Address comments

Author: varkor

src/librustc/ty/sty.rs

@@ -1495,8 +1495,12 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
         // but we only return `true` for types that are definitely uninhabited.
         match self.sty {
             ty::Never => true,
+            ty::Adt(def, _) if def.is_union() => {
+                // For now, `union`s are never considered uninhabited.
+                false
+            }
             ty::Adt(def, _) => {
-                // Any ADT is uninhabited if:
+                // Any ADT is uninhabited if either:
                 // (a) It has no variants (i.e. an empty `enum`);
                 // (b) Each of its variants (a single one in the case of a `struct`) has at least
                 //     one uninhabited field.

src/librustc_codegen_llvm/mir/block.rs

@@ -457,7 +457,7 @@ impl FunctionCx<'a, 'll, 'tcx> {
                         // we can do what we like. Here, we declare that transmuting
                         // into an uninhabited type is impossible, so anything following
                         // it must be unreachable.
-                        assert!(sig.output().conservative_is_uninhabited(bx.tcx()));
+                        assert_eq!(bx.cx.layout_of(sig.output()).abi, layout::Abi::Uninhabited);
                         bx.unreachable();
                     }
                     return;