RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v11]

[Martin Doerr]

On Tue, 1 Oct 2024 15:46:01 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>>> Indeed, I could re-enable all tests in:
>>> 
>>> ```
>>> test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationMismatchedAccess.java
>>> test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationNotRun.java
>>> test/hotspot/jtreg/compiler/loopopts/superword/TestIndependentPacksWithCyclicDependency.java
>>> ```
>>> 
>>> but unfortunately not those others:
>>> 
>>> ```
>>> > > > test/hotspot/jtreg/compiler/loopopts/superword/TestAlignVector.java
>>> > > > test/hotspot/jtreg/compiler/loopopts/superword/TestMulAddS2I.java
>>> ```
>>> 
>>> I think the issue with all of them is that vectorization in those scenarios only works when the operations inside the loop start at an array index that addresses an element at 8-byte-aligned offset.
>>> 
>>> I have filed https://bugs.openjdk.org/browse/JDK-8340010 to track it.
>> 
>> @rkennke A test run of the current changeset in our internal CI system revealed that the following tests fail (because of missing vectorization) when using `-XX:+UnlockExperimentalVMOptions -XX:+UseCompactObjectHeaders -XX:UseSSE=N` with `N <= 3` on an Intel Xeon Platinum 8358 machine:
>> 
>> - test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationNotRun.java
>> - test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationMismatchedAccess.java
>> - test/hotspot/jtreg/compiler/vectorization/runner/LoopCombinedOpTest.java
>> 
>> Here are the failure details:
>> 
>> 
>> test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationNotRun.java:
>> 
>> 1) Method "public static void compiler.c2.irTests.TestVectorizationNotRun.test(byte[],long[])" - [Failed IR rules: 1]:
>>    * @IR rule 1: "@compiler.lib.ir_framework.IR(phase={DEFAULT}, applyIfPlatformAnd={}, applyIfCPUFeatureOr={}, counts={"_#V#LOAD_VECTOR_L#_", ">=1", "_#STORE_VECTOR#_", ">=1"}, applyIfPlatform={}, applyIfPlatformOr={}, failOn={}, applyIfOr={}, applyIfCPUFeatureAnd={}, applyIf={}, applyIfCPUFeature={}, applyIfAnd={}, applyIfNot={})"
>>      > Phase "PrintIdeal":
>>        - counts: Graph contains wrong number of nodes:
>>          * Constraint 1: "(\\d+(\\s){2}(LoadVector.*)+(\\s){2}===.*vector[A-Za-z]\[2\]:\{long\})"
>>            - Failed comparison: [found] 0 >= 1 [given]
>>            - No nodes matched!
>>          * Constraint 2: "(\\d+(\\s){2}(StoreVector.*)+(\\s){2}===.*)"
>>            - Failed comparison: [found] 0 >= 1 [given]
>>            - No nodes matched!
>> 
>> 
>> test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationMismatchedAccess.java:
>> 
>> 1) Method "public static void compiler.c2.irTests.TestVectorizati...
>
>> test/hotspot/jtreg/compiler/c2/irTests/TestVectorizationNotRun.java:
> 
> I think I would disable the tests for now. Is there a good way to say 'run this when UCOH is off OR UseSSE>3?

@rkennke: I have a PPC64 implementation: https://github.com/TheRealMDoerr/jdk/commit/6722f8be9a0940fab6417d4de58ec1538c436702
Do you want to include it? Should we also ask s390 and riscv folks?

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PR Comment: https://git.openjdk.org/jdk/pull/20677#issuecomment-2411867295