vm: optimise emit.Array() to use NEWARRAY0 for zero-lenght arrays

pkg/core/native/oracle.go

@@ -13,7 +13,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/dao"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop/contract"
-	"github.com/nspcc-dev/neo-go/pkg/core/interop/interopnames"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/noderoles"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
@@ -29,7 +28,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/util/slice"
 	"github.com/nspcc-dev/neo-go/pkg/vm/emit"
-	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
@@ -89,11 +87,7 @@ func newOracle() *Oracle {
 	defer o.UpdateHash()
 
 	w := io.NewBufBinWriter()
-	emit.Opcodes(w.BinWriter, opcode.NEWARRAY0)
-	emit.Int(w.BinWriter, int64(callflag.All))
-	emit.String(w.BinWriter, "finish")
-	emit.Bytes(w.BinWriter, o.Hash.BytesBE())
-	emit.Syscall(w.BinWriter, interopnames.SystemContractCall)
+	emit.AppCall(w.BinWriter, o.Hash, "finish", callflag.All)
 	o.oracleScript = w.Bytes()
 
 	desc := newDescriptor("request", smartcontract.VoidType,

pkg/vm/emit/emit.go

@@ -76,6 +76,10 @@ func bigInt(w *io.BinWriter, n *big.Int) {
 
 // Array emits array of elements to the given buffer.
 func Array(w *io.BinWriter, es ...interface{}) {
+	if len(es) == 0 {
+		Opcodes(w, opcode.NEWARRAY0)
+		return
+	}
 	for i := len(es) - 1; i >= 0; i-- {
 		switch e := es[i].(type) {
 		case []interface{}:

pkg/vm/emit/emit_test.go

@@ -177,7 +177,7 @@ func TestEmitArray(t *testing.T) {
 		buf := io.NewBufBinWriter()
 		Array(buf.BinWriter)
 		require.NoError(t, buf.Err)
-		assert.EqualValues(t, []byte{byte(opcode.PUSH0), byte(opcode.PACK)}, buf.Bytes())
+		assert.EqualValues(t, []byte{byte(opcode.NEWARRAY0)}, buf.Bytes())
 	})
 
 	t.Run("invalid type", func(t *testing.T) {