Swift Bridging: use C++ instead of C bridging for BridgedSuccessor

SwiftCompilerSources/Sources/SIL/BasicBlock.swift

@@ -143,19 +143,20 @@ public struct ArgumentArray : RandomAccessCollection {
 }
 
 public struct SuccessorArray : RandomAccessCollection, FormattedLikeArray {
-  private let succArray: BridgedArrayRef
+  private let base: OptionalBridgedSuccessor
+  public let count: Int
 
-  init(succArray: BridgedArrayRef) {
-    self.succArray = succArray
+  init(base: OptionalBridgedSuccessor, count: Int) {
+    self.base = base
+    self.count = count
   }
 
   public var startIndex: Int { return 0 }
-  public var endIndex: Int { return Int(succArray.numElements) }
+  public var endIndex: Int { return count }
 
   public subscript(_ index: Int) -> BasicBlock {
-    assert(index >= 0 && index < endIndex)
-    let s = BridgedSuccessor(succ: succArray.data! + index &* BridgedSuccessorSize);
-    return SILSuccessor_getTargetBlock(s).block
+    assert(index >= startIndex && index < endIndex)
+    return base.advancedBy(index).getTargetBlock().block
   }
 }
 
@@ -165,10 +166,9 @@ public struct PredecessorList : CollectionLikeSequence, IteratorProtocol {
   public init(startAt: OptionalBridgedSuccessor) { currentSucc = startAt }
 
   public mutating func next() -> BasicBlock? {
-    if let succPtr = currentSucc.succ {
-      let succ = BridgedSuccessor(succ: succPtr)
-      currentSucc = SILSuccessor_getNext(succ)
-      return SILSuccessor_getContainingInst(succ).instruction.parentBlock
+    if let succ = currentSucc.successor {
+      currentSucc = succ.getNext()
+      return succ.getContainingInst().instruction.parentBlock
     }
     return nil
   }
@@ -196,3 +196,12 @@ extension Optional where Wrapped == BasicBlock {
     OptionalBridgedBasicBlock(obj: self?.bridged.obj)
   }
 }
+
+extension OptionalBridgedSuccessor {
+  var successor: BridgedSuccessor? {
+    if let succ = succ {
+      return BridgedSuccessor(succ: succ)
+    }
+    return nil
+  }
+}