llvm dev - Jun 2018 - How to force an unused function declaration in clang

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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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
>>
>>
>>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

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
> >>
> >>
> >>
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
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