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

[Marco Elver via cfe-commits]

================
@@ -235,6 +266,20 @@ class FactSet {
     return false;
   }
 
+  std::optional<FactID> replaceLock(FactManager &FM, iterator It,
+                                    std::unique_ptr<FactEntry> Entry) {
+    if (It == end())
+      return std::nullopt;
+    FactID F = FM.newFact(std::move(Entry));
+    *It = F;
+    return F;
+  }
+
+  std::optional<FactID> replaceLock(FactManager &FM, const CapabilityExpr &CapE,
+                                    std::unique_ptr<FactEntry> Entry) {
+    return replaceLock(FM, findLockIter(FM, CapE), std::move(Entry));
+  }
+
----------------
melver wrote:

We could, but it's less efficient, esp. if we used findLockIter():
1. without findLockIter: we save a pop_back() and push_back().
2. with preceding findLockIter: like (1), but also saves a search.

Sure, maybe we're just shaving off some constant overheads, but I also find it makes it less verbose and more readable.

I have this later patch I would send out as a separate PR later:
```
commit 9a41f2b68a28e6a2239b45a11a0cd360dce320af
Author: Marco Elver <elver at google.com>
Date:   Fri Apr 25 18:51:16 2025 +0200

    Thread Safety Analysis: Use replaceLock instead of removeLock+addLock

    In ScopedLockableFactEntry::unlock(), we can avoid a second search,
    pop_back(), and push_back() if we use the already obtained iterator into
    the FactSet to replace the old FactEntry and take its position in the
    vector.

diff --git a/clang/lib/Analysis/ThreadSafety.cpp b/clang/lib/Analysis/ThreadSafety.cpp
index cb62f11d6f15..429f22715886 100644
--- a/clang/lib/Analysis/ThreadSafety.cpp
+++ b/clang/lib/Analysis/ThreadSafety.cpp
@@ -1090,9 +1090,9 @@ private:
         return;
       }

-      FSet.removeLock(FactMan, Cp);
-      FSet.addLock(FactMan,
-                   std::make_unique<LockableFactEntry>(!Cp, LK_Exclusive, loc));
+      FSet.replaceLock(
+          FactMan, It,
+          std::make_unique<LockableFactEntry>(!Cp, LK_Exclusive, loc));
     } else if (Handler) {
       SourceLocation PrevLoc;
       if (const FactEntry *Neg = FSet.findLock(FactMan, !Cp))
```


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