OPTLINK needs to die.

[Tom S]

Walter Bright wrote:
> Tom S wrote:
>> Walter Bright wrote:
>>> The problem appears to be that optlink cannot deal correctly with 
>>> weak references. I've modified the compiler to not emit weak 
>>> references, and the problem goes away. It's not a perfect fix, but it 
>>> works.
>>
>> With the modified compiler, does the following link?
> 
> Yes.
> 
>> If so, is the output correct?
> [...]
>> I'm getting:
>> &aC.x == 419c30
>> &bC.x == 419c30
> 
> Yes, that is correct (there should be only one instance in the executable).
> 
>> I'm afraid that it might refuse to link and then even if OPTLINK 
>> allowed multiple strong symbols of the same name, I'd expect the 
>> assertion to fail. Aren't weak symbols essential to properly handling 
>> templates?
> 
> No. Weak references are: "if this symbol does not get resolved, then 
> default initialize it to this other symbol". In other words, weak 
> references do not cause things to be pulled in from the library.
> 
> Multiple symbols with the same name and same contents, across different 
> object files, are called COMDATs and the linker picks one and discards 
> the duplicates.
> 
> Where the compiler was emitting weak references was in the list of which 
> modules are imported by the object file, so that if nobody actually 
> referred to the import's contents beyond the import statement, the 
> import would not get linked in.
> 
> 
>> Of course compiling the modules together causes only one symbol to be 
>> emitted for the template instantiations. Yet this is not an option for 
>> a larger project, since compilation times and memory usage can get 
>> rather high.
> 
> 
> I know. This is why COMDATs were invented (for C++ templates). C++ drove 
> a number of improvements in obj files.

I'm glad to be proven wrong :) Thanks for the info! I'm sure it will 
come in handy for the dynamic linking I'm doing with DDL. I got the 
silly idea that you'd disable COMDATs... Another case of "Too much blood 
in my caffeine".


-- 
Tomasz Stachowiak
http://h3.team0xf.com/
h3/h3r3tic on #D freenode