[cfe-dev] GSoC 2018

Fri Mar 23 11:39:11 PDT 2018

Indeed the constraints start to appear when there are
multiplications/divisions/remainders, but I noticed that it only prints the
constraints when it's able to solve them.

Maybe in a higher level it's dropping constraints without querying if the
solver can handle it?

I'll keep looking into it.

2018-03-23 18:25 GMT+00:00 Artem Dergachev <noqnoqneo at gmail.com>:

> Try making assumptions over 2 * x, these should work if i recall correctly.
>
>
> On 3/23/18 10:51 AM, Mikhail Ramalho via cfe-dev wrote:
>
> Hi,
>
>
>> We would have to find an easier example first, where the core
>> modification are not necessary.
>> For the easier example: I think it would have to be simple arithmetics
>> over integers, even negation would work.
>> The current solver can not handle any relational constraints.
>>
>>
> I'm having some problems finding a simple benchmark where the constraints
> are not dropped.
>
> For instance, consider the following (safe) program:
>
> void foo(unsigned x, unsigned y)
> {
>   if (x > y)
>     return;
>
>   int base;
>
>   if (x <= y)
>     base = 1;
>
>   assert(base == 1);
> }
>
> But the constraints are empty (both when I print the graph and the SMT
> formula). I'm calling the analyzer:
>
> $ ~/myclang/bin/clang --analyze -Xclang -analyzer-viz-egraph-graphviz
> -Xanalyzer -analyzer-checker=debug.DumpCFG main2.c
>
> I'm assuming that the constraints are being dropped somehow but is there
> any other way to check it?
>
> Btw, I'm using the head of the release_60 branch.
>
> Thank you,
>
>
>> BTW instead of looking into the Z3ConstraintManager I think it would be
>> easier to look at the exploded graph (using the option I have previously
>> described)
>> and see what formulas are mentioned there.
>>
>>
>> Thank you,
>>
>>
>> 2018-03-22 20:34 GMT+00:00 George Karpenkov <ekarpenkov at apple.com>:
>>
>>> Hi Mikhail,
>>>
>>> That’s a good improvement!
>>>
>>> I think an awesome next step would be to see whether the analyzer
>>> already has the formula required to solve your motivational example.
>>> This would be a preliminary feasibility study: if the formula is there,
>>> it’s just a matter of converting it and giving it to Z3, and otherwise,
>>> the exercise is much harder and might require substantial changes.
>>>
>>> Perhaps an easiest way to see what formulas the analyzer has is to
>>> launch it with an extra flag
>>> `-Xclang -analyzer-viz-egraph-graphviz` which would dump a graph in a
>>> GraphViz format containing all the information analyzer has along all the
>>> states.
>>>
>>> This is important for judging feasibility, as it might be the case that
>>> analyzer at some point decides to get rid of the “complex” constraint.
>>> While it would be possible to change that, that would be a second step
>>> of the project,
>>> and for preliminary evaluation a simpler example would be needed.
>>>
>>> Also, the information above could be helpful for structuring the
>>> project: a first stage would be checking most trivial examples, a second
>>> stage would be seeing how far
>>> can we get with only minimal modifications to the core.
>>>
>>> Regards,
>>> George
>>>
>>> On Mar 22, 2018, at 1:19 PM, Mikhail Ramalho <mikhail.ramalho at gmail.com>
>>> wrote:
>>>
>>> Hi all,
>>>
>>> Thank you for the feedback, George and Dominic.
>>>
>>> I updated my proposal with an example, showing the encoded SMT formula
>>> for the program and a brief explanation of the verification process. I used
>>> a simplified program from a bug report in Bugzilla.
>>>
>>> May I ask for some feedback in this section?
>>>
>>> ~
>>>
>>> I addressed most of the comments, except for:
>>>
>>> George: stretch goals are great, but for now I think it would be better
>>> to focus on writing a considerably more detailed proposal on how and why
>>> the main goal would be implemented.
>>>
>>> I tried to explain the motivation in the Overview section, do you think
>>> a motivation section would be better?
>>>
>>> Regarding the how, I'll have another look in the BugReportVisitor and
>>> update the proposal with a more concrete solution.
>>>
>>> Thank you,
>>>
>>>
>>> 2018-03-21 17:54 GMT+00:00 George Karpenkov <ekarpenkov at apple.com>:
>>>
>>>> Hi Mikhail,
>>>>
>>>> I’ve added some feedback.
>>>> Overall, I think we should be aiming for something more low-level and
>>>> concrete:
