SwiftCompilerSources: add IgnoredUseInst as incidental

Fixes rdar://148540048 (Assigning span value to `_` results in an incorrect escape diagnostic)

Author: atrick

SwiftCompilerSources/Sources/Optimizer/Utilities/LifetimeDependenceUtils.swift

@@ -638,7 +638,7 @@ extension LifetimeDependenceDefUseWalker {
          is DestroyNotEscapedClosureInst, is ClassMethodInst, is SuperMethodInst,
          is ClassifyBridgeObjectInst, is DebugValueInst,
          is ObjCMethodInst, is ObjCSuperMethodInst, is UnmanagedRetainValueInst,
-         is UnmanagedReleaseValueInst, is SelectEnumInst:
+         is UnmanagedReleaseValueInst, is SelectEnumInst, is IgnoredUseInst:
       // Catch .instantaneousUse operations that are dependence leaf uses.
       return leafUse(of: operand)
 

SwiftCompilerSources/Sources/SIL/Instruction.swift

@@ -149,7 +149,8 @@ public class Instruction : CustomStringConvertible, Hashable {
   /// their operand.
   public final var isIncidentalUse: Bool {
     switch self {
-    case is DebugValueInst, is FixLifetimeInst, is EndLifetimeInst:
+    case is DebugValueInst, is FixLifetimeInst, is EndLifetimeInst,
+         is IgnoredUseInst:
       return true
     default:
       return isEndOfScopeMarker