Add OwnershipTransitionInstruction.

These instructions carry lifetime dependence from a single operand to a single result. They are not forwarding
instructions because we use them to indicate the boundaries of a forwarded lifetime.

Author: atrick

SwiftCompilerSources/Sources/SIL/ForwardingInstruction.swift

@@ -397,3 +397,33 @@ extension LinearFunctionExtractInst: ForwardingInstruction {
   public var canForwardGuaranteedValues: Bool { true }
   public var canForwardOwnedValues: Bool { true }
 }
+
+// -----------------------------------------------------------------------------
+// ownership transition instructions
+
+/// An instruction that transfers lifetime dependence from a single operand to a single result. The operand and result
+/// have the same identity, but they are not part of the same forwarded lifetime:
+/// copy_value, move_value, begin_borrow.
+public protocol OwnershipTransitionInstruction: UnaryInstruction {
+  var ownershipResult: Value { get }
+}
+
+extension OwnershipTransitionInstruction where Self: SingleValueInstruction {
+  public var ownershipResult: Value { self }
+}
+
+// CopyingInstruction implies OwnershipTransitionInstruction
+
+extension MoveValueInst: OwnershipTransitionInstruction {}
+
+extension BeginBorrowInst: OwnershipTransitionInstruction {}
+
+extension BeginCOWMutationInst: OwnershipTransitionInstruction {
+  public var ownershipResult: Value { instanceResult }
+}
+
+extension EndCOWMutationInst: OwnershipTransitionInstruction {}
+
+extension EndInitLetRefInst: OwnershipTransitionInstruction {}
+
+extension BeginDeallocRefInst: OwnershipTransitionInstruction {}

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -1041,7 +1041,7 @@ final public class ProjectBoxInst : SingleValueInstruction, UnaryInstruction {
 
 final public class ProjectExistentialBoxInst : SingleValueInstruction, UnaryInstruction {}
 
-public protocol CopyingInstruction : SingleValueInstruction, UnaryInstruction {}
+public protocol CopyingInstruction : SingleValueInstruction, UnaryInstruction, OwnershipTransitionInstruction {}
 
 final public class CopyValueInst : SingleValueInstruction, CopyingInstruction {
   public var fromValue: Value { operand.value }