[Bug tree-optimization/30398] memmove for string operations

[tobi at gcc dot gnu dot org]

------- Comment #3 from tobi at gcc dot gnu dot org  2007-04-13 16:27 -------
With FX' patch to inline REPEAT (see PR31304), we are left with this as final
dump after a -O compilation:
;; Function MAIN__ (MAIN__)

MAIN__ ()
{
  char[1:] * pstr.1;
  char s[1:1];
  char c[1:2];
  void * D.1004;

<bb 2>:
  _gfortran_set_std (68, 127, 0, 0, 0);
  s[1]{lb: 1 sz: 1} = 97;
  D.1004 = _gfortran_internal_malloc (2);
  pstr.1 = (char[1:] *) D.1004;
  __builtin_memcpy ((char *) pstr.1, &s, 1);
  __builtin_memcpy (pstr.1 + 1B, &s, 1);
  __builtin_memmove (&c, pstr.1, 2);
  _gfortran_internal_free (pstr.1);
  return;

}

The call to memmove makes it way into the assembly, even though pstr and c
can't alias.  This is now an optimizer issue, moving to component
tree-optimization, as the tree-ssa optimizers should be able to eliminate the
memmove in favor of a memcpy.  Or even better, get rid of the whole copying
business and predict the correct results.  If that's possible it would be great
to have a way to get rid of the then unnecessary temporary allocation.


-- 

tobi at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tobi at gcc dot gnu dot org,
                   |                            |fxcoudert at gcc dot gnu dot
                   |                            |org
          Component|fortran                     |tree-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30398