[Bug c++/102420] New: null pointer dereference constant

[Bug c++/102420] New: null pointer dereference constant

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102420

            Bug ID: 102420
           Summary: null pointer dereference constant
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johelegp at gmail dot com
                CC: johelegp at gmail dot com
  Target Milestone: ---

[Bug c++/102420] null pointer dereference during constant evaluation not rejected

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102420

Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|null pointer dereference    |null pointer dereference
                   |constant                    |during constant evaluation
                   |                            |not rejected
             Blocks|                            |55004

--- Comment #1 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
See https://godbolt.org/z/r5zxPTcK6.
```C++
struct X {
  constexpr void f() { }
};
int main() {
  []() consteval {
    X* x{nullptr};
    x->f();
  }();
}
```


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55004
[Bug 55004] [meta-bug] constexpr issues

[Bug c++/102420] null pointer dereference during constant evaluation not rejected

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102420

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-09-20
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, here is a testcase which does not require C++20 (though it does use
a GNU extension):

struct X {
  constexpr int f() { return 0; }
};
constexpr int g() {
    return (X*){nullptr}->f();
}

int t = g();
---- CUT ----
here is one which is invalid C++14 (and does not use the GNU extension):
struct X {
  constexpr int f() { return 0; }
};
constexpr int g() {
    X *x = nullptr;
    return x->f();
}

int t = g();
-------- CUT ------
I only noticed that clang rejects it while ICC and MSVC accept it also.

[Bug c++/102420] null pointer dereference during constant evaluation not rejected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102420

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:

https://gcc.gnu.org/g:5ba949c096f5250aa4efb94fb7c94d1304c1bf39

commit r14-6722-g5ba949c096f5250aa4efb94fb7c94d1304c1bf39
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Sun Dec 17 12:46:02 2023 +1100

    c++: Check null pointer deref when calling memfn in constexpr [PR102420]

    Calling a non-static member function on a null pointer is undefined
    behaviour (see [expr.ref] p8) and should error in constant evaluation,
    even if the 'this' pointer is never actually accessed within that
    function.

    One catch is that currently, the function pointer conversion operator
    for lambdas passes a null pointer as the 'this' pointer to the
    underlying 'operator()', so for now we ignore such calls.

            PR c++/102420

    gcc/cp/ChangeLog:

            * constexpr.cc (cxx_bind_parameters_in_call): Check for calling
            non-static member functions with a null pointer.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-memfn2.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>