Re: [patch tree-ssa-reassoc.c]: Better reassoication for comparision and boolean-logic

[Kai Tietz <ktietz70@googlemail.com>]

2011/5/19 Richard Guenther <richard.guenther@gmail.com>:
> On Thu, May 19, 2011 at 3:30 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> 2011/5/19 Richard Guenther <richard.guenther@gmail.com>:
>>> On Thu, May 19, 2011 at 3:08 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>>> 2011/5/19 Richard Guenther <richard.guenther@gmail.com>:
>>>>> On Thu, May 19, 2011 at 2:59 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>>>>> 2011/5/19 Richard Guenther <richard.guenther@gmail.com>:
>>>>>>> On Thu, May 19, 2011 at 2:48 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>>>>>>> Hello,
>>>>>>>>
>>>>>>>> This patch improves reassociation folding for comparision. It expands
>>>>>>>> expressions within binary-AND/OR expression like (X | Y) == 0 to (X ==
>>>>>>>> 0 && Y == 0)
>>>>>>>> and (X | Y) != 0 to (X != 0 || Y != 0).  This is necessary to allow
>>>>>>>> better reassociation
>>>>>>>> on weak pre-folded logical expressions.  This unfolding gets undone
>>>>>>>> anyway later by pass,
>>>>>>>> so no disadvantage gets introduced.
>>>>>>>> Also while going through BB-list, it tries to do some little
>>>>>>>> type-sinking for SSA sequences
>>>>>>>> like "D1 = (type) bool1; D2 = (type) bool2; D3 = D1 & D2;' to 'D1 =
>>>>>>>> bool1 & bool2; D2 = (type) D1;'.
>>>>>>>> This folding has the advantage to see better through intermediate
>>>>>>>> results with none-boolean type.
>>>>>>>> The function eliminate_redundant_comparison () got reworded so, that
>>>>>>>> doesn't break in all cases.
>>>>>>>> It now continues to find duplicates and tries to find inverse variant
>>>>>>>> (folded to constant). By this
>>>>>>>> change we don't combine possible weak optimizations too fast, before
>>>>>>>> we can find and handle
>>>>>>>> inverse or duplicates.
>>>>>>>
>>>>>>> sinking casting belongs not here but instead to tree-ssa-forwprop.
>>>>>>> I'm not sure that a != 0 | b != 0 is the better canonical variant than
>>>>>>> a | b != 0 though.
>>>>>>>
>>>>>>> is_boolean_compatible_type_p looks like a strange remanent.
>>>>>>>
>>>>>>> Richard.
>>>>>>
>>>>>> Well, a | b != 0 is for sure more optimal, but for reassociation we
>>>>>> need to see the unfolded variant temporary. This is necessary as
>>>>>> fold-const can't see through SSA statements.  But this kind of
>>>>>> expansion should be reversed then by pass to the form (a | b) != 0
>>>>>> back.
>>>>>
>>>>> ?  fold-const shouldn't deal with this at all as we are in gimple and in
>>>>> SSA form.  Surely re-association comes to play only with chains of
>>>>> the above with more than two operands.
>>>>>
>>>>> Richard.
>>>>>
>>>>>>
>>>>>> Regards,
>>>>>> Kai
>>>>>>
>>>>>
>>>>
>>>> The issue you can see by testcase binop_tor4.c, as here are the
>>>> intermediate variables d and e (with int type) are destroying the
>>>> reassociation pass. This testcase for example needs this sinking.
>>>
>>> hoisting would work equally well
>>
>> Well, but just if then all operands in combined BIT_AND/OR block are
>> getting hoisting. And well, there might be still some cases where we
>> wouldn't find the equivalent. As hoisting leads to following
>> sequences, eg:
>>
>> D1 = a != 0;
>> D2 = b != 0;
>> D3 = a == 0;
>> D4 = b == 0;
>> D5 = (long) D1
>> D6 = (long) D2
>> D7 = (long) D3
>> D8 = (long) D4
>> D9 = D5 & D6;
>> D10 = D8 & D9
>> D11 = D9 & D10;
>>
>> which means that comparision folding will never will happen as the
>> statement passed to fold algorithm is a cast to a comparison and not
>> the comparison itself.  So sinking looks more sane IMHO.
>
> The above is what you do.

No, I don't do this. Please see function sink_cast_and_expand function in patch.

  if (gimple_assign_cast_p (s1)
      && gimple_assign_cast_p (s2)
      && is_boolean_compatible_type_p (TREE_TYPE (gimple_assign_rhs1 (s1)))
      && is_boolean_compatible_type_p (TREE_TYPE (gimple_assign_rhs1 (s2)))
      && useless_type_conversion_p (TREE_TYPE (gimple_assign_rhs1 (s1)),
      				    TREE_TYPE (gimple_assign_rhs1 (s2))))
    {
      gimple_stmt_iterator gsi;
      gimple sum;
      tree op1a, op1b, tmpvar;

      tmpvar = create_tmp_reg (TREE_TYPE (gimple_assign_rhs1 (s1)), NULL);

      add_referenced_var (tmpvar);
      sum = build_and_add_sum (tmpvar, gimple_assign_rhs1 (s1),
      			       gimple_assign_rhs1 (s2), code);
      op1 = gimple_get_lhs (sum);
      op1 = fold_convert (type, op1);

      op1a = gimple_assign_rhs1 (stmt);
      op1b = gimple_assign_rhs2 (stmt);
      gsi = gsi_for_stmt (stmt);
      gimple_assign_set_rhs_from_tree (&gsi, op1);
      update_stmt (stmt);
      remove_visited_stmt_chain (op1a);
      remove_visited_stmt_chain (op1b);
      ret = true;
    }

The none-boolean cast get moved outer, not inner.

Regards,
Kai