[Bug c++/97913] New: -fno-delete-null-pointer-checks not working properly with constexpr

[Bug c++/97913] New: -fno-delete-null-pointer-checks not working properly with constexpr

[mfarazma.ext at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97913

            Bug ID: 97913
           Summary: -fno-delete-null-pointer-checks not working properly
                    with constexpr
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mfarazma.ext at gmail dot com
  Target Milestone: ---

Compiling this code:

```
constexpr int test(const int *arr) {
  if(arr == 0){
     //
   }
  return 5;
}

int main(){
  static constexpr int arr[] = {1,2,3};
  static constexpr int b =  test(arr);
  return 0;
}

```
With "g++ -fno-delete-null-pointer-check test.cc" generates this error:

error '(((const int*)(& arr)) == 0u)' is not a constant expression.  

Seems like an odd behaviour as clang++ is able to compile this successfully.
I have tested it on gcc 6, 7, 9 as well has "HEAD 11.0.0".

[Bug c++/97913] -fno-delete-null-pointer-checks not working properly with constexpr

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97913

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
*** Bug 97914 has been marked as a duplicate of this bug. ***

[Bug c++/97913] -fno-delete-null-pointer-checks not working properly with constexpr

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97913

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2020-11-19

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed, but could be a dup of one of the other constexpr issues we've
accrued .

[Bug c++/97913] -fno-delete-null-pointer-checks not working properly with constexpr

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97913

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
-fno-delete-null-pointer-check means that objects can live at address zero
so (((const int*)(& arr)) == 0u) is indeed not a constant expression.  I
suppose
with -fno-delete-null-pointer-check C++ lacks a way to query for "no object"
(since &arr is certainly the address of an object - it just may reside at
address zero!).