mariadb/include/my_compiler.h

#ifndef MY_COMPILER_INCLUDED
#define MY_COMPILER_INCLUDED

/* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
   Copyright (c) 2017, 2020, MariaDB Corporation.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */

/**
  Header for compiler-dependent features.

  Intended to contain a set of reusable wrappers for preprocessor
  macros, attributes, pragmas, and any other features that are
  specific to a target compiler.
*/

/**
  Compiler-dependent internal convenience macros.
*/

/* C vs C++ */
#ifdef __cplusplus
#define CONSTEXPR constexpr
#else
#define CONSTEXPR
#endif /* __cplusplus */


/* GNU C/C++ */
#if defined __GNUC__
/* Convenience macro to test the minimum required GCC version. */
# define MY_GNUC_PREREQ(maj, min) \
    ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
/* Any after 2.95... */
# define MY_ALIGN_EXT
/* Comunicate to the compiler the unreachability of the code. */
# if MY_GNUC_PREREQ(4,5)
#   define MY_ASSERT_UNREACHABLE()   __builtin_unreachable()
# endif

/* Microsoft Visual C++ */
#elif defined _MSC_VER
# define MY_ALIGNOF(type)   __alignof(type)
# define MY_ALIGNED(n)      __declspec(align(n))

/* Oracle Solaris Studio */
#elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
# if __SUNPRO_C >= 0x590
#   define MY_ALIGN_EXT
# endif

/* IBM XL C/C++ */
#elif defined __xlC__
# if __xlC__ >= 0x0600
#   define MY_ALIGN_EXT
# endif

/* HP aCC */
#elif defined(__HP_aCC) || defined(__HP_cc)
# if (__HP_aCC >= 60000) || (__HP_cc >= 60000)
#   define MY_ALIGN_EXT
# endif
#endif

#ifdef MY_ALIGN_EXT
/** Specifies the minimum alignment of a type. */
# define MY_ALIGNOF(type)   __alignof__(type)
/** Determine the alignment requirement of a type. */
# define MY_ALIGNED(n)      __attribute__((__aligned__((n))))
#endif

/**
  Generic (compiler-independent) features.
*/

#ifndef MY_GNUC_PREREQ
# define MY_GNUC_PREREQ(maj, min) (0)
#endif

#ifndef MY_ALIGNOF
# ifdef __cplusplus
    template<typename type> struct my_alignof_helper { char m1; type m2; };
    /* Invalid for non-POD types, but most compilers give the right answer. */
#   define MY_ALIGNOF(type)   offsetof(my_alignof_helper<type>, m2)
# else
#   define MY_ALIGNOF(type)   offsetof(struct { char m1; type m2; }, m2)
# endif
#endif

#ifndef MY_ASSERT_UNREACHABLE
# define MY_ASSERT_UNREACHABLE()  do { assert(0); } while (0)
#endif

/**
  C++ Type Traits
*/

#ifdef __cplusplus

/**
  Opaque storage with a particular alignment.
*/
# if defined(MY_ALIGNED)
/* Partial specialization used due to MSVC++. */
template<size_t alignment> struct my_alignment_imp;
template<> struct MY_ALIGNED(1) my_alignment_imp<1> {};
template<> struct MY_ALIGNED(2) my_alignment_imp<2> {};
template<> struct MY_ALIGNED(4) my_alignment_imp<4> {};
template<> struct MY_ALIGNED(8) my_alignment_imp<8> {};
template<> struct MY_ALIGNED(16) my_alignment_imp<16> {};
/* ... expand as necessary. */
# else
template<size_t alignment>
struct my_alignment_imp { double m1; };
# endif

/**
  A POD type with a given size and alignment.

  @remark If the compiler does not support a alignment attribute
          (MY_ALIGN macro), the default alignment of a double is
          used instead.

  @tparam size        The minimum size.
  @tparam alignment   The desired alignment: 1, 2, 4, 8 or 16.
*/
template <size_t size, size_t alignment>
struct my_aligned_storage
{
  union
  {
    char data[size];
    my_alignment_imp<alignment> align;
  };
};

#endif /* __cplusplus */

# ifndef MY_ALIGNED
/*
  Make sure MY_ALIGNED can be used also on platforms where we don't
  have a way of aligning data structures.
*/
#define MY_ALIGNED(size)
#endif

#ifdef __GNUC__
# define ATTRIBUTE_NORETURN __attribute__((noreturn))
# define ATTRIBUTE_NOINLINE __attribute__((noinline))
# if MY_GNUC_PREREQ(4,3)
/** Starting with GCC 4.3, the "cold" attribute is used to inform the
compiler that a function is unlikely executed.  The function is
optimized for size rather than speed and on many targets it is placed
into special subsection of the text section so all cold functions
appears close together improving code locality of non-cold parts of
program.  The paths leading to call of cold functions within code are
marked as unlikely by the branch prediction mechanism.  optimize a
rarely invoked function for size instead for speed. */
#  define ATTRIBUTE_COLD __attribute__((cold))
# endif
#elif defined _MSC_VER
# define ATTRIBUTE_NORETURN __declspec(noreturn)
# define ATTRIBUTE_NOINLINE __declspec(noinline)
#else
# define ATTRIBUTE_NORETURN /* empty */
# define ATTRIBUTE_NOINLINE /* empty */
#endif

#ifndef ATTRIBUTE_COLD
# define ATTRIBUTE_COLD /* empty */
#endif

#include <my_attribute.h>

#endif /* MY_COMPILER_INCLUDED */