Add mir-opt test for better drop elaboration

Author: ecstatic-morse

src/test/mir-opt/no-drop-for-inactive-variant.rs

@@ -0,0 +1,41 @@
+// Ensure that there are no drop terminators in `unwrap<T>` (except the one along the cleanup
+// path).
+
+fn unwrap<T>(opt: Option<T>) -> T {
+    match opt {
+        Some(x) => x,
+        None => panic!(),
+    }
+}
+
+fn main() {
+    let _ = unwrap(Some(1i32));
+}
+
+// END RUST SOURCE
+// START rustc.unwrap.SimplifyCfg-elaborate-drops.after.mir
+// fn unwrap(_1: std::option::Option<T>) -> T {
+//     ...
+//     bb0: {
+//         ...
+//         switchInt(move _2) -> [0isize: bb2, 1isize: bb4, otherwise: bb3];
+//     }
+//     bb1 (cleanup): {
+//         resume;
+//     }
+//     bb2: {
+//         ...
+//         const std::rt::begin_panic::<&'static str>(const "explicit panic") -> bb5;
+//     }
+//     bb3: {
+//         unreachable;
+//     }
+//     bb4: {
+//         ...
+//         return;
+//     }
+//     bb5 (cleanup): {
+//         drop(_1) -> bb1;
+//     }
+// }
+// END rustc.unwrap.SimplifyCfg-elaborate-drops.after.mir