[Bug c/124660] Missed optimization for reusing stack space of temporary objects in C

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124660

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |mpolacek at gcc dot gnu.org
           Keywords|                            |missed-optimization
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2026-03-27

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We fail to emit CLOBBERs for the returns of f, or rather the C frontend fails
to
push appropriate cleanups.

void test1 ()
{
  struct S D.2971;
  struct S D.2970;

  <bb 2> [local count: 1073741824]:
  D.2970 = f (); [return slot optimization]
  g (&D.2970.a);
  D.2971 = f (); [return slot optimization]
  g (&D.2971.a);
  return;