[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
>>
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