Re: the failure in store motion

[Jan Hubicka <jh at suse dot cz>]

> (I also changed find_loads to look at set dests the same way
> store_killed_in_insn does, so that it can handle parallels).
> 
> Even if you just tell it to remove available stores, we add testsuite
> failures.
Looking at the code, other place looks dubious:

  if (GET_CODE (PATTERN (insn)) == SET)
    {
      rtx pat = PATTERN (insn);
      /* Check for memory stores to aliased objects.  */
      if (GET_CODE (SET_DEST (pat)) == MEM && !expr_equiv_p (SET_DEST (pat), x))
	/* pretend its a load and check for aliasing.  */
	if (find_loads (SET_DEST (pat), x))
	  return 1;
      return find_loads (SET_SRC (pat), x);
    }
  else
    return find_loads (PATTERN (insn), x);

This code handles the real stores to an aliased objects by returning 1,
but in case the instruction is not plain set, but it is an parallel containing
set, it does not - it just calls find_loads, that hapilly ignores SET_DEST
of the instructions.

One of oddities of i386 backend is the heavy use of PARALLELs, so this looks
like probably bug in this area. Usually stores are just plain move
instructions, that does not have the parallel, but even before GCSE there can
be exceptions IMO.

Whole gcse is somewhat PARALLEL unhappy. Once I will have more time, I will
try to do pass over that and figure out what else needs to be changed.
> 
> I wonder if it has to do with trapping or something? (We kill trapping
> stores on abnormal edges before performing the reverse LCM, but we
> don't kill them before we remove available loads)
> 
> However, even if you comment out removing the redundant avail stores,
> always set not transparent and killed if it's killed in a basic block,
> etc, you *still* get wrong answers.
> 
> So store_killed_in_insn isn't quite right, even in the above version.
Hope this helps,

Honza
> 
> --Dan
> 
> -- 
> "When I was a baby, I kept a diary.  Recently, I was rereading
> it.  It said, "Day 1 -- Still tired from the move.  Day 2 --
> Everybody talks to me like I'm an idiot."
> "-Steven Wright