RFR: 8357258: x86: Improve receiver type profiling reliability [v6]

[Vladimir Ivanov]

On Mon, 1 Dec 2025 13:04:08 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See the bug for discussion what issues current machinery has. 
>> 
>> This PR executes the plan outlined in the bug:
>>  1. Common the receiver type profiling code in interpreter and C1
>>  2. Rewrite receiver type profiling code to only do atomic receiver slot installations
>>  3. Trim `C1OptimizeVirtualCallProfiling` to only claim slots when receiver is installed 
>> 
>> This PR does _not_ do atomic counter updates themselves, as it may have much wider performance implications, including regressions. This PR should be at least performance neutral.
>> 
>> Additional testing:
>>   - [x] Linux x86_64 server fastdebug, `compiler/`
>>   - [x] Linux x86_64 server fastdebug, `all`
>
> Aleksey Shipilev has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Simplify third case: no need to loop, just restart the search
>  - Actually have a second "fast" case: receiver is not found in the table, and the table is full
>  - Pushing/popping for rare CAS path is counter-productive

src/hotspot/cpu/x86/macroAssembler_x86.cpp line 4826:

> 4824:   // and never duplicate the receivers in the list.
> 4825:   //
> 4826:   // It is tempting to combine these cases into a single loop, and claim the first

Can you elaborate, please, why it is the case? Is it a result of class unloading or something else?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/25305#discussion_r2579069740