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Sunil via llvm-dev

2020-Feb-04 16:24 UTC

[llvm-dev] How to distinguish between user defined function in a program and library functions

Say, I have the following program:

    #include <iostream>
    int main(){
      std::cout << "hello\n";
      return 0;
    }

After generating llvm bitcode using the following command:
       $ clang++ -c -emit-llvm -O -Xclang -disable-llvm-passes a.cpp
the bitcode has the following function with define.
__cxx_global_var_init
    main
    _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
_ZNSt9basic_iosIcSt11char_traitsIcEE8setstateESt12_Ios_Iostate
    _ZNSt11char_traitsIcE6lengthEPKc
    _ZStorSt12_Ios_IostateS_
    _ZNKSt9basic_iosIcSt11char_traitsIcEE7rdstateEv
    _GLOBAL__sub_I_a.cpp

In a pass, I want to know what are the functions defined by the user e.g 
'main' and what are not e.g. other than 'main'.

Regards,
    Sunil
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David Blaikie via llvm-dev

2020-Feb-04 23:53 UTC

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[llvm-dev] How to distinguish between user defined function in a program and library functions

Generally, you can't - and optimizations/the compiler shouldn't
differentiate between them.

On Tue, Feb 4, 2020 at 3:25 PM Sunil via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> Say, I have the following program:
>    #include <iostream>
>    int main(){
>      std::cout << "hello\n";
>      return 0;
>    }
>
> After generating llvm bitcode using the following command:
>       $ clang++ -c -emit-llvm -O -Xclang -disable-llvm-passes a.cpp
> the bitcode has the following function with define.
>       __cxx_global_var_init
>    main
>    _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
>    _ZNSt9basic_iosIcSt11char_traitsIcEE8setstateESt12_Ios_Iostate
>    _ZNSt11char_traitsIcE6lengthEPKc
>    _ZStorSt12_Ios_IostateS_
>    _ZNKSt9basic_iosIcSt11char_traitsIcEE7rdstateEv
>    _GLOBAL__sub_I_a.cpp
>
> In a pass, I want to know what are the functions defined by the user e.g
> 'main' and what are not e.g. other than 'main'.
>
> Regards,
>    Sunil
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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sunilps via llvm-dev

2020-Feb-05 04:01 UTC

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[llvm-dev] How to distinguish between user defined function in a program and library functions

<div dir="ltr"><br>
</div><div dir="ltr">Actually I want to run some analysis
pass only on the user defined functions but not on the library functions. Is
there any boolean method that can tell which is a library function and which is
not? </div><div class="wps_quotion">On 5 Feb 2020 5:23
a.m., David Blaikie <dblaikie@gmail.com> wrote:<br
type="attribution"><blockquote class="quote"
style="margin:0 0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex"><div dir="ltr">Generally, you
can't - and optimizations/the compiler shouldn't differentiate between
them.</div><br><div class="gmail_quote"><div
dir="ltr" class="gmail_attr">On Tue, Feb 4, 2020 at 3:25
PM Sunil via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>>
wrote:<br></div><blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">

  



    

  

  <div>

    <p>Say, I have the following program:</p>

    <div><font face="Courier New, Courier, monospace">  
#include

        <iostream><br>

           int main(){<br>

             std::cout << "hello\n";<br>

             return 0;</font></div>

    <div><font face="Courier New, Courier, monospace">  
}</font><br>

    </div>

    <div><br>

    </div>

    <div>After generating llvm bitcode using the following
command: </div>

    <div>      $ <font face="Courier New, Courier,
monospace">clang++

        -c -emit-llvm -O -Xclang -disable-llvm-passes
a.cpp</font><br>

    </div>

    <div>the bitcode has the following function with define.</div>

    <div>      <font face="Courier New, Courier,
monospace">__cxx_global_var_init<br>

           main<br>

           _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc<br>

          

