[IRGen] Ensure that empty structs respect non-trivial destruction of members

An empty struct that is noncopyable can nonetheless have a `deinit`, so
it is not trivially destructible. In such cases, embedded them in
another empty struct means that the outer struct should also not be
trivially destructible. Make it so.

Author: DougGregor

lib/IRGen/StructLayout.cpp

@@ -178,10 +178,10 @@ StructLayout::StructLayout(IRGenModule &IGM, std::optional<CanType> type,
       SpareBits.clear();
       IsFixedLayout = true;
       IsLoadable = true;
-      IsKnownTriviallyDestroyable = deinit;
-      IsKnownBitwiseTakable = IsBitwiseTakable;
-      IsKnownAlwaysFixedSize = IsFixedSize;
-      IsKnownCopyable = copyable;
+      IsKnownTriviallyDestroyable = deinit & builder.isTriviallyDestroyable();
+      IsKnownBitwiseTakable = builder.isBitwiseTakable();
+      IsKnownAlwaysFixedSize = builder.isAlwaysFixedSize();
+      IsKnownCopyable = copyable & builder.isCopyable();
       Ty = (typeToFill ? typeToFill : IGM.OpaqueTy);
     } else {
       MinimumAlign = builder.getAlignment();

test/IRGen/moveonly_deinits.swift

@@ -373,3 +373,18 @@ public func testKlassEnumPairWithDeinit() {
         consumeKlassEnumPairWithDeinit(f)
     }
 }
+
+struct EmptyMoveOnlyWithDeinit: ~Copyable {
+  deinit {}
+}
+
+struct EnclosesEmptyMoveOnlyWithDeinit: ~Copyable {
+  var stored: EmptyMoveOnlyWithDeinit
+}
+
+// IR-LABEL: define {{.*}}swiftcc void @"$s16moveonly_deinits35testEnclosesEmptyMoveOnlyWithDeinityyF"()
+func testEnclosesEmptyMoveOnlyWithDeinit() {
+  // CHECK-NOT: ret
+  // CHECK: call swiftcc void @"$s16moveonly_deinits23EmptyMoveOnlyWithDeinitVfD"()
+  _ = EnclosesEmptyMoveOnlyWithDeinit(stored: EmptyMoveOnlyWithDeinit())
+}