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llvm-project/clang/lib/Analysis/CloneDetection.cpp

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//===--- CloneDetection.cpp - Finds code clones in an AST -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// This file implements classes for searching and anlyzing source code clones.
///
//===----------------------------------------------------------------------===//
#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");
assert(StartIndex < EndIndex && "Given array should not be empty");
assert(EndIndex <= Stmt->size() && "Given array too big for this Stmt");
}
StmtSequence::StmtSequence(const Stmt *Stmt, ASTContext &Context)
: S(Stmt), Context(&Context), StartIndex(0), EndIndex(0) {}
StmtSequence::StmtSequence()
: S(nullptr), Context(nullptr), StartIndex(0), EndIndex(0) {}
bool StmtSequence::contains(const StmtSequence &Other) const {
// If both sequences reside in different translation units, they can never
// contain each other.
if (Context != Other.Context)
return false;
const SourceManager &SM = Context->getSourceManager();
// Otherwise check if the start and end locations of the current sequence
// surround the other sequence.
bool StartIsInBounds =
SM.isBeforeInTranslationUnit(getStartLoc(), Other.getStartLoc()) ||
getStartLoc() == Other.getStartLoc();
if (!StartIsInBounds)
return false;
bool EndIsInBounds =
SM.isBeforeInTranslationUnit(Other.getEndLoc(), getEndLoc()) ||
Other.getEndLoc() == getEndLoc();
return EndIsInBounds;
}
StmtSequence::iterator StmtSequence::begin() const {
if (!holdsSequence()) {
return &S;
}
auto CS = cast<CompoundStmt>(S);
return CS->body_begin() + StartIndex;
}
StmtSequence::iterator StmtSequence::end() const {
if (!holdsSequence()) {
return reinterpret_cast<StmtSequence::iterator>(&S) + 1;
}
auto CS = cast<CompoundStmt>(S);
return CS->body_begin() + EndIndex;
}
SourceLocation StmtSequence::getStartLoc() const {
return front()->getLocStart();
}
SourceLocation StmtSequence::getEndLoc() const { return back()->getLocEnd(); }
namespace {
/// \brief Analyzes the pattern of the referenced variables in a statement.
class VariablePattern {
/// \brief Describes an occurence of a variable reference in a statement.
struct VariableOccurence {
/// The index of the associated VarDecl in the Variables vector.
size_t KindID;
/// The source range in the code where the variable was referenced.
SourceRange Range;
VariableOccurence(size_t KindID, SourceRange Range)
: KindID(KindID), Range(Range) {}
};
/// All occurences of referenced variables in the order of appearance.
std::vector<VariableOccurence> Occurences;
/// List of referenced variables in the order of appearance.
/// Every item in this list is unique.
std::vector<const VarDecl *> Variables;
/// \brief Adds a new variable referenced to this pattern.
/// \param VarDecl The declaration of the variable that is referenced.
/// \param Range The SourceRange where this variable is referenced.
void addVariableOccurence(const VarDecl *VarDecl, SourceRange Range) {
// First check if we already reference this variable
for (size_t KindIndex = 0; KindIndex < Variables.size(); ++KindIndex) {
if (Variables[KindIndex] == VarDecl) {
// If yes, add a new occurence that points to the existing entry in
// the Variables vector.
Occurences.emplace_back(KindIndex, Range);
return;
}
}
// If this variable wasn't already referenced, add it to the list of
// referenced variables and add a occurence that points to this new entry.
Occurences.emplace_back(Variables.size(), Range);
Variables.push_back(VarDecl);
}
/// \brief Adds each referenced variable from the given statement.
void addVariables(const Stmt *S) {
// Sometimes we get a nullptr (such as from IfStmts which often have nullptr
// children). We skip such statements as they don't reference any
// variables.
if (!S)
return;
// Check if S is a reference to a variable. If yes, add it to the pattern.
if (auto D = dyn_cast<DeclRefExpr>(S)) {
if (auto VD = dyn_cast<VarDecl>(D->getDecl()->getCanonicalDecl()))
addVariableOccurence(VD, D->getSourceRange());
}
// Recursively check all children of the given statement.
for (const Stmt *Child : S->children()) {
addVariables(Child);
}
}
public:
/// \brief Creates an VariablePattern object with information about the given
/// StmtSequence.
