private static void checkCodeBlock(
     final PsiCodeBlock body, final Set<PsiField> candidates, Set<PsiField> usedFields) {
   try {
     final ControlFlow controlFlow =
         ControlFlowFactory.getInstance(body.getProject())
             .getControlFlow(body, AllVariablesControlFlowPolicy.getInstance());
     final List<PsiVariable> usedVars =
         ControlFlowUtil.getUsedVariables(controlFlow, 0, controlFlow.getSize());
     for (PsiVariable usedVariable : usedVars) {
       if (usedVariable instanceof PsiField) {
         final PsiField usedField = (PsiField) usedVariable;
         if (!usedFields.add(usedField)) {
           candidates.remove(usedField); // used in more than one code block
         }
       }
     }
     final List<PsiReferenceExpression> readBeforeWrites =
         ControlFlowUtil.getReadBeforeWrite(controlFlow);
     for (final PsiReferenceExpression readBeforeWrite : readBeforeWrites) {
       final PsiElement resolved = readBeforeWrite.resolve();
       if (resolved instanceof PsiField) {
         final PsiField field = (PsiField) resolved;
         PsiElement parent = body.getParent();
         if (!(parent instanceof PsiMethod)
             || !((PsiMethod) parent).isConstructor()
             || field.getInitializer() == null
             || field.hasModifierProperty(PsiModifier.STATIC)) {
           candidates.remove(field);
         }
       }
     }
   } catch (AnalysisCanceledException e) {
     candidates.clear();
   }
 }
 public List<PsiVariable> getUsedVariables(int start, int end) {
   return ControlFlowUtil.getUsedVariables(myControlFlow, start, end);
 }