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 CRASHREPORTING_LLVM_SUPPORT_COMPILER_H
  #define CRASHREPORTING_LLVM_SUPPORT_COMPILER_H
  
  #include "llvm-config.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
  
  /// \macro LLVM_MSC_PREREQ
  /// \brief Is the compiler MSVC of at least the specified version?
  /// The common \param version values to check for are:
  ///  * 1800: Microsoft Visual Studio 2013 / 12.0
  ///  * 1900: Microsoft Visual Studio 2015 / 14.0
  #ifdef _MSC_VER
  #define LLVM_MSC_PREREQ(version) (_MSC_VER >= (version))
  
  // We require at least MSVC 2013.
  #if !LLVM_MSC_PREREQ(1800)
  #error LLVM requires at least MSVC 2013.
  #endif
  
  #else
  #define LLVM_MSC_PREREQ(version) 0
  #endif
  
  #if !defined(_MSC_VER) || defined(__clang__) || LLVM_MSC_PREREQ(1900)
  #define LLVM_NOEXCEPT noexcept
  #else
  #define LLVM_NOEXCEPT throw()
  #endif
  
  /// \brief Does the compiler support ref-qualifiers for *this?
  ///
  /// Sadly, this is separate from just rvalue reference support because GCC
  /// and MSVC implemented this later than everything else.
  #if __has_feature(cxx_rvalue_references) || LLVM_GNUC_PREREQ(4, 8, 1)
  #define LLVM_HAS_RVALUE_REFERENCE_THIS 1
  #else
  #define LLVM_HAS_RVALUE_REFERENCE_THIS 0
  #endif
  
  /// Expands to '&' if ref-qualifiers for *this are supported.
  ///
  /// This can be used to provide lvalue/rvalue overrides of member functions.
  /// The rvalue override should be guarded by LLVM_HAS_RVALUE_REFERENCE_THIS
  #if LLVM_HAS_RVALUE_REFERENCE_THIS
  #define LLVM_LVALUE_FUNCTION &
  #else
  #define LLVM_LVALUE_FUNCTION
  #endif
  
  #if __has_feature(cxx_constexpr) || defined(__GXX_EXPERIMENTAL_CXX0X__)
  # define LLVM_CONSTEXPR constexpr
  #else
  # define LLVM_CONSTEXPR
  #endif
  
  /// LLVM_LIBRARY_VISIBILITY - If a class marked with this attribute is linked
  /// into a shared library, then the class should be private to the library and
  /// not accessible from outside it.  Can also be used to mark variables and
  /// functions, making them private to any shared library they are linked into.
  /// On PE/COFF targets, library visibility is the default, so this isn't needed.
  #if (__has_attribute(visibility) || LLVM_GNUC_PREREQ(4, 0, 0)) &&              \
      !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32)
  #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
  #else
  #define LLVM_LIBRARY_VISIBILITY
  #endif
  
  #if __has_attribute(sentinel) || LLVM_GNUC_PREREQ(3, 0, 0)
  #define LLVM_END_WITH_NULL __attribute__((sentinel))
  #else
  #define LLVM_END_WITH_NULL
  #endif
  
  #if __has_attribute(used) || LLVM_GNUC_PREREQ(3, 1, 0)
  #define LLVM_ATTRIBUTE_USED __attribute__((__used__))
  #else
  #define LLVM_ATTRIBUTE_USED
  #endif
  
  #if __has_attribute(warn_unused_result) || LLVM_GNUC_PREREQ(3, 4, 0)
  #define LLVM_ATTRIBUTE_UNUSED_RESULT __attribute__((__warn_unused_result__))
  #else
  #define LLVM_ATTRIBUTE_UNUSED_RESULT
  #endif
  
  // Some compilers warn about unused functions. When a function is sometimes
  // used or not depending on build settings (e.g. a function only called from
  // within "assert"), this attribute can be used to suppress such warnings.
  //
  // However, it shouldn't be used for unused *variables*, as those have a much
  // more portable solution:
  //   (void)unused_var_name;
  // Prefer cast-to-void wherever it is sufficient.
  #if __has_attribute(unused) || LLVM_GNUC_PREREQ(3, 1, 0)
  #define LLVM_ATTRIBUTE_UNUSED __attribute__((__unused__))
  #else
  #define LLVM_ATTRIBUTE_UNUSED
  #endif
  