VariablePattern(const StmtSequence &Sequence) {
for (const Stmt *S : Sequence)
addVariables(S);
}
/// \brief Counts the differences between this pattern and the given one.
/// \param Other The given VariablePattern to compare with.
/// \param FirstMismatch Output parameter that will be filled with information
/// about the first difference between the two patterns. This parameter
/// can be a nullptr, in which case it will be ignored.
/// \return Returns the number of differences between the pattern this object
/// is following and the given VariablePattern.
///
/// For example, the following statements all have the same pattern and this
/// function would return zero:
///
/// if (a < b) return a; return b;
/// if (x < y) return x; return y;
/// if (u2 < u1) return u2; return u1;
///
/// But the following statement has a different pattern (note the changed
/// variables in the return statements) and would have two differences when
/// compared with one of the statements above.
///
/// if (a < b) return b; return a;
///
/// This function should only be called if the related statements of the given
/// pattern and the statements of this objects are clones of each other.
unsigned countPatternDifferences(
const VariablePattern &Other,
CloneDetector::SuspiciousClonePair *FirstMismatch = nullptr) {
unsigned NumberOfDifferences = 0;
assert(Other.Occurences.size() == Occurences.size());
for (unsigned i = 0; i < Occurences.size(); ++i) {
auto ThisOccurence = Occurences[i];
auto OtherOccurence = Other.Occurences[i];
if (ThisOccurence.KindID == OtherOccurence.KindID)
continue;
++NumberOfDifferences;
// If FirstMismatch is not a nullptr, we need to store information about
// the first difference between the two patterns.
if (FirstMismatch == nullptr)
continue;
// Only proceed if we just found the first difference as we only store
// information about the first difference.
if (NumberOfDifferences != 1)
continue;
const VarDecl *FirstSuggestion = nullptr;
// If there is a variable available in the list of referenced variables
// which wouldn't break the pattern if it is used in place of the
// current variable, we provide this variable as the suggested fix.
if (OtherOccurence.KindID < Variables.size())
FirstSuggestion = Variables[OtherOccurence.KindID];
// Store information about the first clone.
FirstMismatch->FirstCloneInfo =
CloneDetector::SuspiciousClonePair::SuspiciousCloneInfo(
Variables[ThisOccurence.KindID], ThisOccurence.Range,
FirstSuggestion);
// Same as above but with the other clone. We do this for both clones as
// we don't know which clone is the one containing the unintended
// pattern error.
const VarDecl *SecondSuggestion = nullptr;
if (ThisOccurence.KindID < Other.Variables.size())
SecondSuggestion = Other.Variables[ThisOccurence.KindID];
// Store information about the second clone.
FirstMismatch->SecondCloneInfo =
CloneDetector::SuspiciousClonePair::SuspiciousCloneInfo(
Variables[ThisOccurence.KindID], OtherOccurence.Range,
SecondSuggestion);
// SuspiciousClonePair guarantees that the first clone always has a
// suggested variable associated with it. As we know that one of the two
// clones in the pair always has suggestion, we swap the two clones
// in case the first clone has no suggested variable which means that
// the second clone has a suggested variable and should be first.
if (!FirstMismatch->FirstCloneInfo.Suggestion)
std::swap(FirstMismatch->FirstCloneInfo,
FirstMismatch->SecondCloneInfo);
// This ensures that we always have at least one suggestion in a pair.
assert(FirstMismatch->FirstCloneInfo.Suggestion);
}
return NumberOfDifferences;
}
};
}
/// \brief Prints the macro name that contains the given SourceLocation into
/// the given raw_string_ostream.
static void printMacroName(llvm::raw_string_ostream &MacroStack,
ASTContext &Context, SourceLocation Loc) {
MacroStack << Lexer::getImmediateMacroName(Loc, Context.getSourceManager(),
Context.getLangOpts());
// Add an empty space at the end as a padding to prevent
// that macro names concatenate to the names of other macros.
