RFR: 8072070: Improve interpreter stack banging [v2]

[Aleksey Shipilev]

On Mon, 7 Feb 2022 14:23:38 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/cpu/x86/templateInterpreterGenerator_x86.cpp line 758:
>> 
>>> 756:     }
>>> 757: 
>>> 758:     __ cmpptr(rsp, Address(thread, JavaThread::shadow_zone_safe_limit()));
>> 
>> stack watermark starts at stack_base, increase to current rsp to optimize away stack banging for rsp greater than this.  Cannot increase watermark if esp < shadow_zone_safe_limit because of ...
>
> looking for a brief comment why here.

See new commit. I realized I need to write down explicitly that growth watermark is always above the safe limit, for the check to be safe.

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PR: https://git.openjdk.java.net/jdk/pull/7247