[Bug c++/91344] New: Function pointers in templates with restrict semantics may fail to compile.

[a-yee at u dot northwestern.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91344

            Bug ID: 91344
           Summary: Function pointers in templates with restrict semantics
                    may fail to compile.
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: a-yee at u dot northwestern.edu
  Target Milestone: ---

The following code compiles on Clang, MSVC, and ICC. But it fails on GCC.

https://godbolt.org/z/zHq0qi


#include <iostream>
using namespace std;

#ifdef _WIN32
#define RESTRICT __restrict
#else
#define RESTRICT __restrict__
#endif


//  Works
//template <typename type> using r_ptr = type *;

//  Fails
template <typename type> using r_ptr = type *RESTRICT;


template <void (*fp)(r_ptr<int> ptr)>
void foo(){
    int x = 123;
    fp(&x);
}

void fp(r_ptr<int> ptr){
    cout << ptr[0] << endl;
}

int main(int argc, char* argv[]) {

    foo<fp>();

}



But on GCC, it gives:

<source>: In function 'int main(int, char**)':

<source>:30:13: error: no matching function for call to 'foo<fp>()'

   30 |     foo<fp>();

      |             ^

<source>:19:6: note: candidate: 'template<void (* fp)(r_ptr<int>)> void foo()'

   19 | void foo(){

      |      ^~~

<source>:19:6: note:   template argument deduction/substitution failed:

<source>:30:13: error: could not convert template argument 'fp' from
'void(r_ptr<int>)' {aka 'void(int*)'} to 'void (*)(int* __restrict__)'

   30 |     foo<fp>();

      |             ^

ASM generation compiler returned: 1

<source>: In function 'int main(int, char**)':

<source>:30:13: error: no matching function for call to 'foo<fp>()'

   30 |     foo<fp>();

      |             ^

<source>:19:6: note: candidate: 'template<void (* fp)(r_ptr<int>)> void foo()'

   19 | void foo(){

      |      ^~~

<source>:19:6: note:   template argument deduction/substitution failed:

<source>:30:13: error: could not convert template argument 'fp' from
'void(r_ptr<int>)' {aka 'void(int*)'} to 'void (*)(int* __restrict__)'

   30 |     foo<fp>();

      |