[llvm-dev] Scalar Evolution Analysis

[Bangtian Liu via llvm-dev]

Hi,

I have the following code as an example:  
 int j=-1; 
for (int i = 0; i < 100; ++i)
{       
     if (c[i] > 0.) {     
              j++;     
              e[j] = d[i];   
 }  }

How can I use LLVM's existing SCEV module to infer that e[j] could be consecutive if consecutive iterations' conditions are true?

Bests,

Bangtian

--

Bangtian Liu   刘 邦天 

CS PhD Candidate

Department of Computer Science 
University of Toronto
Pratt 265C, 6 King's College Road, Toronto, ON M5S 3G4, Canada

[Min-Yih Hsu via llvm-dev]

Maybe llvm::PredicatedScalarEvolution is the one you’re looking for.

IIRC, it was created for loop versioning, so it might insert some runtime checks.

-Min

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[Philip Reames via llvm-dev]

I don't believe we have any good way to model a conditionally incremented induction variable when the condition is loop varying and data dependent.  This is not exactly a common or interesting case.

Just out of curiosity, what do you expect to be able to do with this loop optimization wise?  We could maybe vectorize if we had bounds information on 'c', but that's about all I see here.

Philip