[Bug c++/95003] New: coroutines: Wrong code for some reference capture cases.

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95003

            Bug ID: 95003
           Summary: coroutines: Wrong code for some reference capture
                    cases.
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iains at gcc dot gnu.org
  Target Milestone: ---

Created attachment 48479
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48479&action=edit
patch under test

The following code does not work correctly, the loop is executed but the loop
body is discarded during gimplifcation.

There are several places where we insert bind expressions while making the
coroutine AST transforms.  These should be marked as having side-effects where
relevant, which had been omitted - leading to the fail - since, at least in
some cases, such bind expressions are dropped during gimplification.


struct Awaitable {
  int v;
  Awaitable (int _v) : v(_v) {}
  bool await_ready() { return false; }
  void await_suspend(std::coroutine_handle<coro1::promise_type>) {}
  int await_resume() { return v; }
  auto operator co_await() { return *this; }
};

coro1
my_coro
(int x)
{
  int sum = 0;
  for (unsigned i = 0; i < 100; ++i) {
    sum += co_await Awaitable{x+1};
  }
  co_return sum;
}