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* [Bug c++/112360] New: [coroutines] unreachable 'co_await' still creates a suspension point
@ 2023-11-03 6:30 oremanj at mit dot edu
2023-11-03 19:04 ` [Bug c++/112360] [coroutines] unreachable 'co_await' still can suspend the coroutine pinskia at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: oremanj at mit dot edu @ 2023-11-03 6:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112360
Bug ID: 112360
Summary: [coroutines] unreachable 'co_await' still creates a
suspension point
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: oremanj at mit dot edu
Target Milestone: ---
A coroutine function of the form:
task example() {
do {
co_await awaitable{};
} while (false && co_await awaitable{});
co_return;
}
will execute the awaitable's await_ready() and await_suspend() methods twice,
even though execution of the abstract machine only reaches one co_await
statement. This reproduces on several tested versions from 11.1 to current
master, at either of optimization level -O0 or -O2. While the construct may
seem a bit nonsensical, it does show up in practice; it's simplified from
something that appears after macro expansion when using the popular Catch2
testing library if you write an assertion about the value of a co_await
expression.
Compiler Explorer link: https://godbolt.org/z/EoP7EnEnf
Full test case is below. On gcc it prints:
ready
suspend
resume
ready
suspend
returned
final suspend
clang (14 through 17) shows the more expected
ready
suspend
resume
returned
final suspend
command line: gcc -std=c++20 -Wall -Wextra t.c -o t
--- test case follows ---
#include <coroutine>
extern "C" int puts(const char* s);
struct task {
struct promise_type {
std::suspend_always initial_suspend() { return {}; }
std::suspend_always final_suspend() noexcept {
puts("final suspend");
return {};
}
void return_void() { puts("returned"); }
void unhandled_exception() {}
task get_return_object() { return task{this}; }
};
promise_type* promise;
};
struct awaitable {
bool await_ready() const noexcept { puts("ready"); return false; }
void await_suspend(std::coroutine_handle<> h) {
puts("suspend");
h.resume();
}
bool await_resume() {
puts("resume");
return false;
}
};
task example() {
do {
co_await awaitable{};
} while (false && co_await awaitable{});
co_return;
}
int main() {
using handle = std::coroutine_handle<task::promise_type>;
task t = example();
handle h = handle::from_promise(*t.promise);
h.resume();
}
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug c++/112360] [coroutines] unreachable 'co_await' still can suspend the coroutine
2023-11-03 6:30 [Bug c++/112360] New: [coroutines] unreachable 'co_await' still creates a suspension point oremanj at mit dot edu
@ 2023-11-03 19:04 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-11-03 19:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112360
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 101027.
*** This bug has been marked as a duplicate of bug 101027 ***
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-11-03 6:30 [Bug c++/112360] New: [coroutines] unreachable 'co_await' still creates a suspension point oremanj at mit dot edu
2023-11-03 19:04 ` [Bug c++/112360] [coroutines] unreachable 'co_await' still can suspend the coroutine pinskia at gcc dot gnu.org
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