[-Wcalled-once-parameter] Fix false positives for cleanup attr

[vsavchenko]

Summary

Cleanup attribute allows users to attach a destructor-like functions
to variable declarations to be called whenever they leave the scope.
The logic of such functions is not supported by the Clang's CFG and
is too hard to be reasoned about. In order to avoid false positives
in this situation, we assume that we didn't see ALL of the executtion
paths of the function and, thus, can warn only about multiple call
violation.

rdar://74441906

[NoQ]

LGTM!

clang/lib/Analysis/CalledOnceCheck.cpp

for (const auto &IndexedStatus : llvm::enumerate(EntryStatus)) {
         // as "interesting" for further analysis.
         NotCalledOnEveryPath[IndexedStatus.index()] = true;
         break;
       default:
         break;
       }
     }
 
-    // Early exit if we don't have parameters for extra analysis.
-    if (NotCalledOnEveryPath.none() && NotUsedOnEveryPath.none())
+    // Early exit if we don't have parameters for extra analysis...
+    if (NotCalledOnEveryPath.none() && NotUsedOnEveryPath.none() &&
+        // ... or if we've seen variables with cleanup functions.
+        // We can't reason that we've seen every path in this case,
+        // and thus abandon reporting any warnings that imply that.
+        !FunctionHasCleanupVars)
       return;
 
     // We are looking for a pair of blocks A, B so that the following is true:
     //   * A is a predecessor of B
     //   * B is marked as NotCalled
     //   * A has at least one successor marked as either
     //     Escaped or DefinitelyCalled
     //
void VisitDeclStmt(const DeclStmt *DS) {
     // separately.
     //
     // Multiple declarations can be a part of declaration statement.
     for (const auto *Declaration : DS->getDeclGroup()) {
       if (const auto *Var = dyn_cast<VarDecl>(Declaration)) {
         if (Var->getInit()) {
           checkEscapee(Var->getInit());
         }
+
+        if (Var->hasAttr<CleanupAttr>()) {
+          FunctionHasCleanupVars = true;
+        }
       }
     }
   }
 
   void VisitCStyleCastExpr(const CStyleCastExpr *Cast) {
     // We consider '(void)parameter' as a manual no-op escape.
     // It should be used to explicitly tell the analysis that this parameter
     // is intentionally not called on this path.
private:
   // As of now, we turn this behavior off.  So, we still are going to report
   // missing calls on paths that look like it was intentional.
   // Technically such reports are true positives, but they can make some users
   // grumpy because of the sheer number of warnings.
   // It can be turned back on if we decide that we want to have the other way
   // around.
   bool SuppressOnConventionalErrorPaths = false;
 
+  // The user can annotate variable declarations with cleanup functions, which
+  // essentially imposes a custom destructor logic on that variable.
+  // It is possible to use it, however, to call tracked parameters on all exits
+  // from the function.  For this reason, we track the fact that the function
+  // actually has these.
+  bool FunctionHasCleanupVars = false;
+
   State CurrentState;
   ParamSizedVector<const ParmVarDecl *> TrackedParams;
   CFGSizedVector<State> States;
 };
 
 } // end anonymous namespace
 
 namespace clang {
 void checkCalledOnceParameters(AnalysisDeclContext &AC,
                                CalledOnceCheckHandler &Handler,
                                bool CheckConventionalParameters) {
   CalledOnceChecker::check(AC, Handler, CheckConventionalParameters);
 }
 } // end namespace clang

clang/test/SemaObjC/warn-called-once.m

- (void)test_escape_after_branch:(int)cond
   if (cond) {
     // no-warning
     handler();
   }
 
   escape(handler);
 }
 
+// rdar://74441906
+typedef void (^DeferredBlock)(void);
+static inline void DefferedCallback(DeferredBlock *inBlock) { (*inBlock)(); }
+#define _DEFERCONCAT(a, b) a##b
+#define _DEFERNAME(a) _DEFERCONCAT(__DeferredVar_, a)
+#define DEFER __extension__ __attribute__((cleanup(DefferedCallback), unused)) \
+                  DeferredBlock _DEFERNAME(__COUNTER__) = ^
+
+- (void)test_cleanup_1:(int)cond
+        withCompletion:(void (^)(void))handler {
+  int error = 0;
+  DEFER {
+    if (error)
+      handler();
+  };
+
+  if (cond) {
+    error = 1;
+  } else {
+    // no-warning
+    handler();
+  }
+}
+
+- (void)test_cleanup_2:(int)cond
+        withCompletion:(void (^)(void))handler {
+  int error = 0;
+  DEFER {
+    if (error)
+      handler();
+  };
+
+  if (cond) {
+    error = 1;
+  } else {
+    handler(); // expected-note{{previous call is here}}
+  }
+
+  // We still can warn about double call even in this case.
+  handler(); // expected-warning{{completion handler is called twice}}
+}
+
 @end