[master] RFR: Eliminate Klass* word [v2]

[Roman Kennke]

On Tue, 22 Feb 2022 08:12:28 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Looks fine to me for the experimental code.

Thanks! I want to fix one more failing (because of changed object size) test in tier3 before I push it.

> src/hotspot/share/gc/parallel/psOldGen.cpp line 390:
> 
>> 388: 
>> 389:   virtual void do_object(oop obj) {
>> 390:     HeapWord* test_addr = cast_from_oop<HeapWord*>(obj);
> 
> A bit confused by this change, why?

The code there checks whether a routine can find the start of an object (by looking up in an offset table), starting from somewhere in the middle of an object. It allocates a minimal object, which is 2 words length, increases offset by 1, and starts searching from there. However, with this change, objects may be a single word, and increasing offset by one would find the next object instead. TBH, I wasn't quite sure what to do with that code.

> test/langtools/ProblemList.txt line 76:
> 
>> 74: 
>> 75: 
>> 76: jdk/jshell/ToolTabSnippetTest.java 1234567 generic-all
> 
> This still fails?

Yeah, intermittendly, in GHA. It's not related to this change, but I wanted GHA green.

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PR: https://git.openjdk.java.net/lilliput/pull/40