Add ScopedInstruction.instruction

So we can use existentials of this type.

This seems really inefficient, but I don't have another solution.

Author: atrick

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -1333,6 +1333,8 @@ final public class AllocExistentialBoxInst : SingleValueInstruction, Allocation
 /// scope ending instruction such as `begin_access` (ending with `end_access`) and `begin_borrow` (ending with
 /// `end_borrow`).
 public protocol ScopedInstruction {
+  var instruction: Instruction { get }
+
   var endOperands: LazyFilterSequence<UseList> { get }
 
   var endInstructions: EndInstructions { get }
@@ -1349,7 +1351,12 @@ extension Instruction {
 }
 
 /// Instructions beginning a borrow-scope which must be ended by `end_borrow`.
-public protocol BorrowIntroducingInstruction : SingleValueInstruction, ScopedInstruction {}
+public protocol BorrowIntroducingInstruction : SingleValueInstruction, ScopedInstruction {
+}
+
+extension BorrowIntroducingInstruction {
+  public var instruction: Instruction { get { self } }
+}
 
 final public class EndBorrowInst : Instruction, UnaryInstruction {
   public var borrow: Value { operand.value }
@@ -1428,6 +1435,8 @@ final public class EndAccessInst : Instruction, UnaryInstruction {
 }
 
 extension BeginAccessInst : ScopedInstruction {
+  public var instruction: Instruction { get { self } }
+
   public var endOperands: LazyFilterSequence<UseList> {
     return uses.lazy.filter { $0.instruction is EndAccessInst }
   }
@@ -1462,6 +1471,8 @@ final public class AbortApplyInst : Instruction, UnaryInstruction {
 }
 
 extension BeginApplyInst : ScopedInstruction {
+  public var instruction: Instruction { get { self } }
+
   public var endOperands: LazyFilterSequence<UseList> {
     return token.uses.lazy.filter { $0.isScopeEndingUse }
   }