[WalkUtils] Walk through move_value instructions.

Addresses the following regressions

StackPromo                                10100   14400   +42.6%   **0.70x**

seen when enabling lexical lifetimes in the standard library.

Author: nate-chandler

SwiftCompilerSources/Sources/Optimizer/Utilities/WalkUtils.swift

@@ -341,7 +341,7 @@ extension ValueDefUseWalker {
         return unmatchedPath(value: operand, path: path)
       }
     case is InitExistentialRefInst, is OpenExistentialRefInst,
-      is BeginBorrowInst, is CopyValueInst,
+      is BeginBorrowInst, is CopyValueInst, is MoveValueInst,
       is UpcastInst, is UncheckedRefCastInst, is EndCOWMutationInst,
       is RefToBridgeObjectInst, is BridgeObjectToRefInst, is MarkMustCheckInst:
       return walkDownUses(ofValue: (instruction as! SingleValueInstruction), path: path)
@@ -608,7 +608,7 @@ extension ValueUseDefWalker {
         return rootDef(value: mvr, path: path)
       }
     case is InitExistentialRefInst, is OpenExistentialRefInst,
-      is BeginBorrowInst, is CopyValueInst,
+      is BeginBorrowInst, is CopyValueInst, is MoveValueInst,
       is UpcastInst, is UncheckedRefCastInst, is EndCOWMutationInst,
       is RefToBridgeObjectInst, is BridgeObjectToRefInst, is MarkMustCheckInst:
       return walkUp(value: (def as! Instruction).operands[0].value, path: path)

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -618,6 +618,8 @@ final public class ProjectBoxInst : SingleValueInstruction, UnaryInstruction {
 
 final public class CopyValueInst : SingleValueInstruction, UnaryInstruction {}
 
+final public class MoveValueInst : SingleValueInstruction, UnaryInstruction {}
+
 final public class EndCOWMutationInst : SingleValueInstruction, UnaryInstruction {}
 
 final public

SwiftCompilerSources/Sources/SIL/Registration.swift

@@ -119,6 +119,7 @@ public func registerSILClasses() {
   register(BeginBorrowInst.self)
   register(ProjectBoxInst.self)
   register(CopyValueInst.self)
+  register(MoveValueInst.self)
   register(EndCOWMutationInst.self)
   register(ClassifyBridgeObjectInst.self)
   register(PartialApplyInst.self)