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diff --git a/clang-r344140b/include/llvm/Support/MutexGuard.h b/clang-r344140b/include/llvm/Support/MutexGuard.h
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+++ b/clang-r344140b/include/llvm/Support/MutexGuard.h
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+//===-- Support/MutexGuard.h - Acquire/Release Mutex In Scope ---*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a guard for a block of code that ensures a Mutex is locked
+// upon construction and released upon destruction.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_MUTEXGUARD_H
+#define LLVM_SUPPORT_MUTEXGUARD_H
+
+#include "llvm/Support/Mutex.h"
+
+namespace llvm {
+  /// Instances of this class acquire a given Mutex Lock when constructed and
+  /// hold that lock until destruction. The intention is to instantiate one of
+  /// these on the stack at the top of some scope to be assured that C++
+  /// destruction of the object will always release the Mutex and thus avoid
+  /// a host of nasty multi-threading problems in the face of exceptions, etc.
+  /// Guard a section of code with a Mutex.
+  class MutexGuard {
+    sys::Mutex &M;
+    MutexGuard(const MutexGuard &) = delete;
+    void operator=(const MutexGuard &) = delete;
+  public:
+    MutexGuard(sys::Mutex &m) : M(m) { M.lock(); }
+    ~MutexGuard() { M.unlock(); }
+    /// holds - Returns true if this locker instance holds the specified lock.
+    /// This is mostly used in assertions to validate that the correct mutex
+    /// is held.
+    bool holds(const sys::Mutex& lock) const { return &M == &lock; }
+  };
+}
+
+#endif // LLVM_SUPPORT_MUTEXGUARD_H