1. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT Optimizing Compilers CISC 673 Spring 2009 Dynamic Compilation I John Cavazos University of Delaware

2. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT Quiz Time What’s a managed language?

3. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT Quiz Time What’s a managed language? Java or C# Runs under management of a VM Object Oriented, Garbage collected Dynamic compilation

4. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 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?

5. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT What is a VM?

6. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT What is a VM? A software execution engine that provides a machine-independent language implementation

7. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT What’s in a VM for a Managed Language?

8. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 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

9. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT Basic VM Structure Executing Program Program/Bytecode Dynamic Compilation Subsystem Class Loader, Verifier, etc. Heap Thread Scheduler Garbage Collector

10. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT Adaptive Optimization Hall of Fame 1958-1962: LISP 1974: Adaptive Fortran 1980-1984: ParcPlace Smalltalk 1986-1994: Self 1995-present: Java

11. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 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

12. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 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

13. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 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

14. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 14 Promise of Dynamic Optimization á Compilation tailored to current execution context performs better than ahead-of-time compiler

15. U NIVERSITY OF D ELAWARE C OMPUTER & I NFORMATION S CIENCES D EPARTMENT 15 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