A Region-Based Compilation Technique for a Java Just-In-Time Compiler

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A Region-Based Compilation Technique for a Java
Just-In-Time Compiler

• Toshio Suganuma, Toshiaki Yasue and Toshio
  Nakatani

Presenter Ioana Burcea
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Agenda

• Research question
• FBC function based compilation
• VS
• RBC region based compilation
• System overview
• Region exit handling
• Region selection
• Special optimizations
• Partial inlining
• Partial dead code elimination
• Escape analysis
• Experimental results

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Research Question

• Method the right unit of compilation?
• Methods often contain rarely or never executed
  code
• Waste of compilation time
• Conservative data flow analysis
• Restrictive method inlining
• Possible solution
• Region-based compilation (RBC)
• Region selection
• Partial inlining
• Region exit handling

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Dynamic Optimization Framework

• Sampling profiler
• The more CPU time used the hotter the method
• Instrumenting profiler
• Basic block execution frequency
• Virtual/interface call receiver type
  distribution

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Region-Based Compilation
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Intra-Procedural Region Selection

• Static heuristics
• Rare
• Backup blocks / guards (e.g., devirtualizations)
• Blocks that end with an exception throwing
  instruction
• Exception handler blocks
• Blocks containing unresolved or uninitialized
  class references
• Non-rare
• Blocks that end with normal return instructions
• Dynamic profile information
• A block is non-rare if its dynamic count is
  beyond a certain threshold (which value they
  use?)
• Higher priority when conflicting with static
  heuristics
• Iterative framework for region selection

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Region Exit Handling

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Partial Inlining
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Special Optimizations

• Partial dead code elimination
• Pushing computations that are only live in the
  region exit paths to the region exit BB
• Partial escape analysis
• Objects that are local to the method are
  allocated to the stack
• Objects that are local to a single thread do not
  need synchronization

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Partial Escape Analysis
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Experimental Results

• Machine
• Pentium 4 Xeon 2.8GHz, 1Gb
• WinXP
• Benchmarks
• SPECjvm98-1.04
• Initial and max heap 128 Mb
• SPECjbb2000-1.02
• Initial and max heap 256 Mb
• Thresholds
• MMI to level-0 compilation 500
• Timer interval for sampling profiler 3 ms
• The number of samples 10,000
• The max number of OSR 10
• Other thresholds (rare bb, promotion to level-1
  level-2 compilation) ??

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Configurations

• 5 configurations
• FBC function based compilation (the baseline)
• RBC-noopt RBC without any special optimizations
• RBC-nopi RBC with partial dead code elimination
  and partial escape analysis, without partial
  inlining
• RBC-full all optimizations on
• RBC-offline RBC-full with offline profile
  information
• No OSR, no recompilation (?)

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Statistics for RBC
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Performance Improvement
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Compile Time Ratio
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Compiled Code Size Ratio
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Peak Work Memory Usage Ratio
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Discussion