RFR: 8252505: C1/C2 compiler support for blackholes [v16]

[Aleksey Shipilev]

On Thu, 3 Dec 2020 11:41:28 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Formatting touchups
>
> src/hotspot/share/opto/library_call.cpp line 6860:
> 
>> 6858: // This matches methods that were requested to be blackholed through compile commands.
>> 6859: //
>> 6860: bool LibraryCallKit::inline_blackhole() {
> 
> I can't see where receiver null check comes from. Don't you have to explicitly insert it in the intrinsic?

Dang. We should do receiver null-checks in intrinsics. Added. It looks like C2 is able to elide null-checks in JMH hot loops, while C1 leaves the first null-check in subsequent `Blackhole` calls.

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PR: https://git.openjdk.java.net/jdk/pull/1203