[Bug c/59193] Unused postfix operator temporaries

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59193

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Take:
int f(int a)
{
  a++;
  return a;
}

int g(int a)
{
  ++a;
  return a;
}
------------------- CUT ------------------- 

The gimplifier produces the exact same IR for both cases:
f (int a)
{
  int D.1790;

  a = a + 1;
  D.1790 = a;
  return D.1790;
}


g (int a)
{
  int D.1792;

  a = a + 1;
  D.1792 = a;
  return D.1792;
}
------------------- CUT ------------------- 

So the compiler is already smart enough to remove the "temporary storage" even
at -O0.

With:
int f(int a)
{
  int b = a++;
  return a;
}
It does not remove it but that is because the result of a++ is not unused.

So it is the gimplifier knows if the result is unused and will not use them
otherwise.  This is the same issue as memcpy and its return value.