  // FIXME: Provide this for PE/COFF targets.
  #if (__has_attribute(weak) || LLVM_GNUC_PREREQ(4, 0, 0)) &&                    \
      (!defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32))
  #define LLVM_ATTRIBUTE_WEAK __attribute__((__weak__))
  #else
  #define LLVM_ATTRIBUTE_WEAK
  #endif
  
  // Prior to clang 3.2, clang did not accept any spelling of
  // __has_attribute(const), so assume it is supported.
  #if defined(__clang__) || defined(__GNUC__)
  // aka 'CONST' but following LLVM Conventions.
  #define LLVM_READNONE __attribute__((__const__))
  #else
  #define LLVM_READNONE
  #endif
  
  #if __has_attribute(pure) || defined(__GNUC__)
  // aka 'PURE' but following LLVM Conventions.
  #define LLVM_READONLY __attribute__((__pure__))
  #else
  #define LLVM_READONLY
  #endif
  
  #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
  
  /// LLVM_ATTRIBUTE_NOINLINE - On compilers where we have a directive to do so,
  /// mark a method "not for inlining".
  #if __has_attribute(noinline) || LLVM_GNUC_PREREQ(3, 4, 0)
  #define LLVM_ATTRIBUTE_NOINLINE __attribute__((noinline))
  #elif defined(_MSC_VER)
  #define LLVM_ATTRIBUTE_NOINLINE __declspec(noinline)
  #else
  #define LLVM_ATTRIBUTE_NOINLINE
  #endif
  
  /// LLVM_ATTRIBUTE_ALWAYS_INLINE - On compilers where we have a directive to do
  /// so, mark a method "always inline" because it is performance sensitive. GCC
  /// 3.4 supported this but is buggy in various cases and produces unimplemented
  /// errors, just use it in GCC 4.0 and later.
  #if __has_attribute(always_inline) || LLVM_GNUC_PREREQ(4, 0, 0)
  #define LLVM_ATTRIBUTE_ALWAYS_INLINE __attribute__((always_inline))
  #elif defined(_MSC_VER)
  #define LLVM_ATTRIBUTE_ALWAYS_INLINE __forceinline
  #else
  #define LLVM_ATTRIBUTE_ALWAYS_INLINE
  #endif
  
  #ifdef __GNUC__
  #define LLVM_ATTRIBUTE_NORETURN __attribute__((noreturn))
  #elif defined(_MSC_VER)
  #define LLVM_ATTRIBUTE_NORETURN __declspec(noreturn)
  #else
  #define LLVM_ATTRIBUTE_NORETURN
  #endif
  
  #if __has_attribute(returns_nonnull) || LLVM_GNUC_PREREQ(4, 9, 0)
  #define LLVM_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull))
  #else
  #define LLVM_ATTRIBUTE_RETURNS_NONNULL
  #endif
  
  /// \macro LLVM_ATTRIBUTE_RETURNS_NOALIAS Used to mark a function as returning a
  /// pointer that does not alias any other valid pointer.
  #ifdef __GNUC__
  #define LLVM_ATTRIBUTE_RETURNS_NOALIAS __attribute__((__malloc__))
  #elif defined(_MSC_VER)
  #define LLVM_ATTRIBUTE_RETURNS_NOALIAS __declspec(restrict)
  #else
  #define LLVM_ATTRIBUTE_RETURNS_NOALIAS
  #endif
  
  /// LLVM_EXTENSION - Support compilers where we have a keyword to suppress
  /// pedantic diagnostics.
  #ifdef __GNUC__
  #define LLVM_EXTENSION __extension__
  #else
  #define LLVM_EXTENSION
  #endif
  
  // LLVM_ATTRIBUTE_DEPRECATED(decl, "message")
  #if __has_feature(attribute_deprecated_with_message)
  # define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
    decl __attribute__((deprecated(message)))
  #elif defined(__GNUC__)
  # define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
    decl __attribute__((deprecated))
  #elif defined(_MSC_VER)
  # define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
    __declspec(deprecated(message)) decl
  #else
  # define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
    decl
  #endif
  
  /// LLVM_BUILTIN_UNREACHABLE - On compilers which support it, expands
  /// to an expression which states that it is undefined behavior for the
  /// compiler to reach this point.  Otherwise is not defined.
  #if __has_builtin(__builtin_unreachable) || LLVM_GNUC_PREREQ(4, 5, 0)
  # define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
  #elif defined(_MSC_VER)
  # define LLVM_BUILTIN_UNREACHABLE __assume(false)
  #endif
  
