llvm dev - Apr 2008 - [LLVMdev] Getting the trip count of a loop

Hi,

I am trying to add a new loop pass in which I making a call to get the trip
count of the loop using

Value *TripCountValue = L->getTripCount()

However I am always getting NULL for TripCountValue (confirmed through gdb).
I am running this pass after the canonicalization of induction variables:

opt --debug-pass=Structure -stats -indvars -loop-rotate -my-loop-pass <
main.bc > main.unroll.s
Pass Arguments:  -domtree -loops -scalar-evolution -loopsimplify
-domfrontier -scalar-evolution -lcssa -indvars -loop-rotate -domfrontier
-scalar-evolution -lcssa -my-loop-pass -preverify -domtree -verify
Target Data Layout
  ModulePass Manager
    FunctionPass Manager
      Dominator Tree Construction
      Natural Loop Construction
      Scalar Evolution Analysis
--      Scalar Evolution Analysis
      Canonicalize natural loops
      Dominance Frontier Construction
      Scalar Evolution Analysis
      Loop Pass Manager
        Loop-Closed SSA Form Pass
        Canonicalize Induction Variables
--        Canonicalize Induction Variables
        Rotate Loops
--        Loop-Closed SSA Form Pass
--        Rotate Loops
--      Dominance Frontier Construction
--      Scalar Evolution Analysis
      Dominance Frontier Construction
      Scalar Evolution Analysis
      Loop Pass Manager
        Loop-Closed SSA Form Pass
*        <My Loop Pass>*
--       * <My Loop Pass>*
--        Loop-Closed SSA Form Pass
--      Natural Loop Construction
--      Canonicalize natural loops
--      Dominance Frontier Construction
--      Dominator Tree Construction
--      Scalar Evolution Analysis
      Preliminary module verification
      Dominator Tree Construction
      Module Verifier
--      Preliminary module verification
--      Dominator Tree Construction
--      Module Verifier
    Bitcode Writer
--    Bitcode Writer

I have two loops in my source program which have statically-determinable
bounds:

for (i=1; i < 99999; i++)
{
....
}

Is there anything else I should be doing before invoking the getTripCount()
method ?

thanks,
Prakash
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Prakash Prabhu wrote:
> I am trying to add a new loop pass in which I making a call to get the 
> trip count of the loop using
> 
> Value *TripCountValue = L->getTripCount()
That should work.

Could you file a bug and attach the bytecode after 'opt -indvars 
-loop-rotate'? I would need that to determine why LoopInfo::getTripCount 
isn't returning any value.

Nick

Thanks for the quick reply. Created Bug 2253:
http://llvm.org/bugs/show_bug.cgi?id=2253

- Prakash

On Sat, Apr 26, 2008 at 2:15 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
> Prakash Prabhu wrote:
> > I am trying to add a new loop pass in which I making a call to get the
> > trip count of the loop using
> >
> > Value *TripCountValue = L->getTripCount()
>
> That should work.
>
> Could you file a bug and attach the bytecode after 'opt -indvars
> -loop-rotate'? I would need that to determine why
LoopInfo::getTripCount
> isn't returning any value.
>
> Nick
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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