J9's MethodHandle Compilation Pipeline #JFokus2015
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The document details the J9 virtual machine's approach to method handle compilation, provided by Dan Heidinga, emphasizing the importance of understanding its structure and performance nuances. It discusses a developed method handle hierarchy designed to separate different kinds of method handles for improved performance and maintainability in just-in-time (JIT) compilation. Furthermore, the presentation highlights various optimization strategies and future directions for enhancing method handle efficiency.
J9's MethodHandle Compilation Pipeline #JFokus2015
- 1. A detailed look at J9’s approach to MethodHandle compilation Dan Heidinga, J9 Virtual Machine Team Lead @DanHeidinga 2015-02-02 MethodHandle compilation pipeline
- 2. Important disclaimers THE INFORMATION CONTAINED IN THIS PRESENTATION IS PROVIDED FOR INFORMATIONAL PURPOSES ONLY. WHILST EFFORTS WERE MADE TO VERIFY THE COMPLETENESS AND ACCURACY OF THE INFORMATION CONTAINED IN THIS PRESENTATION, IT IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. ALL PERFORMANCE DATA INCLUDED IN THIS PRESENTATION HAVE BEEN GATHERED IN A CONTROLLED ENVIRONMENT. YOUR OWN TEST RESULTS MAY VARY BASED ON HARDWARE, SOFTWARE OR INFRASTRUCTURE DIFFERENCES. ALL DATA INCLUDED IN THIS PRESENTATION ARE MEANT TO BE USED ONLY AS A GUIDE. IN ADDITION, THE INFORMATION CONTAINED IN THIS PRESENTATION IS BASED ON IBM’S CURRENT PRODUCT PLANS AND STRATEGY, WHICH ARE SUBJECT TO CHANGE BY IBM, WITHOUT NOTICE. IBM AND ITS AFFILIATED COMPANIES SHALL NOT BE RESPONSIBLE FOR ANY DAMAGES ARISING OUT OF THE USE OF, OR OTHERWISE RELATED TO, THIS PRESENTATION OR ANY OTHER DOCUMENTATION. NOTHING CONTAINED IN THIS PRESENTATION IS INTENDED TO, OR SHALL HAVE THE EFFECT OF: – CREATING ANY WARRANT OR REPRESENTATION FROM IBM, ITS AFFILIATED COMPANIES OR ITS OR THEIR SUPPLIERS AND/OR LICENSORS 2
- 3. Who am I? I've been involved with virtual machine development at IBM since 2007 and am now the J9 Virtual Machine Team Lead. J9 is IBM's independent implementation of the JVM. I've represented IBM on both the JSR 292 ('invokedynamic') and JSR 335 ('lambda') expert groups and lead J9's implementation of both JSRs. I also maintain the bytecode verifier and deal with various other parts of the runtime. 3
- 5. J9’s MethodHandle hierarchy Original prototype had 1 class: MethodHandle – “kind” field to determine which operation – “type” field to hold the MethodType – “vmSlot” field to hold the address, offset, vtable or itable index Grab bag of data necessary to support field access and method sends 2 major problems with this approach 5 MethodHandle
- 6. J9’s MethodHandle hierarchy Original prototype had 1 class: MethodHandle – “kind” field to determine which operation – “type” field to hold the MethodType – “vmSlot” field to hold the address, offset, vtable or itable index Grab bag of data necessary to support field access and method sends 6 MethodHandle http://commons.wikimedia.org/wiki/File:MudBall03.jpg Public domain.
