[cfe-dev] Libclang: Bad performance on reparse

[Alex L via cfe-dev]

Hi Janosch.

Thanks for providing a clear test-case. I'd be interested in following up
on this, can you file a bug report?

Cheers,
Alex

On 16 August 2017 at 09:18, Janosch Machowinski via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
> while testing kdevelop 5, I ran into some problems with the code
> completion.
> I debugged it and tracked it down to the reparse step in libclang taking
> 5 seconds in an i7-5930K.
>
> In my concrete example, I got a cpp file that consists of 173 line of code,
> with minor template usage.
> This program includes a big amount of headers, that use heavy templating.
>
> The initial parse takes 13 seconds, which is fine. What makes me wonder is
> the reparse step taking so long, as everything in the headers should be
> cached by the PCH.
>
> I prepared a git repo with an example, if you want to look at the code I
> used,
> or try it yourself.
>
> https://github.com/jmachowinski/clangTest
>
> It should be noted, that I do not set CXTranslationUnit_Incomplete,
> as kdevelop needs the flag to be NOT set. Setting the flag speeds up
> reparse
> to 0.5 seconds.
>
> Greetings
>     Janosch
>
>
> Debug output :
>
> Parse start
> Precompiling preamble:   8.2960 (100.0%)   0.2760 (100.0%)   8.5720
> (100.0%)   8.5706 (100.0%)
> Parsing ../test/tdot_asguard.cpp:   4.8320 (100.0%)   0.0200 (100.0%)
>  4.8520 (100.0%)   4.8499 (100.0%)
>   ASTContext: expressions, declarations, and types: 254289451
>   ASTContext: identifiers: 507904
>   ASTContext: selectors: 4096
>   ASTContext: side tables: 9053176
>   Code completion: cached global results: 0
>   SourceManager: content cache allocator: 86016
>   SourceManager: malloc'ed memory buffers: 2070147
>   SourceManager: mmap'ed memory buffers: 0
>   SourceManager: data structures and tables: 124472904
>   ExternalASTSource: malloc'ed memory buffers: 0
>   ExternalASTSource: mmap'ed memory buffers: 188282552
>   Preprocessor: malloc'ed memory: 306782
>   Preprocessor: PreprocessingRecord: 838904
>   Preprocessor: header search tables: 43
> Parse took 13.4559
> Cache global code completions for ../test/tdot_asguard.cpp:   0.1280
> (100.0%)   0.1280 (100.0%)   0.1267 (100.0%)
> Reparsing ../test/tdot_asguard.cpp:   5.0600 (100.0%)   0.0440 (100.0%)
>  5.1040 (100.0%)   5.1043 (100.0%)
>   ASTContext: expressions, declarations, and types: 259532331
>   ASTContext: identifiers: 2326528
>   ASTContext: selectors: 4096
>   ASTContext: side tables: 9151480
>   Code completion: cached global results: 4063232
>   SourceManager: content cache allocator: 111147
>   SourceManager: malloc'ed memory buffers: 2082327
>   SourceManager: mmap'ed memory buffers: 0
>   SourceManager: data structures and tables: 124472904
>   ExternalASTSource: malloc'ed memory buffers: 0
>   ExternalASTSource: mmap'ed memory buffers: 188282552
>   Preprocessor: malloc'ed memory: 8324702
>   Preprocessor: PreprocessingRecord: 1775864
>   Preprocessor: header search tables: 43
> ReParse took 5.10452
>
>
>
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