Add SwitchTargetValue.

This is much clearer than `Option<u128>`.

compiler/rustc_mir_dataflow/src/impls/initialized.rs

@@ -4,7 +4,9 @@ use rustc_abi::VariantIdx;
 use rustc_index::Idx;
 use rustc_index::bit_set::{DenseBitSet, MixedBitSet};
 use rustc_middle::bug;
-use rustc_middle::mir::{self, Body, CallReturnPlaces, Location, TerminatorEdges};
+use rustc_middle::mir::{
+    self, Body, CallReturnPlaces, Location, SwitchTargetValue, TerminatorEdges,
+};
 use rustc_middle::ty::util::Discr;
 use rustc_middle::ty::{self, TyCtxt};
 use tracing::{debug, instrument};
@@ -424,7 +426,7 @@ impl<'tcx> Analysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
         state: &mut Self::Domain,
         edge: SwitchIntTarget,
     ) {
-        if let Some(value) = edge.value {
+        if let SwitchTargetValue::Normal(value) = edge.value {
             // Kill all move paths that correspond to variants we know to be inactive along this
             // particular outgoing edge of a `SwitchInt`.
             drop_flag_effects::on_all_inactive_variants(
@@ -537,7 +539,7 @@ impl<'tcx> Analysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
         state: &mut Self::Domain,
         edge: SwitchIntTarget,
     ) {
-        if let Some(value) = edge.value {
+        if let SwitchTargetValue::Normal(value) = edge.value {
             // Mark all move paths that correspond to variants other than this one as maybe
             // uninitialized (in reality, they are *definitely* uninitialized).
             drop_flag_effects::on_all_inactive_variants(