[Bug c++/107615] New: Segfault on accessing to methods of optional class through member pointer

[Bug c++/107615] New: Segfault on accessing to methods of optional class through member pointer

[socurahlem at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107615

            Bug ID: 107615
           Summary: Segfault on accessing to methods of optional class
                    through member pointer
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: socurahlem at yandex dot ru
  Target Milestone: ---

Example link: https://godbolt.org/z/K7bqeh9sG

If we access methods of optional class through pointer to member, the program
exited with segfault. I tried the example with previous versions of gcc and got
correct result. With clang the same

[Bug c++/107615] Segfault on accessing to methods of optional class through member pointer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107615

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 53874
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53874&action=edit
testcase

Next time please attach the testcase instead of just linking to godbolt.

[Bug c++/107615] Segfault on accessing to methods of optional class through member pointer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107615

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
With -W -Wall I get
<source>: In function 'int main()':
<source>:17:39: warning: 'aStr' is used uninitialized [-Wuninitialized]
   17 |     std::cout << (aClass->*aStr).value() << std::endl;;
      |                  ~~~~~~~~~~~~~~~~~~~~~^~
<source>:14:15: note: 'aStr' was declared here
   14 |     A::member aStr;
      |               ^~~~

The code is undefined because of the uninitialized variable.

Once you initialize it, the code works as expected:
    A::member aStr = &A::str;

[Bug c++/107615] Segfault on accessing to methods of optional class through member pointer

[socurahlem at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107615

--- Comment #3 from Danil Kolotushkin <socurahlem at yandex dot ru> ---
Oh, sorry!
Pointers to the members are a bit confusing for me. Interestingly, previous
versions of gcc and clang work fine in that case. I added more fields to the
object, and it seems that they are by default pointing to the first member
which has this type. With the first type different (for example integer) clang
works fine, but doesn't print anything and gcc exits with segfault. Quite
interesting.

Thank you very much for your answer, Andrew! :)