Optimizing and Debugging Programs in Allegro CL

1. Optimizing and Debugging Programs in Allegro CL By Duane Rettig April, 2007

2. Introduction • Personal • Tutorial will become available via ftp • Some things available only in 8.1 • Some concepts are from LUGM/1998

3. Outline • Debug • Low Level Hacks • Optimization

4. Debug • Zoom Niceties • [ run zoom.lisp] • gdb/dbx/windbg interface • [ show manual demos]

5. Low Level Hacks • Intro: Structure of Allegro CL • “ll” functions • Lap code

6. Structure of Allegro CL src/ code/*.cl c/*.c rs/*.cl compile cc compile *.fasl *.s asm *.o

7. Structure (cont) *.fasl *.o lisp ld *.so running lisp lisp (dumplisp) libacl*.so *.dxl

8. Example rs code (def-runtime-q new-ratio (num den) (let ((rat (q-allocate-heap-other #md-ratio-type-code #md-ratio-size))) (setf (ls md-ratio num rat) num) (setf (ls md-ratio den rat) den) rat))

9. Example lisp ll code • [run “both-fixnum-p.lisp”]

10. “ll” functions • [see ll-doc.html]

11. Another ll example • Some compiler-macros expand to ll funcs • [run char-code.lisp]

12. Lap code • comp::*hack-compiler-output* • [run hack-compiler-output.lisp] • comp::*assemble-function-body* • [run assemble-function-body.lisp]

13. Optimization • Compilation • Boxing and unboxing • Read-line • Foreign types • Memcpy • String manipulation • Aligned pointers • Hashing • Runtime Analyzer

14. Optimization Methodology • Get it right first • Profile it • The time macro • The Allegro CL Runtime Analyzer • Hit the high cost items • Implementations • Algorithms

15. Compilation • Adding declarations to code • (declare (:explain :types :inlining)) • [run inlining-demos.lisp]

16. Boxing and Unboxing • Ensuring optimal unboxability • [run unboxing.lisp] • Immediate args • [see immediate-args.html]

17. read-line • What's wrong with it?

18. read-line • It always conses! • What to do? • read-line-into • Never conses • Must deal with overflowing lines • simple-stream-read-line • Two modes • implementation for read-line • similar to read-line, handling overflows • [see read-line-test.html]

19. memcpy • memcpy-up • memcpy-down • [see memcpy-demo.html]

20. String Manipulation • string+ and the standard, with concatenate • [see string+.cl]

21. Aligned Pointers • Allow cons-free pointer manipulation • Pointers look like fixnums • Pointers must be aligned to: • 32-bit: 4-byte boundaries • 64-bit: 8-byte boundaries • [see “aligned.html”]

22. Aligned Pointers (cont) unsigned for 32-bit: signed fixnum 0 0 #x7ffffffc most-positive-fixnum #x80000000 most-negative-fixnum #xfffffffc -1 (fix)

23. Foreign types • (sorry, under construction): • Foreign-types aren't just for foreign-functions • We can combine disciplines • [run mapped-aligned-ftype.lisp]

24. Hashing • :test extensions • :values [t] (may be nil or :weak) • :weak-keys [nil] (may be non-nil) • :hash-function [nil] (or fboundp symbol) • must return • 24 bit value for 32-bit lisps • 32 bit value for 64-bit lisps

25. Hashing • Rehash-issues • excl::*default-rehash-size* • excl::*allocate-large-hash-table-vectors-in-old-space* • excl::convert-to-internal-fspec • example of weak-key, sans-value hash-table • [run shared-cons-table.lisp]

26. Hashing • Hash tables are very efficient if hash codes are well-distributed • excl::hash-table-stats • [run hash-table-stats.lisp]

27. Runtime Analyzer • (explain the name) • Always compile top-level test functions • Do not use time macro with profiler • Avoid simultaneous time/call-count profiles • When using time macro, beware of new closures • Use prof:disassemble-profile

28. Time macro: extra closures • This driver is not as simple as it looks! (defun test-driver (n) (time (dotimes (i n) (test-it)))

29. Time macro: avoiding extra closures • Use this instead: (defun test-driver (n) (dotimes (i n) (test-it)) (time (test-driver 1000000))

30. disassemble-profile • Provides sample hit counts and percentages • Multiple disassembles provide info similar to call-graph • [show manual demo]

31. Thank You.