Check discriminant types before span_mirbug

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1270,14 +1270,17 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 if let Err(terr) =
                     self.sub_types(rv_ty, place_ty, location.to_locations(), category)
                 {
-                    span_mirbug!(
-                        self,
-                        stmt,
-                        "bad assignment ({:?} = {:?}): {:?}",
-                        place_ty,
-                        rv_ty,
-                        terr
-                    );
+                    // HACK(ouz-a): Bypasses ICE for #91633
+                    if rv_ty.discriminant_ty(self.tcx()) != place_ty.discriminant_ty(self.tcx()) {
+                        span_mirbug!(
+                            self,
+                            stmt,
+                            "bad assignment ({:?} = {:?}): {:?}",
+                            place_ty,
+                            rv_ty,
+                            terr
+                        );
+                    }
                 }
 
                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {

src/test/ui/typeck/issue-91633.rs

@@ -0,0 +1,8 @@
+// check-pass
+fn f<T> (it: &[T])
+where
+    [T] : std::ops::Index<usize>,
+{
+    let _ = &it[0];
+}
+fn main(){}