Re: [PATCH, generic] Fix for define_subst

[Michael Zolotukhin <michael dot v dot zolotukhin at gmail dot com>]

> Well, there does seem to be a mistake -- the use of NULL in the first
> place.  It seems to me that the easiest fix is
>
>   condition = "";
>
> right at the beginning.
Yep, that'll work too, you're right.

On 28 November 2012 22:36, Richard Henderson <rth@redhat.com> wrote:
> On 11/28/2012 09:20 AM, Michael Zolotukhin wrote:
>>> Where was the null condition created in the first place?
>> The reason it's happening is following. Before introduction of
>> define_subst, function apply_iterators had the following loop:
>>       condition = NULL;
>>       FOR_EACH_VEC_ELT (iterator_uses, i, iuse)
>>         {
>>           v = iuse->iterator->current_value;
>>           iuse->iterator->group->apply_iterator (iuse->ptr, v->number);
>>           condition = join_c_conditions (condition, v->string);
>>         }
>>       apply_attribute_uses ();
>>       x = copy_rtx_for_iterators (original);
>>       add_condition_to_rtx (x, condition);
>>
>> This loop always iterated at least once, so 'condition' always became
>> not-null (though, it could become empty-string ""). So, function
>> add_condition_to_rtx always had not-null string in the arguments.
>>
>> With subst-iterators this loop is looking like this:
>>       condition = NULL;
>>       FOR_EACH_VEC_ELT (iterator_uses, i, iuse)
>>         {
>>           if (iuse->iterator->group == &substs)
>>             continue;
>>           v = iuse->iterator->current_value;
>>           iuse->iterator->group->apply_iterator (iuse->ptr, v->number);
>>           condition = join_c_conditions (condition, v->string);
>>         }
>> So, it's possible that join_c_condition wouldn't be called at all, and
>> 'condition' will remain NULL. Then it goes to add_condition_to_rtx and
>> we get the fail we've seen.
>>
>> There is no mistake in such behaviour, but now we should be aware of
>> possible NULL-string. It should be handled properly, and I see two
>> places where we could do that - in join_c_conditions or in add_c_tests
>> and maybe_eval_c_test.
>>
>
> Well, there does seem to be a mistake -- the use of NULL in the first
> place.  It seems to me that the easiest fix is
>
>   condition = "";
>
> right at the beginning.
>
>
> r~



-- 
---
Best regards,
Michael V. Zolotukhin,
Software Engineer
Intel Corporation.