2011/4/20 Jakub Jelinek <ja...@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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