*: use (*VM).IstackLen() where appropriate

pkg/compiler/vm_test.go

@@ -57,7 +57,7 @@ func evalWithArgs(t *testing.T, src string, op []byte, args []stackitem.Item, re
 
 func assertResult(t *testing.T, vm *vm.VM, result interface{}) {
 	assert.Equal(t, result, vm.PopResult())
-	assert.Equal(t, 0, vm.Istack().Len())
+	assert.Equal(t, 0, vm.IstackLen())
 }
 
 func vmAndCompile(t *testing.T, src string) *vm.VM {

pkg/core/interop/contract/call.go

@@ -157,12 +157,12 @@ var ErrNativeCall = errors.New("failed native call")
 
 // CallFromNative performs synchronous call from native contract.
 func CallFromNative(ic *interop.Context, caller util.Uint160, cs *state.Contract, method string, args []stackitem.Item, hasReturn bool) error {
-	startSize := ic.VM.Istack().Len()
+	startSize := ic.VM.IstackLen()
 	if err := callExFromNative(ic, caller, cs, method, args, callflag.All, hasReturn, false, true); err != nil {
 		return err
 	}
 
-	for !ic.VM.HasStopped() && ic.VM.Istack().Len() > startSize {
+	for !ic.VM.HasStopped() && ic.VM.IstackLen() > startSize {
 		if err := ic.VM.Step(); err != nil {
 			return fmt.Errorf("%w: %v", ErrNativeCall, err)
 		}

pkg/core/interop/runtime/engine.go

@@ -38,7 +38,7 @@ func GetCallingScriptHash(ic *interop.Context) error {
 
 // GetEntryScriptHash returns entry script hash.
 func GetEntryScriptHash(ic *interop.Context) error {
-	return ic.VM.PushContextScriptHash(ic.VM.Istack().Len() - 1)
+	return ic.VM.PushContextScriptHash(ic.VM.IstackLen() - 1)
 }
 
 // GetScriptContainer returns transaction or block that contains the script

pkg/vm/invocation_tree_test.go

@@ -24,7 +24,7 @@ func TestInvocationTree(t *testing.T) {
 	cnt := 0
 	v := newTestVM()
 	v.SyscallHandler = func(v *VM, _ uint32) error {
-		if v.Istack().Len() > 4 { // top -> call -> syscall -> call -> syscall -> ...
+		if v.IstackLen() > 4 { // top -> call -> syscall -> call -> syscall -> ...
 			v.Estack().PushVal(1)
 			return nil
 		}