[analyzer] Add checker modeling potential C++ self-assignment

This checker checks copy and move assignment operators whether they are
protected against self-assignment. Since C++ core guidelines discourages
explicit checking for `&rhs==this` in general we take a different approach: in
top-frame analysis we branch the exploded graph for two cases, where &rhs==this
and &rhs!=this and let existing checkers (e.g. unix.Malloc) do the rest of the
work. It is important that we check all copy and move assignment operator in top
frame even if we checked them already since self-assignments may happen
undetected even in the same translation unit (e.g. using random indices for an
array what may or may not be the same).

This reapplies r275820 after fixing a string-lifetime issue discovered by the
bots.

A patch by Ádám Balogh!

Differential Revision: https://reviews.llvm.org/D19311

llvm-svn: 276365

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -247,6 +247,10 @@ def NewDeleteLeaksChecker : Checker<"NewDeleteLeaks">,
   HelpText<"Check for memory leaks. Traces memory managed by new/delete.">,
   DescFile<"MallocChecker.cpp">;
 
+def CXXSelfAssignmentChecker : Checker<"SelfAssignment">,
+  HelpText<"Checks C++ copy and move assignment operators for self assignment">,
+  DescFile<"CXXSelfAssignmentChecker.cpp">;
+
 } // end: "cplusplus"
 
 let ParentPackage = CplusplusAlpha in {

clang/include/clang/StaticAnalyzer/Core/BugReporter/BugReporterVisitor.h

@@ -331,6 +331,22 @@ public:
                                  BugReport &BR) override;
 };
 
+class CXXSelfAssignmentBRVisitor final
+  : public BugReporterVisitorImpl<CXXSelfAssignmentBRVisitor> {
+  
+  bool Satisfied;
+
+public:
+  CXXSelfAssignmentBRVisitor() : Satisfied(false) {}
+
+  void Profile(llvm::FoldingSetNodeID &ID) const override {}
+
+  PathDiagnosticPiece *VisitNode(const ExplodedNode *Succ,
+                                 const ExplodedNode *Pred,
+                                 BugReporterContext &BRC,
+                                 BugReport &BR) override;
+};
+
 namespace bugreporter {
 
 /// Attempts to add visitors to trace a null or undefined value back to its

clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt

@@ -22,6 +22,7 @@ add_clang_library(clangStaticAnalyzerCheckers
   CheckerDocumentation.cpp
   ChrootChecker.cpp
   ClangCheckers.cpp
+  CXXSelfAssignmentChecker.cpp
   DeadStoresChecker.cpp
   DebugCheckers.cpp
   DereferenceChecker.cpp

clang/lib/StaticAnalyzer/Checkers/CXXSelfAssignmentChecker.cpp

@@ -0,0 +1,62 @@
+//=== CXXSelfAssignmentChecker.cpp -----------------------------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines CXXSelfAssignmentChecker, which tests all custom defined
+// copy and move assignment operators for the case of self assignment, thus
+// where the parameter refers to the same location where the this pointer
+// points to. The checker itself does not do any checks at all, but it
+// causes the analyzer to check every copy and move assignment operator twice:
+// once for when 'this' aliases with the parameter and once for when it may not.
+// It is the task of the other enabled checkers to find the bugs in these two
+// different cases.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+
+class CXXSelfAssignmentChecker : public Checker<check::BeginFunction> {
+public:
+  CXXSelfAssignmentChecker();
+  void checkBeginFunction(CheckerContext &C) const;
+};
+}
+
+CXXSelfAssignmentChecker::CXXSelfAssignmentChecker() {}
+
+void CXXSelfAssignmentChecker::checkBeginFunction(CheckerContext &C) const {
+  if (!C.inTopFrame())
+    return;
+  const auto *LCtx = C.getLocationContext();
+  const auto *MD = dyn_cast<CXXMethodDecl>(LCtx->getDecl());
+  if (!MD)
+    return;
+  if (!MD->isCopyAssignmentOperator() && !MD->isMoveAssignmentOperator())
+    return;
+  auto &State = C.getState();
+  auto &SVB = C.getSValBuilder();
+  auto ThisVal =
+      State->getSVal(SVB.getCXXThis(MD, LCtx->getCurrentStackFrame()));
+  auto Param = SVB.makeLoc(State->getRegion(MD->getParamDecl(0), LCtx));
+  auto ParamVal = State->getSVal(Param);
+  ProgramStateRef SelfAssignState = State->bindLoc(Param, ThisVal);
+  C.addTransition(SelfAssignState);
+  ProgramStateRef NonSelfAssignState = State->bindLoc(Param, ParamVal);
+  C.addTransition(NonSelfAssignState);
+}
+
+void ento::registerCXXSelfAssignmentChecker(CheckerManager &Mgr) {
+  Mgr.registerChecker<CXXSelfAssignmentChecker>();
+}

