AD Cleanup: break-elimination during the CFG normalization step can cause the loop condition to be evaluated an extra time.

[saipraveenb25]

This is typically not a problem, except for when the loop condition evaluates functions with side-effects.

Example:

int x = 0;
for (int i = 0; i < f(i); i++)
{
     x = x + i;
     if (x > 5)
          break;
}

gets replaced with:

int x = 0;
bool bflag = true;
for (int i = 0; i < f(i) && bflag; i++)
{
     x = x + i;
     if (x > 5)
          bflag = false;
}

Here f(i) can be evaluated an extra time, since instead of immediately breaking out of the loop, we evaluate the condition an extra time. The evaluated result is unimportant since bflag=false, but if f(i) has side-effects, the primal part of the computation would be incorrect since it runs one extra time than the user intended.

The fix is simply to enclose the condition block in another condition, but this is tricky to do since most of the AD passes assume that the loop's condition check is in the block immediately following the loop condition.