MacroStack << " ";
}
/// \brief Returns a string that represents all macro expansions that
/// expanded into the given SourceLocation.
///
/// If 'getMacroStack(A) == getMacroStack(B)' is true, then the SourceLocations
/// A and B are expanded from the same macros in the same order.
static std::string getMacroStack(SourceLocation Loc, ASTContext &Context) {
std::string MacroStack;
llvm::raw_string_ostream MacroStackStream(MacroStack);
SourceManager &SM = Context.getSourceManager();
// Iterate over all macros that expanded into the given SourceLocation.
while (Loc.isMacroID()) {
// Add the macro name to the stream.
printMacroName(MacroStackStream, Context, Loc);
Loc = SM.getImmediateMacroCallerLoc(Loc);
}
MacroStackStream.flush();
return MacroStack;
}
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.
///
/// 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;
/// \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 DataConsumer 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) {
DataConsumer.update(
StringRef(reinterpret_cast<char *>(&Integer), sizeof(Integer)));
}
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) \
void Visit##CLASS(const CLASS *S) { \
CODE; \
ConstStmtVisitor<StmtDataCollector>::Visit##CLASS(S); \
}
DEF_ADD_DATA(Stmt, {
addData(S->getStmtClass());
// This ensures that macro generated code isn't identical to macro-generated
// code.
addData(getMacroStack(S->getLocStart(), Context));
addData(getMacroStack(S->getLocEnd(), Context));
})
DEF_ADD_DATA(Expr, { addData(S->getType()); })
//--- Builtin functionality ----------------------------------------------//
DEF_ADD_DATA(ArrayTypeTraitExpr, { addData(S->getTrait()); })
DEF_ADD_DATA(ExpressionTraitExpr, { addData(S->getTrait()); })
DEF_ADD_DATA(PredefinedExpr, { addData(S->getIdentType()); })
DEF_ADD_DATA(TypeTraitExpr, {
addData(S->getTrait());
for (unsigned i = 0; i < S->getNumArgs(); ++i)
addData(S->getArg(i)->getType());
})
//--- Calls --------------------------------------------------------------//
DEF_ADD_DATA(CallExpr, {
// Function pointers don't have a callee and we just skip hashing it.
if (const FunctionDecl *D = S->getDirectCallee()) {
// If the function is a template specialization, we also need to handle
// the template arguments as they are not included in the qualified name.
if (auto Args = D->getTemplateSpecializationArgs()) {
std::string ArgString;
// Print all template arguments into ArgString
llvm::raw_string_ostream OS(ArgString);
for (unsigned i = 0; i < Args->size(); ++i) {
Args->get(i).print(Context.getLangOpts(), OS);
// Add a padding character so that 'foo<X, XX>()' != 'foo<XX, X>()'.
