`buffer::get_host_access()` can't be compiled with gcc 8.4

[AlexeySachkov]

Describe the bug

While working on some unit-tests for #6815, I discovered that not all host APIs can be compiled with gcc.

To Reproduce

Try to compile the following example with gcc:

#include <sycl/sycl.hpp>

#include <vector>

class A {
public:
  template <int Dimensions, typename T = int>
  void foo(const sycl::range<Dimensions> &range) {
    std::vector<T> data(range.size());
    sycl::buffer<T, Dimensions> buffer(data.data(), range);
    auto accessor = buffer.get_host_access();
    assert(accessor[0] == 42);
  }

  void bar() { foo(sycl::range<1>{10}); }
};

int main() {
  A a;
  a.bar();
  return 0;
}

g++ reproducer.cpp -I path/to/sycl/headers -std=c++17

You will see the following error:

In file included from include/sycl/sycl.hpp:11,
                 from reproducer.cpp:1:
include/sycl/accessor.hpp: In instantiation of ‘auto sycl::_V1::buffer<T, Dimensions, AllocatorT, Enable>::get_host_access(Ts ...) [with Ts = {}; T = int; int dimensions = 1; AllocatorT = sycl::_V1::detail::aligned_allocator<int>; __Enabled = void]’:
reproducer.cpp:11:10:   required from ‘void A::foo(const sycl::_V1::range<Dims>&) [with int Dimensions = 1; T = int]’
reproducer.cpp:15:38:   required from here
include/sycl/accessor.hpp:2805:44: error: ‘IsSameAsBuffer’ was not declared in this scope
             typename = detail::enable_if_t<IsSameAsBuffer<T, Dims>()>>
                                            ^~~~~~~~~~~~~~~~~~~~~~~
include/sycl/accessor.hpp:2805:44: note: suggested alternative: ‘IsSubBuffer’
             typename = detail::enable_if_t<IsSameAsBuffer<T, Dims>()>>
                                            ^~~~~~~~~~~~~~~~~~~~~~~
                                            IsSubBuffer
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template
include/sycl/accessor.hpp:2805:44: error: ‘<typeprefixerror>IsSameAsBuffer’ is not a function template

Additional context

Note that this code can be compiled just fine by clang++. I haven't tried gcc versions other than 8.4

[romanovvlad]

Compiles OK with gcc 9.3.

[uditagarwal97]

Looks like this issue has already been resolved: I tried compiling the reproducer.cpp file from with GCC 8.4 and it compiled fine.
Perhaps, we can close this issue now.