RFR: 8315735: VerifyError when switch statement used with synchronized block

[Vicente Romero]

On Wed, 6 Sep 2023 09:36:35 GMT, Rémi Forax <forax at openjdk.org> wrote:

>> Having code like:
>> 
>>     public static void main(String... args) {
>>         int i1 = 0 + switch (args.length) {
>>             default -> {
>>                 synchronized (args) {
>>                     yield 1;
>>                 }
>>             }
>>         };
>>     }
>> 
>> 
>> fails with a verification error at runtime. In the classfile, the synchronized block is basically a try-finally (which has an implicit "catch (any)" block), and so it needs the same handling as ordinary try statements.
>> 
>> (When there's a try statement inside a switch expression, the pre-existing stack is stored in local variables, and restored at return from the case. This is because catch clauses start with an empty stack.)
>
> src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java line 1292:
> 
>> 1290:                     hasTry[0] = true;
>> 1291:                 }
>> 1292: 
> 
> You can make this code slightly more efficient by using the fact that 'var' is enable to reference the type of an anonymous class.
> 
> 
> private boolean hasTry(JCSwitchExpression tree) {
>             var treeScanner = new TreeScanner() {
>                 private boolean hasTry;                
>  
>                 @Override
>                 public void visitTry(JCTry tree) {
>                     hasTry = true;
>                 }
> 
>                 @Override
>                 public void visitSynchronized(JCSynchronized tree) {
>                     hasTry = true;
>                 }
> 
>                 @Override
>                 public void visitClassDef(JCClassDecl tree) {
>                 }
>                 @Override
>                 public void visitLambda(JCLambda tree) {
>                 }
>             };
>             treeScanner.scan(tree);
>             return treeScanner.hasTry;
>         }

nice suggestion

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/15584#discussion_r1317686885