[cfe-dev] Finding redundant #includes

[Chandler Carruth]

On Sat, Dec 12, 2009 at 1:01 PM, Ted Kremenek <kremenek at apple.com> wrote:
> Just a thought: I wonder if for top-level #includes, one possibility is to remove the #include and see if it produces the same translation afterwards in the main source file.  That would avoid the issues with explicitly reasoning about preprocessor logic, and would (I believe) handle the simplest case that people care about.

For reference, we do this and have found it be effective, especially
combined with a distributed compilation framework which can do even
the preprocessing phase
(http://google-opensource.blogspot.com/2008/08/distccs-pump-mode-new-design-for.html).
I'd be interested if there are less expensive ways to achieve these
results though.

>
> On Dec 12, 2009, at 12:26 PM, steve naroff wrote:
>
>> Good points. I think the diagnostics would need some interpretation (by a human).
>>
>> If we wanted to get "fancy", we could devise some way to determine if a declaration occurred within a #ifdef clause (special casing the #ifndef that is commonly at the begin/end of every C header). Unfortunately, any feature involving the preprocessor is usually more complex than it should be (given the ability to arbitrary mutate headers in different contexts...including the same compilation unit:-(
>>
>> Fortunately, ObjC headers and user-defined (i.e. non-system) headers usually aren't as gross...
>>
>> snaroff
>>
>> On Dec 12, 2009, at 2:56 PM, Ted Kremenek wrote:
>>
>>> Doing it correctly wouldn't be too hard from the AST perspective, but would be tricky when considering preprocessor logic.  Any macros defined in a header and later used outside that header causes a dependency.  Moreover, if a file can be compiled under different contexts, e.g., on Mac OS X one can compile for i386, x86_64, etc., then the "liveness" of a #include can change between translations.
>>>
>>> On Dec 12, 2009, at 8:51 AM, steve naroff wrote:
>>>
>>>> Hi Andrew,
>>>>
>>>> I don't believe we currently have such a feature (though it's an
>>>> interesting idea).
>>>>
>>>> Implementing this wouldn't be too difficult, however it certainly
>>>> isn't a "quick hack".
>>>>
>>>> snaroff
>>>>
>>>> On Dec 12, 2009, at 11:13 AM, Andrew Price wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> Can clang's analysis features help me find #includes which are no
>>>>> longer
>>>>> required in a C source file? I'm working on cleaning up some old
>>>>> crufty
>>>>> code and it would be good to have this functionality.
>>>>>
>>>>> Andrew
>>>>> _______________________________________________
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>>>>
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>>
>
>
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