[master] RFR: Load Klass from header, C1/x86 implementation [v7]

[Andrew Haley]

On Fri, 3 Dec 2021 09:52:52 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> This implements loading the Klass* from object header (instead of dedicated Klass* field) in C1 generated code. It introduces a new C1 LIR opcode (LoadKlass) and related CodeStub for the slow-path runtime-call.
>> 
>> The original implementation was brittle in that it emits the decode_klass() whenever it encounters a load that is T_ADDRESS and from klass_offset_in_bytes() (e.g. 4 or 8). Lucky that we did not seem to emit any unrelated such loads. This new implementation uses a dedicated C1 op instead, and expands this to the corresponding load of the header word, and call into slow-path upon fast-path-failure, in the LIR assembler.
>> 
>> Testing:
>>  - [x] tier1 (x86_64,x86_32)
>>  - [x] tier2 (x86_64,x86_32)
>>  - [x] tier3 (x86_64,x86_32)
>>  - [ ] tier4 (x86_64,x86_32)
>
> Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 36 commits:
> 
>  - Merge remote-tracking branch 'origin/klass-from-header-c1' into klass-from-header-c1
>  - Merge remote-tracking branch 'upstream/master' into klass-from-header-c1
>  - Increase code size estimate
>  - Merge branch 'master' into klass-from-header-c1
>  - Merge remote-tracking branch 'jdk-upstream/master' into klass-from-header-c1
>  - Merge remote-tracking branch 'upstream/master' into klass-from-header-c1
>  - Basic arm implementation
>  - Basic s390 implementation
>  - Basic ppc implementation
>  - Use long jump
>  - ... and 26 more: https://git.openjdk.java.net/lilliput/compare/4390f5f0...6b24f6c6

This all looks reasonable and straightforward.

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PR: https://git.openjdk.java.net/lilliput/pull/20