
+
+  std::vector<CloneGroup> CloneGroups;
+
+  // Check for each CloneSignature if its successor has the same hash value.
+  // We don't check the last CloneSignature as it has no successor.
+  // Note: The 'size - 1' in the condition is safe because we check for an empty
+  // Sequences vector at the beginning of this function.
+  for (unsigned i = 0; i < Sequences.size() - 1; ++i) {
+    const auto Current = Sequences[i];
+    const auto Next = Sequences[i + 1];
+
+    if (Current.first.Hash != Next.first.Hash)
+      continue;
+
+    // It's likely that we just found an sequence of CloneSignatures that
+    // represent a CloneGroup, so we create a new group and start checking and
+    // adding the CloneSignatures in this sequence.
+    CloneGroup Group;
+    Group.Signature = Current.first;
+
+    for (; i < Sequences.size(); ++i) {
+      const auto &Signature = Sequences[i];
+
+      // A different hash value means we have reached the end of the sequence.
+      if (Current.first.Hash != Signature.first.Hash) {
+        // The current Signature could be the start of a new CloneGroup. So we
+        // decrement i so that we visit it again in the outer loop.
+        // Note: i can never be 0 at this point because we are just comparing
+        // the hash of the Current CloneSignature with itself in the 'if' above.
+        assert(i != 0);
+        --i;
+        break;
+      }
+
+      // Skip CloneSignatures that won't pass the complexity requirement.
+      if (Signature.first.Complexity < MinGroupComplexity)
+        continue;
+
+      Group.Sequences.push_back(Signature.second);
+    }
+
+    // There is a chance that we haven't found more than two fitting
+    // CloneSignature because not enough CloneSignatures passed the complexity
+    // requirement. As a CloneGroup with less than two members makes no sense,
+    // we ignore this CloneGroup and won't add it to the result.
+    if (!Group.isValid())
+      continue;
+
+    CloneGroups.push_back(Group);
+  }
+
   // Add every valid clone group that fulfills the complexity requirement.
   for (const CloneGroup &Group : CloneGroups) {
-    if (Group.isValid() && Group.Complexity >= MinGroupComplexity) {
-      if (CheckPatterns)
-        createCloneGroups(Result, Group);
-      else
-        Result.push_back(Group);
-    }
+    createCloneGroups(Result, Group, CheckPatterns);
   }
 
   std::vector<unsigned> IndexesToRemove;
 
   // Compare every group in the result with the rest. If one groups contains
   // another group, we only need to return the bigger group.
   // Note: This doesn't scale well, so if possible avoid calling any heavy
   // function from this loop to minimize the performance impact.

lib/StaticAnalyzer/Checkers/CloneChecker.cpp

void CloneChecker::reportClones(SourceManager &SM, AnalysisManager &Mgr,
 
   unsigned WarnID = DiagEngine.getCustomDiagID(DiagnosticsEngine::Warning,
                                                "Detected code clone.");
 
   unsigned NoteID = DiagEngine.getCustomDiagID(DiagnosticsEngine::Note,
                                                "Related code clone is here.");
 
   for (CloneDetector::CloneGroup &Group : CloneGroups) {
-    // For readability reasons we sort the clones by line numbers.
-    std::sort(Group.Sequences.begin(), Group.Sequences.end(),
-              [&SM](const StmtSequence &LHS, const StmtSequence &RHS) {
-                return SM.isBeforeInTranslationUnit(LHS.getStartLoc(),
-                                                    RHS.getStartLoc()) &&
-                       SM.isBeforeInTranslationUnit(LHS.getEndLoc(),
-                                                    RHS.getEndLoc());
-              });
-
     // We group the clones by printing the first as a warning and all others
     // as a note.
     DiagEngine.Report(Group.Sequences.front().getStartLoc(), WarnID);
     for (unsigned i = 1; i < Group.Sequences.size(); ++i) {
       DiagEngine.Report(Group.Sequences[i].getStartLoc(), NoteID);
     }
   }
 }