[Bug c++/116880] New: [15 Regression] too early coroutine destruction of co_await on nix-2.24.8

[slyfox at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116880

            Bug ID: 116880
           Summary: [15 Regression] too early coroutine destruction of
                    co_await on nix-2.24.8
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Initially observed the failure as a SIGSEGV on a nix-2.24.8 testsuite. The test
runs on gcc-14 and fails on gcc-15 from r15-3941-g2531f014fb2364.

I think I managed to convert it to a build failure that complains about use of
a destroyed object:

// $ substitution-goal.cc
#include <coroutine>

struct promise_type;
using handle_type = std::coroutine_handle<promise_type>;

struct Co {
    handle_type handle;
    using promise_type = ::promise_type;

    explicit Co(handle_type handle) : handle(handle) {}

    bool await_ready() { return false; }
    std::coroutine_handle<> await_suspend(handle_type handle);
    void await_resume() {}
};

struct Done {};

struct promise_type {
    Co get_return_object();

    std::suspend_always initial_suspend() { return {}; };
    std::suspend_always final_suspend() noexcept { return {}; };
    void return_value(Done) {}
    void return_value(Co&&);
    void unhandled_exception() { throw; };
    Co&& await_transform(Co&& co) { return static_cast<Co&&>(co); }
};

Co tryToRun();

Co init()
{
    co_await tryToRun();
    co_return Done{};
}

Good gcc-14:

$ g++-14 -o bug.o -c substitution-goal.cc -std=c++2a -Werror=dangling-pointer
-Wall

Bad gcc-15:

$ g++-15 -o bug.o -c substitution-goal.cc -std=c++2a -Werror=dangling-pointer
-Wall
substitution-goal.cc: In function 'void init(_Z4initv.Frame*)':
substitution-goal.cc:36:23: error: using a dangling pointer to an unnamed
temporary [-Werror=dangling-pointer=]
   36 |     co_await tryToRun();
      |                       ^
substitution-goal.cc:36:22: note: unnamed temporary defined here
   36 |     co_await tryToRun();
      |              ~~~~~~~~^~
cc1plus: some warnings being treated as errors

$ g++-15 -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-15.0.0/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-15.0.0/libexec/gcc/x86_64-unknown-linux-gnu/15.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../source/configure --prefix=/<<NIX>>/gcc-15.0.0
--with-gmp-include=/<<NIX>>/gmp-6.3.0-dev/include
--with-gmp-lib=/<<NIX>>/gmp-6.3.0/lib
--with-mpfr-include=/<<NIX>>/mpfr-4.2.1-dev/include
--with-mpfr-lib=/<<NIX>>/mpfr-4.2.1/lib --with-mpc=/<<NIX>>/libmpc-1.3.1
--with-native-system-header-dir=/<<NIX>>/glibc-2.40-36-dev/include
--with-build-sysroot=/
--with-gxx-include-dir=/<<NIX>>/gcc-15.0.0/include/c++/15.0.0/
--program-prefix= --enable-lto --disable-libstdcxx-pch
--without-included-gettext --with-system-zlib --enable-checking=release
--enable-static --enable-languages=c,c++ --disable-multilib --enable-plugin
--disable-libcc1 --with-isl=/<<NIX>>/isl-0.20 --disable-bootstrap
--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu
--target=x86_64-unknown-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 99999999 (experimental) (GCC)