[Bug c++/91217] [8/9/10 Regression] Returning std::array from lambda results in an extra copy step on return

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91217

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-07-22
   Target Milestone|---                         |8.4
            Summary|Returning std::array from   |[8/9/10 Regression]
                   |lambda results in an extra  |Returning std::array from
                   |copy step on return         |lambda results in an extra
                   |                            |copy step on return
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
I can confirm that with -O2 and GCC 8 there is

hello_1 ()
{
..
  <bb 5> [local count: 12777528]:
  return <retval>;
}

while

hello_2 ()
{
...
  <bb 5> [local count: 1073741826]:
  <retval>.m_data = ret;
  ret ={v} {CLOBBER};
  return <retval>;
}

with GCC 9 TestB::TestB isn't inlined in addition (-O3 helps for that but
not the other issue).

GCC 7 manages to produce the code as hello_1 in both cases.