[llvm-dev] Obtaining bounds of loops

[Philip Reames via llvm-dev]

JFYI, the infrastructure on Loop itself is very very limited. Honestly, 
it probably shouldn't exist at all.

ScalarEvolution exists to analyze loops.  In particular, it can compute 
symbolic execute counts for a much much broader family of loops.

Without knowing your use case, I can't say for sure, but I suspect you 
want to be using ScalarEvolution.

Philip

On 2/22/21 8:48 AM, bodhisatwa via llvm-dev wrote:
> Hi,
>
> I am trying to test out the getBounds() method from LoopInfo. However, 
> the method doesn't seem to obtain the bounds of simple loops like -
>
>        for (int j = 0; j < 10; j ++)
>            B[j] = 6;
>
>        int i = 10, j = 2,
>
>        while ( i != j)
>              j++;
>
>  My code snippet in the function pass is as follows (which gives the 
> output as "No value for loop bounds" for all the loops):
>
>       LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
>
>       for (auto loop = LI.begin(), e = LI.end(); loop != e; ++loop )
>       {
>           ScalarEvolution *SE = 
> &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
>           auto b = (*loop)->getBounds(*SE);
>
>           if (!b.hasValue())
>                {
>                   errs() << "No value for loop bounds\n";
>                }
>       }
>
>  Is there something that I am missing here?
>
>
>  Thanks,
>  Bodhi
>
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