[LifetimeSafety] Add loan expiry analysis

Author: usx95

clang/include/clang/Analysis/Analyses/LifetimeSafety.h

@@ -33,6 +33,7 @@ namespace internal {
 class Fact;
 class FactManager;
 class LoanPropagationAnalysis;
+class ExpiredLoansAnalysis;
 struct LifetimeFactory;
 
 /// A generic, type-safe wrapper for an ID, distinguished by its `Tag` type.
@@ -53,6 +54,11 @@ template <typename Tag> struct ID {
   }
 };
 
+template <typename Tag>
+inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, ID<Tag> ID) {
+  return OS << ID.Value;
+}
+
 using LoanID = ID<struct LoanTag>;
 using OriginID = ID<struct OriginTag>;
 
@@ -81,6 +87,9 @@ class LifetimeSafetyAnalysis {
   /// Returns the set of loans an origin holds at a specific program point.
   LoanSet getLoansAtPoint(OriginID OID, ProgramPoint PP) const;
 
+  /// Returns the set of loans that have expired at a specific program point.
+  LoanSet getExpiredLoansAtPoint(ProgramPoint PP) const;
+
   /// Finds the OriginID for a given declaration.
   /// Returns a null optional if not found.
   std::optional<OriginID> getOriginIDForDecl(const ValueDecl *D) const;
@@ -96,6 +105,7 @@ class LifetimeSafetyAnalysis {
   std::unique_ptr<LifetimeFactory> Factory;
   std::unique_ptr<FactManager> FactMgr;
   std::unique_ptr<LoanPropagationAnalysis> LoanPropagation;
+  std::unique_ptr<ExpiredLoansAnalysis> ExpiredLoans;
 };
 } // namespace internal
 } // namespace clang::lifetimes

clang/lib/Analysis/LifetimeSafety.cpp

@@ -23,14 +23,15 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/TimeProfiler.h"
 #include <cstdint>
+#include <memory>
 
 namespace clang::lifetimes {
 namespace internal {
 namespace {
-template <typename Tag>
-inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, ID<Tag> ID) {
-  return OS << ID.Value;
-}
+// template <typename Tag>
+// inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, ID<Tag> ID) {
+//   return OS << ID.Value;
+// }
 } // namespace
 
 /// Represents the storage location being borrowed, e.g., a specific stack
@@ -832,6 +833,65 @@ class LoanPropagationAnalysis
   }
 };
 
+// ========================================================================= //
+//                         Expired Loans Analysis
+// ========================================================================= //
+
+/// The dataflow lattice for tracking the set of expired loans.
+struct ExpiredLattice {
+  LoanSet Expired;
+
+  ExpiredLattice() : Expired(nullptr) {};
+  explicit ExpiredLattice(LoanSet S) : Expired(S) {}
+
+  bool operator==(const ExpiredLattice &Other) const {
+    return Expired == Other.Expired;
+  }
+  bool operator!=(const ExpiredLattice &Other) const {
+    return !(*this == Other);
+  }
+
+  void dump(llvm::raw_ostream &OS) const {
+    OS << "ExpiredLattice State:\n";
+    if (Expired.isEmpty())
+      OS << "  <empty>\n";
+    for (const LoanID &LID : Expired)
+      OS << "  Loan " << LID << " is expired\n";
+  }
+};
+
+/// The analysis that tracks which loans have expired.
+class ExpiredLoansAnalysis
+    : public DataflowAnalysis<ExpiredLoansAnalysis, ExpiredLattice,
+                              Direction::Forward> {
+
+  LoanSet::Factory &Factory;
+
+public:
+  ExpiredLoansAnalysis(const CFG &C, AnalysisDeclContext &AC, FactManager &F,
+                       LifetimeFactory &Factory)
+      : DataflowAnalysis(C, AC, F), Factory(Factory.LoanSetFactory) {}
+
+  using Base::transfer;
+
+  StringRef getAnalysisName() const { return "ExpiredLoans"; }
+
+  Lattice getInitialState() { return Lattice(Factory.getEmptySet()); }
+
+  /// Merges two lattices by taking the union of the expired loan sets.
+  Lattice join(Lattice L1, Lattice L2) const {
+    return Lattice(utils::join(L1.Expired, L2.Expired, Factory));
+  }
+
+  Lattice transfer(Lattice In, const ExpireFact &F) {
+    return Lattice(Factory.add(In.Expired, F.getLoanID()));
+  }
+
+  Lattice transfer(Lattice In, const IssueFact &F) {
+    return Lattice(Factory.remove(In.Expired, F.getLoanID()));
+  }
+};
+
 // ========================================================================= //
 //  TODO:
 // - Modify loan expiry analysis to answer `bool isExpired(Loan L, Point P)`
@@ -873,6 +933,10 @@ void LifetimeSafetyAnalysis::run() {
   LoanPropagation =
       std::make_unique<LoanPropagationAnalysis>(Cfg, AC, *FactMgr, *Factory);
   LoanPropagation->run();
+
+  ExpiredLoans =
+      std::make_unique<ExpiredLoansAnalysis>(Cfg, AC, *FactMgr, *Factory);
+  ExpiredLoans->run();
 }
 
