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

[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

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

[rguenth at gcc dot gnu.org]

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

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Maybe we shouldn't sanitize constexpr stuff?

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
No, we just need to ignore the sanitization builtins during constant
evaluation.
We already do for some of them.
We can ignore sanitization only in consteval functions, constexpr just means
that the compiler attempts to evaluate it at compile time if called in constant
expression contexts or with constant arguments, but it is still emitted out of
line and can be called at runtime.

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2020-09-21
     Ever confirmed|0                           |1

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 49251
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49251&action=edit
gcc11-pr97145.patch

Untested fix.

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

[cvs-commit at gcc dot gnu.org]

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

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:bc13106e0414b86af8f6878e7681e6a959921b9e

commit r11-3368-gbc13106e0414b86af8f6878e7681e6a959921b9e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Sep 22 21:06:32 2020 +0200

    c++: Ignore __sanitizer_ptr_{sub,cmp} builtin calls during constant
expression evaluation [PR97145]

    These two builtin calls are added already during parsing before pointer
    subtractions or comparisons, normally they perform runtime verification
    of whether the pointers point to the same object or different objects,
    but during constant expressione valuation we don't really need those
    builtins for anything.

    2020-09-22  Jakub Jelinek  <jakub@redhat.com>

            PR c++/97145
            * constexpr.c (cxx_eval_builtin_function_call): Return void_node
for
            calls to __sanitize_ptr_{sub,cmp} builtins.

            * g++.dg/asan/pr97145.C: New test.

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

[cvs-commit at gcc dot gnu.org]

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

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:3f56563cf84f97ef271ef0f949a571c13cdd06e2

commit r10-8850-g3f56563cf84f97ef271ef0f949a571c13cdd06e2
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Sep 22 21:06:32 2020 +0200

    c++: Ignore __sanitizer_ptr_{sub,cmp} builtin calls during constant
expression evaluation [PR97145]

    These two builtin calls are added already during parsing before pointer
    subtractions or comparisons, normally they perform runtime verification
    of whether the pointers point to the same object or different objects,
    but during constant expressione valuation we don't really need those
    builtins for anything.

    2020-09-22  Jakub Jelinek  <jakub@redhat.com>

            PR c++/97145
            * constexpr.c (cxx_eval_builtin_function_call): Return void_node
for
            calls to __sanitize_ptr_{sub,cmp} builtins.

            * g++.dg/asan/pr97145.C: New test.

    (cherry picked from commit bc13106e0414b86af8f6878e7681e6a959921b9e)

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

[chfast at gmail dot com]

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

Paweł Bylica <chfast at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Paweł Bylica <chfast at gmail dot com> ---
This looks to be fixed in trunk. Thanks.