Update compiler/rustc_const_eval/src/interpret/memory.rs

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: saethlin

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -505,7 +505,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// This function is used by Miri's provenance GC to remove unreachable entries from the dead_alloc_map.
     pub fn remove_unreachable_allocs(&mut self, reachable_allocs: &FxHashSet<AllocId>) {
         // Unlike all the other GC helpers where we check if an `AllocId` is found in the interpreter or
-        // is live, here all the IDs in the map are for dead allocations.
+        // is live, here all the IDs in the map are for dead allocations so we don't
+        // need to check for liveness.
         #[allow(rustc::potential_query_instability)] // Only used from Miri, not queries.
         self.memory.dead_alloc_map.retain(|id, _| reachable_allocs.contains(id));
     }