RFR: 8331117: [PPC64] secondary_super_cache does not scale well [v5]

[Andrew Haley]

On Thu, 13 Jun 2024 13:35:39 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove pointless assertion.
>
> src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2166:
> 
>> 2164: 
>> 2165: // Return true: we succeeded in generating this code
>> 2166: bool MacroAssembler::lookup_secondary_supers_table(Register r_sub_klass,
> 
> The method always returns `true`. Should even return a value?

It's there to communicate failure, if there was any. Some ports can fail to generate code because of space exhaustion, and we need to communicate this to the caller.

> src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2232:
> 
>> 2230: 
>> 2231:   // Linear probe. Rotate the bitmap so that the next bit to test is
>> 2232:   // in Bit 1.
> 
> It's bit 2 that's tested next after the rotation, isn't it? See L2331 in `lookup_secondary_supers_table_slow_path`
> Suggestion:
> 
>   // in Bit 2.

Yes, it's rather confusing language. In fact, the bit we just tested is in Bit 1.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19368#discussion_r1640920059
PR Review Comment: https://git.openjdk.org/jdk/pull/19368#discussion_r1640918956