[Bug c++/97145] New: Sanitizer pointer-subtract breaks constexpr functions subtracting pointers

[chfast at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97145

            Bug ID: 97145
           Summary: Sanitizer pointer-subtract breaks constexpr functions
                    subtracting pointers
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chfast at gmail dot com
  Target Milestone: ---

Having a constexpr function that subtracts two pointers does not work in
constexpr context when building with -fsanitize=address,pointer-subtract.

GCC version: starts with 8.1 where pointer-subtract was introduced, up to
trunk.

Minimal code:

constexpr char* a = nullptr;
constexpr auto d = a - a;

<source>:3:22: error: '__builtin___sanitizer_ptr_sub(0, 0)' is not a constant
expression

    3 | constexpr auto d = a - a;

      |                    ~~^~~

https://godbolt.org/z/qWxT9v