https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101355
Bug ID: 101355
Summary: compiling coroutines with ubsan emits bogus
-Wmaybe-uninitialized warnings
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: daklishch at gmail dot com
Target Milestone: ---
Created attachment 51111
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51111&action=edit
preprocessed source
Compiling the following program with UBSan emits -Wmaybe-uninitialized on
`<anonymous>' variables.
The compiler and runtime behavior is somewhat inconsistent. Normally, there is
only one warning per function and the program is not affected. However, for
example, compiling provided program with -O2 emits two identical warnings and
makes the program crash with `member call on null pointer of type 'struct a''.
$ cat testcode.cc
#include <coroutine>
struct coro {
struct promise_type {
coro get_return_object() { return {}; }
std::suspend_never initial_suspend() noexcept { return {}; }
std::suspend_never final_suspend() noexcept { return {}; }
void unhandled_exception() {}
void return_void() {}
};
bool await_ready() { return true; }
void await_resume() {}
template <typename U>
void await_suspend(U &) {}
};
struct b {
~b() {}
};
struct a {
a(b) {}
~a() {}
};
coro f(b obj) {
auto obj2 = a{obj};
co_return;
}
int main() {
f({});
}
$ ~/gcc-dev/bin/gccdev -O2 -std=c++20 -Wall -fsanitize=undefined testcode.cc
-lstdc++
testcode.cc: In function ‘void _Z1f1b.actor(f(b)::_Z1f1b.frame*)’:
testcode.cc:30:1: warning: ‘<anonymous>’ may be used uninitialized
[-Wmaybe-uninitialized]
30 | }
| ^
testcode.cc:30:1: note: ‘<anonymous>’ was declared here
30 | }
| ^
In function ‘void _Z1f1b.actor(f(b)::_Z1f1b.frame*)’,
inlined from ‘coro f(b)’ at testcode.cc:27:6:
testcode.cc:30:1: warning: ‘<anonymous>’ is used uninitialized
[-Wuninitialized]
30 | }
| ^
testcode.cc: In function ‘coro f(b)’:
testcode.cc:30:1: note: ‘<anonymous>’ was declared here
30 | }
| ^
$ ./a.out
testcode.cc:30:1: runtime error: member call on null pointer of type 'struct a'
