Re: [PATCH, generic] Fix for define_subst

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

So, ok for commit this patch?

Changelog:
2012-11-29  Michael Zolotukhin  <michael.v.zolotukhin@intel.com>

        * gensupport.c (maybe_eval_c_test): Remove not-null check for expr.
        * read-rtl.c (apply_iterators): Initialize condition with "" instead
        of NULL.

On 28 November 2012 23:46, Michael Zolotukhin
<michael.v.zolotukhin@gmail.com> wrote:
>> 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.



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

Attachment: null-condition-fix.patch
Description: Binary data