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diff --git a/testing/gtest/benchmark/BlackBox.h b/testing/gtest/benchmark/BlackBox.h
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+++ b/testing/gtest/benchmark/BlackBox.h
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+// Copyright 2015 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef GTEST_BLACKBOX_H
+#define GTEST_BLACKBOX_H
+
+#include "mozilla/Attributes.h"
+#if defined(_MSC_VER)
+#  include <intrin.h>
+#endif  // _MSC_VER
+
+namespace mozilla {
+
+#if defined(_MSC_VER)
+
+char volatile* UseCharPointer(char volatile*);
+
+MOZ_ALWAYS_INLINE_EVEN_DEBUG void* BlackBoxVoidPtr(void* aPtr) {
+  aPtr = const_cast<char*>(UseCharPointer(reinterpret_cast<char*>(aPtr)));
+  _ReadWriteBarrier();
+  return aPtr;
+}
+
+#else
+
+// See: https://youtu.be/nXaxk27zwlk?t=2441
+MOZ_ALWAYS_INLINE_EVEN_DEBUG void* BlackBoxVoidPtr(void* aPtr) {
+  // "g" is what we want here, but the comment in the Google
+  // benchmark code suggests that GCC likes "i,r,m" better.
+  // However, on Mozilla try server i,r,m breaks GCC but g
+  // works in GCC, so using g for both clang and GCC.
+  // godbolt.org indicates that g works already in GCC 4.9,
+  // which is the oldest GCC we support at the time of this
+  // code landing. godbolt.org suggests that this clearly
+  // works is LLVM 5, but it's unclear if this inhibits
+  // all relevant optimizations properly on earlier LLVM.
+  asm volatile("" : "+g"(aPtr) : "g"(aPtr) : "memory");
+  return aPtr;
+}
+
+#endif  // _MSC_VER
+
+template <class T>
+MOZ_ALWAYS_INLINE_EVEN_DEBUG T* BlackBox(T* aPtr) {
+  return static_cast<T*>(BlackBoxVoidPtr(aPtr));
+}
+
+}  // namespace mozilla
+
+#endif  // GTEST_BLACKBOX_H