x/staking: add ValidateGenesis benchmark (cosmos#8746)

This benchmark examines how ValidateGenesis behaves.
In a follow-up issue, I'll show how it reveals an inefficiency
that'll affect trying to load repeatedly retrieve Validators'
ConsAddress values.

Updates cosmos#8744

x/staking/bench_test.go

@@ -0,0 +1,56 @@
+package staking_test
+
+import (
+	"testing"
+
+	"github.com/cosmos/cosmos-sdk/crypto/keys/ed25519"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/staking"
+	"github.com/cosmos/cosmos-sdk/x/staking/teststaking"
+	"github.com/cosmos/cosmos-sdk/x/staking/types"
+)
+
+func BenchmarkValidateGenesis10Validators(b *testing.B) {
+	benchmarkValidateGenesis(b, 10)
+}
+
+func BenchmarkValidateGenesis100Validators(b *testing.B) {
+	benchmarkValidateGenesis(b, 100)
+}
+
+func BenchmarkValidateGenesis400Validators(b *testing.B) {
+	benchmarkValidateGenesis(b, 400)
+}
+
+func benchmarkValidateGenesis(b *testing.B, n int) {
+	b.ReportAllocs()
+
+	validators := make([]types.Validator, 0, n)
+	addressL, pubKeyL := makeRandomAddressesAndPublicKeys(n)
+	for i := 0; i < n; i++ {
+		addr, pubKey := addressL[i], pubKeyL[i]
+		validator := teststaking.NewValidator(b, addr, pubKey)
+		ni := int64(i + 1)
+		validator.Tokens = sdk.NewInt(ni)
+		validator.DelegatorShares = sdk.NewDec(ni)
+		validators = append(validators, validator)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		genesisState := types.DefaultGenesisState()
+		genesisState.Validators = validators
+		if err := staking.ValidateGenesis(genesisState); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func makeRandomAddressesAndPublicKeys(n int) (accL []sdk.ValAddress, pkL []*ed25519.PubKey) {
+	for i := 0; i < n; i++ {
+		pk := ed25519.GenPrivKey().PubKey().(*ed25519.PubKey)
+		pkL = append(pkL, pk)
+		accL = append(accL, sdk.ValAddress(pk.Address()))
+	}
+	return accL, pkL
+}