[Support/CrashRecoveryContext] Make sure CrashRecoveryContext does no…

…t clear the thread-local "CurrentContext"

in the "parent" thread, when we are using CrashRecoveryContext::RunSafelyOnThread.

When using CrashRecoveryContext::RunSafelyOnThread, we would set a CrashRecoveryContextImpl* to a thread-local variable
for the "child" thread, but CrashRecoveryContext would erroneously clear it in the "parent" thread.

The result was that if CrashRecoveryContext::RunSafelyOnThread was called again in the "child" thread it would mess up
crash-recovery for its parent.

A test for this will be added in the clang repository.
rdar://14204560

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184380 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/CrashRecoveryContext.cpp

@@ -28,16 +28,23 @@ struct CrashRecoveryContextImpl {
   std::string Backtrace;
   ::jmp_buf JumpBuffer;
   volatile unsigned Failed : 1;
+  unsigned SwitchedThread : 1;
 
 public:
   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
-                                                        Failed(false) {
+                                                        Failed(false),
+                                                        SwitchedThread(false) {
     CurrentContext.set(this);
   }
   ~CrashRecoveryContextImpl() {
-    CurrentContext.erase();
+    if (!SwitchedThread)
+      CurrentContext.erase();
   }
 
+  /// \brief Called when the separate crash-recovery thread was finished, to
+  /// indicate that we don't need to clear the thread-local CurrentContext.
+  void setSwitchedThread() { SwitchedThread = true; }
+
   void HandleCrash() {
     // Eliminate the current context entry, to avoid re-entering in case the
     // cleanup code crashes.
@@ -342,5 +349,7 @@ bool CrashRecoveryContext::RunSafelyOnThread(void (*Fn)(void*), void *UserData,
                                              unsigned RequestedStackSize) {
   RunSafelyOnThreadInfo Info = { Fn, UserData, this, false };
   llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
+  if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl)
+    CRC->setSwitchedThread();
   return Info.Result;
 }