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* [Bug c++/101976] New: When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially
@ 2021-08-19 10:43 alois1@gmx-topmail.de
2022-08-11 23:05 ` [Bug c++/101976] " dprokoptsev at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: alois1@gmx-topmail.de @ 2021-08-19 10:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101976
Bug ID: 101976
Summary: When constructing object, calling function and
performing co_await in same statement, temporary is
erroneously moved trivially
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: alois1@gmx-topmail.de
Target Milestone: ---
Created attachment 51324
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51324&action=edit
Reduced preprocessed code
GCC miscompiles the following C++ program:
$ cat test.cpp
#include <coroutine>
struct task
{
struct promise_type
{
task get_return_object() { return
{std::coroutine_handle<promise_type>::from_promise(*this)}; }
std::suspend_never initial_suspend() { return {}; }
std::suspend_never final_suspend() noexcept { return {}; }
void unhandled_exception() {}
void return_void() {}
};
bool await_ready() { return true; }
void await_suspend(std::coroutine_handle<>) {}
void await_resume() { }
std::coroutine_handle<promise_type> m_handle;
};
extern "C" int puts(const char *s);
struct nontrivial_move
{
nontrivial_move() { puts("nontrivial_move()"); }
nontrivial_move(nontrivial_move &&) {
puts("nontrivial_move(nontrivial_move &&)"); }
~nontrivial_move() { puts("~nontrivial_move()"); }
char buf[128]{};
};
struct wrapper
{
nontrivial_move member;
};
task subtask(wrapper)
{
co_return;
}
task main_task()
{
co_await subtask({});
}
int main()
{
main_task();
}
$ gcc -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin
--enable-initfini-array
--with-isl=/builddir/build/BUILD/gcc-11.2.1-20210728/obj-x86_64-redhat-linux/isl-install
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-gnu-indirect-function --enable-cet --with-tune=generic
--with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.1 20210728 (Red Hat 11.2.1-1) (GCC)
$ g++ -std=c++20 test.cpp; ./a.out
nontrivial_move()
nontrivial_move(nontrivial_move &&)
~nontrivial_move()
~nontrivial_move()
~nontrivial_move()
Examination of the generated assembly code shows that the temporary wrapper
object is erroneously copied under the assumption that it has trivial move
constructor (the large buffer in nontrivial_move is just there to make this
fact obvious).
This behavior does not happen if the construction of the wrapper object or the
co_await happens in a separate statement. Furthermore, the behavior does not
happen if the only argument of subtask is changed to have type nontrivial_move
(the move is elided entirely in this case, which is acceptable as far as I can
tell).
A manually reduced version of the preprocessed code is attached, which I have
confirmed to show the same behavior.
I think that the observed incorrect behavior might be a symptom of the same
underlying issue as one or more of the bugs 99576, 100611, 101243, 101367.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/101976] When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially
2021-08-19 10:43 [Bug c++/101976] New: When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially alois1@gmx-topmail.de
@ 2022-08-11 23:05 ` dprokoptsev at gmail dot com
2022-12-04 10:41 ` cvs-commit at gcc dot gnu.org
2024-02-05 14:18 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: dprokoptsev at gmail dot com @ 2022-08-11 23:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101976
--- Comment #1 from Dmitry Prokoptsev <dprokoptsev at gmail dot com> ---
I believe I stumbled on this one as well -- see
https://godbolt.org/z/or31cz6eW, although it's not as trivial as the snippet
provided here.
Reproduces in 10.3 and all subsequent versions.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/101976] When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially
2021-08-19 10:43 [Bug c++/101976] New: When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially alois1@gmx-topmail.de
2022-08-11 23:05 ` [Bug c++/101976] " dprokoptsev at gmail dot com
@ 2022-12-04 10:41 ` cvs-commit at gcc dot gnu.org
2024-02-05 14:18 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-12-04 10:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101976
--- 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:58a7b1e354530d8dfe7d8fb859c8b8b5a9140f1f
commit r13-4479-g58a7b1e354530d8dfe7d8fb859c8b8b5a9140f1f
Author: Iain Sandoe <iain@sandoe.co.uk>
Date: Wed Nov 30 17:05:56 2022 +0000
coroutines: Do not promote temporaries that will be elided.
We usually need to 'promote' (i.e. save to the coroutine frame) any
temporary
variable that is in a target expression that must persist across an await
expression. However, if the TE is just used as a direct initializer for
another object it will be elided - and we should not promote it since that
would lead to a DTOR call for something that is never constructed.
Since we now have a mechanism to tell if TEs will be elided, use that.
Although the PRs referenced initially appear to be different issues, they
all
stem from this.
Co-Authored-By: Adrian Perl <adrian.perl@web.de>
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
PR c++/100611
PR c++/101367
PR c++/101976
PR c++/99576
gcc/cp/ChangeLog:
* coroutines.cc (find_interesting_subtree): Do not promote
temporaries
that are only used as direct initializers for some other object.
gcc/testsuite/ChangeLog:
* g++.dg/coroutines/pr100611.C: New test.
* g++.dg/coroutines/pr101367.C: New test.
* g++.dg/coroutines/pr101976.C: New test.
* g++.dg/coroutines/pr99576_1.C: New test.
* g++.dg/coroutines/pr99576_2.C: New test.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/101976] When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially
2021-08-19 10:43 [Bug c++/101976] New: When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially alois1@gmx-topmail.de
2022-08-11 23:05 ` [Bug c++/101976] " dprokoptsev at gmail dot com
2022-12-04 10:41 ` cvs-commit at gcc dot gnu.org
@ 2024-02-05 14:18 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2024-02-05 14:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101976
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |C++-coroutines
Status|UNCONFIRMED |NEW
Last reconfirmed| |2024-02-05
CC| |iains at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Iain, this one seems to be fixed. Should we close it?
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-08-19 10:43 [Bug c++/101976] New: When constructing object, calling function and performing co_await in same statement, temporary is erroneously moved trivially alois1@gmx-topmail.de
2022-08-11 23:05 ` [Bug c++/101976] " dprokoptsev at gmail dot com
2022-12-04 10:41 ` cvs-commit at gcc dot gnu.org
2024-02-05 14:18 ` redi at gcc dot gnu.org
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