clang/lib/StaticAnalyzer/Core/BugReporter.cpp

@@ -3104,6 +3104,7 @@ bool GRBugReporter::generatePathDiagnostic(PathDiagnostic& PD,
     R->addVisitor(llvm::make_unique<NilReceiverBRVisitor>());
     R->addVisitor(llvm::make_unique<ConditionBRVisitor>());
     R->addVisitor(llvm::make_unique<LikelyFalsePositiveSuppressionBRVisitor>());
+    R->addVisitor(llvm::make_unique<CXXSelfAssignmentBRVisitor>());
 
     BugReport::VisitorList visitors;
     unsigned origReportConfigToken, finalReportConfigToken;

clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp

@@ -1693,3 +1693,56 @@ UndefOrNullArgVisitor::VisitNode(const ExplodedNode *N,
   }
   return nullptr;
 }
+
+PathDiagnosticPiece *
+CXXSelfAssignmentBRVisitor::VisitNode(const ExplodedNode *Succ,
+                                      const ExplodedNode *Pred,
+                                      BugReporterContext &BRC, BugReport &BR) {
+  if (Satisfied)
+    return nullptr;
+
+  auto Edge = Succ->getLocation().getAs<BlockEdge>();
+  if (!Edge.hasValue())
+    return nullptr;
+
+  auto Tag = Edge->getTag();
+  if (!Tag)
+    return nullptr;
+
+  if (Tag->getTagDescription() != "cplusplus.SelfAssignment")
+    return nullptr;
+
+  Satisfied = true;
+
+  const auto *Met =
+      dyn_cast<CXXMethodDecl>(Succ->getCodeDecl().getAsFunction());
+  assert(Met && "Not a C++ method.");
+  assert((Met->isCopyAssignmentOperator() || Met->isMoveAssignmentOperator()) &&
+         "Not a copy/move assignment operator.");
+
+  const auto *LCtx = Edge->getLocationContext();
+
+  const auto &State = Succ->getState();
+  auto &SVB = State->getStateManager().getSValBuilder();
+
+  const auto Param =
+      State->getSVal(State->getRegion(Met->getParamDecl(0), LCtx));
+  const auto This =
+      State->getSVal(SVB.getCXXThis(Met, LCtx->getCurrentStackFrame()));
+
+  auto L = PathDiagnosticLocation::create(Met, BRC.getSourceManager());
+
+  if (!L.isValid() || !L.asLocation().isValid())
+    return nullptr;
+
+  SmallString<256> Buf;
+  llvm::raw_svector_ostream Out(Buf);
+
+  Out << "Assuming " << Met->getParamDecl(0)->getName() <<
+    ((Param == This) ? " == " : " != ") << "*this";
+
+  auto *Piece = new PathDiagnosticEventPiece(L, Out.str());
+  Piece->addRange(Met->getSourceRange());
+
+  return Piece;
+}

clang/lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp

@@ -426,6 +426,13 @@ static bool shouldSkipFunction(const Decl *D,
   //   Count naming convention errors more aggressively.
   if (isa<ObjCMethodDecl>(D))
     return false;
+  // We also want to reanalyze all C++ copy and move assignment operators to
+  // separately check the two cases where 'this' aliases with the parameter and
+  // where it may not. (cplusplus.SelfAssignmentChecker)
+  if (const auto *MD = dyn_cast<CXXMethodDecl>(D)) {
+    if (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator())
+      return false;
+  }
 