>>>> adding examples with explanations would be a great improvement.
>>>>
>>>> Regards,
>>>> George
>>>>
>>>>
>>>> On Mar 21, 2018, at 10:12 AM, Mikhail Ramalho <
>>>> mikhail.ramalho at gmail.com> wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I've written a first draft of my proposal:
>>>>
>>>> https://docs.google.com/document/d/1-zNSv0l4WyoxYpJUAw8LFnQq
>>>> _TY4AGjIpPu1VPkmO-g/edit?usp=sharing
>>>>
>>>> I've added a few comments in places I think need improvement.
>>>>
>>>> May I ask the community to have a look and give some feedback?
>>>>
>>>> Thank you,
>>>>
>>>>
>>>> 2018-03-12 18:24 GMT+00:00 George Karpenkov <ekarpenkov at apple.com>:
>>>>
>>>>> Hi Mikhail,
>>>>>
>>>>> I’m assuming Dominic have answered your questions regarding the point
>>>>> (3).
>>>>>
>>>>> On point (1) I have recently sent an email on the list answering, I
>>>>> believe, to essentially the same question:
>>>>> http://lists.llvm.org/pipermail/cfe-dev/2018-March/057064.html
>>>>>
>>>>> (yes, unfortunately we do not have better archives, so messages might
>>>>> be often hard to track)
>>>>>
>>>>> 2. I still don't quite understand how dynamic memory track works in
>>>>> the analyzer, is the double checker expected to work for pointers and
>>>>> dynamic memory as well? I'm assuming yes here and that Z3ConstraintManager might
>>>>> need to be extended somehow (a plan will be added to the proposal).
>>>>>
>>>>>
>>>>> I think here we should get the extra precision for free by adding a
>>>>> bug reporter visitor, as described in the email thread I have linked to.
>>>>>
>>>>> Please feel free to ask any further questions, bug reporter visitors
>>>>> are quite messy in the analyzer.
>>>>>
>>>>> Regards,
>>>>> George
>>>>>
>>>>>
>>>>> ~
>>>>>
>>>>> 3. This is a list of the TODOs in Z3ConstraintManager, from more
>>>>> important to less important, in my opinion. I just want to know if the
>>>>> analyzer's developers (and the project mentor) agree with this list, as it
>>>>> might go into my proposal:
>>>>>
>>>>> 3.1. Don't assume nearest ties to even rounding mode: currently, only
>>>>> rounding to even is supported, even if the code changes the rounding mode
>>>>> using fesetround.
>>>>>
>>>>> 3.2. Don't add all the constraints, only the relevant ones: adding
>>>>> unnecessary constraints will slowdown the solver.
>>>>>
>>>>> 3.3. Refactor doTypeConversion to use built-in conversion functions (Refactor
>>>>> to Sema::FindCompositePointerType(), and
>>>>> Sema::CheckCompareOperands(); Refine behavior for invalid type casts)
>>>>> 3.4. Refactor doIntTypeConversion to use Sema::handleIntegerConversion(
>>>>> )
>>>>> 3.5. Refactor doFloatTypeConversion to use
>>>>> Sema::handleFloatConversion()
>>>>>
>>>>> I bundled this together because, although the conversion seems
>>>>> incomplete (based on the comments), it's about removing duplicated code.
>>>>>
>>>>> 3.6. Refactor getAPSIntType(const llvm::APSInt &Int) const to put
>>>>> elsewhere.
>>>>>
>>>>> ~
>>>>>
>>>>> Thank you,
>>>>>
>>>>>
>>>>> 2018-02-24 1:03 GMT+00:00 Devin Coughlin <dcoughlin at apple.com>:
>>>>>
>>>>>>
>>>>>>
>>>>>> > On Feb 23, 2018, at 9:29 AM, Mikhail Ramalho via cfe-dev <
>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>> >
>>>>>> > I also have a question about the proposal. I understand that ideas
>>>>>> about the project will be discussed in the mailing list. However, once
>>>>>> that's settled and I write my first draft proposal, should I send it to the
>>>>>> mailing list for discussion again or should I send it only to the mentor?
>>>>>>
>>>>>> Please make sure to keep email discussions on the mailing list rather
>>>>>> than just personal email. This is a topic that members of the community
>>>>>> will be interested in and will have valuable feedback on.
>>>>>>
>>>>>> Devin
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Mikhail Ramalho.
>>>>> _______________________________________________
>>>>> cfe-dev mailing list
>>>>> cfe-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> Mikhail Ramalho.
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>>
>>> Mikhail Ramalho.
>>>
>>>
>>>
>>
>>
>> --
>>
>> Mikhail Ramalho.
>>
>>
>>
>
>
> --
>
> Mikhail Ramalho.
>
> _______________________________________________
> cfe-dev mailing listcfe-dev at lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
>
>

-- 

Mikhail Ramalho.
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