[rfc][gold plugin] Fix pr19901

[Rafael Espíndola]

ping. Rebased patch attached.


On 6 August 2014 11:32, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>> I don't think we drop them yet, but I see it is as just a convenience
>> so that it is easy to test it with llc. While developing this patch I
>> did a few clang bootstraps and only once noticed a unused linkonce_odr
>> in a .bc produced by clang. The previous passes should drop it. We
>> could add an option to do it, I am just not sure it would have a big
>> impact (I will write a patch to check).
>
> And I can't even reproduce that anymore.
>
> I applied the attached patch to llvm to make it assert when writing
> bitcode or assembly with a dead linkonce_odr. It will correctly crash
> in llvm-as or llc when given just
>
> define linkonce_odr void @g() {
>   ret void
> }
>
> But it can successfully build a stage2 with or without LTO, so it
> looks we are pretty good at dropping unused linkonce_odr and dropping
> it in codegen proper would not add any real value.
>
> Cheers,
> Rafael
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