OS << '\n';
}
OS.flush();
addData(ArgString);
}
addData(D->getQualifiedNameAsString());
}
})
//--- Exceptions ---------------------------------------------------------//
DEF_ADD_DATA(CXXCatchStmt, { addData(S->getCaughtType()); })
//--- C++ OOP Stmts ------------------------------------------------------//
DEF_ADD_DATA(CXXDeleteExpr, {
addData(S->isArrayFormAsWritten());
addData(S->isGlobalDelete());
})
//--- Casts --------------------------------------------------------------//
DEF_ADD_DATA(ObjCBridgedCastExpr, { addData(S->getBridgeKind()); })
//--- Miscellaneous Exprs ------------------------------------------------//
DEF_ADD_DATA(BinaryOperator, { addData(S->getOpcode()); })
DEF_ADD_DATA(UnaryOperator, { addData(S->getOpcode()); })
//--- Control flow -------------------------------------------------------//
DEF_ADD_DATA(GotoStmt, { addData(S->getLabel()->getName()); })
DEF_ADD_DATA(IndirectGotoStmt, {
if (S->getConstantTarget())
addData(S->getConstantTarget()->getName());
})
DEF_ADD_DATA(LabelStmt, { addData(S->getDecl()->getName()); })
DEF_ADD_DATA(MSDependentExistsStmt, { addData(S->isIfExists()); })
DEF_ADD_DATA(AddrLabelExpr, { addData(S->getLabel()->getName()); })
//--- Objective-C --------------------------------------------------------//
DEF_ADD_DATA(ObjCIndirectCopyRestoreExpr, { addData(S->shouldCopy()); })
DEF_ADD_DATA(ObjCPropertyRefExpr, {
addData(S->isSuperReceiver());
addData(S->isImplicitProperty());
})
DEF_ADD_DATA(ObjCAtCatchStmt, { addData(S->hasEllipsis()); })
//--- Miscellaneous Stmts ------------------------------------------------//
DEF_ADD_DATA(CXXFoldExpr, {
addData(S->isRightFold());
addData(S->getOperator());
})
DEF_ADD_DATA(GenericSelectionExpr, {
for (unsigned i = 0; i < S->getNumAssocs(); ++i) {
addData(S->getAssocType(i));
}
})
DEF_ADD_DATA(LambdaExpr, {
for (const LambdaCapture &C : S->captures()) {
addData(C.isPackExpansion());
addData(C.getCaptureKind());
if (C.capturesVariable())
addData(C.getCapturedVar()->getType());
}
addData(S->isGenericLambda());
addData(S->isMutable());
})
DEF_ADD_DATA(DeclStmt, {
auto numDecls = std::distance(S->decl_begin(), S->decl_end());
addData(static_cast<CloneDetector::DataPiece>(numDecls));
for (const Decl *D : S->decls()) {
if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
addData(VD->getType());
}
}
})
DEF_ADD_DATA(AsmStmt, {
addData(S->isSimple());
addData(S->isVolatile());
addData(S->generateAsmString(Context));
for (unsigned i = 0; i < S->getNumInputs(); ++i) {
addData(S->getInputConstraint(i));
}
for (unsigned i = 0; i < S->getNumOutputs(); ++i) {
addData(S->getOutputConstraint(i));
}
for (unsigned i = 0; i < S->getNumClobbers(); ++i) {
addData(S->getClobber(i));
}
})
DEF_ADD_DATA(AttributedStmt, {
for (const Attr *A : S->getAttrs()) {
addData(std::string(A->getSpelling()));
}
})
};
} // end anonymous namespace
namespace {
/// Generates CloneSignatures for a set of statements and stores the results in
/// a CloneDetector object.
class CloneSignatureGenerator {
CloneDetector &CD;
ASTContext &Context;
/// \brief Generates CloneSignatures for all statements in the given statement
/// tree and stores them in the CloneDetector.
///
/// \param S The root of the given statement tree.
/// \param ParentMacroStack A string representing the macros that generated
/// the parent statement or an empty string if no
/// 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;
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 ParentMacroStack 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
// statement, we reduce the initial complexity of this statement to zero.
// This causes that a group of statements that were generated by a single
// macro expansion will only increase the total complexity by one.
// Note: This is not the final complexity of this statement as we still
// add the complexity of the child statements to the complexity value.
if (!ParentMacroStack.empty() && (StartMacroStack == ParentMacroStack &&
EndMacroStack == ParentMacroStack)) {
Signature.Complexity = 0;
}
// Storage for the signatures of the direct child statements. This is only
// needed if the current statement is a CompoundStmt.
std::vector<CloneDetector::CloneSignature> ChildSignatures;
const CompoundStmt *CS = dyn_cast<const CompoundStmt>(S);
// The signature of a statement includes the signatures of its children.
// Therefore we create the signatures for every child and add them to the
// current signature.
for (const Stmt *Child : S->children()) {
// Some statements like 'if' can have nullptr children that we will skip.
if (!Child)
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.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.
/// \param CS The given CompoundStmt.
