[Bug middle-end/57485] memcpy in aggregate return not eliminated

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57485

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-06-01
                 CC|                            |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1
      Known to fail|                            |4.8.3, 4.9.3, 5.3.0, 6.2.0,
                   |                            |7.1.0

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with 7.1 with the following test case.  The assembly shows the memcpy
(expanded  inline).

$ cat t.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout t.c
struct S { int a[100]; };
struct S f (void);

void g(struct S *p);

void h (void) {
        struct S s = f();  // no local temporary
        g(&s);
}

void j (void) {
        struct S s;
        s = f();           // local temporary and memcpy
        g(&s);
}


;; Function h (h, funcdef_no=0, decl_uid=1799, cgraph_uid=0, symbol_order=0)

h ()
{
  struct S s;

  <bb 2> [100.00%]:
  s = f (); [return slot optimization]
  g (&s);
  s ={v} {CLOBBER};
  return;

}



;; Function j (j, funcdef_no=1, decl_uid=1803, cgraph_uid=1, symbol_order=1)

j ()
{
  struct S s;

  <bb 2> [100.00%]:
  s = f ();
  g (&s);
  s ={v} {CLOBBER};
  return;

}