Moves SignatureAnalyzer and ArgumentDescriptor/ResultDescriptor into a separate

analysis pass.

This pass is run on every function and the optimized signature is return'ed through the
getArgDescList and getResultDescList.

Next step is to split to cloning and callsite rewriting into their own function passes.

rdar://24730896

lib/SIL/Projection.cpp

@@ -1172,6 +1172,16 @@ ProjectionTree::~ProjectionTree() {
     N->~ProjectionTreeNode();
 }
 
+void
+ProjectionTree::initializeWithExistingTree(const ProjectionTree &PT) {
+  Kind = PT.Kind;
+  EpilogueReleases = PT.EpilogueReleases;
+  LiveLeafIndices = PT.LiveLeafIndices;
+  for (const auto &N : PT.ProjectionTreeNodes) {
+    ProjectionTreeNodes.push_back(new (Allocator) ProjectionTreeNode(*N));
+  }
+}
+
 SILValue
 ProjectionTree::computeExplodedArgumentValueInner(SILBuilder &Builder,
                                                   SILLocation Loc,