We continue our discussion on the WRL research report on the Swift Java compiler.  We discussed building the IR. We now discuss the inter procedural analysis and Optimizations. The Swift compiler has numerous such optimizations which can be individually turned on or off. Customary analysis including class hierarchy analysis, type-propagation, type and field based analysis, escape analysis are applied and in addition, a new form of analysis called the field analysis is also used.  Recall that when building the SSA graph, we already came across common sub expression elimination. Values that load the field of an object will be candidates for CSE only if they access the same field of the same object and they have the same global store input. This simple rule was applied to reduce the number of nodes created. Besides the analysis, some optimizations include method resolution, method inlining, elimination of runtime checks, removal of unnecessary data dependence edges, stack allocation, and synchronization removal.
Several inter procedural optimizations are combined into a single pass and they are applied repeatedly because one optimization can enable further optimization For example, by inlining a method we may be able to tell the type of receiver of another method call, which in turn may enable that method to be inlined as well.
We first review class and method analysis. Swift contains modules that compute and cache useful pieces of information about classes and methods. The basic information about classes is the class hierarch.  It is built only as necessary to help resolve method calls. However, the Swift compiler can optionally use the Class Hierarchy analysis in resolving method calls. The compiler assumes that it is aware of the entire set of classes and that when it encounters a virtual method call, it can resolve to one of the classes or subclass implementation. If the CHA is turned on, all the known classes are loaded and a representation for the hierarchy is built. Then the compiler can scan all the subclasses of any class. If CHA was not being used, the compiler can only tell the subclasses from the classes with the usage of the keyword final.
#codingexercise
Double GetAlternateEvenNumberRangeSumTenthPowerRootSquare (Double [] A)
{
if (A == null) return 0;
Return A.AlternateEvenNumberRangeSumTenthPowerRootSquare();
}