[clang] e64ef63 - Thread Safety Analysis: Differentiate between lock sets at real join points and expected/actual sets at function end (#105526)

[via cfe-commits]

Author: Malek Ben Slimane
Date: 2024-09-04T16:18:11+02:00
New Revision: e64ef634bbd940dfaae23d9fb43e6385014ffd10

URL: https://github.com/llvm/llvm-project/commit/e64ef634bbd940dfaae23d9fb43e6385014ffd10
DIFF: https://github.com/llvm/llvm-project/commit/e64ef634bbd940dfaae23d9fb43e6385014ffd10.diff

LOG: Thread Safety Analysis: Differentiate between lock sets at real join points and expected/actual sets at function end (#105526)

This fixes false positives related to returning a scoped lockable
object. At the end of a function, we check managed locks instead of
scoped locks.

At real join points, we skip checking managed locks because we assume
that the scope keeps track of its underlying mutexes and will release
them at its destruction. So, checking for the scopes is sufficient.
However, at the end of a function, we aim at comparing the expected and
the actual lock sets. There, we skip checking scoped locks to prevent to
get duplicate warnings for the same lock.

Added: 
    

Modified: 
    clang/lib/Analysis/ThreadSafety.cpp
    clang/test/SemaCXX/warn-thread-safety-analysis.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Analysis/ThreadSafety.cpp b/clang/lib/Analysis/ThreadSafety.cpp
index e25b843c9bf83e..c4a83b069e0792 100644
--- a/clang/lib/Analysis/ThreadSafety.cpp
+++ b/clang/lib/Analysis/ThreadSafety.cpp
@@ -922,6 +922,9 @@ class ScopedLockableFactEntry : public FactEntry {
   handleRemovalFromIntersection(const FactSet &FSet, FactManager &FactMan,
                                 SourceLocation JoinLoc, LockErrorKind LEK,
                                 ThreadSafetyHandler &Handler) const override {
+    if (LEK == LEK_LockedAtEndOfFunction || LEK == LEK_NotLockedAtEndOfFunction)
+      return;
+
     for (const auto &UnderlyingMutex : UnderlyingMutexes) {
       const auto *Entry = FSet.findLock(FactMan, UnderlyingMutex.Cap);
       if ((UnderlyingMutex.Kind == UCK_Acquired && Entry) ||
@@ -2224,7 +2227,7 @@ void ThreadSafetyAnalyzer::intersectAndWarn(FactSet &EntrySet,
       if (join(FactMan[*EntryIt], ExitFact,
                EntryLEK != LEK_LockedSomeLoopIterations))
         *EntryIt = Fact;
-    } else if (!ExitFact.managed()) {
+    } else if (!ExitFact.managed() || EntryLEK == LEK_LockedAtEndOfFunction) {
       ExitFact.handleRemovalFromIntersection(ExitSet, FactMan, JoinLoc,
                                              EntryLEK, Handler);
     }
@@ -2236,7 +2239,8 @@ void ThreadSafetyAnalyzer::intersectAndWarn(FactSet &EntrySet,
     const FactEntry *ExitFact = ExitSet.findLock(FactMan, *EntryFact);
 
     if (!ExitFact) {
-      if (!EntryFact->managed() || ExitLEK == LEK_LockedSomeLoopIterations)
+      if (!EntryFact->managed() || ExitLEK == LEK_LockedSomeLoopIterations ||
+          ExitLEK == LEK_NotLockedAtEndOfFunction)
         EntryFact->handleRemovalFromIntersection(EntrySetOrig, FactMan, JoinLoc,
                                                  ExitLEK, Handler);
       if (ExitLEK == LEK_LockedSomePredecessors)

diff  --git a/clang/test/SemaCXX/warn-thread-safety-analysis.cpp b/clang/test/SemaCXX/warn-thread-safety-analysis.cpp
index af9254508d8050..8477200456d985 100644
--- a/clang/test/SemaCXX/warn-thread-safety-analysis.cpp
+++ b/clang/test/SemaCXX/warn-thread-safety-analysis.cpp
@@ -6077,24 +6077,20 @@ namespace ReturnScopedLockable {
 class Object {
 public:
   MutexLock lock() EXCLUSIVE_LOCK_FUNCTION(mutex) {
-    // TODO: False positive because scoped lock isn't destructed.
-    return MutexLock(&mutex); // expected-note {{mutex acquired here}}
-  }                           // expected-warning {{mutex 'mutex' is still held at the end of function}}
+    return MutexLock(&mutex);
+  }
 
   ReaderMutexLock lockShared() SHARED_LOCK_FUNCTION(mutex) {
-    // TODO: False positive because scoped lock isn't destructed.
-    return ReaderMutexLock(&mutex); // expected-note {{mutex acquired here}}
-  }                                 // expected-warning {{mutex 'mutex' is still held at the end of function}}
+    return ReaderMutexLock(&mutex);
+  }
 
   MutexLock adopt() EXCLUSIVE_LOCKS_REQUIRED(mutex) {
-    // TODO: False positive because scoped lock isn't destructed.
-    return MutexLock(&mutex, true); // expected-note {{mutex acquired here}}
-  }                                 // expected-warning {{mutex 'mutex' is still held at the end of function}}
+    return MutexLock(&mutex, true);
+  }
 
   ReaderMutexLock adoptShared() SHARED_LOCKS_REQUIRED(mutex) {
-    // TODO: False positive because scoped lock isn't destructed.
-    return ReaderMutexLock(&mutex, true); // expected-note {{mutex acquired here}}
-  }                                       // expected-warning {{mutex 'mutex' is still held at the end of function}}
+    return ReaderMutexLock(&mutex, true);
+  }
 
   int x GUARDED_BY(mutex);
   void needsLock() EXCLUSIVE_LOCKS_REQUIRED(mutex);