[Bug target/35714] x86 poor code with pmaddwd

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from ubizjak at gmail dot com  2008-05-06 12:55 -------
This is due to this code snippet from i386.c, ix86_expand_binop_builtin ():

--cut here--
  /* ??? Using ix86_fixup_binary_operands is problematic when
     we've got mismatched modes.  Fake it.  */

  xops[0] = target;
  xops[1] = op0;
  xops[2] = op1;

  if (tmode == mode0 && tmode == mode1)
    {
      target = ix86_fixup_binary_operands (UNKNOWN, tmode, xops);
      op0 = xops[1];
      op1 = xops[2];
    }
  else if (optimize || !ix86_binary_operator_ok (UNKNOWN, tmode, xops))
    {
      op0 = force_reg (mode0, op0);
      op1 = force_reg (mode1, op1);
      target = gen_reg_rtx (tmode);
    }
--cut here--

Since UNKNOWN is not commutative operator, this code disables many
optimizations that can be performed by treating builtins individually using
ix86_fixup_binary_operands_no_copy ().


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35714