Fix LowerAggregateInstrs to avoid lowering move-only types

Fixes rdar://109849028 ([move-only] LowerAggregateInstrs eliminates struct deinitialization)

Author: atrick

lib/SILOptimizer/Transforms/SILLowerAggregateInstrs.cpp

@@ -43,12 +43,21 @@ static llvm::cl::opt<bool> EnableExpandAll("sil-lower-agg-instrs-expand-all",
 //                                  Utility
 //===----------------------------------------------------------------------===//
 
+/// Expansion of struct-with-deinit is illegal because it drops the deinit. For
+/// now, simply avoid all move-only AST types.
+static bool canExpandType(SILType type) {
+  return type.isPureMoveOnly();
+}
+
 /// We only expand if we are not in ownership and shouldExpand is true. The
 /// reason why is that this was originally done to help the low level ARC
 /// optimizer. To the high level ARC optimizer, this is just noise and
 /// unnecessary IR. At the same time for testing purposes, we want to provide a
 /// way even with ownership enabled to expand so we can check correctness.
 static bool shouldExpandShim(SILFunction *fn, SILType type) {
+  if (!canExpandType(type))
+    return false;
+
   return EnableExpandAll ||
          (!fn->hasOwnership() && shouldExpand(fn->getModule(), type));
 }

test/SILOptimizer/loweraggregateinstrs_moveonly.sil

@@ -0,0 +1,32 @@
+// RUN: %target-sil-opt -enable-sil-verify-all -lower-aggregate-instrs %s | %FileCheck %s
+
+sil_stage canonical
+
+import Builtin
+
+struct S : ~Copyable {
+  deinit {}
+}
+struct S2 : ~Copyable {
+  var s1 = S()
+  var s2 = S()
+}
+
+// Test that a struct-with-deinit is not expanded. Doing so would
+// forget the deinit.
+//
+// public func testDeinitTwo() {
+//   var s = S2()
+// }
+//
+// CHECK-LABEL: sil @testDeinitTwo : $@convention(thin) () -> () {
+// CHECK:         release_value %{{.*}} : $S2
+// CHECK-LABEL: } // end sil function 'testDeinitTwo'
+sil @testDeinitTwo : $@convention(thin) () -> () {
+bb0:
+  %0 = struct $S ()
+  %1 = struct $S2 (%0 : $S, %0 : $S)
+  release_value %1 : $S2
+  %5 = tuple ()
+  return %5 : $()
+}