2011/7/13 Richard Guenther <richard.guent...@gmail.com>:
> On Wed, Jul 13, 2011 at 1:08 PM, Kai Tietz <ktiet...@googlemail.com> wrote:
>> 2011/7/13 Richard Guenther <richard.guent...@gmail.com>:
>>> On Wed, Jul 13, 2011 at 11:04 AM, Kai Tietz <ktiet...@googlemail.com> wrote:
>>>> Sorrty, the TRUTH_NOT_EXPR isn't here the point at all. The underlying
>>>> issue is that fold-const re-inttroduces TRUTH_AND/OR and co.
>>>
>>> I'm very sure it doesn't re-constrct TRUTH_ variants out of thin air
>>> when you present it with BIT_ variants as input.
>>
>> Well, look into fold-const's fold_binary_loc function and see
>>
>> /* ARG0 is the first operand of EXPR, and ARG1 is the second operand.
>>
>> First check for cases where an arithmetic operation is applied to a
>> compound, conditional, or comparison operation. Push the arithmetic
>> operation inside the compound or conditional to see if any folding
>> can then be done. Convert comparison to conditional for this purpose.
>> The also optimizes non-constant cases that used to be done in
>> expand_expr.
>>
>> Before we do that, see if this is a BIT_AND_EXPR or a BIT_IOR_EXPR,
>> one of the operands is a comparison and the other is a comparison, a
>> BIT_AND_EXPR with the constant 1, or a truth value. In that case, the
>> code below would make the expression more complex. Change it to a
>> TRUTH_{AND,OR}_EXPR. Likewise, convert a similar NE_EXPR to
>> TRUTH_XOR_EXPR and an EQ_EXPR to the inversion of a TRUTH_XOR_EXPR. */
>>
>> if ((code == BIT_AND_EXPR || code == BIT_IOR_EXPR
>> || code == EQ_EXPR || code == NE_EXPR)
>> && ((truth_value_p (TREE_CODE (arg0))
>> && (truth_value_p (TREE_CODE (arg1))
>> || (TREE_CODE (arg1) == BIT_AND_EXPR
>> && integer_onep (TREE_OPERAND (arg1, 1)))))
>> || (truth_value_p (TREE_CODE (arg1))
>> && (truth_value_p (TREE_CODE (arg0))
>> || (TREE_CODE (arg0) == BIT_AND_EXPR
>> && integer_onep (TREE_OPERAND (arg0, 1)))))))
>> {
>> tem = fold_build2_loc (loc, code == BIT_AND_EXPR ? TRUTH_AND_EXPR
>> : code == BIT_IOR_EXPR ? TRUTH_OR_EXPR
>> : TRUTH_XOR_EXPR,
>> boolean_type_node,
>> fold_convert_loc (loc, boolean_type_node, arg0),
>> fold_convert_loc (loc, boolean_type_node, arg1));
>>
>> if (code == EQ_EXPR)
>> tem = invert_truthvalue_loc (loc, tem);
>>
>> return fold_convert_loc (loc, type, tem);
>> }
>>
>> Here unconditionally TRUTH_AND/TRUTH_OR gets introduced, if operands
>> are of kind truth. This is btw the point, why you see that those
>> cases are handled. But as soon as this part is turned off for BIT_-
>> IOR/AND, we need to do the folding for 1-bit precision case explicit.
>
> First of all this checks for a quite complex pattern - where do we pass
> such complex pattern from the gimple level to fold? For the EQ/NE_EXPR
> case forwprop probably might be able to feed it that, but then how does
> it go wrong? The above could also simply be guarded by !in_gimple_form.
>
> Richard.
See reassoc pass as example and this hacky maybe_fold_and_comparisons
/ maybe_fold_or_comparisons functions. As indeed we want still be
able to do comparison foldings without getting back an TRUTH-op.
Additionally we have a lot of passes - like vectorizer - which are
happily try to build new condition on tree-level. This is another
place I saw issues and tree-cfg failures. And last but not least those
truth-ops might be reintroduced in gimple_fold, as soon as we see
bitwise-ops on one-bit precision integral type as truth_value.
Kai
