[Bug c++/97587] New: [coroutines] promise_type constructor is called with original parameters, not parameter copies

[Bug c++/97587] New: [coroutines] promise_type constructor is called with original parameters, not parameter copies

[jehelset at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97587

            Bug ID: 97587
           Summary: [coroutines] promise_type constructor is called with
                    original parameters, not parameter copies
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jehelset at gmail dot com
  Target Milestone: ---

Created attachment 49443
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49443&action=edit
Program that results in assertion-failure due to wrong arguments to promise.

The promise-type constructor should be called with the parameter copies from
the coroutine-frame. I couldn't quite understand that this is supposed to be
the case from the current draft of the standard, but I got some help from Lewis
Baker who also referred me to this rewording, where in the previous version it
is clear: 

https://github.com/cplusplus/draft/commit/0b4ab68a54e197eba9d894a8f91270bb0dcdb546

The attached code triggers an assertion that show that this is not the case on
gcc. I initially had the problem on gcc-10.2.0, but reproduced it on gcc-trunk
on godbolt. Compile either version with -fcoroutines, or see
https://gcc.godbolt.org/z/j16Wqx.

I speculated that the logic here,
https://github.com/gcc-mirror/gcc/blob/master/gcc/cp/coroutines.cc#L4491-L4494,
was inverted. It seemed to pass the copied version of a by-reference parameter,
but the original version of a by-value parameter. The opposite would not
trigger the assertion. But I am not that familiar.

[Bug c++/97587] [coroutines] promise_type constructor is called with original parameters, not parameter copies

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97587

Iain Sandoe <iains at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-02-16
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |iains at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Iain Sandoe <iains at gcc dot gnu.org> ---
Created attachment 50194
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50194&action=edit
Patch under test

this needs a changelog, and some wider testing.

[Bug c++/97587] [coroutines] promise_type constructor is called with original parameters, not parameter copies

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97587

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Iain D Sandoe <iains@gcc.gnu.org>:

https://gcc.gnu.org/g:b8ff3f8efeda02a6bedebfaf20b93645ae3bb5b8

commit r11-7403-gb8ff3f8efeda02a6bedebfaf20b93645ae3bb5b8
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Mon Feb 15 16:13:36 2021 +0000

    coroutines : Call promise CTOR with parm copies [PR97587].

    As the PR notes, we were calling the promise CTOR with the original
    function parameters, not the copy (as pointed, a previous wording of
    the section was unambiguous).  Fixed thus.

    gcc/cp/ChangeLog:

            PR c++/97587
            * coroutines.cc (struct param_info): Track rvalue refs.
            (morph_fn_to_coro): Track rvalue refs, and call the promise
            CTOR with the frame copy of passed parms.

    gcc/testsuite/ChangeLog:

            PR c++/97587
            * g++.dg/coroutines/coro1-refs-and-ctors.h: Add a CTOR with two
            reference parms, to distinguish the rvalue ref. variant.
            * g++.dg/coroutines/pr97587.C: New test.

[Bug c++/97587] [coroutines] promise_type constructor is called with original parameters, not parameter copies

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97587

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Iain D Sandoe
<iains@gcc.gnu.org>:

https://gcc.gnu.org/g:88bb77a8dcf75f556b8dcb24b8785b4567d24e4f

commit r10-9511-g88bb77a8dcf75f556b8dcb24b8785b4567d24e4f
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Mon Feb 15 16:13:36 2021 +0000

    coroutines : Call promise CTOR with parm copies [PR97587].

    As the PR notes, we were calling the promise CTOR with the original
    function parameters, not the copy (as pointed, a previous wording of
    the section was unambiguous).  Fixed thus.

    gcc/cp/ChangeLog:

            PR c++/97587
            * coroutines.cc (struct param_info): Track rvalue refs.
            (morph_fn_to_coro): Track rvalue refs, and call the promise
            CTOR with the frame copy of passed parms.

    gcc/testsuite/ChangeLog:

            PR c++/97587
            * g++.dg/coroutines/coro1-refs-and-ctors.h: Add a CTOR with two
            reference parms, to distinguish the rvalue ref. variant.
            * g++.dg/coroutines/pr97587.C: New test.

    (cherry picked from commit b8ff3f8efeda02a6bedebfaf20b93645ae3bb5b8)

[Bug c++/97587] [coroutines] promise_type constructor is called with original parameters, not parameter copies

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97587

Iain Sandoe <iains at gcc dot gnu.org> changed:

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

--- Comment #4 from Iain Sandoe <iains at gcc dot gnu.org> ---
fixed for master and 10.3