 LoanSet LifetimeSafetyAnalysis::getLoansAtPoint(OriginID OID,
@@ -881,6 +945,11 @@ LoanSet LifetimeSafetyAnalysis::getLoansAtPoint(OriginID OID,
   return LoanPropagation->getLoans(OID, PP);
 }
 
+LoanSet LifetimeSafetyAnalysis::getExpiredLoansAtPoint(ProgramPoint PP) const {
+  assert(ExpiredLoans && "ExpiredLoansAnalysis has not been run.");
+  return ExpiredLoans->getState(PP).Expired;
+}
+
 std::optional<OriginID>
 LifetimeSafetyAnalysis::getOriginIDForDecl(const ValueDecl *D) const {
   assert(FactMgr && "FactManager not initialized");

clang/unittests/Analysis/LifetimeSafetyTest.cpp

@@ -20,6 +20,7 @@ namespace clang::lifetimes::internal {
 namespace {
 
 using namespace ast_matchers;
+using ::testing::Not;
 using ::testing::UnorderedElementsAreArray;
 
 // A helper class to run the full lifetime analysis on a piece of code
@@ -45,7 +46,10 @@ class LifetimeTestRunner {
       return;
     }
     AnalysisCtx = std::make_unique<AnalysisDeclContext>(nullptr, FD);
-    AnalysisCtx->getCFGBuildOptions().setAllAlwaysAdd();
+    CFG::BuildOptions &BuildOptions = AnalysisCtx->getCFGBuildOptions();
+    BuildOptions.setAllAlwaysAdd();
+    BuildOptions.AddImplicitDtors = true;
+    BuildOptions.AddTemporaryDtors = true;
 
     // Run the main analysis.
     Analysis = std::make_unique<LifetimeSafetyAnalysis>(*AnalysisCtx);
@@ -115,6 +119,13 @@ class LifetimeTestHelper {
     return Analysis.getLoansAtPoint(OID, PP);
   }
 
+  std::optional<LoanSet> getExpiredLoansAtPoint(llvm::StringRef Annotation) {
+    ProgramPoint PP = Runner.getProgramPoint(Annotation);
+    if (!PP)
+      return std::nullopt;
+    return Analysis.getExpiredLoansAtPoint(PP);
+  }
+
 private:
   template <typename DeclT> DeclT *findDecl(llvm::StringRef Name) {
     auto &Ctx = Runner.getASTContext();
@@ -134,6 +145,15 @@ class LifetimeTestHelper {
 //                         GTest Matchers & Fixture
 // ========================================================================= //
 
+// A helper class to represent the subject of a check, e.g., "the loan to 'x'".
+class LoanInfo {
+public:
+  LoanInfo(llvm::StringRef LoanVar, LifetimeTestHelper &Helper)
+      : LoanVar(LoanVar), Helper(Helper) {}
+  llvm::StringRef LoanVar;
+  LifetimeTestHelper &Helper;
+};
+
 // It holds the name of the origin variable and a reference to the helper.
 class OriginInfo {
 public:
@@ -185,6 +205,33 @@ MATCHER_P2(HasLoansToImpl, LoanVars, Annotation, "") {
                             ActualLoans, result_listener);
 }
 
+/// Matcher to verify if a loan to a specific variable has expired at a given
+// program point.
+MATCHER_P(IsExpiredAt, Annotation, "") {
+  const LoanInfo &Info = arg;
+  std::optional<LoanID> TargetLoanIDOpt =
+      Info.Helper.getLoanForVar(Info.LoanVar);
+  if (!TargetLoanIDOpt) {
+    *result_listener << "could not find a loan for variable '"
+                     << Info.LoanVar.str() << "'";
+    return false;
+  }
+
+  std::optional<LoanSet> ExpiredLoansSetOpt =
+      Info.Helper.getExpiredLoansAtPoint(Annotation);
+  if (!ExpiredLoansSetOpt) {
+    *result_listener << "could not get a valid expired loan set at point '"
+                     << Annotation << "'";
+    return false;
+  }
+
+  if (ExpiredLoansSetOpt->contains(*TargetLoanIDOpt))
+    return true;
+
+  *result_listener << "was expected to be expired, but was not";
+  return false;
+}
+
 // Base test fixture to manage the runner and helper.
 class LifetimeAnalysisTest : public ::testing::Test {
 protected:
@@ -197,6 +244,10 @@ class LifetimeAnalysisTest : public ::testing::Test {
     return OriginInfo(OriginVar, *Helper);
   }
 