        _ZNSt9basic_iosIcSt11char_traitsIcEE8setstateESt12_Ios_Iostate<br>

           _ZNSt11char_traitsIcE6lengthEPKc<br>

           _ZStorSt12_Ios_IostateS_<br>

           _ZNKSt9basic_iosIcSt11char_traitsIcEE7rdstateEv<br>

           _GLOBAL__sub_I_a.cpp<br>

      </font></div>

    <div><br>

    </div>

    <div>In a pass, I want to know what are the functions defined by the

      user e.g 'main' and what are not e.g. other than
'main'.</div>

    <div><br>

    </div>

    <div>Regards,</div>

    <div>   Sunil</div>

  </div>



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target="_blank">llvm-dev@lists.llvm.org</a><br>

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rel="noreferrer"
target="_blank">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><br>

</blockquote></div>

</blockquote></div>

Jacob Carlborg via llvm-dev

2020-Feb-05 18:16 UTC

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[llvm-dev] How to distinguish between user defined function in a program and library functions

On 2020-02-04 17:24, Sunil via llvm-dev wrote:> Say, I have the following program:
> 
>     #include <iostream>
>     int main(){
>       std::cout << "hello\n";
>       return 0;
>     }
> 
> After generating llvm bitcode using the following command:
>        $ clang++ -c -emit-llvm -O -Xclang -disable-llvm-passes a.cpp
> the bitcode has the following function with define.
> __cxx_global_var_init
>     main
>     _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
> _ZNSt9basic_iosIcSt11char_traitsIcEE8setstateESt12_Ios_Iostate
>     _ZNSt11char_traitsIcE6lengthEPKc
>     _ZStorSt12_Ios_IostateS_
>     _ZNKSt9basic_iosIcSt11char_traitsIcEE7rdstateEv
>     _GLOBAL__sub_I_a.cpp
> 
> In a pass, I want to know what are the functions defined by the user e.g 
> 'main' and what are not e.g. other than 'main'.
Perhaps you can check where a function is defined and treat all 
functions defined in a file passed to the compiler as user defined and 
all other as system defined. Not sure if that's good enough for you.

-- 
/Jacob Carlborg

George Burgess IV via llvm-dev

2020-Feb-08 00:04 UTC

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[llvm-dev] How to distinguish between user defined function in a program and library functions

I'd imagine you can tweak clang's CodeGen to add a Metadata node to all
`llvm::Function`s clang emits that basically says whether or not the code
appeared in a system header. SourceManager::isInSystemHeader should help
you figure out what's where. You'll probably need special handling for
generated code, like `__cxx_global_var_init`

I offer no guarantees about the LLVM community accepting this patch, though
:)

To Mehdi's point, inlining can make things materially more difficult.

On Wed, Feb 5, 2020 at 10:16 AM Jacob Carlborg via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 2020-02-04 17:24, Sunil via llvm-dev wrote:
> > Say, I have the following program:
> >
> >     #include <iostream>
> >     int main(){
> >       std::cout << "hello\n";
> >       return 0;
> >     }
> >
> > After generating llvm bitcode using the following command:
> >        $ clang++ -c -emit-llvm -O -Xclang -disable-llvm-passes a.cpp
> > the bitcode has the following function with define.
> > __cxx_global_var_init
> >     main
> >     _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
> > _ZNSt9basic_iosIcSt11char_traitsIcEE8setstateESt12_Ios_Iostate
> >     _ZNSt11char_traitsIcE6lengthEPKc
> >     _ZStorSt12_Ios_IostateS_
> >     _ZNKSt9basic_iosIcSt11char_traitsIcEE7rdstateEv
> >     _GLOBAL__sub_I_a.cpp
> >
> > In a pass, I want to know what are the functions defined by the user
e.g
> > 'main' and what are not e.g. other than 'main'.
>
> Perhaps you can check where a function is defined and treat all
> functions defined in a file passed to the compiler as user defined and
> all other as system defined. Not sure if that's good enough for you.
>
> --
> /Jacob Carlborg
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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