Question on the inline type flattening decision

[Xiaohong Gong]

Hi,

I guess this is the right place to ask this question related to the flattening decision on inline type fields?

I met an issue when I was running the tests under "hotspot/jtreg/compiler/valhalla/inlinetypes" with "-XX:InlineFieldMaxFlatSize=0". The intention is doing some testing by forcing the inline type fields not be flattened.  And I debugged some C2 code in `inlinetypenode.cpp` like `InlineTypeNode::load()`.  But I found that the code path has no difference, which means this flag cannot work and the field is flattened as without this flag.

And then, I checked the relative code https://github.com/openjdk/valhalla/blob/lworld/src/hotspot/share/classfile/fieldLayoutBuilder.cpp#L759 to find out the reason. It checks the three necessary conditions (i.e. "the code size comparison with `InlineFieldMaxSize`", "atomic" or "volatile" fields) firstly, which is the right behavior I think. But then the result is "||" with the `final` access flag. Which means if the field is `final`, it will be flattened anyway regardless of the necessary three limitations.

So is this the expected behavior? Does this mean the inline type field can always be flattened if it is declared with `final`? But I didn't find any descriptions on the flattening decision related to the `final` flag.

Many thanks if any help on this!

Best Regards,
Xiaohong

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