testing/gtest/benchmark/BlackBox.h

   1 // Copyright 2015 Google Inc. All rights reserved.
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //     http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 #ifndef GTEST_BLACKBOX_H
  16 #define GTEST_BLACKBOX_H
  17
  18 #include "mozilla/Attributes.h"
  19 #if defined(_MSC_VER)
  20 #  include <intrin.h>
  21 #endif  // _MSC_VER
  22
  23 namespace mozilla {
  24
  25 #if defined(_MSC_VER)
  26
  27 char volatile* UseCharPointer(char volatile*);
  28
  29 MOZ_ALWAYS_INLINE_EVEN_DEBUG void* BlackBoxVoidPtr(void* aPtr) {
  30   aPtr = const_cast<char*>(UseCharPointer(reinterpret_cast<char*>(aPtr)));
  31   _ReadWriteBarrier();
  32   return aPtr;
  33 }
  34
  35 #else
  36
  37 // See: https://youtu.be/nXaxk27zwlk?t=2441
  38 MOZ_ALWAYS_INLINE_EVEN_DEBUG void* BlackBoxVoidPtr(void* aPtr) {
  39   // "g" is what we want here, but the comment in the Google
  40   // benchmark code suggests that GCC likes "i,r,m" better.
  41   // However, on Mozilla try server i,r,m breaks GCC but g
  42   // works in GCC, so using g for both clang and GCC.
  43   // godbolt.org indicates that g works already in GCC 4.9,
  44   // which is the oldest GCC we support at the time of this
  45   // code landing. godbolt.org suggests that this clearly
  46   // works is LLVM 5, but it's unclear if this inhibits
  47   // all relevant optimizations properly on earlier LLVM.
  48   asm volatile("" : "+g"(aPtr) : "g"(aPtr) : "memory");
  49   return aPtr;
  50 }
  51
  52 #endif  // _MSC_VER
  53
  54 template <class T>
  55 MOZ_ALWAYS_INLINE_EVEN_DEBUG T* BlackBox(T* aPtr) {
  56   return static_cast<T*>(BlackBoxVoidPtr(aPtr));
  57 }
  58
  59 }  // namespace mozilla
  60
  61 #endif  // GTEST_BLACKBOX_H