RFR: 8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter

[Richard Reingruber]

On Wed, 25 Dec 2024 15:40:23 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> PPC64 implementation of https://github.com/openjdk/jdk/commit/ead0116f2624e0e34529e47e4f509142d588b994. I have implemented a couple of rotate instructions.
> The first commit only implements `lookup_secondary_supers_table_var` and uses it in C2. The second commit makes the changes to use it in the interpreter, runtime and C1.
> C1 part is refactored such that the same code as before this patch is generated when `UseSecondarySupersTable` is disabled. Some stubs are modified to provide one more temp register.
> 
> Performance difference can be observed when C2 is disabled (measured on Power10):
> 
> 
> -XX:TieredStopAtLevel=1 -XX:-UseSecondarySupersTable:
> SecondarySuperCacheHits.test  avgt   15  13.028 ± 0.005  ns/op
> SecondarySuperCacheInterContention.test     avgt   15  417.746 ± 19.046  ns/op
> SecondarySuperCacheInterContention.test:t1  avgt   15  417.852 ± 17.814  ns/op
> SecondarySuperCacheInterContention.test:t2  avgt   15  417.641 ± 23.431  ns/op
> SecondarySuperCacheIntraContention.test  avgt   15  340.995 ± 5.620  ns/op
> 
> 
> 
> -XX:TieredStopAtLevel=1 -XX:+UseSecondarySupersTable:
> SecondarySuperCacheHits.test  avgt   15  14.539 ± 0.002  ns/op
> SecondarySuperCacheInterContention.test     avgt   15  25.667 ± 0.576  ns/op
> SecondarySuperCacheInterContention.test:t1  avgt   15  25.709 ± 0.655  ns/op
> SecondarySuperCacheInterContention.test:t2  avgt   15  25.626 ± 0.820  ns/op
> SecondarySuperCacheIntraContention.test  avgt   15  22.466 ± 1.554  ns/op
> 
> 
> `SecondarySuperCacheHits` seems to be slightly slower, but `SecondarySuperCacheInterContention` and `SecondarySuperCacheIntraContention` are much faster (when C2 is disabled).

src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2157:

> 2155: 
> 2156:   bind(fallthru);
> 2157:   if (L_success != nullptr && result_reg == noreg) {

Is there a problem if `L_success == nullptr && result_reg == noreg` and there aren't any secondary supers?
In that case we would reach here with CR0.eq from L2134 and we would fallthrough with CR0.eq. Due to the change in `C1StubId::slow_subtype_check_id` we would return there with CR0.eq.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22881#discussion_r1925229785