[LLVMdev] How to unroll loop with non-constant boundary

[Николай Лихогруд]

Dear LLVM,

    Consider two loops with one interation -
    First with constant lower bound, second with usual non-constant lower
bound:

    int main(int argc, char ** argv)
    {
        int numOfIterations= 1;
        int stride=1;
        int lowerBound = 1000; - 1st | int lowerBound = argc; - 2nd
        int upperBound = lowerBound + (numOfIterations - 1)*stride;

        int i = lowerBound;

        int s = 0;
        while(i <= upperBound)
        {
           s += i;
           i++;
        }
        return s;
    }
   After the application of -O3 optimization:

   The first loop was unrolled:

       define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable
readnone {
       entry:
         ret i32 1000
       }

   But the second was not:

       define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable
readnone {
       entry:
         br label %"3"

       "3":                                              ; preds = %entry,
%"3"
          %0 = phi i32 [ 0, %entry ], [ %2, %"3" ]
          %1 = phi i32 [ %argc, %entry ], [ %3, %"3" ]
          %2 = add i32 %0, %1
          %3 = add i32 %1, 1
          %4 = icmp sgt i32 %3, %argc
          br i1 %4, label %"5", label %"3"

       "5":                                              ; preds = %"3"
          ret i32 %2
      }

    The questions:
      Is it possible to unroll loop with non-constant boundary using
standard LLVM 3.1 facilities, and, if it is, how I can do that?
Best regards,
     Nicolas
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