[cfe-dev] extending ClangTool libASTUnit saving and loading

[Manuel Klimek]

On Wed Dec 17 2014 at 4:57:08 PM mobi phil <mobi at mobiphil.com> wrote:

> Well, there are currently multiple use cases in clang: pch files
>> (precompiled headers), pcm files (modules), and I think arcmigrate uses
>> ASTUnit (but I don't know the details).
>>
>
> though does make sense to tell to the compiler to say generate pch from a
> C++ file as it does not make sense, it makes sense to generate AST, which
> is possible, but.. still... it is impossible to load AST, regardless of the
> size. Any usecase I was thinking about would hold the AST temporary, so
> would not be an issue. Did some test and in avarage ast files are bit more
> than double larger as an object file with debug information.
>
>
>> The problem is that when you store the AST for a full TU, it's *huge*
>> (all the transitive headers are in it) and I'm not sure why you would want
>> to do that.
>>
> Well, from a TU point of view it makes sense to have the header
> information. When you analyze or (do code completion, I assume), you need
> the full bagage. Though having symbols that are not required by the cpp
> file is overhead. Is there any feature to say: discard unreferenced symbols
> (types, globals etc.). Still not sure how code completion works and how
> adding new symbols added to the code are updated (if at all) in the AST.
>
>
>> If you think tools are too slow, then our proposed solution for that is
>> using C++ modules (which will also dump the AST, but in a much more nuanced
>> and smart fashion).
>>
>
> well, did some research if it would be possible to build llvm and clang
> with C++ modules. No luck? Any hints?
>

C++ modules are still pretty experimental.


>
>
>> That's why the use case matters; if you're interested in processing
>> speed, the solution is modules (and the way it serializes the AST).
>>
> happy with that... would be happy to see llvm/clang built with modules. I
> am sure one could find all info in module based AST's that can be found in
> non-module AST's.
>
>
>> If your use case is something else, the answer might be something
>> different :)
>>
>
> so far I can do my job, I found enough examples in libclang to load from
> AST, just was wondering what is the point to dump AST with clang without
> being able to explicitly load it in most of the tools.
>
>
>
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