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Optimizing and Debugging Programs in Allegro CL

By Duane Rettig

April, 2007

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Introduction

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

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Outline

• Debug• Low Level Hacks• Optimization

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Debug

• Zoom Niceties– [ run zoom.lisp]

• gdb/dbx/windbg interface– [ show manual demos]

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Low Level Hacks

• Intro: Structure of Allegro CL• “ll” functions• Lap code

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Structure of Allegro CLsrc/

c/*.crs/*.clcode/*.cl

compilecompile

asm*.s *.o*.fasl

cc

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Structure (cont)*.o

*.so ld

*.fasl

libacl*.so

lisp

lisp

(dumplisp)

running lisp

*.dxl

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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))

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

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“ll” functions• [see ll-doc.html]

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Another ll example

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

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Lap code

• comp::*hack-compiler-output*– [run hack-compiler-output.lisp]

• comp::*assemble-function-body*– [run assemble-function-body.lisp]

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Optimization

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

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Optimization Methodology

• Get it right first• Profile it

– The time macro– The Allegro CL Runtime Analyzer

• Hit the high cost items– Implementations– Algorithms

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Compilation

• Adding declarations to code• (declare (:explain :types :inlining))

– [run inlining-demos.lisp]

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Boxing and Unboxing

• Ensuring optimal unboxability– [run unboxing.lisp]

• Immediate args– [see immediate-args.html]

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read-line

• What's wrong with it?

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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]

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memcpy

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

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String Manipulation

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

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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”]

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Aligned Pointers (cont)

most-positive-fixnum

most-negative-fixnum

for 32-bit: signed fixnumunsigned

0

#x7ffffffc

#x80000000

0

#xfffffffc -1 (fix)

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Foreign types• (sorry, under construction):• Foreign-types aren't just for foreign-functions• We can combine disciplines

– [run mapped-aligned-ftype.lisp]

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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

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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]

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Hashing

• Hash tables are very efficient if hash codes are well-distributed

• excl::hash-table-stats– [run hash-table-stats.lisp]

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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

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•Time macro: extra closures

• This driver is not as simple as it looks!

(defun test-driver (n)

(time

(dotimes (i n)

(test-it)))

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•Time macro: avoiding extra closures

• Use this instead:

(defun test-driver (n)

(dotimes (i n)

(test-it))

(time (test-driver 1000000))

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disassemble-profile

• Provides sample hit counts and percentages• Multiple disassembles provide info similar to

call-graph• [show manual demo]

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Thank You.