[libcxx-dev] Option to disable inline namespacing completely?

JF Bastien via libcxx-dev libcxx-dev at lists.llvm.org
Thu Nov 15 17:06:01 PST 2018



> On Nov 15, 2018, at 3:59 PM, Kristina Brooks via libcxx-dev <libcxx-dev at lists.llvm.org> wrote:
> 
> Yes exactly, seems like an obvious win on a mono-ABI system, if preserving debug data
> this saves a lot, not to mention symbol table strings. Also, I'm purely speculating here
> but this would also speed up compilation and linking time by an insignificant margin, but
> nevertheless, it's an improvement.
> 
> If the ABI ever needs to change, on those kinds of systems, it's easy enough with an OS
> update.

Or, we could update the Itanium ABI so that the current mangling still works and is compatible with a new mangling which is shorter for libc++ (yet remains purposefully incompatible with libstdc++’s mangling) 🙂


> Thanks.
> 
> On 14/11/2018 17:06, Eric Fiselier wrote:
>> 
>> 
>> On Wed, Nov 14, 2018 at 12:04 PM Eric Fiselier <eric at efcs.ca <mailto:eric at efcs.ca>> wrote:
>> 
>>    The itanium specification provides special compressed mangled names for std::string when it's not in an inline
>>    namespace [1]
>> 
>>    Specifically, `Ss` vs `St3__112basic_string`
>> 
>> 
>> Correction... `Ss` vs `NSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE`
>>  
>> 
>> 
>>    [1] https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling-compression
>> 
>>    On Wed, Nov 14, 2018 at 10:03 AM Marshall Clow via libcxx-dev <libcxx-dev at lists.llvm.org
>>    <mailto:libcxx-dev at lists.llvm.org>> wrote:
>> 
>>        On Sun, Nov 11, 2018 at 9:49 PM Kristina Brooks via libcxx-dev <libcxx-dev at lists.llvm.org
>>        <mailto:libcxx-dev at lists.llvm.org>> wrote:
>> 
>>            Hi,
>> 
>>            I was wondering, would it be possible to add an option to disable inline namespacing completely (as a CMake
>>            configuration flag) in libc++ for the sake of being able to use shorthand mangling and without having to
>>            resort to
>>            handling it on IA64 mangler level. This has many use cases for example distributions of anything that
>>            includes libc++ as
>>            one and only libc++ and does not allow non-vendor software to be installed. On an embedded system, assuming
>>            debug info
>>            is generated, and given how common some of the debug data takes a very significant amount of space given the
>>            complex
>>            definition of something like `std::__2::basic_string<...>` versus the short form (`std::string` having a
>>            shorthand
>>            mangling is a godsend since it's 95% shorter, not an accurate figure but basically definitely above 90%).
>> 
>> 
>>        I'm confused here.
>>        Why are you comparing `std::string` to `std::__2::basic_string<......" ?
>> 
>>        `std::__2::string` is quite short.<http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev>
>> 
>>        -- Marshall
>> 
>>        _______________________________________________
>>        libcxx-dev mailing list
>>        libcxx-dev at lists.llvm.org <mailto:libcxx-dev at lists.llvm.org>
>>        http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev
>> 
> _______________________________________________
> libcxx-dev mailing list
> libcxx-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev



More information about the libcxx-dev mailing list