RFR: 8299795: Relativize locals in interpreter frames [v4]

[Martin Doerr]

On Tue, 17 Jan 2023 17:02:04 GMT, Fredrik Bredberg <duke at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/templateInterpreterGenerator_ppc.cpp line 1035:
>> 
>>> 1033:   __ sub(R12_scratch2, R18_locals, R1_SP);
>>> 1034:   __ srdi(R12_scratch2, R12_scratch2, Interpreter::logStackElementSize);
>>> 1035:   // Now &fp()[R12_scratch2] == R18_locals
>> 
>> I think this comment makes no sense. Please remove it. Otherwise, PPC64 code LGTM.
>
> My intention was to show how the contents of R18_locals (the absolute address to locals) can be recreated by using R12_scratch2 as an index from the frame pointer. Before we stored R18_locals in the stackframe, now we store R12_scratch2. Does that make more sense?

The code uses &sp()[R12_scratch2]. I think your comment is confusing. Please remove it or write something comprehensive. E.g. save R18_locals in compressed format relative to the frame's SP.

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PR: https://git.openjdk.org/jdk/pull/11902