Optimize performance of SlotMap a bit #1670
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rPraml
commented
Oct 2, 2024
| @@ -257,9 +256,8 @@ private static void copyTable(Slot[] oldSlots, Slot[] newSlots) { | |||
| */ | |||
| private static void addKnownAbsentSlot(Slot[] addSlots, Slot slot) { | |||
| final int insertPos = getSlotIndex(addSlots.length, slot.indexOrHash); | |||
| Slot old = addSlots[insertPos]; | |||
| slot.next = addSlots[insertPos]; | |||
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Both changes in embeddedSlotMap save ~ 5 bytecode instructions: https://godbolt.org/z/1EjhsWs7E
| @@ -82,7 +82,7 @@ int getAttributes() { | |||
| return attributes; | |||
| } | |||
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| synchronized void setAttributes(int value) { | |||
| void setAttributes(int value) { | |||
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I don't understand why you should use "synchronized" here. attributes is not a long or double and write should be atomic: https://docs.oracle.com/javase/specs/jls/se9/html/jls-17.html#jls-17.7
(even if it is a long/double, it would be atomic on 64bit jvms)
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I will check this myself later, but you can also verify the effects
yourself, by running:
BENCHMARK=SlotMap ./gradlew jmh
(or the equivalent on Windows)
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FWIW this didn't result in any measurable changes (Java does a ton of optimization of bytecode including making uncontended synchronization very cheap). But if you all think it makes sense -- less bytecode is always good -- I'm happy to merge it. |
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This is a small improvement, but I imagine it is measurable