Track a Bank's parent slot independently from parent bank (#7131)

core/src/broadcast_stage/standard_broadcast_run.rs

@@ -141,13 +141,7 @@ impl StandardBroadcastRun {
         {
             self.slot_broadcast_start = Some(Instant::now());
             let slot = bank.slot();
-            let parent_slot = {
-                if let Some(parent_bank) = bank.parent() {
-                    parent_bank.slot()
-                } else {
-                    0
-                }
-            };
+            let parent_slot = bank.parent_slot();
 
             self.current_slot_and_parent = Some((slot, parent_slot));
             receive_elapsed = Duration::new(0, 0);

runtime/src/bank.rs

@@ -180,6 +180,8 @@ pub struct Bank {
     /// Hash of this Bank's parent's state
     parent_hash: Hash,
 
+    parent_slot: u64,
+
     /// The number of transactions processed without error
     #[serde(serialize_with = "serialize_atomicu64")]
     #[serde(deserialize_with = "deserialize_atomicu64")]
@@ -358,6 +360,7 @@ impl Bank {
             epoch_stakes: parent.epoch_stakes.clone(),
             storage_accounts: RwLock::new(parent.storage_accounts.read().unwrap().clone()),
             parent_hash: parent.hash(),
+            parent_slot: parent.slot(),
             collector_id: *collector_id,
             collector_fees: AtomicU64::new(0),
             ancestors: HashMap::new(),
@@ -662,6 +665,10 @@ impl Bank {
         self.rc.parent.read().unwrap().clone()
     }
 
+    pub fn parent_slot(&self) -> u64 {
+        self.parent_slot
+    }
+
     fn process_genesis_config(&mut self, genesis_config: &GenesisConfig) {
         // Bootstrap leader collects fees until `new_from_parent` is called.
         self.fee_calculator = genesis_config.fee_calculator.clone();