Just-In-Time Compilation
Keith W. Krajewski3/4/2011
paper:A Brief History of Just-In-Time (2003)
John Aycock
Overview
What is JIT? Why know about JIT? Who has used JIT (and to what end)? Simulation JIT in modern languages Classifying JIT techniques Tools for JIT compilation
What is JIT?
Dynamic compilation “JIT” itself a new term to computing, ~1993 Theoretically unnecessary
Goals of JIT
Compiled programs are faster Interpreted programs are smaller Interpreted programs are more portable Interpreter has access to runtime info
Why know about JIT?
Because JIT is like the cure for scurvy.
Who has used JIT (and how)?
Early sightings LC^2 APL mixed/throw-away
code Fortran Smalltalk Self
Oberon Erlang O'caml Modern stuff
Ancient Runes
McCarthy, Lisp (1960), punch cards! Univ. of Michigan IBM 7060 (1966) Thompson, regular expressions (1968)
LC^2
Language for conversational computing Mitchell, Perlis, & van Zoeren (1968) Mostly forgettable Cached the actions it performed
APL
Phillip S. Abrams, 1970 Drag-along Beating
Mixed & Throw-Away Code
Mixed – Dakin & Poole (1973) & Dawson (1973)
Throw-away – Basic
Fortran
Hansen's 1974 optimization Frequency-of-execution counter Threshold levels Ordered set of machine-specific optimizations
Smalltalk
Lazy compilation to native code No pagination of compiled code
Self
David Ungar, Randall Smith, 1987 Pure OO, dynamically typed 3 generations
Customization (Pitfall: over-customization) Optimized type info for loops (Pitfall: compilation
time) Illusion of speed
Influenced Sun's later works (Java)
Oberon
Niklaus Wirth, 1986 Compiled to “slim binary” Supported dynamic loading of modules Continuous re-optimization in background
Erlang
Ericsson, 1986 HiPe – explicit invocation Mixed code, switch upon method invocation or
exception
O'caml
Specialized the interpreter's instruction set to include “macro opcodes”
… without much benefit
Simulation
1st gen – straight 1 by 1 translation 2nd gen – 1 by 1 translation with cache 3rd gen – blocks of source 4th gen
Profiled execution Hot path detection Code generation Bailout
HP Dynamo
Compiled HPA-8000 code into HPA-8000 code ...amazingly, this worked. 30% performance
increase Important to be able to bail out
Java
Static explicit compilation to JVM bytecode Early JVM did straight interpretation Motivation for JIT research Now very portable and relatively quick
C#/.Net
Static compilation to CIL (MSIL), then bytecode Dynamic per-method compilation to native
machine
Classifying JIT
3 properties Invocation – explicit/implicit Executability – monoexecutable/polyexecutable Concurrency
Toolkits for JIT compilation
Keppel (1991), Engler & Proebsting (1994), Ramsey & Fernandez (1995), Engler (1996), Fraser & Proebsting (1999)
Address three main problems Binary code generation Cache coherence Execution
Summary
Dynamic compilation Combines best features of both compiled and
interpreted programs Lazy compilation, incremental optimization,
mixed code, throw-away code, hotspot detection, machine-specific optimization, customization, simulation
Don't re-invent the wheel again
Works cited
Aycock, John. A Brief History Of Just-In-Time. 2003.
Petzold, Charles. .NET Book Zero. 2006.http://www.charlespetzold.com/dotnet/DotNetBookZero11.pdf
Wikipedia: Just-In-Time Compilation.http://en.wikipedia.org/wiki/JIT_compilation
