[Bug c++/102191] New: Can't return prvalue with potentially-throwing destructor during constant evaluation

[Bug c++/102191] New: Can't return prvalue with potentially-throwing destructor during constant evaluation

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

            Bug ID: 102191
           Summary: Can't return prvalue with potentially-throwing
                    destructor during constant evaluation
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          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: ---

See https://godbolt.org/z/8evPWv7cb.
```C++
struct X {
  struct A {
    constexpr ~A() noexcept(false) { }
  };

  constexpr A operator()(auto...) { return {}; }
};

void f() { []() consteval { X{}(); }(); }
```
```
<source>: In function 'void f()':
<source>:9:37:   in 'constexpr' expansion of '<lambda closure
object>f()::<lambda()>().f()::<lambda()>()'
<source>:9:37:   in 'constexpr' expansion of 'X::operator()(auto:1 ...) [with
auto:1 = {}]()'
<source>:9:37: error: modification of '<anonymous>' is not a constant
expression
    9 | void f() { []() consteval { X{}(); }(); }
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~^~
Compiler returned: 1
```

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Last reconfirmed|                            |2022-01-06
            Summary|Can't return prvalue with   |[C++20] Can't return
                   |potentially-throwing        |prvalue with
                   |destructor during constant  |potentially-throwing
                   |evaluation                  |destructor during constant
                   |                            |evaluation
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:b10e031458d541f794dfaa08ba606487603a4bb6

commit r12-6333-gb10e031458d541f794dfaa08ba606487603a4bb6
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jan 5 17:01:12 2022 -0500

    c++: destroy retval on throwing cleanup in try [PR33799]

    My earlier attempt to fix this bug didn't handle the case where both the
    return and the throwing cleanup are within a try-block that catches and
    discards the exception.  Fixed by adding the retval cleanup to any
    try-blocks as well as the function body.  PR102191 pointed out that we also
    weren't handling templates properly, so I moved the call out of the parser.

            PR c++/33799
            PR c++/102191

    gcc/cp/ChangeLog:

            * except.c (maybe_splice_retval_cleanup): Check
            current_binding_level.
            * semantics.c (do_poplevel): Call it here.
            * parser.c (cp_parser_compound_statement): Not here.

    gcc/testsuite/ChangeLog:

            * g++.dg/eh/return1.C: Add temporary in try block case.
            * g++.dg/cpp2a/constexpr-dtor11.C: New test.

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for GCC 12.

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:ae07265381d934ee97fb1ce8915731158c91babc

commit r14-5086-gae07265381d934ee97fb1ce8915731158c91babc
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Oct 30 17:44:54 2023 -0400

    c++: retval dtor on rethrow [PR112301]

    In r12-6333 for PR33799, I fixed the example in [except.ctor]/2.  In that
    testcase, the exception is caught and the function returns again,
    successfully.

    In this testcase, however, the exception is rethrown, and hits two separate
    cleanups: one in the try block and the other in the function body.  So we
    destroy twice an object that was only constructed once.

    Fortunately, the fix for the normal case is easy: we just need to clear the
    "return value constructed by return" flag when we do it the first time.

    This gets more complicated with the named return value optimization, since
    we don't want to destroy the return value while the NRV variable is still
in
    scope.

            PR c++/112301
            PR c++/102191
            PR c++/33799

    gcc/cp/ChangeLog:

            * except.cc (maybe_splice_retval_cleanup): Clear
            current_retval_sentinel when destroying retval.
            * semantics.cc (nrv_data): Add in_nrv_cleanup.
            (finalize_nrv): Set it.
            (finalize_nrv_r): Fix handling of throwing cleanups.

    gcc/testsuite/ChangeLog:

            * g++.dg/eh/return1.C: Add more cases.

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:7fae9873a74c7a5a62044bb6a4cde8e3ac1a5e5d

commit r12-9990-g7fae9873a74c7a5a62044bb6a4cde8e3ac1a5e5d
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Oct 30 17:44:54 2023 -0400

    c++: retval dtor on rethrow [PR112301]

    In r12-6333 for PR33799, I fixed the example in [except.ctor]/2.  In that
    testcase, the exception is caught and the function returns again,
    successfully.

    In this testcase, however, the exception is rethrown, and hits two separate
    cleanups: one in the try block and the other in the function body.  So we
    destroy twice an object that was only constructed once.

    Fortunately, the fix for the normal case is easy: we just need to clear the
    "return value constructed by return" flag when we do it the first time.

    This gets more complicated with the named return value optimization, since
    we don't want to destroy the return value while the NRV variable is still
in
    scope.

            PR c++/112301
            PR c++/102191
            PR c++/33799

    gcc/cp/ChangeLog:

            * except.cc (maybe_splice_retval_cleanup): Clear
            current_retval_sentinel when destroying retval.
            * semantics.cc (nrv_data): Add in_nrv_cleanup.
            (finalize_nrv): Set it.
            (finalize_nrv_r): Fix handling of throwing cleanups.

    gcc/testsuite/ChangeLog:

            * g++.dg/eh/return1.C: Add more cases.

[Bug c++/102191] [C++20] Can't return prvalue with potentially-throwing destructor during constant evaluation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102191

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:d237e7b291ff52095d600e6489a54b4ba8aaf608

commit r13-8079-gd237e7b291ff52095d600e6489a54b4ba8aaf608
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Oct 30 17:44:54 2023 -0400

    c++: retval dtor on rethrow [PR112301]

    In r12-6333 for PR33799, I fixed the example in [except.ctor]/2.  In that
    testcase, the exception is caught and the function returns again,
    successfully.

    In this testcase, however, the exception is rethrown, and hits two separate
    cleanups: one in the try block and the other in the function body.  So we
    destroy twice an object that was only constructed once.

    Fortunately, the fix for the normal case is easy: we just need to clear the
    "return value constructed by return" flag when we do it the first time.

    This gets more complicated with the named return value optimization, since
    we don't want to destroy the return value while the NRV variable is still
in
    scope.

            PR c++/112301
            PR c++/102191
            PR c++/33799

    gcc/cp/ChangeLog:

            * except.cc (maybe_splice_retval_cleanup): Clear
            current_retval_sentinel when destroying retval.
            * semantics.cc (nrv_data): Add in_nrv_cleanup.
            (finalize_nrv): Set it.
            (finalize_nrv_r): Fix handling of throwing cleanups.

    gcc/testsuite/ChangeLog:

            * g++.dg/eh/return1.C: Add more cases.