We will continue our reading of this WRL research report. SSA improves the effectiveness of peephole optimizations. SSA form exposes all the users of a value and not just a limited window.The Swift compiler therefore looks for patterns and applies the peephole optimizations where the peephole is the whole method. The values in the pattern can be spread anywhere in the control flow. As an example, the length property of an array can be replaced by the size argument to the allocation operation. This optimization can be applied no matter where the allocation and the length operations are used in the method. When the array is allocated at the beginning of the method and the length operations are generated for bound checks, this optimization is quite effective.
Let us now look at what constraints the SSA form may put on the Swift compiler. First and most importantly the register allocator must be quite effective and general purpose.It should minimize copies and spills.because they can overshadow the gains from SSA.Similarly the passes that do the final placement of values in blocks and the scheduling within blocks are quite important. The SSA form gives a lot  of freedom to do this final schedule so it must be made use of most.
Lastly one limitation mentioned by some groups is that the SSA form is difficult to use for restructuring optimizations, since it may be difficult to add required phi nodes correctly as code is restructured and new join points are created. However the authors did not encounter any such difficulty for all their optimizations. including many that modify the CFG. These included method inlining, method splitting, conditional constant propagation etc. Loop peeling, Loop unrolling or Loop interchange may be the only exceptions where it may be difficult.
#codingexercise

Double GetAlternateEvenNumberRangeSumSixthPowerRootSquare (Double [] A)

{
if (A == null) return 0;
Return A.AlternateEvenNumberRangeSumSixthPowerRootSquare();
}