Fix MoveOnlyAddressChecker to handle value deinits.

Track liveness of self so we don't accidentally think that such types
can be memberwise reinitialized.

Author: atrick

lib/SIL/Utils/FieldSensitivePrunedLiveness.cpp

@@ -70,8 +70,13 @@ TypeSubElementCount::TypeSubElementCount(SILType type, SILModule &mod,
           type.getFieldType(fieldDecl, mod, context), mod, context);
     number = numElements;
 
+    if (type.isValueTypeWithDeinit()) {
+      // 'self' has its own liveness represented as an additional field at the
+      // end of the structure.
+      ++number;
+    }
     // If we do not have any elements, just set our size to 1.
-    if (numElements == 0)
+    if (number == 0)
       number = 1;
 
     return;
@@ -350,6 +355,10 @@ void TypeTreeLeafTypeRange::constructFilteredProjections(
       callback(newValue, TypeTreeLeafTypeRange(start, next));
       start = next;
     }
+    if (type.isValueTypeWithDeinit()) {
+      // 'self' has its own liveness
+      ++start;
+    }
     assert(start == endEltOffset);
     return;
   }

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -437,6 +437,7 @@ static bool memInstMustConsume(Operand *memOper) {
 
   SILInstruction *memInst = memOper->getUser();
 
+  // FIXME: drop_deinit must be handled here!
   switch (memInst->getKind()) {
   default:
     return false;

test/Interpreter/moveonly_discard.swift

@@ -91,7 +91,34 @@ struct SillyEmptyGeneric<T>: ~Copyable {
   deinit { fatalError("ran unexpectedly!") }
 }
 
+struct SingleMutableField: ~Copyable {
+  var value = 0
+
+  consuming func justDiscard() {
+    discard self
+  }
+
+  deinit {
+    print("SingleMutableField.deinit")
+  }
+}
+
+// rdar://110232973 ([move-only] Checker should distinguish in between
+// field of single field struct vs parent field itself (was: mutation
+// of field in noncopyable struct should not trigger deinit))
+//
+// This test must not be in a closure.
+@inline(never)
+func testSingleMutableFieldNoMemberReinit() {
+  var x = SingleMutableField()
+  x.value = 20 // should not trigger deinit.
+  // CHECK-NOT: SingleMutableField.deinit
+  x.justDiscard()
+}
+
 func main() {
+  testSingleMutableFieldNoMemberReinit()
+
   let _ = {
     let x = FileDescriptor() // 0
     x.close()