[Support] Fix memory leak in Timer.cpp on shutdown

[aganea]

This used to happen in the global destruction, after main() has exited. Previously, we were re-creating the llvm::TimerGlobals object at this point.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Alexandre Ganea (aganea)

Changes

This used to happen in the global destruction, after main() has exited. Previously, we were re-creating the llvm::TimerGlobals object at this point.

<img width="855" height="270" alt="image" src="https://github.com/user-attachments/assets/757e9416-a74a-406a-841e-d3e4cc6a69a1" />

---

Full diff: https://github.com/llvm/llvm-project/pull/159983.diff

1 Files Affected:

• (modified) llvm/lib/Support/Timer.cpp (+19-4)

diff --git a/llvm/lib/Support/Timer.cpp b/llvm/lib/Support/Timer.cpp
index 75ec299a98376..20f51afe4ee74 100644
--- a/llvm/lib/Support/Timer.cpp
+++ b/llvm/lib/Support/Timer.cpp
@@ -57,6 +57,7 @@ static SignpostEmitter &signposts();
 static sys::SmartMutex<true> &timerLock();
 static TimerGroup &defaultTimerGroup();
 static Name2PairMap &namedGroupedTimers();
+static bool isTimerGlobalsConstructed();
 
 //===----------------------------------------------------------------------===//
 //
@@ -305,14 +306,24 @@ TimerGroup::~TimerGroup() {
     PrintQueuedTimers(*OutStream);
   }
 
+  auto unlink = [&]() {
+    *Prev = Next;
+    if (Next)
+      Next->Prev = Prev;
+  };
+
+  // If the managed instance is already dead, it means we're in the CRT
+  // destruction, so no need to lock.
+  if (!isTimerGlobalsConstructed()) {
+    unlink();
+    return;
+  }
+
   // Remove the group from the TimerGroupList.
   sys::SmartScopedLock<true> L(timerLock());
-  *Prev = Next;
-  if (Next)
-    Next->Prev = Prev;
+  unlink();
 }
 
-
 void TimerGroup::removeTimer(Timer &T) {
   sys::SmartScopedLock<true> L(timerLock());
 
@@ -557,3 +568,7 @@ void TimerGroup::constructForStatistics() {
 }
 
 void *TimerGroup::acquireTimerGlobals() { return ManagedTimerGlobals.claim(); }
+
+static bool isTimerGlobalsConstructed() {
+  return ManagedTimerGlobals.isConstructed();
+}

[MaskRay]

I am confused by this comment.

llvm::TimerGroup::acquireTimerGlobals() frees ManagedStatic. Is the leak due to timerLock() re-constructing the ManagedStatic?

[aganea]

Yes, exactly.

[aganea]

I will clarify the comment.