[omworld-jdk] RFR: 8326752: Lilliput: OMCache: Add cache lookup unrolling

[Roman Kennke]

On Tue, 27 Feb 2024 10:11:48 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Implement unrolling of OM cache lookups in C2 so experiments and an evaluation can be performed.
>> 
>> Adds `OMC2UnrollCacheLookup`, `OMC2UnrollCacheLookupLoopTail` and `OMC2UnrollCacheEntires` flags which can be tuned cache lookup unrolling in C2. 
>> 
>> `OMC2UnrollCacheLookup` will unroll up to `OMC2UnrollCacheEntires` (depending on `OMCacheSize`) and if `OMC2UnrollCacheLookupLoopTail` is set and entries are left the rest of the cache will be checked.
>> 
>> All of these flags are temporary to allow for evaluation of the cache lookup in C2 (size and unrolling). See issue JDK-8326759
>
> src/hotspot/share/runtime/globals.hpp line 1997:
> 
>> 1995:   product(bool, OMC2UnrollCacheLookupLoopTail, true, "")                    \
>> 1996:                                                                             \
>> 1997:   product(int, OMC2UnrollCacheEntires, 8, "")                               \
> 
> There is a typo: Entires -> Entries

Also, could perhaps collapse some flags, e.g. treat OMC2UnrollCacheEntries==0 as OMC2UnrollCacheLookup==false, and get rid of the latter.

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PR Review Comment: https://git.openjdk.org/lilliput/pull/139#discussion_r1503979220