Use the actual discriminant instead of always choosing the dataful variant

src/librustc_mir/hair/pattern/mod.rs

@@ -878,8 +878,10 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
                                             );
                                     })
                             }
-                            ty::layout::Variants::NicheFilling { dataful_variant, .. } =>
-                                dataful_variant,
+                            ty::layout::Variants::NicheFilling { .. } => {
+                                assert_eq!(discr_val as usize as u128, discr_val);
+                                discr_val as usize
+                            },
                         };
                         let subpatterns = adt_subpatterns(
                             adt_def.variants[variant_index].fields.len(),

src/test/run-pass/match-arm-statics.rs

@@ -94,6 +94,13 @@ fn issue_14576() {
     const F : C = C::D;
 
     assert_eq!(match C::D { F => 1, _ => 2, }, 1);
+
+    // test gaps
+    #[derive(PartialEq, Eq)]
+    enum G { H = 3, I = 5 }
+    const K : G = G::I;
+
+    assert_eq!(match G::I { K => 1, _ => 2, }, 1);
 }
 
 fn issue_13731() {