text: //===-- llvm/Support/Compiler.h - Compiler abstraction support --*- 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 several macros, based on the current compiler.  This allows
  // use of compiler-specific features in a way that remains portable.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_SUPPORT_COMPILER_H
  #define LLVM_SUPPORT_COMPILER_H
  
  #ifndef __has_feature
  # define __has_feature(x) 0
  #endif
  
  #ifndef __has_extension
  # define __has_extension(x) 0
  #endif
  
  #ifndef __has_attribute
  # define __has_attribute(x) 0
  #endif
  
  #ifndef __has_builtin
  # define __has_builtin(x) 0
  #endif
  
  /// \macro LLVM_GNUC_PREREQ
  /// \brief Extend the default __GNUC_PREREQ even if glibc's features.h isn't
  /// available.
  #ifndef LLVM_GNUC_PREREQ
  # if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
  #  define LLVM_GNUC_PREREQ(maj, min, patch) \
      ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >= \
       ((maj) << 20) + ((min) << 10) + (patch))
  # elif defined(__GNUC__) && defined(__GNUC_MINOR__)
  #  define LLVM_GNUC_PREREQ(maj, min, patch) \
      ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
  # else
  #  define LLVM_GNUC_PREREQ(maj, min, patch) 0
  # endif
  #endif
  
  #ifndef LLVM_CONSTEXPR
  # ifdef _MSC_VER
  #  if _MSC_VER >= 1900
  #   define LLVM_CONSTEXPR constexpr
  #  else
  #   define LLVM_CONSTEXPR
  #  endif
  # elif defined(__has_feature)
  #  if __has_feature(cxx_constexpr)
  #   define LLVM_CONSTEXPR constexpr
  #  else
  #   define LLVM_CONSTEXPR
  #  endif
  # elif defined(__GXX_EXPERIMENTAL_CXX0X__)
  #  define LLVM_CONSTEXPR constexpr
  # elif defined(__has_constexpr)
  #  define LLVM_CONSTEXPR constexpr
  # else
  #  define LLVM_CONSTEXPR
  # endif
  #endif
  
  #ifndef LLVM_ATTRIBUTE_UNUSED_RESULT
  #if __has_attribute(warn_unused_result) || LLVM_GNUC_PREREQ(3, 4, 0)
  #define LLVM_ATTRIBUTE_UNUSED_RESULT __attribute__((__warn_unused_result__))
  #elif defined(_MSC_VER)
  #define LLVM_ATTRIBUTE_UNUSED_RESULT _Check_return_
  #else
  #define LLVM_ATTRIBUTE_UNUSED_RESULT
  #endif
  #endif
  
  #ifndef LLVM_UNLIKELY
  #if __has_builtin(__builtin_expect) || LLVM_GNUC_PREREQ(4, 0, 0)
  #define LLVM_LIKELY(EXPR) __builtin_expect((bool)(EXPR), true)
  #define LLVM_UNLIKELY(EXPR) __builtin_expect((bool)(EXPR), false)
  #else
  #define LLVM_LIKELY(EXPR) (EXPR)
  #define LLVM_UNLIKELY(EXPR) (EXPR)
  #endif
  #endif
  
  #endif
  