[HIP]: explicit instantiated constexpr functions calling non-constexpr functions fail to compile (`__host__ __device__` function references `__host__` function)

[MiroPalmu]

Following HIP code doesn't compile (https://godbolt.org/z/9Y16zxv6a):

void fail();

template <typename T>
constexpr void foo(bool x) {
    if (x) fail();
}

template void foo<int>(bool);

<source>:5:12: error: reference to __host__ function 'fail' in __host__ __device__ function
    5 |     if (x) fail();
      |            ^
<source>:8:15: note: in instantiation of function template specialization 'foo<int>' requested here
    8 | template void foo<int>(bool);
      |               ^
<source>:1:6: note: 'fail' declared here
    1 | void fail();
      |      ^
1 error generated when compiling for gfx906.
Compiler returned: 1

In C++ calling non-constexpr functions from constexpr functions is allowed as long as they are not used during compile time.
If I understand correctly, in HIP constexpr functions are implicitly annotated with __host__ __device__ and
this explains the error: reference to __host__ function 'fail' in __host__ __device__ function

However there must be some additional logic which fails for the explicit instantiation as following is accepted (https://godbolt.org/z/7asfWPefs):

void fail();

constexpr void foo(bool x) {
    if (x) fail();
}

This problem comes up when trying to use external library in host code as part of HIP project (e.g. spdlog with bundeled fmt).

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Miro Palmu (MiroPalmu)

Following *HIP* code doesn't compile (https://godbolt.org/z/9Y16zxv6a):

void fail();

template <typename T>
constexpr void foo(bool x) {
    if (x) fail();
}

template void foo<int>(bool);

<source>:5:12: error: reference to __host__ function 'fail' in __host__ __device__ function
    5 |     if (x) fail();
      |            ^
<source>:8:15: note: in instantiation of function template specialization 'foo<int>' requested here
    8 | template void foo<int>(bool);
      |               ^
<source>:1:6: note: 'fail' declared here
    1 | void fail();
      |      ^
1 error generated when compiling for gfx906.
Compiler returned: 1

In C++ calling non-constexpr functions from constexpr functions is allowed as long as they are not used during compile time.
If I understand correctly, in HIP constexpr functions are implicitly annotated with __host__ __device__ and
this explains the error: reference to __host__ function 'fail' in __host__ __device__ function

However there must be some additional logic which fails for the explicit instantiation as following is accepted (https://godbolt.org/z/7asfWPefs):

void fail();

constexpr void foo(bool x) {
    if (x) fail();
}

This problem comes up when trying to use external library in host code as part of HIP project (e.g. spdlog with bundeled fmt).

[MiroPalmu]

Similar thing happens with explicitly instantiated class which derives from class which has member new and delete and virtual destructor (https://godbolt.org/z/h7nsMTh9Y):

#include <cstdlib>

struct Foo {
    static void *operator new(std::size_t len) {
        return std::malloc(len);
    }

    static void operator delete(void * ptr) { std::free(ptr); }

    virtual ~Foo() = default;
};

template <typename T>
struct Bar : Foo { };

template class Bar<int>

<source>:16:16: error: reference to __host__ function 'operator delete' in __host__ __device__ function
   16 | template class Bar<int>;
      |                ^
<source>:16:16: note: in implicit destructor for 'Bar<int>' first required here
<source>:8:17: note: 'operator delete' declared here
    8 |     static void operator delete(void * ptr) { std::free(ptr); }
      |                 ^
<source>:10:13: error: reference to __host__ function 'operator delete' in __host__ __device__ function
   10 |     virtual ~Foo() = default;
      |             ^
<source>:10:13: note: called by '~Bar'
<source>:8:17: note: 'operator delete' declared here
    8 |     static void operator delete(void * ptr) { std::free(ptr); }
      |                 ^
2 errors generated when compiling for gfx906.
Compiler returned: 1