Switch statement containing both null and guarded pattern freezes during execution

[Jan Lahoda]

Hi Ilyas,


Please see:

https://bugs.openjdk.java.net/browse/JDK-8269146


This should report a compile-time error in more recent builds:

$ javac --enable-preview -source 17 T.java
T.java:44: error: illegal fall-through to a pattern
             case Integer ii && ii != null:
                  ^

Jan


On 15. 07. 21 12:07, Ilyas Selimov wrote:
> Hello!
>
> I tried to execute the following code using OpenJDK 17 (build 
> 17-ea+30-2618) and got the freeze:
>
>     public static void main(String[] args) {
>         test(null);
>     }
>
>     static void test(Integer i) {
>         switch (i) {
>             case null:
>             case Integer ii && ii != null:
>                 System.out.println("int");
>                 break;
>             default:
>                 System.out.println("def");
>         }
>     }
>
> Looking at the test method's bytecode, it seems the issue is related 
> to the "goto" instruction on the 44's position:
>
>   static void test(java.lang.Integer);
>     Code:
>        0: aload_0
>        1: astore_1
>        2: iconst_0
>        3: istore_2
>        4: aload_1
>        5: iload_2
>        6: invokedynamic #13,  0             // InvokeDynamic 
> #0:typeSwitch:(Ljava/lang/Object;I)I
>       11: lookupswitch  { // 2
>                     -1: 36
>                      0: 36
>                default: 58
>           }
>       36: aload_1
>       37: astore_3
>       38: aload_3
>       39: ifnonnull     47
>       42: iconst_1
>       43: istore_2
>       44: goto          4
>       47: getstatic     #17                 // Field 
> java/lang/System.out:Ljava/io/PrintStream;
>       50: ldc           #23                 // String int
>       52: invokevirtual #25                 // Method 
> java/io/PrintStream.println:(Ljava/lang/String;)V
>       55: goto          66
>       58: getstatic     #17                 // Field 
> java/lang/System.out:Ljava/io/PrintStream;
>       61: ldc           #31                 // String def
>       63: invokevirtual #25                 // Method 
> java/io/PrintStream.println:(Ljava/lang/String;)V
>       66: return
>
> The third_var = null, as third_var = first_var = null.
> So the result of "ifnonnull" instruction seems false and we meet 
> "goto" instruction, jump before the "lookupswitch" position again.
>
> Seems the issue is related to 
> https://bugs.openjdk.java.net/browse/JDK-8269141 
> <https://bugs.openjdk.java.net/browse/JDK-8269141>.
> Could somebody take a look?
>
> Thanks,
> Ilyas