   // Otherwise, if we visited the function before, do not reanalyze it.
   return Visited.count(D);
@@ -437,9 +444,7 @@ AnalysisConsumer::getInliningModeForFunction(const Decl *D,
   // We want to reanalyze all ObjC methods as top level to report Retain
   // Count naming convention errors more aggressively. But we should tune down
   // inlining when reanalyzing an already inlined function.
-  if (Visited.count(D)) {
-    assert(isa<ObjCMethodDecl>(D) &&
-           "We are only reanalyzing ObjCMethods.");
+  if (Visited.count(D) && isa<ObjCMethodDecl>(D)) {
     const ObjCMethodDecl *ObjCM = cast<ObjCMethodDecl>(D);
     if (ObjCM->getMethodFamily() != OMF_init)
       return ExprEngine::Inline_Minimal;

clang/test/Analysis/self-assign.cpp

@@ -0,0 +1,89 @@
+// RUN: %clang_cc1 -std=c++11 -analyze -analyzer-checker=core,cplusplus,unix.Malloc,debug.ExprInspection %s -verify -analyzer-output=text
+
+extern "C" char *strdup(const char* s);
+extern "C" void free(void* ptr);
+
+namespace std {
+template<class T> struct remove_reference      { typedef T type; };
+template<class T> struct remove_reference<T&>  { typedef T type; };
+template<class T> struct remove_reference<T&&> { typedef T type; };
+template<class T> typename remove_reference<T>::type&& move(T&& t);
+}
+
+void clang_analyzer_eval(int);
+
+class StringUsed {
+public:
+  StringUsed(const char *s = "") : str(strdup(s)) {}
+  StringUsed(const StringUsed &rhs) : str(strdup(rhs.str)) {}
+  ~StringUsed();
+  StringUsed& operator=(const StringUsed &rhs);
+  StringUsed& operator=(StringUsed &&rhs);
+  operator const char*() const;
+private:
+  char *str;
+};
+
+StringUsed::~StringUsed() {
+  free(str);
+}
+
+StringUsed& StringUsed::operator=(const StringUsed &rhs) { // expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs != *this}}
+  clang_analyzer_eval(*this == rhs); // expected-warning{{TRUE}} expected-warning{{UNKNOWN}} expected-note{{TRUE}} expected-note{{UNKNOWN}}
+  free(str); // expected-note{{Memory is released}}
+  str = strdup(rhs.str); // expected-warning{{Use of memory after it is freed}}  expected-note{{Use of memory after it is freed}}
+  return *this;
+}
+
+StringUsed& StringUsed::operator=(StringUsed &&rhs) { // expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs != *this}}
+  clang_analyzer_eval(*this == rhs); // expected-warning{{TRUE}} expected-warning{{UNKNOWN}} expected-note{{TRUE}} expected-note{{UNKNOWN}}
+  str = rhs.str;
+  rhs.str = nullptr; // FIXME: An improved leak checker should warn here
+  return *this;
+}
+
+StringUsed::operator const char*() const {
+  return str;
+}
+
+class StringUnused {
+public:
+  StringUnused(const char *s = "") : str(strdup(s)) {}
+  StringUnused(const StringUnused &rhs) : str(strdup(rhs.str)) {}
+  ~StringUnused();
+  StringUnused& operator=(const StringUnused &rhs);
+  StringUnused& operator=(StringUnused &&rhs);
+  operator const char*() const;
+private:
+  char *str;
+};
+
+StringUnused::~StringUnused() {
+  free(str);
+}
+
+StringUnused& StringUnused::operator=(const StringUnused &rhs) { // expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs != *this}}
+  clang_analyzer_eval(*this == rhs); // expected-warning{{TRUE}} expected-warning{{UNKNOWN}} expected-note{{TRUE}} expected-note{{UNKNOWN}}
+  free(str); // expected-note{{Memory is released}}
+  str = strdup(rhs.str); // expected-warning{{Use of memory after it is freed}}  expected-note{{Use of memory after it is freed}}
+  return *this;
+}
+
+StringUnused& StringUnused::operator=(StringUnused &&rhs) { // expected-note{{Assuming rhs == *this}} expected-note{{Assuming rhs != *this}}
+  clang_analyzer_eval(*this == rhs); // expected-warning{{TRUE}} expected-warning{{UNKNOWN}} expected-note{{TRUE}} expected-note{{UNKNOWN}}
+  str = rhs.str;
+  rhs.str = nullptr; // FIXME: An improved leak checker should warn here
+  return *this;
+}
+
+StringUnused::operator const char*() const {
+  return str;
+}
+
+
+int main() {
+  StringUsed s1 ("test"), s2;
+  s2 = s1;
+  s2 = std::move(s1);
+  return 0;
+}