  /// LLVM_BUILTIN_TRAP - On compilers which support it, expands to an expression
  /// which causes the program to exit abnormally.
  #if __has_builtin(__builtin_trap) || LLVM_GNUC_PREREQ(4, 3, 0)
  # define LLVM_BUILTIN_TRAP __builtin_trap()
  #elif defined(_MSC_VER)
  // The __debugbreak intrinsic is supported by MSVC, does not require forward
  // declarations involving platform-specific typedefs (unlike RaiseException),
  // results in a call to vectored exception handlers, and encodes to a short
  // instruction that still causes the trapping behavior we want.
  # define LLVM_BUILTIN_TRAP __debugbreak()
  #else
  # define LLVM_BUILTIN_TRAP *(volatile int*)0x11 = 0
  #endif
  
  /// \macro LLVM_ASSUME_ALIGNED
  /// \brief Returns a pointer with an assumed alignment.
  #if __has_builtin(__builtin_assume_aligned) || LLVM_GNUC_PREREQ(4, 7, 0)
  # define LLVM_ASSUME_ALIGNED(p, a) __builtin_assume_aligned(p, a)
  #elif defined(LLVM_BUILTIN_UNREACHABLE)
  // As of today, clang does not support __builtin_assume_aligned.
  # define LLVM_ASSUME_ALIGNED(p, a) \
             (((uintptr_t(p) % (a)) == 0) ? (p) : (LLVM_BUILTIN_UNREACHABLE, (p)))
  #else
  # define LLVM_ASSUME_ALIGNED(p, a) (p)
  #endif
  
  /// \macro LLVM_ALIGNAS
  /// \brief Used to specify a minimum alignment for a structure or variable. The
  /// alignment must be a constant integer. Use LLVM_PTR_SIZE to compute
  /// alignments in terms of the size of a pointer.
  ///
  /// Note that __declspec(align) has special quirks, it's not legal to pass a
  /// structure with __declspec(align) as a formal parameter.
  #ifdef _MSC_VER
  # define LLVM_ALIGNAS(x) __declspec(align(x))
  #elif __GNUC__ && !__has_feature(cxx_alignas) && !LLVM_GNUC_PREREQ(4, 8, 0)
  # define LLVM_ALIGNAS(x) __attribute__((aligned(x)))
  #else
  # define LLVM_ALIGNAS(x) alignas(x)
  #endif
  
  /// \macro LLVM_PACKED
  /// \brief Used to specify a packed structure.
  /// LLVM_PACKED(
  ///    struct A {
  ///      int i;
  ///      int j;
  ///      int k;
  ///      long long l;
  ///   });
  ///
  /// LLVM_PACKED_START
  /// struct B {
  ///   int i;
  ///   int j;
  ///   int k;
  ///   long long l;
  /// };
  /// LLVM_PACKED_END 
  #ifdef _MSC_VER
  # define LLVM_PACKED(d) __pragma(pack(push, 1)) d __pragma(pack(pop))
  # define LLVM_PACKED_START __pragma(pack(push, 1))
  # define LLVM_PACKED_END   __pragma(pack(pop))
  #else
  # define LLVM_PACKED(d) d __attribute__((packed))
  # define LLVM_PACKED_START _Pragma("pack(push, 1)")
  # define LLVM_PACKED_END   _Pragma("pack(pop)")
  #endif
  
  /// \macro LLVM_PTR_SIZE
  /// \brief A constant integer equivalent to the value of sizeof(void*).
  /// Generally used in combination with LLVM_ALIGNAS or when doing computation in
  /// the preprocessor.
  #ifdef __SIZEOF_POINTER__
  # define LLVM_PTR_SIZE __SIZEOF_POINTER__
  #elif defined(_WIN64)
  # define LLVM_PTR_SIZE 8
  #elif defined(_WIN32)
  # define LLVM_PTR_SIZE 4
  #elif defined(_MSC_VER)
  # error "could not determine LLVM_PTR_SIZE as a constant int for MSVC"
  #else
  # define LLVM_PTR_SIZE sizeof(void *)
  #endif
  
  /// \macro LLVM_FUNCTION_NAME
  /// \brief Expands to __func__ on compilers which support it.  Otherwise,
  /// expands to a compiler-dependent replacement.
  #if defined(_MSC_VER)
  # define LLVM_FUNCTION_NAME __FUNCTION__
  #else
  # define LLVM_FUNCTION_NAME __func__
  #endif
  