/// \param ChildSignatures A list of calculated signatures for each child in
/// the given CompoundStmt.
void handleSubSequences(
const CompoundStmt *CS,
const std::vector<CloneDetector::CloneSignature> &ChildSignatures) {
// FIXME: This function has quadratic runtime right now. Check if skipping
// this function for too long CompoundStmts is an option.
// The length of the sub-sequence. We don't need to handle sequences with
// the length 1 as they are already handled in CollectData().
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::MD5 SubHash;
for (unsigned i = Pos; i < Pos + Length; ++i) {
SubSignature.Complexity += ChildSignatures[i].Complexity;
size_t ChildHash = ChildSignatures[i].Hash;
SubHash.update(StringRef(reinterpret_cast<char *>(&ChildHash),
sizeof(ChildHash)));
}
// Create the final hash code for the current signature.
llvm::MD5::MD5Result HashResult;
SubHash.final(HashResult);
// Copy as much of the generated hash code to the signature's hash code.
std::memcpy(&SubSignature.Hash, &HashResult,
std::min(sizeof(SubSignature.Hash), sizeof(HashResult)));
// Save the signature together with the information about what children
// sequence we selected.
CD.add(StmtSequence(CS, Context, Pos, Pos + Length), SubSignature);
}
}
}
public:
explicit CloneSignatureGenerator(CloneDetector &CD, ASTContext &Context)
: CD(CD), Context(Context) {}
/// \brief Generates signatures for all statements in the given function body.
void consumeCodeBody(const Stmt *S) { generateSignatures(S, ""); }
};
} // end anonymous namespace
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) {
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))
return true;
}
return false;
}
/// \brief Returns true if and only if all sequences in \p OtherGroup are
/// contained by a sequence in \p Group.
bool containsGroup(CloneDetector::CloneGroup &Group,
CloneDetector::CloneGroup &OtherGroup) {
// We have less sequences in the current group than we have in the other,
// so we will never fulfill the requirement for returning true. This is only
// possible because we know that a sequence in Group can contain at most
// one sequence in OtherGroup.
if (Group.Sequences.size() < OtherGroup.Sequences.size())
return false;
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.
/// \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 CheckVariablePattern 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,
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.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 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) {
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.
for (unsigned i = 0; i < Result.size(); ++i) {
for (unsigned j = 0; j < Result.size(); ++j) {
// Don't compare a group with itself.
if (i == j)
continue;
if (containsGroup(Result[j], Result[i])) {
IndexesToRemove.push_back(i);
break;
}
}
}
// Erasing a list of indexes from the vector should be done with decreasing
// indexes. As IndexesToRemove is constructed with increasing values, we just
// reverse iterate over it to get the desired order.
for (auto I = IndexesToRemove.rbegin(); I != IndexesToRemove.rend(); ++I) {
Result.erase(Result.begin() + *I);
}
}
void CloneDetector::findSuspiciousClones(
std::vector<CloneDetector::SuspiciousClonePair> &Result,
unsigned MinGroupComplexity) {
std::vector<CloneGroup> Clones;
// Reuse the normal search for clones but specify that the clone groups don't
// need to have a common referenced variable pattern so that we can manually
// search for the kind of pattern errors this function is supposed to find.
findClones(Clones, MinGroupComplexity, false);
for (const CloneGroup &Group : Clones) {
for (unsigned i = 0; i < Group.Sequences.size(); ++i) {
VariablePattern PatternA(Group.Sequences[i]);
for (unsigned j = i + 1; j < Group.Sequences.size(); ++j) {
VariablePattern PatternB(Group.Sequences[j]);
CloneDetector::SuspiciousClonePair ClonePair;
// For now, we only report clones which break the variable pattern just
// once because multiple differences in a pattern are an indicator that
// those differences are maybe intended (e.g. because it's actually
// a different algorithm).
// TODO: In very big clones even multiple variables can be unintended,
// so replacing this number with a percentage could better handle such
// cases. On the other hand it could increase the false-positive rate
// for all clones if the percentage is too high.
if (PatternA.countPatternDifferences(PatternB, &ClonePair) == 1) {
Result.push_back(ClonePair);
break;
}
}
}
}
}
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