Swift SIL: add BuiltinInst.ID.stackAlloc

And make all the case identifiers lowercase.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Utilities/EscapeInfo.swift

@@ -396,7 +396,7 @@ fileprivate struct EscapeInfoWalker<V: EscapeInfoVisitor> : ValueDefUseWalker,
       return walkDownUses(ofAddress: pta, path: path.with(knownType: nil))
     case let bi as BuiltinInst:
       switch bi.id {
-      case .DestroyArray:
+      case .destroyArray:
         // If it's not the array base pointer operand -> bail. Though, that shouldn't happen
         // because the other operands (metatype, count) shouldn't be visited anyway.
         if operand.index != 1 { return isEscaping }

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -321,13 +321,16 @@ final public class LoadBorrowInst : SingleValueInstruction, UnaryInstruction {}
 final public class BuiltinInst : SingleValueInstruction {
   // TODO: find a way to directly reuse the BuiltinValueKind enum
   public enum ID  {
-    case None
-    case DestroyArray
+    case none
+    case destroyArray
+    case stackAlloc
   }
-  public var id: ID? {
+
+  public var id: ID {
     switch BuiltinInst_getID(bridged) {
-      case DestroyArrayBuiltin: return .DestroyArray
-      default: return .None
+      case DestroyArrayBuiltin: return .destroyArray
+      case StackAllocBuiltin: return .stackAlloc
+      default: return .none
     }
   }
 }