Optimizing Compilers CISC 673 Spring 2009 Dynamic Compilation I

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Optimizing CompilersCISC 673

Spring 2009Dynamic Compilation I

John CavazosUniversity of Delaware


Quiz Time

What’s a managed language?


Quiz Time

What’s a managed language? Java or C# Runs under management of a VM Object Oriented, Garbage

collected Dynamic compilation


Quiz Time

True or False? Because they execute at runtime,

dynamic compilers must be blazingly fast?

Dynamic class loading is a fundamental roadblock to cross-method optimization?

A static compiler will always produce better code than a dynamic compiler?

Sophisticated profiling is too expensive to perform online?


What is a VM?


What is a VM?

A software execution engine that provides a machine-independent language implementation


What’s in a VM for a Managed Language?


What’s in a VM for a Managed Language?

Program loader Program “checkers”, e.g., bytecode

verifiers, security services Dynamic compilation system Memory management Thread scheduler Profiling & monitoring Libraries


Basic VM Structure

Executing Program

Program/Bytecode

Dynamic Compilation Subsystem

Class Loader, Verifier, etc. Heap

Thread Scheduler

Garbage Collector


Adaptive Optimization Hall of Fame

1958-1962: LISP

1974: Adaptive Fortran

1980-1984: ParcPlace Smalltalk

1986-1994: Self

1995-present: Java


Quick History of VMs

Adaptive Fortran [Hansen’74] First in-depth exploration of adaptive

optimization Selective optimization, models, multiple

optimization levels, online profiling and control systems

LISP Interpreters [McCarthy’78] First widely used VM Pioneered VM services

memory management, Eval -> dynamic loading


Quick History of VMs ParcPlace

Smalltalk[Deutsch&Schiffman’84] First modern VM Introduced full-fledge JIT compiler Demonstrated software-only VMs were viable

Self [Chambers&Ungar’91, Hölzle&Ungar’94] Developed many advanced VM techniques Introduced polymorphic inline caches, on-

stack replacement, dynamic de-optimization, advanced selective optimization, type prediction and splitting, profile-directed inlining integrated with adaptive recompilation


Quick History of VMs

Java/JVM [Gosling, Joy, Steele ‘96] First VM with mainstream market

penetration Java vendors embraced and improved

Smalltalk and Self technology Encouraged VM adoption by others →

CLR

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Promise of Dynamic Optimization

Compilation tailored to current execution context performs better than ahead-of-time compiler

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Promise of Dynamic Optimization

Common wisdom: C will always be better

Proof? Not much One interesting comparison: VM

performace HotSpot, J9, Apache DRLVM written in C Jikes RVM, Java-in-Java 1999: they performed with in 10% 2007: Jikes RVM ~20% slower than HotSpot &

J9, Jikes RVM ~60-0% faster Apache DRLVM Aside: GCC code 20-10% slower than product

compilers

Documents

Optimizing Compilers CISC 673 Spring 2009 Dynamic Compilation I