more speedups

* evaluate block attestations under the epochref of the block - this is
what the state transition function does
* avoid copying attestation seq unnecessarily
* avoid unnecessary hashset for unslashed indices

beacon_chain/fork_choice/fork_choice.nim

@@ -290,8 +290,6 @@ proc process_block*(self: var ForkChoice,
       continue
     if attestation.data.beacon_block_root in self.backend:
       let
-        epochRef =
-          dag.getEpochRef(targetBlck, attestation.data.target.epoch)
         participants = get_attesting_indices(
           epochRef, attestation.data, attestation.aggregation_bits)
 

beacon_chain/spec/beaconstate.nim

@@ -595,8 +595,6 @@ proc process_attestation*(
   # In the spec, attestation validation is mixed with state mutation, so here
   # we've split it into two functions so that the validation logic can be
   # reused when looking for suitable blocks to include in attestations.
-  # TODO don't log warnings when looking for attestations (return
-  #      Result[void, cstring] instead of logging in check_attestation?)
 
   let proposer_index = get_beacon_proposer_index(state, cache)
   if proposer_index.isNone:

beacon_chain/spec/state_transition_epoch.nim

@@ -66,8 +66,8 @@ func get_total_active_balance*(state: BeaconState, cache: var StateCache): Gwei
     state, cache.get_shuffled_active_validator_indices(state, epoch))
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#helper-functions-1
-func get_matching_source_attestations(state: BeaconState,
-                                      epoch: Epoch): seq[PendingAttestation] =
+template get_matching_source_attestations(state: BeaconState,
+                                          epoch: Epoch): seq[PendingAttestation] =
   doAssert epoch in [get_current_epoch(state), get_previous_epoch(state)]
   if epoch == get_current_epoch(state):
     state.current_epoch_attestations.asSeq
@@ -309,10 +309,11 @@ func get_source_deltas*(
     state: BeaconState, total_balance: Gwei, cache: var StateCache):
     tuple[a: seq[Gwei], b: seq[Gwei]] =
   # Return attester micro-rewards/penalties for source-vote for each validator.
-  let matching_source_attestations =
-    get_matching_source_attestations(state, get_previous_epoch(state))
+
   get_attestation_component_deltas(
-    state, matching_source_attestations, total_balance, cache)
+    state,
+    get_matching_source_attestations(state, get_previous_epoch(state)),
+    total_balance, cache)
 
 func get_target_deltas*(
     state: BeaconState, total_balance: Gwei, cache: var StateCache):

beacon_chain/spec/state_transition_helpers.nim

@@ -31,9 +31,9 @@ func get_attesting_indices*(
 func get_unslashed_attesting_indices*(
     state: BeaconState, attestations: openArray[PendingAttestation],
     cache: var StateCache): HashSet[ValidatorIndex] =
-  result = get_attesting_indices(state, attestations, cache)
-  var slashedIndices = initHashSet[ValidatorIndex]()
-  for index in result:
-    if state.validators[index].slashed:
-      slashedIndices.incl index
-  result.excl slashedIndices
+  result = initHashSet[ValidatorIndex]()
+  for a in attestations:
+    for idx in get_attesting_indices(
+        state, a.data, a.aggregation_bits, cache):
+      if not state.validators[idx].slashed:
+        result.incl idx