[patch middle-end]: Missed optimization for (x & ~y) | (~x & y)

[Kai Tietz]

2011/4/20 Jakub Jelinek <jakub@redhat.com>:
> On Wed, Apr 20, 2011 at 05:22:31PM +0200, Kai Tietz wrote:
>> --- gcc.orig/gcc/fold-const.c 2011-04-20 17:10:39.478091900 +0200
>> +++ gcc/gcc/fold-const.c      2011-04-20 17:11:22.901039400 +0200
>> @@ -10660,6 +10660,28 @@ fold_binary_loc (location_t loc,
>>         && reorder_operands_p (arg0, TREE_OPERAND (arg1, 0)))
>>       return omit_one_operand_loc (loc, type, arg0, TREE_OPERAND (arg1, 0));
>>
>> +      /* (X & ~Y) | (~X & Y) is X ^ Y */
>> +      if (TREE_CODE (arg0) == BIT_AND_EXPR
>> +       && TREE_CODE (arg1) == BIT_AND_EXPR)
>> +        {
>> +       tree a0, a1, l0, l1, n0, n1;
>> +
>> +       a0 = fold_convert_loc (loc, type, TREE_OPERAND (arg1, 0));
>> +       a1 = fold_convert_loc (loc, type, TREE_OPERAND (arg1, 1));
>> +
>> +       l0 = fold_convert_loc (loc, type, TREE_OPERAND (arg0, 0));
>> +       l1 = fold_convert_loc (loc, type, TREE_OPERAND (arg0, 1));
>> +
>> +       n0 = fold_build1_loc (loc, BIT_NOT_EXPR, type, l0);
>> +       n1 = fold_build1_loc (loc, BIT_NOT_EXPR, type, l1);
>> +
>> +       if ((operand_equal_p (n0, a0, 0)
>> +            && operand_equal_p (n1, a1, 0))
>> +           || (operand_equal_p (n0, a1, 0)
>> +               && operand_equal_p (n1, a0, 0)))
>> +         return fold_build2_loc (loc, TRUTH_XOR_EXPR, type, l0, n1);
>> +     }
>> +
>
> I must say I don't like first folding/building new trees, then testing
> and then maybe optimizing, that is slow and creates unnecessary garbage
> in the likely case the optimization can't do anything.
>
> Wouldn't something like:
>    int arg0_not = TREE_CODE (TREE_OPERAND (arg0, 1)) == BIT_NOT_EXPR;
>    int arg1_not = TREE_CODE (TREE_OPERAND (arg1, 1)) == BIT_NOT_EXPR;
>    if (TREE_CODE (TREE_OPERAND (arg0, arg0_not)) == BIT_NOT_EXPR
>        && TREE_CODE (TREE_OPERAND (arg1, arg1_not)) == BIT_NOT_EXPR
>        && operand_equal_p (TREE_OPERAND (TREE_OPERAND (arg0, arg0_not), 0),
>                            TREE_OPERAND (arg1, 1 - arg1_not), 0)
>        && operand_equal_p (TREE_OPERAND (TREE_OPERAND (arg1, arg1_not), 0),
>                            TREE_OPERAND (arg0, 1 - arg0_not), 0))
>      return fold_build2_loc (loc, TRUTH_XOR_EXPR, type,
>                              fold_convert_loc (loc, type,
>                                                TREE_OPERAND (arg0, 1 - arg0_not)),
>                              fold_convert_loc (loc, type,
>                                                TREE_OPERAND (arg1, 1 - arg1_not)));
> work better?
>
>        Jakub
>

Well, as special case we could use that, but we have here also to
handle integer-values, so I used fold to make sure I get inverse. Also
there might be some transformations, which otherwise might be not
caught, like !(X || Y) == !X && !Y ...

Regards,
Kai


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