RFR: 8240567: MethodTooLargeException thrown while creating a jlink image [v12]

[Oliver Kopp]

On Mon, 3 Jul 2023 20:00:40 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> Oliver Kopp has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Fix test
>>  - Fix ArrayList initialization and off-by-one errors
>
> src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java line 543:
> 
>> 541:         private static final int MAX_LOCAL_VARS = 256;
>> 542: 
>> 543:         private final int BUILDER_VAR    = MAX_LOCAL_VARS + 1;
> 
> why this one can't use the next available local variables?   i.e.  if no splitting, 1 is the next available slot (btw it looks like using 0 in the current implementation is a bug because this is an instance method).   If module descriptors are done in multiple helper methods, 3 is the next available slot.

I tried that multiple times and always failed.  With following hack, I "debugged" the value of nextLocalVar at the beginning of the split:

    Files.writeString(Path.of("C:\\temp\\test.log"), "nextlocavar" + nextLocalVar, StandardOpenOption.CREATE, StandardOpenOption.APPEND);

The values are always 4. I did not dare to overwrite these "magic" slots 1, 2, 3. Despite using IntelliJ's call hierarchy feature, I could not find out where in the code this happens or for what reasons.

I moved `BUILDER_VAR` and `DEDUP_LIST_VAR` two "away".

I think, using `0` was "intentional", because `this` was not needed in the method and thus, this slot could be reused.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14408#discussion_r1251281097