[llvm-dev] How to force an unused function declaration in clang

[Soham Sinha via llvm-dev]

I realize that gcc also doesn't provide <https://godbolt.org/g/ismnEj> this
feature if the function doesn't have a body. I was wondering if there is
any elegant way to achieve this, instead of the "hack" I mentioned earlier.

Regards,
Soham Sinha
PhD Student, Department of Computer Science
Boston University


On Tue, Jun 26, 2018 at 10:58 AM Soham Sinha <soham1 at bu.edu> wrote:

> It does, when the function has a body. When it doesn't, it ignores
> <https://godbolt.org/g/2BCvht>. The body might be provided later on in
> the toolchain via linking a library.
>
> Regards,
> Soham Sinha
> PhD Student, Department of Computer Science
> Boston University
>
>
> On Tue, Jun 26, 2018 at 10:25 AM Hans Wennborg <hans at chromium.org> wrote:
>
>> It works for me:
>>
>> https://godbolt.org/g/3QzqAH
>>
>> Can you share an example?
>>
>> On Tue, Jun 26, 2018 at 5:21 PM, Soham Sinha via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > For the same reason GCC allowed the attribute. Even if I want to
>> use/inline
>> > a function later on in the pipeline.
>> >
>> > Regards,
>> > Soham Sinha
>> > PhD Student, Department of Computer Science
>> > Boston University
>> >
>> >
>> > On Tue, Jun 26, 2018 at 8:30 AM mayuyu.io <admin at mayuyu.io> wrote:
>> >>
>> >> Out of curiosity, how does an unused declaration affect the emitted
>> object
>> >> file
>> >>
>> >> Zhang
>> >>
>> >> > 在 2018年6月26日，08:48，Soham Sinha via llvm-dev <llvm-dev at lists.llvm.org
>> >
>> >> > 写道：
>> >> >
>> >> > clang doesn't seem to respect __attribute__((used)) in C functions.
>> Even
>> >> > if I declare a function like the following:   __attribute__((used))
>> void
>> >> > function(), then also it doesn't declare the function in its IR file
>> if I
>> >> > don't use the function. Is there any other way to force the
>> declaration of
>> >> > "unused" function declarations with clang.
>> >> >
>> >> > I have hacked in clang 6.0.0 in
>> >> > tools/clang/lib/CodeGen/CodeGenModule.cpp file. I changed in
>> EmitGlobal
>> >> > function to detect if the function has "used" attribute and then if
>> it has
>> >> > then use "GetOrCreateLLVMFunction" this to create the function
>> declaration.
>> >> > However, this hack fails in some other cases. Therefore I am looking
>> for a
>> >> > proper way to do this.
>> >> >
>> >> > Regards,
>> >> > Soham Sinha
>> >> > PhD Student, Department of Computer Science
>> >> > Boston University
>> >> > _______________________________________________
>> >> > LLVM Developers mailing list
>> >> > llvm-dev at lists.llvm.org
>> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >>
>> >>
>> >
>> > _______________________________________________
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>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>>
>
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