SLIDE 1
A bytecode set for adaptive
- ptimizations
Clément Béra & Eliot Miranda
Thursday, August 21, 14
Introduction
- The Cog
VM is the standard VM for:
- Pharo
- Squeak
- Newspeak
Thursday, August 21, 14
A bytecode set for adaptive optimizations Clment Bra & Eliot - - PowerPoint PPT Presentation
A bytecode set for adaptive optimizations Clment Bra & Eliot - - PowerPoint PPT Presentation
A bytecode set for adaptive optimizations Clment Bra & Eliot Miranda Thursday, August 21, 14 Introduction The Cog VM is the standard VM for: Pharo Squeak Newspeak Thursday, August 21, 14 Introduction Working
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SLIDE 3
Introduction
- Working runtime bytecode to bytecode
- ptimizer for Cog’s JIT
- The optimizer
- depends the bytecode set quality
- needs new bytecode instructions
Thursday, August 21, 14
SLIDE 4
Introduction
- Design of a new bytecode set
Thursday, August 21, 14
SLIDE 5
Plan
- Context
- Challenges for a good bytecode set
- Current Issues
- New bytecode set
- Switching between bytecode sets
Thursday, August 21, 14
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Context
- Compiled methods are objects
- Shared between the
VM and the image
Thursday, August 21, 14
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Object header (8 bytes) literals (4 bytes per literal) compiled method header (4 bytes) bytecodes (variable) source pointer (variable, usually 4 bytes)
Memory representation of Compiled Method in 32 bits with the new Memory Manager Spur
Thursday, August 21, 14
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Object header (8 bytes) literals (4 bytes per literal) compiled method header (4 bytes) bytecodes (variable) source pointer (variable, usually 4 bytes)
Memory representation of Compiled Method in 32 bits with the new Memory Manager Spur
Thursday, August 21, 14
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Bytecode set
- Stack based
- Interpreted by the StackInterpreter
- Compiled to machine code by Cogit
- Generated by the in-image compiler
Thursday, August 21, 14
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Challenges
- Generic challenges
- Challenges for the bytecode optimizer
Thursday, August 21, 14
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Generic challenges
- Platform-independent
- Compact
- Easy to decode
- Backward compatibility
Thursday, August 21, 14
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Optimizer challenges
...
Thursday, August 21, 14
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Optimizer
Thursday there’s a talk about it.
- Inlining
- Primitive specialization
Thursday, August 21, 14
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Optimizer challenges
- Inlined primitives / unsafe operations
- Large methods
- Access to non receiver instance variable
- Extendable
Thursday, August 21, 14
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Current issues
- Large method unsupported
- Few available bytes
- Primitive encoding forbidding inlining
- DoubleExtendedDoAnything bytecode
- Immediate objects compaction
- Late addition of the closure bytecode
Thursday, August 21, 14
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New bytecode set
- Extendable instructions (prefix)
- Inlined primitives / unsafe operations
- Extendable (available bytes)
- Maximum number of literals increased
Thursday, August 21, 14
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New bytecode set
- Overall bytecode size smaller
- Immediate objects compaction
- Easier decoding
- Sorted by number of bytes
- Sorted by functionalities
- Closure decoding improved
Thursday, August 21, 14
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Bytecode set switch
- Offline converter: hard to debug
- VM supporting two bytecode set
- Bit in compiled method header
Thursday, August 21, 14
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Conclusion
- Designed a bytecode set for runtime
bytecode to bytecode optimizations
- Next step is to work on the optimizer
- Come at my talk thursday about it
Thursday, August 21, 14
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Questions
Thursday, August 21, 14