[cfe-dev] Semantic Analysis in Clang

Fri Jan 25 07:26:18 PST 2013

Hi,
  I am interested in helping any way I can. I am a research assistant and
always looking to help the community. Unfortunately, I am new to compiler
theory. If you can give me a few guidelines on how to achieve that, I would
be glad to help. Also, can you please name a few good resources on compiler
theory (my university isn't focusing on compilers so not many people here
to help).
   Regarding clang, what exactly happens when clang encounters an error (I
mean i want to pause the recursive visitor at the point when it encounters
an error and not end the program). Also, is it possible to parse the code
in rewriter buffer without saving it (parse on the fly).

Regards,
Adil

On Fri, Jan 25, 2013 at 7:52 PM, Manuel Klimek <klimek at google.com> wrote:

> On Fri, Jan 25, 2013 at 3:43 PM, Mohammad Adil <madil90 at gmail.com> wrote:
>
>> Let us say that I write some code which has some errors. Now I am
>> reparsing it. Can I halt the parsing when I encounter an error so that I
>> can remedy it? If so, what happens to the AST? I mean, does it break at
>> that point or does it contain the rest of the code too with some kind
>> of substitution for the error part?
>>
>
> No, if you reparse it and it breaks, all you know is that what you wanted
> to do was incorrect... As I mentioned, whether this is a practical approach
> depends on what your fallback strategy is - for example, if you don't want
> to do anything in case of an error, simply not saving after getting an
> error in the reparsing would solve the problem.
>
> That said, it would be really cool to have full access to the lookup after
> the semantic analysis - so if you're interested in tackling this, I'd
> expect that you'd make a lot of people very happy :D
>
> Cheers,
> /Manuel
>
>
>>
>>
>>
>> On Fri, Jan 25, 2013 at 7:31 PM, Manuel Klimek <klimek at google.com> wrote:
>>
>>> On Fri, Jan 25, 2013 at 2:57 PM, Mohammad Adil <madil90 at gmail.com>wrote:
>>>
>>>> I need to insert some code in the file being parser. I need to make
>>>> sure that the resulting file compiles fine. The code that I am inserting
>>>> will mostly be " ostream << type_x ;". Now before I do that, I need to
>>>> ensure that "type_x" has a stream operator defined. Is that possible any
>>>> other way? I am very grateful for your help.
>>>>
>>>
>>> What we do in the c++11 transition tools in clang-extra is:
>>> - parse
>>> - detect place to insert
>>> - insert
>>> - reparse, look for errors
>>>
>>> Whether that's viable depends on how big the chance is that you're
>>> making an error, and what fallbacks you have.
>>>
>>> Cheers,
>>> /Manuel
>>>
>>>
>>>
>>>>
>>>> Regards,
>>>> Adil
>>>>
>>>>
>>>> On Fri, Jan 25, 2013 at 6:34 PM, Manuel Klimek <klimek at google.com>wrote:
>>>>
>>>>> On Fri, Jan 25, 2013 at 1:13 PM, Mohammad Adil <madil90 at gmail.com>wrote:
>>>>>
>>>>>> Thanks for the reply. Well, here's the detailed problem. Once all the
>>>>>> syntax checking has been done, the next step before generating IR is to do
>>>>>> semantic analysis and type checking. Let us say that I encounter a code
>>>>>> like this:
>>>>>>
>>>>>> string b;
>>>>>> vector<T> a;
>>>>>> cout<<b;
>>>>>> cout<<a;
>>>>>>
>>>>>>       How does clang figure out that the 3rd statement is valid
>>>>>> because an operator for string exists, while the 4rth statement is not
>>>>>> valid. More specifically, I want to know how clang searches through all the
>>>>>> operators (or functions). I have to use this functionality. Does the clang
>>>>>> api allow me to do this easily or will I have to replicate this
>>>>>> functionality?
>>>>>>
>>>>>
>>>>> As far as I know the clang API does not allow you to do that easily -
>>>>> you need the full semantic analysis state at that point during parsing, and
>>>>> as far as I'm aware this only exists implicitly in the Sema* classes.
>>>>> Overload resolution is one of those really complex and messy parts of C++ :)
>>>>>
>>>>> If you let us know what actual problem you're trying to solve, there
>>>>> might be solutions to that which are simpler than using overload resolution
>>>>> :)
>>>>>
>>>>> Cheers,
>>>>> /Manuel
>>>>>
>>>>>
>>>>>> Regards,
>>>>>> Adil
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Fri, Jan 25, 2013 at 4:35 PM, Manuel Klimek <klimek at google.com>wrote:
>>>>>>
>>>>>>> On Thu, Jan 24, 2013 at 12:49 PM, madil90 <madil90 at gmail.com> wrote:
>>>>>>>
>>>>>>>> Hi,
>>>>>>>>    I am looking to perform some semantic analysis in clang. More
>>>>>>>> specifically, I want to know whether a function exists for a
>>>>>>>> certain type.
>>>>>>>> The function is global. e.g.
>>>>>>>>
>>>>>>>> String toString(A a);
>>>>>>>>
>>>>>>>>     I want to differentiate that this function exists for type A
>>>>>>>> and not for
>>>>>>>> type B. I have built an AST and am parsing it. How can I achieve
>>>>>>>> this?
>>>>>>>> (Whenever I encounter a type)
>>>>>>>>
>>>>>>>
>>>>>>> I'd loop over all declarations of toString and see which type they
>>>>>>> take... Perhaps I'm misunderstanding your problem though :)
>>>>>>>
>>>>>>> Cheers,
>>>>>>> /Manuel
>>>>>>>
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Adil
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> View this message in context:
>>>>>>>> http://clang-developers.42468.n3.nabble.com/Semantic-Analysis-in-Clang-tp4030012.html
>>>>>>>> Sent from the Clang Developers mailing list archive at Nabble.com.
>>>>>>>> _______________________________________________
>>>>>>>> cfe-dev mailing list
>>>>>>>> cfe-dev at cs.uiuc.edu
>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Mohammad Adil
>>>>>> LUMS SSE
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Mohammad Adil
>>>> LUMS SSE
>>>>
>>>
>>>
>>
>>
>> --
>> Mohammad Adil
>> LUMS SSE
>>
>
>

-- 
Mohammad Adil
LUMS SSE
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