RFR: 8280872: Reorder code cache segments to improve code density [v8]

[Vladimir Kozlov]

On Thu, 24 Mar 2022 13:36:27 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

>> Currently the codecache segment order is [non-nmethod, non-profiled, profiled]. With this change we move the non-nmethod segment between two code segments. Currently only the aarch64 backend is adapted to make use of these changes.
>> 
>> In AARCH the offset limit for a branch instruction is 128MB. The bigger jumps are encoded with three instructions. Most of far branches are jumps into the non-nmethod blobs. With the non-nmethod segment in between code segments the jump distance from method to the stub becomes shorter. The result is a 4% reduction in generated code size for the CodeCache range from 128MB to 240MB.
>> 
>> As a side effect, the performance of some tests is slightly improved:
>> ``ArraysFill.testCharFill      10  thrpt   15  170235.720 -> 178477.212  ops/ms``
>> 
>> Testing: jdk/hotspot jtreg and microbenchmarks on AMD and AARCH
>
> Boris Ulasevich has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:
> 
>  - Merge branch 'openjdk:master' into codecache_segments_order
>  - review findings: use instruction_size istead of raw constant, strengthen the assert, check alignment, move comments, segments order: profiled - non_method - non_profiled
>  - rename, adding test
>  - moving nops out of far_jump
>  - minor renaming
>  - review comments. remove far_call limit. undo trampoline-to-farcall. add trampoline_needs_far_jump func
>  - fix name: is_non_nmethod, adding target_needs_far_branch func
>  - change codecache segments order: nonprofiled-nonmethod-profiled
>    increase far jump threshold: sideof(codecache)=128M -> sizeof(nonprofiled+nonmethod)=128M

My performance testing shows that there is regression in some startup benchmarks on aarch64.

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PR: https://git.openjdk.java.net/jdk/pull/7517