Optimize ReplayBlocks for Zero Diff (#13198)

* Stategen: replay block return early when zero diff

* Fix test setup

beacon-chain/state/stategen/mock_test.go

@@ -250,9 +250,11 @@ func newMockHistory(t *testing.T, hist []mockHistorySpec, current primitives.Slo
 		b, err = blocktest.SetBlockParentRoot(b, pr)
 		require.NoError(t, err)
 
-		// now do process_block
-		s, err = transition.ProcessBlockForStateRoot(ctx, s, b)
-		require.NoError(t, err)
+		// now do process_block only if block slot is greater than latest header slot
+		if b.Block().Slot() > s.LatestBlockHeader().Slot {
+			s, err = transition.ProcessBlockForStateRoot(ctx, s, b)
+			require.NoError(t, err)
+		}
 
 		sr, err := s.HashTreeRoot(ctx)
 		require.NoError(t, err)

beacon-chain/state/stategen/replayer.go

@@ -93,6 +93,10 @@ func (rs *stateReplayer) ReplayBlocks(ctx context.Context) (state.BeaconState, e
 		msg := fmt.Sprintf("error subtracting state.slot %d from replay target slot %d", s.Slot(), rs.target)
 		return nil, errors.Wrap(err, msg)
 	}
+	if diff == 0 {
+		return s, nil
+	}
+
 	log.WithFields(logrus.Fields{
 		"startSlot": s.Slot(),
 		"endSlot":   rs.target,

beacon-chain/state/stategen/replayer_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/v4/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/v4/testing/require"
+	logTest "github.com/sirupsen/logrus/hooks/test"
 )
 
 func headerFromBlock(b interfaces.ReadOnlySignedBeaconBlock) (*ethpb.BeaconBlockHeader, error) {
@@ -27,6 +28,17 @@ func headerFromBlock(b interfaces.ReadOnlySignedBeaconBlock) (*ethpb.BeaconBlock
 	}, nil
 }
 
+func TestReplayBlocks_ZeroDiff(t *testing.T) {
+	logHook := logTest.NewGlobal()
+	ctx := context.Background()
+	specs := []mockHistorySpec{{slot: 0}}
+	hist := newMockHistory(t, specs, 0)
+	ch := NewCanonicalHistory(hist, hist, hist)
+	_, err := ch.ReplayerForSlot(0).ReplayBlocks(ctx)
+	require.NoError(t, err)
+	require.LogsDoNotContain(t, logHook, "Replaying canonical blocks from most recent state")
+}
+
 func TestReplayBlocks(t *testing.T) {
 	ctx := context.Background()
 	var zero, one, two, three, four, five primitives.Slot = 50, 51, 150, 151, 152, 200