[LLVMdev] Identifying loop variables

[Tobias Grosser]

On 01/16/2012 12:51 PM, Adarsh HV wrote:
> Hi everyone,
> Are there any functions to identify the initiation,condition and
> iteration part of the loop?
> Example: for(i=0;i<10;i++)
>    {
>      a[i]+=1;
>    }
> I want to know the name of the variable used in the loop(i) , the
> initiation(i=0), condition(i<10) and the iteration(i++) part of the loop.
> Thank you:)

Hi Adarsh,

the main question is where to do this analysis. You have two options

1. Do it in clang

As pointed out by chenwj, you can do this in clang. This will basically 
be a pattern matching approach or, if more advanced, some source code 
based induction variable recognition.

Working on clang has the advantage that your results directly relate to 
the C code. However, performing advanced induction variable analysis on 
C code is more difficult. I am not sure, if there already exists an 
induction variable analysis.

2. Do it in LLVM

Here you would work on LLVM-IR and use the LoopInfo and the 
ScalarEvolution analysis. These analysis perform advanced induction 
variable recognition and will give you good results for a wider range of 
code (including while loops, goto, pointer arithmetic). However, it will 
be hard to relate the results to the original C code. You can try to use 
debugging information, but I doubt this will work in all cases.

Cheers
Tobi