[cfe-dev] Cross Translation Unit Support in Clang

Mon Jun 26 07:16:58 PDT 2017

On Mon, Jun 26, 2017 at 4:08 PM Gábor Horváth via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> Some benchmarks of the binary size after introducing the libTooling
> dependency to clang (using static linking on Linux):
>
> Release:
> 85457072 -> 85505864
> Debug:
> 1777932672 -> 1779938696
>
> The increase is less than 1% in both cases. So, in my opinion, the binary
> size is not really a problem here.
> Of course, the link times might increase a bit as well.
>
> A question is, who should make the call whether this penalty is ok or not?
>

(after replying on the patch without noticing that this thread is not part
of the patch, here it goes again :)
Richard (cc'ed) usually owns decisions around clang itself. Writing an
email to cfe-dev with the numbers and wait for whether others have concerns
would probably also be good (many will probably not continue reading this
thread).

> On 23 June 2017 at 22:06, Anna Zaks <ganna at apple.com> wrote:
>
>>
>> On Jun 23, 2017, at 12:39 PM, Gábor Horváth <xazax.hun at gmail.com> wrote:
>>
>> This is a dependency for the Static Analyzer component within clang (to
>> another component, which is in clang as well).
>>
>>
>> OK. This means that we are talking about adding a dependency on
>> libTooling to clang. This would not only effect the static analyzer, so
>> we’d need an OK from a greater clang community.
>>
>> It is a similar dependency to this:
>> https://github.com/llvm-mirror/clang/commit/a994aad333a56b8c9dd49bcfb5090a393d193387
>>
>>
>> There are 2 differences from the dependency on ASTMatchers:
>>  - Nothing that is presently in libTooling us used by clang.
>>
>
> This is actually not a difference. When the commit above was excepted, it
> was the first use of ASTMatchers in the clang binary.
>
>
>>  - The new component that the analyzer will depend on will be supporting
>> a very experimental feature.
>>
>> The other expedient options that I can see are:
>>  - Adding a separate library with just the functionality that this
>> feature needs.
>>  - Making the dependency conditional, following the same style as Z3
>> support, and keeping it that way until the feature is fully implemented.
>> This solution definitely has downsides.
>>
>> Yet another solution is to pull the analyzer out of clang, but
>> unfortunately that is non-trivial, so I am not sure if there are volunteers
>> for the task.
>>
>
> I agree that pulling the analyzer out is a big task and would also break
> the backward compatibility of the command line. So it is not the best
> solution for the users.
>
> Regards,
> Gábor
>
>
>>
>> Anna.
>>
>> On 23 June 2017 at 19:48, Anna Zaks <ganna at apple.com> wrote:
>>
>>>
>>> On Jun 23, 2017, at 1:40 AM, Gábor Horváth <xazax.hun at gmail.com> wrote:
>>>
>>> Anna,
>>>
>>> Are you ok having libTooling as a dependency of the Static Analyzer?
>>>
>>>
>>> Are we talking about introducing dependency for scan-build or clang
>>> itself?
>>>
>>> I think this is not a bad direction since it has other good utilities
>>> that the Static Analyzer could use in the future such as Replacements,
>>> FixIts.
>>>
>>> Regards,
>>> Gábor
>>>
>>> On 22 June 2017 at 12:10, Manuel Klimek <klimek at google.com> wrote:
>>>
>>>> For clang tooling, I don't really expect us to do cross-TU AST loading
>>>> outside of what modules will provide, as that inherently doesn't scale.
>>>> Instead, we usually design pipelined approaches where the first "scan" over
>>>> the codebase provides data which are reduced to the information needed for
>>>> the tool.
>>>>
>>>> That said, I can't predict the future, and people have expressed
>>>> interest in that functionality, so
>>>> a) I agree it's a good idea to add and
>>>> b) I think it's a good fit for libtooling
>>>>
>>>> Cheers,
>>>> /Manuel
>>>>
>>>>
>>>> On Thu, Jun 22, 2017 at 11:58 AM Aleksei Sidorin <a.sidorin at samsung.com>
>>>> wrote:
>>>>
>>>>> Hello Gabor,
>>>>>
>>>>> Internally, we have created XTU module inside clang (lib/XTU). I think
>>>>> it is the best way because importing is not related to analyzer
>>>>> directly. We're not going to use it outside of CSA but I think future
>>>>> users should have such possibility.
>>>>>
>>>>> 22.06.2017 12:41, Gábor Horváth пишет:
>>>>> > Hi!
>>>>> >
>>>>> > It looks like there is a consensus to accept the cross translation
>>>>> > unit analysis patch into the clang static analyzer:
>>>>> > https://reviews.llvm.org/D30691
>>>>> >
>>>>> > There is one part of the patch that is independent of the static
>>>>> > analyzer. The logic which can look up a function in an index and load
>>>>> > a serialized AST that contains the definition of the function.
>>>>> > The lookup is cached, and after the AST is loaded, the function
>>>>> > definition will be merged into the original AST.
>>>>> >
>>>>> > Right now, in the current patch, this functionality is in the
>>>>> > ASTContext. This is definitely not the right place to put this. So
>>>>> the
>>>>> > question is, do you plan to utilize similar functionality in Clang
>>>>> > tooling or clang tidy?
>>>>> >
>>>>> > If yes, we might end up creating a new module for that (or add it to
>>>>> > an existing commonly used one like libtooling?). If no, we will move
>>>>> > the corresponding code to the static analyzer.
>>>>> >
>>>>> > What do you think?
>>>>> >
>>>>> > In case you are interested in how it works, you can check out the
>>>>> > EuroLLVM talk:
>>>>> > http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#7
>>>>> >
>>>>> > Regards,
>>>>> > Gábor
>>>>>
>>>>>
>>>>> --
>>>>> Best regards,
>>>>> Aleksei Sidorin,
>>>>> SRR, Samsung Electronics
>>>>>
>>>>>
>>>
>>>
>>
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