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

[Roman Kennke]

On Tue, 27 Feb 2024 09:18:46 GMT, Axel Boldt-Christmas <aboldtch 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

Hi Axel, only some minor nits.

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

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Changes requested by rkennke (Reviewer).

PR Review: https://git.openjdk.org/lilliput/pull/139#pullrequestreview-1903083863
PR Review Comment: https://git.openjdk.org/lilliput/pull/139#discussion_r1503977665