[PATCH] D104261: Thread safety analysis: Always warn when dropping locks on back edges

[Aaron Puchert via Phabricator via cfe-commits]

aaronpuchert added inline comments.


================
Comment at: clang/lib/Analysis/ThreadSafety.cpp:868
                                 ThreadSafetyHandler &Handler) const override {
-    if (!managed() && !asserted() && !negative() && !isUniversal()) {
+    if (!asserted() && !negative() && !isUniversal()) {
       Handler.handleMutexHeldEndOfScope("mutex", toString(), loc(), JoinLoc,
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One might ask: what about asserted capabilities? I plan to introduce a warning when they are released, because that can't be consistent, and then they can't disappear on back edges without warning.

For negative capabilities we'd presumably see a warning for the "positive" capability instead.

Not sure how universal capabilities are typically used. Presumably one could release such a capability in a loop? Then on the other hand, code using such capabilities is probably not very interested in false negatives.


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Comment at: clang/lib/Analysis/ThreadSafety.cpp:2227-2228
 /// \param LEK2 The error message to report if a mutex is missing from Lset2
 void ThreadSafetyAnalyzer::intersectAndWarn(FactSet &FSet1,
                                             const FactSet &FSet2,
                                             SourceLocation JoinLoc,
----------------
Presumably we should call these `EntrySet` and `ExitSet` instead? The second parameter is always the exit set of an existing block, the first parameter the entry set of a (sometimes new) block.


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Comment at: clang/test/SemaCXX/warn-thread-safety-analysis.cpp:643
     sls_mu.Lock();  // \
-      // expected-note {{the other acquisition of mutex 'sls_mu' is here}}
+      // expected-warning {{mutex 'sls_mu' is acquired exclusively and shared in the same scope}}
   } while (getBool());
----------------
These are just swapped because I'm merging the branches in a different order now. I think that's Ok.


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Comment at: clang/test/SemaCXX/warn-thread-safety-analysis.cpp:2788
+  // We have to warn on this join point despite the lock being managed ...
+  for (unsigned i = 1; i < 10; ++i) { // expected-warning {{expecting mutex 'mu' to be held at start of each loop}}
+    x = 1; // ... because we might miss that this doesn't always happen under lock.
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This warning is new.


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Comment at: clang/test/SemaCXX/warn-thread-safety-analysis.cpp:2813
+      scope.Unlock();
+      continue; // expected-warning {{expecting mutex 'mu' to be held at start of each loop}}
+    }
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This is also new.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D104261/new/

https://reviews.llvm.org/D104261