check-interference-sizes

M4 macro for autoconf to check C++ interference sizes

Unfortunately, many new features of the C ++ standard have not yet been implemented by compilers.

Moreover, compiler check macros often erroneously report the presence of a feature, but there is no implementation.

According to this article, in order to check the possibility of using this feature during configuration, before compilation, an M4 macro was implemented that performs this check.

Macro set specified environment variable to 1 when compilation and run successful (i.e. interference sizes defined and implemented) and 0 otherwise.

To use, add a macro to configure.ac as shown below (for C++ code):

dnl Check if interference_sizes are defined
if test "$HAVE_CXX17" = "1"; then
  AX_INTERFERENCE_SIZES([INTERFERENCE_SIZES])
  if test "$INTERFERENCE_SIZES" = "1"; then
    CXXFLAGS="$CXXFLAGS -DINTERFERENCE_SIZES"
  fi
fi

where the variable HAVE_CXX17 is set earlier by the following code:

dnl If the user did not specify a C++ version.
user_cxx=`echo "$PRESET_CXXFLAGS" | $EGREP -o -E "\-std="`
if test "x$user_cxx" = "x"; then
  dnl Set highest possible C++ support
  AX_CXX_COMPILE_STDCXX(17, [noext], [optional])
  if test "$HAVE_CXX17" = "0"; then
    AX_CXX_COMPILE_STDCXX(14, [noext], [optional])
  elif test "$HAVE_CXX14" = "0"; then
    AX_CXX_COMPILE_STDCXX(11, [noext], [mandatory])
  fi
fi

ACTION-IF-FOUND sets the variable INTERFERENCE_SIZES, which is uses for conditional compilation when determining the size of the cache line (with fallback branch):

#ifndef CACHE_LINE_SIZE
#	if __cpp_lib_hardware_interference_size >= 201703 && defined INTERFERENCE_SIZES
#		define CACHE_LINE_SIZE std::hardware_destructive_interference_size
#	elif __cplusplus >= 201402L
#		define CACHE_LINE_SIZE (2 * sizeof(std::max_align_t) & (2 * sizeof(std::max_align_t) - 1)) == 0 ? \
					2 * sizeof(std::max_align_t) : nearestPowerOf2(2 * sizeof(std::max_align_t))
#	else
#		define CACHE_LINE_SIZE 64
#	endif
#endif