I am trying to compile a code in C , that uses over-aligned variables. If I try to compile the following code (a MWE)

#include <new>
#include <iostream>

int main()
{
    alignas(32) double *r = new (std::align_val_t{32}) double[3];
    std::cout << "alignof(r) is " << alignof(r) << '\n';
    return 0;
}

everything runs smoothly if I use icpx or g (in all the cases, the flag -std=c 17 is given to the compiler). However, when compiling using Intel icpc, I got the following error

mwe.cpp(6): error: no instance of overloaded "operator new[]" matches the argument list
            argument types are: (unsigned long, std::align_val_t)
      alignas(32) double *r = new (std::align_val_t{32}) double[3];
                              ^
/usr/include/c  /9/new(175): note: this candidate was rejected because arguments do not match
  _GLIBCXX_NODISCARD inline void* operator new[](std::size_t, void* __p) _GLIBCXX_USE_NOEXCEPT
                                  ^
/usr/include/c  /9/new(141): note: this candidate was rejected because arguments do not match
  _GLIBCXX_NODISCARD void* operator new[](std::size_t, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
                           ^
/usr/include/c  /9/new(127): note: this candidate was rejected because mismatch in count of arguments
  _GLIBCXX_NODISCARD void* operator new[](std::size_t) _GLIBCXX_THROW (std::bad_alloc)
                           ^

mwe.cpp(7): warning #3464: the standard "alignof" operator does not accept an expression argument (use a type instead)
      std::cout << "alignof(r) is " << alignof(r) << '\n';
                                              ^

compilation aborted for mwe.cpp (code 2)

and I do not understand what the error can be. How can I solve this issue?

CodePudding user response：

It seems that icpc fails to conform with the standard with aligned allocations. Quoting from the documentations for version 2021.5:

In this release of the compiler, all that is necessary in order to get correct dynamic allocation for aligned data is to include a new header:

#include <aligned_new>

After this header is included, a new-expression for any aligned type will automatically allocate memory with the alignment of that type.

Link: https://www.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/optimization-and-programming-guide/automatically-aligned-dynamic-allocation/automatically-aligned-dynamic-allocation-1.html

Live demo: https://godbolt.org/z/5xMqKGrTG

This section is missing in the documentation of icpx: https://www.intel.com/content/www/us/en/develop/documentation/oneapi-dpcpp-cpp-compiler-dev-guide-and-reference/top.html.