llvm dev - Mar 2016 - How to do some dataflow analysis via IR on a large project?

I am learning to do some basic dataflow analysis on C code projects,
such as Apache httpd. Now I am a newbie of LLVM IR, and there are some
problems in doing that.
In the official User Manual of how to write a LLVM PASS, they only
show the way to generate IR of a single ".c" source file. But in fact
there are so many examples that the usage and definition of a function
are not in the same ".c" source file, rising the difficulty of
analzing the dataflow of such functions.
So, I want to know, is there any method of strategies to generate the
IR among many related source files?
Thanks a lot !

Dear Shulin,

Sounds like you'll need an inter-procedural analysis across different
source files. One
option I can think of is to manually update the Makefiles, make compiler
emit bitcode
files, merge them with llvm-link and run it through your optimization pass
as a big bitcode
file. This somehow could involve huge amount of tedious work for a huge
project like
Apache, and may be error-prone.

Another option I can think of is the libLTO. It should link all bitcode
files and run optimization
passes for you.

http://llvm.org/docs/LinkTimeOptimization.html#phase-3-optimize-bitcode-files

I've never dealt with it myself and I don't find abundant tutorials and
examples online. You
probably need to dig into the source code. (in lib/LTO ?)

Correct me where I'm wrong or if there are any other good approaches.

Regards,
Kevin

On Mon, Feb 29, 2016 at 9:15 PM 周书林 via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> I am learning to do some basic dataflow analysis on C code projects,
> such as Apache httpd. Now I am a newbie of LLVM IR, and there are some
> problems in doing that.
> In the official User Manual of how to write a LLVM PASS, they only
> show the way to generate IR of a single ".c" source file. But in
fact
> there are so many examples that the usage and definition of a function
> are not in the same ".c" source file, rising the difficulty of
> analzing the dataflow of such functions.
> So, I want to know, is there any method of strategies to generate the
> IR among many related source files?
> Thanks a lot !
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Dear Kevin,

The first method seems a litttle difficult for me to deal with the
Makefiles of several projects. So the LTO might be the only choice.
Thank you very much.

2016-03-01 13:55 GMT+08:00, Kevin Hu <hxy9243 at
gmail.com>:
> Dear Shulin,
>
> Sounds like you'll need an inter-procedural analysis across different
> source files. One
> option I can think of is to manually update the Makefiles, make compiler
> emit bitcode
> files, merge them with llvm-link and run it through your optimization pass
> as a big bitcode
> file. This somehow could involve huge amount of tedious work for a huge
> project like
> Apache, and may be error-prone.
>
> Another option I can think of is the libLTO. It should link all bitcode
> files and run optimization
> passes for you.
>
>
http://llvm.org/docs/LinkTimeOptimization.html#phase-3-optimize-bitcode-files
>
> I've never dealt with it myself and I don't find abundant tutorials
and
> examples online. You
> probably need to dig into the source code. (in lib/LTO ?)
>
> Correct me where I'm wrong or if there are any other good approaches.
>
> Regards,
> Kevin
>
> On Mon, Feb 29, 2016 at 9:15 PM 周书林 via llvm-dev <llvm-dev at
lists.llvm.org>
> wrote:
>
>> I am learning to do some basic dataflow analysis on C code projects,
>> such as Apache httpd. Now I am a newbie of LLVM IR, and there are some
>> problems in doing that.
>> In the official User Manual of how to write a LLVM PASS, they only
>> show the way to generate IR of a single ".c" source file. But
in fact
>> there are so many examples that the usage and definition of a function
>> are not in the same ".c" source file, rising the difficulty
of
>> analzing the dataflow of such functions.
>> So, I want to know, is there any method of strategies to generate the
>> IR among many related source files?
>> Thanks a lot !
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>