+  LoanInfo LoanTo(llvm::StringRef LoanVar) {
+    return LoanInfo(LoanVar, *Helper);
+  }
+
   // Factory function that hides the std::vector creation.
   auto HasLoansTo(std::initializer_list<std::string> LoanVars,
                   const char *Annotation) {
@@ -435,5 +486,119 @@ TEST_F(LifetimeAnalysisTest, NestedScopes) {
   EXPECT_THAT(Origin("p"), HasLoansTo({"inner"}, "after_inner_scope"));
 }
 
+// ========================================================================= //
+//                       Loan Expiration Tests
+// ========================================================================= //
+
+TEST_F(LifetimeAnalysisTest, SimpleExpiry) {
+  SetupTest(R"(
+    void target() {
+      MyObj* p = nullptr;
+      {
+        MyObj s;
+        p = &s;
+        POINT(before_expiry);
+      } // s goes out of scope here
+      POINT(after_expiry);
+    }
+  )");
+  EXPECT_THAT(LoanTo("s"), Not(IsExpiredAt("before_expiry")));
+  EXPECT_THAT(LoanTo("s"), IsExpiredAt("after_expiry"));
+}
+
+TEST_F(LifetimeAnalysisTest, NestedExpiry) {
+  SetupTest(R"(
+    void target() {
+      MyObj s1;
+      MyObj* p = &s1;
+      POINT(before_inner);
+      {
+        MyObj s2;
+        p = &s2;
+        POINT(in_inner);
+      } // s2 expires
+      POINT(after_inner);
+    }
+  )");
+  EXPECT_THAT(LoanTo("s1"), Not(IsExpiredAt("before_inner")));
+  EXPECT_THAT(LoanTo("s2"), Not(IsExpiredAt("in_inner")));
+  EXPECT_THAT(LoanTo("s1"), Not(IsExpiredAt("after_inner")));
+  EXPECT_THAT(LoanTo("s2"), IsExpiredAt("after_inner"));
+}
+
+TEST_F(LifetimeAnalysisTest, ConditionalExpiry) {
+  SetupTest(R"(
+    void target(bool cond) {
+      MyObj s1;
+      MyObj* p = &s1;
+      POINT(before_if);
+      if (cond) {
+        MyObj s2;
+        p = &s2;
+        POINT(then_block);
+      } // s2 expires here
+      POINT(after_if);
+    }
+  )");
+  EXPECT_THAT(LoanTo("s1"), Not(IsExpiredAt("before_if")));
+  EXPECT_THAT(LoanTo("s2"), Not(IsExpiredAt("then_block")));
+  // After the if-statement, the loan to s2 (created in the 'then' branch)
+  // will have expired.
+  EXPECT_THAT(LoanTo("s2"), IsExpiredAt("after_if"));
+  EXPECT_THAT(LoanTo("s1"), Not(IsExpiredAt("after_if")));
+}
+
+TEST_F(LifetimeAnalysisTest, LoopExpiry) {
+  SetupTest(R"(
+    void target() {
+      MyObj *p = nullptr;
+      for (int i = 0; i < 2; ++i) {
+        MyObj s;
+        p = &s;
+        POINT(in_loop);
+      } // s expires here on each iteration
+      POINT(after_loop);
+    }
+  )");
+  // Inside the loop, before the scope of 's' ends, its loan is not expired.
+  EXPECT_THAT(LoanTo("s"), Not(IsExpiredAt("in_loop")));
+  // After the loop finishes, the loan to 's' from the last iteration has
+  // expired.
+  EXPECT_THAT(LoanTo("s"), IsExpiredAt("after_loop"));
+}
+
+TEST_F(LifetimeAnalysisTest, MultipleExpiredLoans) {
+  SetupTest(R"(
+    void target() {
+      MyObj *p1, *p2, *p3;
+      {
+        MyObj s1;
+        p1 = &s1;
+        POINT(p1);
+      } // s1 expires
+      POINT(p2);
+      {
+        MyObj s2;
+        p2 = &s2;
+        MyObj s3;
+        p3 = &s3;
+        POINT(p3);
+      } // s2, s3 expire
+      POINT(p4);
+    }
+  )");
+  EXPECT_THAT(LoanTo("s1"), Not(IsExpiredAt("p1")));
+
+  EXPECT_THAT(LoanTo("s1"), IsExpiredAt("p2"));
+
+  EXPECT_THAT(LoanTo("s1"), IsExpiredAt("p3"));
+  EXPECT_THAT(LoanTo("s2"), Not(IsExpiredAt("p3")));
+  EXPECT_THAT(LoanTo("s3"), Not(IsExpiredAt("p3")));
+
+  EXPECT_THAT(LoanTo("s1"), IsExpiredAt("p4"));
+  EXPECT_THAT(LoanTo("s2"), IsExpiredAt("p4"));
+  EXPECT_THAT(LoanTo("s3"), IsExpiredAt("p4"));
+}
+
 } // anonymous namespace
 } // namespace clang::lifetimes::internal