You have a large loop dependency because line 57 can't start until line 59 completes. Instead of folding all the complex values into one product, do 2 or 4 separate folds (eg, multiply all the even indices and all the odd indices) and then multiply those products after the end of the loop to get the final result.
Register twinning is copying a value from the A side to B side or vice versa so it can be used on the other side without using a cross path.