llvm dev - May 2010 - [LLVMdev] getTripCount requires which optimization passes?

Hi,

For me, getTripCount always returns null, even for trivial loops such  
as:

void simple(int j) {
     for (int i = 0; i < 10; i++) {
         j++;
     }
}

Looking through the mailing list archive, it appears that getTripCount  
requires certain optimization passes to run first, but it's not clear  
which ones. There doesn't seem to be any documentation on this. Does  
anybody know exactly which passes must run in order for getTripCount  
to work?

Thanks,

Trevor

hi,

On Fri, May 7, 2010 at 8:59 AM, Trevor Harmon <Trevor.W.Harmon at
nasa.gov>wrote:
> Hi,
>
> For me, getTripCount always returns null, even for trivial loops such
> as:
>
> void simple(int j) {
>     for (int i = 0; i < 10; i++) {
>         j++;
>     }
> }
>
> Looking through the mailing list archive, it appears that getTripCount
> requires certain optimization passes to run first, but it's not clear
> which ones. There doesn't seem to be any documentation on this. Does
> anybody know exactly which passes must run in order for getTripCount
> to work?
>
As the comment said:
  /// The IndVarSimplify pass transforms loops to have a form that this
  /// function easily understands.

you could try -indvars.
>
> Thanks,
>
> Trevor
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
best regards
ether
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On May 6, 2010, at 6:32 PM, ether zhhb wrote:
> As the comment said:
>   /// The IndVarSimplify pass transforms loops to have a form that  
> this
>   /// function easily understands.
>
> you could try -indvars.
After adding -indvars to the opt command, getTripCount still returns  
null.

I suppose it's possible, depending on the scheduling of the pass  
manager, that indvars is running after my pass runs. I could force it  
to run first by adding it to my pass's getAnalysisUsage:

void MyPass::getAnalysisUsage(AnalysisUsage &AU) const {
     AU.addRequired<IndVarSimplify>();
}

But this isn't possible because for some reason there's no  
IndVarSimplify.h header file. The IndVarSimplify pass is defined only  
in its IndVarSimplify.cpp, so my pass can't use it.

Not sure where to go from here. Should I post a test case illustrating  
the problem?

Trevor