  /// \macro LLVM_MEMORY_SANITIZER_BUILD
  /// \brief Whether LLVM itself is built with MemorySanitizer instrumentation.
  #if __has_feature(memory_sanitizer)
  # define LLVM_MEMORY_SANITIZER_BUILD 1
  # include <sanitizer/msan_interface.h>
  #else
  # define LLVM_MEMORY_SANITIZER_BUILD 0
  # define __msan_allocated_memory(p, size)
  # define __msan_unpoison(p, size)
  #endif
  
  /// \macro LLVM_ADDRESS_SANITIZER_BUILD
  /// \brief Whether LLVM itself is built with AddressSanitizer instrumentation.
  #if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
  # define LLVM_ADDRESS_SANITIZER_BUILD 1
  # include <sanitizer/asan_interface.h>
  #else
  # define LLVM_ADDRESS_SANITIZER_BUILD 0
  # define __asan_poison_memory_region(p, size)
  # define __asan_unpoison_memory_region(p, size)
  #endif
  
  /// \macro LLVM_THREAD_SANITIZER_BUILD
  /// \brief Whether LLVM itself is built with ThreadSanitizer instrumentation.
  #if __has_feature(thread_sanitizer) || defined(__SANITIZE_THREAD__)
  # define LLVM_THREAD_SANITIZER_BUILD 1
  #else
  # define LLVM_THREAD_SANITIZER_BUILD 0
  #endif
  
  #if LLVM_THREAD_SANITIZER_BUILD
  // Thread Sanitizer is a tool that finds races in code.
  // See http://code.google.com/p/data-race-test/wiki/DynamicAnnotations .
  // tsan detects these exact functions by name.
  extern "C" {
  void AnnotateHappensAfter(const char *file, int line, const volatile void *cv);
  void AnnotateHappensBefore(const char *file, int line, const volatile void *cv);
  void AnnotateIgnoreWritesBegin(const char *file, int line);
  void AnnotateIgnoreWritesEnd(const char *file, int line);
  }
  
  // This marker is used to define a happens-before arc. The race detector will
  // infer an arc from the begin to the end when they share the same pointer
  // argument.
  # define TsanHappensBefore(cv) AnnotateHappensBefore(__FILE__, __LINE__, cv)
  
  // This marker defines the destination of a happens-before arc.
  # define TsanHappensAfter(cv) AnnotateHappensAfter(__FILE__, __LINE__, cv)
  
  // Ignore any races on writes between here and the next TsanIgnoreWritesEnd.
  # define TsanIgnoreWritesBegin() AnnotateIgnoreWritesBegin(__FILE__, __LINE__)
  
  // Resume checking for racy writes.
  # define TsanIgnoreWritesEnd() AnnotateIgnoreWritesEnd(__FILE__, __LINE__)
  #else
  # define TsanHappensBefore(cv)
  # define TsanHappensAfter(cv)
  # define TsanIgnoreWritesBegin()
  # define TsanIgnoreWritesEnd()
  #endif
  
  /// \brief Mark debug helper function definitions like dump() that should not be
  /// stripped from debug builds.
  // FIXME: Move this to a private config.h as it's not usable in public headers.
  #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  #define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED
  #else
  #define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE
  #endif
  
  /// \macro LLVM_THREAD_LOCAL
  /// \brief A thread-local storage specifier which can be used with globals,
  /// extern globals, and static globals.
  ///
  /// This is essentially an extremely restricted analog to C++11's thread_local
  /// support, and uses that when available. However, it falls back on
  /// platform-specific or vendor-provided extensions when necessary. These
  /// extensions don't support many of the C++11 thread_local's features. You
  /// should only use this for PODs that you can statically initialize to
  /// some constant value. In almost all circumstances this is most appropriate
  /// for use with a pointer, integer, or small aggregation of pointers and
  /// integers.
  #if LLVM_ENABLE_THREADS
  #if __has_feature(cxx_thread_local)
  #define LLVM_THREAD_LOCAL thread_local
  #elif defined(_MSC_VER)
  // MSVC supports this with a __declspec.
  #define LLVM_THREAD_LOCAL __declspec(thread)
  #else
  // Clang, GCC, and other compatible compilers used __thread prior to C++11 and
  // we only need the restricted functionality that provides.
  #define LLVM_THREAD_LOCAL __thread
  #endif
  #else // !LLVM_ENABLE_THREADS
  // If threading is disabled entirely, this compiles to nothing and you get
  // a normal global variable.
  #define LLVM_THREAD_LOCAL
  #endif
  
  #endif
  