- 7. J9’s MethodHandle hierarchy Hierarchy that separates each MH kind into its own class Each MH subclass describes the data needed by the MH JITs look at the class rather than the ‘kind’ instance field – Provides a place to put specialized behaviour 7 MethodHandle Direct ReceiverBound Indirect Virtual Interface Constructor Field FieldGetter FieldSetter StaticFieldGetter StaticFieldSetter Collect DynamicInvoker FilterArguments Convert ArgumentConversion AsType ExplicitCast FilterReturn GuardWithTestHnadle Insert Fold FoldNonvoid FoldVoid InvokeExact InvokeGeneric PassThrough ArgumentMover BruteArgumentMover Catch Permute Spread VarargsCollector
- 8. MethodHandle chains 8 "Broad chain closeup" by Toni Lozano - http://www.flickr.com/photos/quiero-un-pantano/176909201. Licensed under CC BY 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Broad_chain_closeup.jpg#mediaviewer/File:Broad_chain_closeup.jp
- 9. MethodHandle chains GuardWithTest Direct Target Direct Direct 9 "Broad chain closeup" by Toni Lozano - http://www.flickr.com/photos/quiero-un-pantano/176909201. Licensed under CC BY 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Broad_chain_closeup.jpg#mediaviewer/File:Broad_chain_closeup.jp
- 10. MethodHandle chains GuardWithTest Direct Target Direct Direct Insert Direct 10 "Broad chain closeup" by Toni Lozano - http://www.flickr.com/photos/quiero-un-pantano/176909201. Licensed under CC BY 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Broad_chain_closeup.jpg#mediaviewer/File:Broad_chain_closeup.jp
- 11. MethodHandle chains GuardWithTest DynamicInvoker ConstantInt Target GuardWithTest Direct Target Direct Direct Insert Direct 11 "Broad chain closeup" by Toni Lozano - http://www.flickr.com/photos/quiero-un-pantano/176909201. Licensed under CC BY 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Broad_chain_closeup.jpg#mediaviewer/File:Broad_chain_closeup.jp
- 12. MethodHandle chains 12 "Broad chain closeup" by Toni Lozano - http://www.flickr.com/photos/quiero-un-pantano/176909201. Licensed under CC BY 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Broad_chain_closeup.jpg#mediaviewer/File:Broad_chain_closeup.jp DynamicInvoker GuardWithTest DynamicInvoker ConstantInt Target GuardWithTest Direct Target Direct Direct Insert Direct
- 13. (Mostly) tail recursive MH interpreter 13 1 2 3 4 A A B C D E F 1 2 3 4 C 1 2 3 D 2 3 1 E
- 14. ThunkTuples Every MethodHandle has a ThunkTuple. ThunkTuples hold onto the compiled code for the MethodHandle – i2jInvokeExactThunk: interpreter to JIT entrypoint – invokeExactThunk: JIT to JIT entrypoint Each ThunkTuple is generated from a bytecode template for the MethodHandle subclass 14 Compiled CodeMethodHandle invocationCount thunks ThunkTuple invocationCount i2jInvokeExactThunk invokeExactThunk
- 15. ThunkArchetypes: MethodHandle templates 15 Signatures are written in terms of ‘int’ and edited at compile time Compile time macros are used to further specialize the code. – ‘numGuardArgs()’ determines how many arguments are passed to the guard handle – ILGenMacros.* are used to do signature editing, argument pushing and popping, etc This the MH equivalent of compiling a single ‘invokevirtual’ instruction – Specialized just enough to get out of the interpreter and into compiled code
- 16. But that’s a lot of duplicate code! 16 ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks Compiled Code Compiled Code Compiled Code
- 17. Avoiding duplicate compiles of equivalent MHs 17 MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks MethodHandle invocationCount thunks Compiled Code
- 18. ThunkTables allow sharing Every MethodHandle subclass has a ThunkTable ThunkTables manage the mapping from MethodHandle to ThunkTuple Goal: Good compiled code with a high degree of sharing. – Stay out of the interpreter. – Don’t waste code cache 18
- 22. Compiled Code Initial JIT compilation 22 Interpreted SharedThunk MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk
- 23. SharedThunk delays With a compile threshold of 25 The SharedThunk is run interpreted 72 times 23 MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks MethodHandle invocationCount thunks 24 24 24 72
- 25. SharedThunk delays resolved 25 MethodHandle invocationCount thunks ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks MethodHandle invocationCount thunks 9 8 8 25 Compiled Code Request Compile
- 26. Addressing the cost of J->I transitions On transition, request MethodHandle compile Continue in the jitted code rather than completing the transition 26 ThunkTuple invocationCount invokeExactThunk MethodHandle invocationCount thunks Compiled Code invokehandle
- 29. Why CustomThunks? 29 MethodHandle invocationCount thunks MethodHandle invocationCount thunks MethodHandle invocationCount thunks Compiled Code Compiled Code Compiled Code
- 31. Invocation counts are not enough 31 A B C D E F A
- 32. Invocation counts are not enough 32 A B C D E F A C
- 33. Invocation counts are not enough 33 A B C D E F A C D
- 34. Invocation counts are not enough 34 A B C D E F A C D E
- 35. Invocation counts are not enough 35 A B C D E F A C D E F
- 36. Wasted compiles Invocation counts are not enough 36 A B C D E F A C D E F Delayed compiles
- 37. 37 "Brisbane Lightening" by Steve Arnold - http://www.flickr.com/photos/stevoarnold/3161660942. Licensed under Attribution 2.0 Generic CC BY 2.0
- 39. Avoiding compile storms 39 A B C D E F A
- 40. Avoid MethodHandles.invoke() 40 A B C D E F AsType AsType AsType MethodHandle Counting occurs on the wrong MethodHandle
- 41. Avoid MethodHandles.invoke() 41 A B C D E F AsType AsType AsType Counting occurs on the AsType handle, not the head of the chain AsType from multiple signatures defeats one-element cache solution
- 44. Static optimizations 44 Drop Constant Insert Permute AsTypeDrop ArgumentMoverHandle Constant Permute Permute F Permute F
- 45. Future directions AOT SharedThunks Additional “super handles” like drop+constant AsType optimizations Faster / smaller MethodHandle compiles UNB PhD candidate looking at data mining MH chains from existing applications 45
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