Thread Safety Analysis: Fix pointer handling of variables with deprecated attributes (#148974)

de10e44 ("Thread Safety Analysis: Support warning on
passing/returning pointers to guarded variables") added checks for
passing pointer to guarded variables. While new features do not
necessarily need to support the deprecated attributes (`guarded_var`,
and `pt_guarded_var`), we need to ensure that such features do not cause
the compiler to crash.

As such, code such as this:

	struct {
	  int v __attribute__((guarded_var));
	} p;

	int *g() {
	  return &p.v;  // handleNoMutexHeld() with POK_ReturnPointer
	}

Would crash in debug builds with the assertion in handleNoMutexHeld()
triggering. The assertion is meant to capture the fact that this helper
should only be used for warnings on variables (which the deprecated
attributes only applied to).

To fix, the function handleNoMutexHeld() should handle all POK cases
that apply to variables explicitly, and produce a best-effort warning.

We refrain from introducing new warnings to avoid unnecessary code bloat
for deprecated features.

Fixes: #140330

Author: melver

clang/lib/Sema/AnalysisBasedWarnings.cpp

@@ -2112,11 +2112,26 @@ class ThreadSafetyReporter : public clang::threadSafety::ThreadSafetyHandler {
 
   void handleNoMutexHeld(const NamedDecl *D, ProtectedOperationKind POK,
                          AccessKind AK, SourceLocation Loc) override {
-    assert((POK == POK_VarAccess || POK == POK_VarDereference) &&
-           "Only works for variables");
-    unsigned DiagID = POK == POK_VarAccess?
-                        diag::warn_variable_requires_any_lock:
-                        diag::warn_var_deref_requires_any_lock;
+    unsigned DiagID = 0;
+    switch (POK) {
+    case POK_VarAccess:
+    case POK_PassByRef:
+    case POK_ReturnByRef:
+    case POK_PassPointer:
+    case POK_ReturnPointer:
+      DiagID = diag::warn_variable_requires_any_lock;
+      break;
+    case POK_VarDereference:
+    case POK_PtPassByRef:
+    case POK_PtReturnByRef:
+    case POK_PtPassPointer:
+    case POK_PtReturnPointer:
+      DiagID = diag::warn_var_deref_requires_any_lock;
+      break;
+    case POK_FunctionCall:
+      llvm_unreachable("Only works for variables");
+      break;
+    }
     PartialDiagnosticAt Warning(Loc, S.PDiag(DiagID)
       << D << getLockKindFromAccessKind(AK));
     Warnings.emplace_back(std::move(Warning), getNotes());

clang/test/SemaCXX/warn-thread-safety-analysis.cpp

@@ -6196,6 +6196,8 @@ class Return {
   Mutex mu;
   Foo foo GUARDED_BY(mu);
   Foo* foo_ptr PT_GUARDED_BY(mu);
+  Foo foo_depr GUARDED_VAR;          // test deprecated attribute
+  Foo* foo_ptr_depr PT_GUARDED_VAR;  // test deprecated attribute
 
   Foo returns_value_locked() {
     MutexLock lock(&mu);
@@ -6297,6 +6299,18 @@ class Return {
     return *foo_ptr;          // expected-warning {{returning the value that 'foo_ptr' points to by reference requires holding mutex 'mu' exclusively}}
   }
 
+  Foo *returns_ptr_deprecated() {
+    return &foo_depr;          // expected-warning {{writing variable 'foo_depr' requires holding any mutex exclusively}}
+  }
+
+  Foo *returns_pt_ptr_deprecated() {
+    return foo_ptr_depr;       // expected-warning {{writing the value pointed to by 'foo_ptr_depr' requires holding any mutex exclusively}}
+  }
+
+  Foo &returns_ref_deprecated() {
+    return *foo_ptr_depr;      // expected-warning {{writing the value pointed to by 'foo_ptr_depr' requires holding any mutex exclusively}}
+  }
+
   // FIXME: Basic alias analysis would help catch cases like below.
   Foo *returns_ptr_alias() {
     mu.Lock();