[cfe-dev] Way to compare two Function bodies.

[Richard Smith]

On Wed, Jul 17, 2013 at 5:20 PM, Pavan Pattanada <pattanad at uci.edu> wrote:

> Yes, What you have mentioned is exactly what I want. So does it mean that
> Stmt::Profile would generate unique ID (llvm::FoldingSetNodeID)
> irrespective of it being a compound statement or not? If so, could I use it
> to compare the two functions using the IDs that are generated using
> FunctionDecl::getBody()::profile() ?
>

Yes, you can Stmt::Profile to compare two function bodies. But as noted
below, it won't quite do what you want, because it doesn't consider
variables declared within the statement to be "the same". You could fix
this by teaching StmtProfiler to map declarations to some kind of
declaration index if they are declared within the statement being profiled.
You'd need similar treatment for LabelDecls. I don't see a good reason why
we wouldn't accept such a patch for upstream Clang.


> Thanks,
> Pavan
>
>
> On Wed, Jul 17, 2013 at 5:01 PM, Richard Smith <richard at metafoo.co.uk>wrote:
>
>> On Wed, Jul 17, 2013 at 4:18 PM, Pavan Pattanada <pattanad at uci.edu>wrote:
>>
>>> By "same", I mean, their ASTs to be the same to start with. I am working
>>> on a tool,  which is used to syntactic/semantic similarity between two
>>> versions of the code base. So far, I have been able to get the
>>> FunctionDecls of both versions of a function into memory. But I am not sure
>>> how to compare them.
>>>
>>
>> This is still a little imprecise. Should functions compare equal if
>> variables have been renamed between them? What if an expression has been
>> rewritten into a trivially equivalent form (for instance, parentheses were
>> added or removed, or p->x was changed to (*p).x)?
>>
>> Stmt::Profile does nearly what you want (it's the mechanism we use to
>> determine if two dependent expressions are equivalent for the purposes of
>> template redeclaration matching), but it will treat
>>
>>   void f() { int n; }
>>   void g() { int n; }
>>
>> as having different bodies, because they do not declare the same
>> variable. That's probably not very hard to fix.
>>
>>
>>> ~Pavan
>>>
>>>
>>> On Wed, Jul 17, 2013 at 3:42 PM, Richard Smith <richard at metafoo.co.uk>wrote:
>>>
>>>> On Wed, Jul 17, 2013 at 10:10 AM, Pavan Pattanada <pattanad at uci.edu>wrote:
>>>>
>>>>> Hi,
>>>>> I need to compare two versions of the same clang::FunctionDecl
>>>>> function body(a function in C). I would need to compare them statement by
>>>>> statement and say if the two versions are the same. Is there a neat way to
>>>>> do this in the clang framework?
>>>>>
>>>>
>>>> This question is too vague to answer: what do you mean by "the same"?
>>>> Same source text, same tokens, same tokens other than variable naming,
>>>> something else?
>>>>
>>>
>>>
>>
>
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