[clang] Thread Safety Analysis: Support reentrant capabilities (PR #137133)

[Marco Elver via cfe-commits]

================
@@ -271,26 +271,32 @@ class CFGWalker {
 // translateAttrExpr needs it, but that should be moved too.
 class CapabilityExpr {
 private:
-  /// The capability expression and whether it's negated.
-  llvm::PointerIntPair<const til::SExpr *, 1, bool> CapExpr;
+  /// The capability expression and flags.
+  llvm::PointerIntPair<const til::SExpr *, 2, unsigned> CapExpr;
 
   /// The kind of capability as specified by @ref CapabilityAttr::getName.
   StringRef CapKind;
 
 public:
-  CapabilityExpr() : CapExpr(nullptr, false) {}
-  CapabilityExpr(const til::SExpr *E, StringRef Kind, bool Neg)
-      : CapExpr(E, Neg), CapKind(Kind) {}
+  static constexpr unsigned FlagNegative = 1u << 0;
+  static constexpr unsigned FlagReentrant = 1u << 1;
----------------
melver wrote:

We need 4 states.

I'm adding this test:
```
+class TestNegativeWithReentrantMutex {
+  ReentrantMutex rmu;
+  int a GUARDED_BY(rmu);
+
+public:
+  void baz() EXCLUSIVE_LOCKS_REQUIRED(!rmu) {
+    rmu.Lock();
+    a = 0;
+    rmu.Unlock();
+  }
+};
```

https://github.com/llvm/llvm-project/pull/137133