Stripping Data Symbols (Win64)

[Rainer Schuetze via Digitalmars-d]

On 30.12.2015 13:25, Benjamin Thaut wrote:
> On Wednesday, 30 December 2015 at 09:43:32 UTC, Rainer Schuetze
> wrote:
>>
>>
>>
>> I noticed something similar recently when compiling a C file with
>> /Gy, see
>> https://github.com/D-Programming-Language/druntime/pull/1446#issuecomment-160880021
>>
>>
>>
>> The compiler puts all functions into COMDATs, but they are all
>> still linked in if only a single symbol is referenced, even if
>> linked with /OPT:REF.
>>
>> So I suspect this is not an issue with dmd, but the Microsoft
>> linker. I still wonder whether the approach to use "function level
>> linking" works at all for Win64.
>>
>>> I noticed by looking at some object file dumps that dmd puts
>> each
>>> function into its own section, but data symbols, like
>> initializers, are
>>> all merged into the same section. Could this be the root
>> issue?
>>
>> Having all data in a single section misses some possible
>> optimizations, and it might be the reason for the behavior in your
>>  case (you can check this with "dumpbin /all objectfile"), but the
>>  issue above does not contain any data.
>
> So if I understand this correctly the microsoft linker only strips
> unused comdats, otherwise always the entire object file gets pulled
> in?

I tried to reproduce the issue right now, but failed to do so (both with 
a C file compiled with /Gy and a D compiled). Only referenced COMDATs 
where included in a link, not other COMDATs in the same object file. 
Maybe it was an issue with my build script back then.

>
> For me stripping of individual data symbols not working is actually a
>  good thing, if it doesn't work, I can't break it. ;-)

Please note that building with -lib puts every function/declaration into 
it's own object file inside the library, and unused class declarations 
are no longer in the linked executable.