llvm dev - Apr 2010 - [LLVMdev] determining the number of iteration of a loop

Hello

I'm wandring to know how many times a block is executed inside a loop  ?
knowing that I can't use  getSmallConstantTripCount() because the number is
unkown  "for (i=0;i<N;i++)  for example"

I'm using a Function pass

for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    if (Loop *L = LI->getLoopFor(BB)) {
            if (L->getHeader() == BB)
               {
                 the code of the loop   (the header)
               }
             else{the code of the block inside the loop}
   else
     the code of a basicblock (outside a loop)


How can I get the variable N (even only the name of this variable !!)   ???

I mean I want to get  "the loop will be executed  "%N" 
times"

Thank you so much

K.H
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On Apr 21, 2010, at 7:31 AM, khaled hamidouche wrote:
> I'm wandring to know how many times a block is executed inside a  
> loop  ?
> knowing that I can't use  getSmallConstantTripCount() because the  
> number is unkown  "for (i=0;i<N;i++)  for example"
In general, the number of iterations is undecidable. For example:

int main(char **argv, int N) {
     for (int i = 0; i < N; i++) {
         std::cout << "arg: " << argv[i] <<
std::endl;
     }
     return 0;
}

If you are parsing code whose iterations can be determined, please  
post it.

Trevor

In your example the the number of iterations is known -- it is N. It
is not known at compile time, but it's known at run-time before you
enter the loop. So you can do transforms like if( N < threshold ) copy
of loop optimized for small iterations count; else copy of loop
optimized for large iterations count;

But you are right, in general, the number of iterations in unknown. I
think Khaled is interested in a large number of cases when it is
known, either as a constant or value.

Eugene

On Wed, Apr 21, 2010 at 10:28 PM, Trevor Harmon
<Trevor.W.Harmon at nasa.gov> wrote:
> On Apr 21, 2010, at 7:31 AM, khaled hamidouche wrote:
>
>> I'm wandring to know how many times a block is executed inside a
>> loop  ?
>> knowing that I can't use  getSmallConstantTripCount() because the
>> number is unkown  "for (i=0;i<N;i++)  for example"
>
> In general, the number of iterations is undecidable. For example:
>
> int main(char **argv, int N) {
>     for (int i = 0; i < N; i++) {
>         std::cout << "arg: " << argv[i] <<
std::endl;
>     }
>     return 0;
> }
>
> If you are parsing code whose iterations can be determined, please
> post it.
>
> Trevor
>
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