[LLVMdev] Irreducible Control-Flow & Loops

Chris Lattner clattner at apple.com
Mon Sep 28 10:45:19 PDT 2009

On Sep 28, 2009, at 2:28 AM, Ralf Karrenberg wrote:

> I am considering writing a patch for LoopInfo instead of creating my  
> own
> data structure for irreducible loops.
> Is such an enhancement desired or even already implemented by someone
> (e.g. in the 2.6 branch)?

I'm not sure that this is a good idea.  LoopInfo is clearly defined to  
represent "natural" loops (where the header dominates the body of the  
loop).  Natural loops have a lot of very useful properties like loop  
headers etc that the loop optimizers depend on.  We already have SCC  
iterators etc, is there a specific reason you want to have LoopInfo do  

If you're writing a pass that converts irreducible control flow to  
reducible loops, I'd think it would be based on SCC iterators, not on  


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