RFR: 8255737: Zero: DO_UPDATE_INSTRUCTION_COUNT should only update when relevant VM flags are set [v2]

[Severin Gehwolf]

On Tue, 3 Nov 2020 12:20:15 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Everywhere else in VM code we effectively do:
>> 
>>   if (CountBytecodes || TraceBytecodes || StopInterpreterAt) BytecodeCounter::...
>>   if (PrintBytecodeHistogram) BytecodeHistogram::...
>> 
>> But not in `DO_UPDATE_INSTRUCTION_COUNT` macro.
>> Adding these flags avoid the writes to statistics what would never be used (and those writes can even contend, afaics).
>> This change drops the Linux x86_64 Zero fastdebug build time from ~18m to ~17.5m.
>> 
>> Testing:
>>  - [x] Ad-hoc runs with Zero and affected flags
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Rewrite the block to hide flags under major check
>  - Merge branch 'master' into JDK-8255737-zero-do-update-flags
>  - 8255737: Zero: DO_UPDATE_INSTRUCTION_COUNT should only update when relevant VM flags are set

LGTM

-------------

Marked as reviewed by sgehwolf (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/997