SIL: The inner type of a SILMoveOnlyWrappedType is a lowered position

Fixes rdar://161968922.

Author: slavapestov

lib/SIL/IR/SILTypeSubstitution.cpp

@@ -420,6 +420,14 @@ class SILTypeSubstituter :
                                          substObjectType));
   }
 
+  /// MoveOnlyWrappedTypes need to have their inner types substituted
+  /// by these rules.
+  CanType visitSILMoveOnlyWrappedType(CanSILMoveOnlyWrappedType origType) {
+    CanType origInnerType = origType->getInnerType();
+    CanType substInnerType = visit(origInnerType);
+    return CanType(SILMoveOnlyWrappedType::get(substInnerType));
+  }
+
   /// Any other type would be a valid type in the AST. Just apply the
   /// substitution on the AST level and then lower that.
   CanType visitType(CanType origType) {

test/SILOptimizer/specialize_move_only_wrapped_type.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend -emit-sil -O %s
+
+public struct Mutex<T> {
+  public init(_: T) {}
+}
+
+public struct Locked<T> {
+  public let mutex: Mutex<T>
+
+  public init(_ rawValue: consuming T) {
+    mutex = Mutex(rawValue)
+  }
+}
+
+_ = Locked { }