[cfe-dev] Decl::dumpXML and -DNDEBUG

[Matthieu Monrocq]

On Mon, Jul 16, 2012 at 7:44 PM, Alexander Kornienko <alexfh at google.com>wrote:

> Hi all,
>
> I've recently implemented a tool named clang-ast-dump, which allows to
> dump selectively an AST of user-specified translation units. It's a really
> simple tool now, most of it's code is node filtering. The rest is done by
> Decl::dumpXML.
>
> Now the problem: Decl::dumpXML does nothing when compiled with -DNDEBUG. I
> assume that initially this method was meant to be only helpful during
> debugging of clang code, but now there are a couple of reasons to review
> this decision, I think:
>   * clang -cc1 mode has a command line option "-ast-dump-xml", which uses
> dumpXML, and currently it won't work with -DNDEBUG (e.g. when builing
> with CMake: Release configuration + LLVM_ASSERTIONS_ENABLED=OFF);
>   * clang-ast-dump tool uses it.
>
> A comment in *DumpXML.cpp* states:
> // Only pay for this in code size in assertions-enabled builds.
>
> But having -ast-dump-xml option conflicts with this idea: either we have
> to disable this option completely in non-assertion-enabled builds, or we
> have to drop this idea of not-having the dumpXML implementation in them.
> The third option would be to drop the -ast-dump-xml option completely and
> instead use clang-ast-dump tool when needed. In this case we could only
> use an implementation of Decl::dumpXML in the tool and exclude it from
> clang binary.
>
> --
> Regards,
> Alexander Kornienko
>
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>
>
I think the latter solution (separate tool) would perhaps make the most
sense. It seems to me that we get the best of both worlds: a lean compiler
and a verbose (and possibly richer and richer) tool for debugging.

If the tool had been maintained on a separate repository, the question of
bitrot would have risen, however if we speak about a tool maintained within
the clang repository (albeit a dedicated directory) then we can have the
build bots verifying that it compiles and its test-suite pass so that
modifications on the AST are propagated.

-- Matthieu
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