Re: [RFC 0/8] Introduce an extensible static analyzer

[Daniel P . Berrangé]

On Mon, Jul 04, 2022 at 08:30:08PM +0100, Alberto Faria wrote:
> On Mon, Jul 4, 2022 at 5:28 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> > Have you done any measurement see how much of the overhead is from
> > the checks you implemented, vs how much is inherantly forced on us
> > by libclang ? ie what does it look like if you just load the libclang
> > framework and run it actross all source files, without doing any
> > checks in python.
> 
> Running the script with all checks disabled, i.e., doing nothing after
> TranslationUnit.from_source():
> 
>     $ time ./static-analyzer.py build
>     [...]
>     Analyzed 8775 translation units in 274.0 seconds.
> 
>     real    4m34.537s
>     user    49m32.555s
>     sys     1m18.731s
> 
>     $ time ./static-analyzer.py build block util
>     Analyzed 162 translation units in 4.2 seconds.
> 
>     real    0m4.804s
>     user    0m40.389s
>     sys     0m1.690s
> 
> This is still with 12 threads on a 12-hardware thread laptop, but
> scalability is near perfect. (The time reported by the script doesn't
> include loading and inspection of the compilation database.)
> 
> So, not great. What's more, TranslationUnit.from_source() delegates
> all work to clang_parseTranslationUnit(), so I suspect C libclang
> wouldn't do much better.
> 
> And with all checks enabled:
> 
>     $ time ./static-analyzer.py build block util
>     [...]
>     Analyzed 162 translation units in 86.4 seconds.
> 
>     real    1m26.999s
>     user    14m51.163s
>     sys     0m2.205s
> 
> Yikes. Also not great at all, although the current implementation does
> many inefficient things, like redundant AST traversals. Cutting
> through some of clang.cindex's abstractions should also help, e.g.,
> using libclang's visitor API properly instead of calling
> clang_visitChildren() for every get_children().
> 
> Perhaps we should set a target for how slow we can tolerate this thing
> to be, as a percentage of total build time, and determine if the
> libclang approach is viable. I'm thinking maybe 10%?
> 
> > If i run 'clang-tidy' across the entire source tree, it takes 3 minutes
> > on my machine, but there's overhead of repeatedly starting the process
> > in there.
> 
> Is that parallelized in some way? It seems strange that clang-tidy
> would be so much faster than libclang.

No, that was me doing a dumb

     for i in `git ls-tree --name-only -r HEAD:`
     do
        clang-tidy $i 1>/dev/null 2>&1
     done

so in fact it was parsing all source files, not just .c files (and
likely whining about non-C files.  This was on my laptop with 6
cores / 2 SMT

With regards,
Daniel
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