Possible LVT regression with labelled block statements

[Vicente-Arturo Romero-Zaldivar]

Hi Liam,

Thanks a lot for the report and the reduced test case. I have created 
bug: https://bugs.openjdk.java.net/browse/JDK-8064857 to track this issue.

Thanks,
Vicente

On 11/13/2014 07:09 PM, Liam Miller-Cushon wrote:
> I found a possible LVT bug in javac8 that affects labelled break 
> statements. It causes incorrect zero-length LVT entries to be emitted 
> for locals that have non-zero live ranges.
>
> Here's a repro:
>
> ===
> class Test {
>   int m(boolean flag) {
>     int myInt;
>     label:
>     {
>       if (flag) {
>         myInt = 1;
>       } else {
>         break label;
>       }
>
>       return myInt;
>     }
>     return -1;
>   }
> }
> ===
>
> With javac8, the code compiles to:
>
> ===
>   int m(boolean);
>     descriptor: (Z)I
>     flags:
>     Code:
>       stack=1, locals=3, args_size=2
>          0: iload_1
>          1: ifeq          8
>          4: iconst_1
>          5: istore_2
>          6: iload_2
>          7: ireturn
>          8: iconst_m1
>          9: ireturn
>       LineNumberTable:
>         line 6: 0
>         line 7: 4
>         line 12: 6
>         line 14: 8
>       LocalVariableTable:
>         Start  Length  Slot  Name   Signature
>             6       0     2 myInt   I
>             0      10     0  this   LTest;
>             0      10     1  flag   Z
> ===
>
> My understanding is that the zero-length LVT entry for 'myInt' is 
> incorrect. With earlier versions of javac (and also ecj) the entry's 
> length is 2.
>
> The behaviour started occurring after the change that 
> fixed JDK-8012868 [1][2], so this affects javac8 and 9. It reproduces 
> with the latest version of javac9 (I tested @c286272a81dd).
>
> The issue was originally discovered because it affects joda time, 
> specifically the local variable 'expectSeparators' in 
> DateTimeFormatterBuilder [3].
>
> [1] http://hg.openjdk.java.net/jdk9/dev/langtools/rev/4932bb04c4b8
> [2] https://bugs.openjdk.java.net/browse/JDK-8012868
> [3] 
> https://github.com/JodaOrg/joda-time/blob/1379098f681f0d4d6f0a3403ab6727dc3437b6df/src/main/java/org/joda/time/format/DateTimeFormatterBuilder.java#L2132
>
> Thanks,
> Liam