[Bug c++/95477] New: [coroutines] coroutine result object not properly freed

[natattak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95477

            Bug ID: 95477
           Summary: [coroutines] coroutine result object not properly
                    freed
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: natattak at gmail dot com
  Target Milestone: ---

In some cases, the result object of a coroutine is not properly destroyed after
the coroutine finishes execution. Consider the following example:


#include <coroutine>

struct simple {
  static inline int alive = 0;
  simple() { ++alive; }
  simple(simple&&) { ++alive; }
  ~simple() { --alive; }

  struct promise_type {
    simple get_return_object() { return simple{}; }
    void return_void() {}
    void unhandled_exception() {}
    auto initial_suspend() noexcept { return std::suspend_never{}; }
    auto final_suspend() noexcept { return std::suspend_never{}; }
  };
};

simple f() { co_return; }

int main() {
  {
    f();
  }
  return simple::alive;
}


The return value should be 0, indicating that all created objects were
destroyed. However, when executing, I get the result 1. After commenting out
the move constructor, the return value is 0 as expected. 

See also:
https://stackoverflow.com/questions/62125871/simple-coroutine-leaking-with-gcc-10

This is compiled using `-std=c++20 -fcoroutines`.
My `gcc -v` is:

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --with-isl
--with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit
--enable-cet=auto --enable-checking=release --enable-clocale=gnu
--enable-default-pie --enable-default-ssp --enable-gnu-indirect-function
--enable-gnu-unique-object --enable-install-libiberty --enable-linker-build-id
--enable-lto --enable-multilib --enable-plugin --enable-shared
--enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-libunwind-exceptions --disable-werror
gdc_include_dir=/usr/include/dlang/gdc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.1.0 (GCC)