llvm dev - Apr 2015 - [LLVMdev] How to dynamically profile LLVM IR, i.e., doing things along the program execution?

Hi, all

I am wondering if it is possible to dynamically profile  LLVM IR? For
example, if I have a

void foo(){
  A a;
  a.goo(); //invoke a virtual function of class A
}

Assume we don't know which "goo()" of class "A" will be
executed at run
time. We may want to print the  body of goo() as well as the bodies of the
function called by goo() and etc., or do something along the execution
trace.

How can we do this kind of dynamic profiling? I recently learned some LLVM
basics. It seems to me that the purpose of LLVM passes is static
profiling, right?

 Thanks for your ideas.

Zhoulai
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On 4/27/15 12:45 PM, Zhoulai wrote:
> Hi, all
>
> I am wondering if it is possible to dynamically profile  LLVM IR? For 
> example, if I have a
>
> void foo(){
>   A a;
>   a.goo(); //invoke a virtual function of class A
> }
> Assume we don’t know which “goo()" of class “A” will be executed at 
> run time.
The DSA CallTargets pass can get you a list of possible targets for an 
indirect function call.
> We may want to print the  body of goo() as well as the bodies of the 
> function called by goo() and etc., or do something along the execution 
> trace.
>
> How can we do this kind of dynamic profiling? I recently learned some 
> LLVM basics. It seems to me that the purpose of LLVM passes is static 
> profiling, right?
I don't know of a pass that does this.  However, it is trivial to write 
an LLVM pass that adds code before every indirect function call and 
prints out the address of the function that will be called.  Using that 
information, you can build a dynamic call graph.

Regards,

John Criswell
>
>  Thanks for your ideas.
>
> Zhoulai
>
>
>
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-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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