CS271 ASSEMBLY LANGUAGE PROGRAMMING

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COMPSCI 322 Language and Compilers Class
Hour Hyer Hall 210 TThu 930am 1015am
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A little bit about the instructor
Assistant professor at UWW since August 2005

• Graduated from the University of Connecticut (05
  Class), Ph.D in Computer Science and Engineering

• Master of Computer Science from UW-Milwaukee
  (96-99)

• Bachelor of Science from Hanoi University of
  Technology (86-91)

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A little bit about the instructor

• Research Experience
• User Modeling, Information Retrieval, Decision
  Theory, Collaborative Filtering, Human Factors
• Teaching Experience
• MCS 220, COMPSCI 172, 181, 271, 381 at UWW
• Introductory courses at UOP and Devry
• TA for Computer Architecture, OO Design,
  Compiler, Artificial Intelligence

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Contact information

• nguyenh_at_uww.edu
• (fastest way to contact me)
• Baker Hall 324
• Office Hours 950am 1050 am, 3-4pm, MWF or by
  appointment
• 262 472 5170

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Course Objectives

• Understand the description and successfully
  design a scanner, parser, semantic checker and
  code generator for this language
• Implement successfully a scanner, parser,
  semantic checker and code generator for this
  given language. Test the implementation with all
  test cases for each component in a compiler.

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Book Requirement

• Engineering a Compiler. 2004. Keith D. Cooper and
  Linda Torczon. Morgan Kaufmann Publisher
  (available in TextBook rental)
• Web site http//www.cs.rice.edu/keith/Errata.htm
  l

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Course detail - Evaluation
GRADABLE POINTS
3 projects 650
Final Exam 150
Presentation 100
In class exercises 100
Total 1000
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Projects

• 3 projects scanner, parser and semantic checker,
  code generator. Preferred language to develop
  them is Java, but C/C are welcomed too.
• Project 3 depends on Project 2, Project 2 depends
  on Project 1.
• ABSOLUTELY no LATE submission for Project 3
  because of the time consuming to grade this
  project.

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In class exercises

• Simple multiple choice questions and simple
  problems will be given in class weekly and
  graded.
• This requires students to read the assigned
  reading (partly also because this is a discussion
  course instead of lecture)
• Not all material will be covered in class
• Book complements the lectures

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Presentation

• Each student will do research on a specific
  programming language of his choice. Please let
  the instructor know ahead of time which language
  do you choose
• Then present 15-20 minutes his research in front
  of class using powerpoint presentation. This will
  be followed by 10 minute questions.

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Grade
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Prerequisite

• Prerequisite COMPSCI 271, and Data Structures
• Students are responsible for meeting these
  requirements.

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Compilers

• What is a compiler?
• A program that translates an executable program
  in one language into an executable program in
  another language
• The compiler should improve the program, in some
  way
• What is an interpreter?
  

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Compilers

• What is a compiler?
• A program that translates an executable program
  in one language into an executable program in
  another language
• The compiler should improve the program, in some
  way
• What is an interpreter?
  
• A program that reads an executable program and
  produces the results of executing that program

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Examples

• C is typically compiled, Basic is typically
  interpreted
• Java is compiled to bytecodes (code for the Java
  VM).
• which are then interpreted
• Or a hybrid strategy is used
• Just-in-time compilation

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Taking a Broader View

• Compiler Technology Off-Line Processing
• Goals improved performance and language
  usability
• Making it practical to use the full power of the
  language
• Trade-off preprocessing time versus execution
  time (or space)
• Rule performance of both compiler and
  application must be acceptable to the end user

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Why study Compilation

• So even though I'd never actually want to
  write a compiler myself, knowing about compiler
  concepts would have made me a better programmer.
  It's one of those gaps that I regret, which is
  why I think I may actually try to struggle
  through a few chapters from this Engineering a
  Compiler book during the holidays, in between all
  the holiday activities like eating. And shopping.
  And listening to "Santa Got Run Over By a
  Reindeer" for the billionth time

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Why Study Compilation?

• Compilers are important system software
  components
• They are intimately interconnected with
  architecture, systems, programming methodology,
  and language design
• Compilers include many applications of theory to
  practice
• Scanning, parsing, static analysis, instruction
  selection
• Many practical applications have embedded
  languages
• Commands, macros, formatting tags

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Why Study Compilation?

• Many applications have input formats that look
  like languages,
• Matlab, Mathematica
• Writing a compiler exposes practical algorithmic
  engineering issues
• Approximating hard problems efficiency
  scalability

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Intrinsic interest

• Compiler construction involves ideas from many
  different parts of computer science

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Intrinsic merit

• Compiler construction poses challenging and
  interesting problems
• Compilers must do a lot but also run fast
• Compilers have primary responsibility for
  run-time performance
• Compilers are responsible for making it
  acceptable to use the full power of the
  programming language
• Computer architects perpetually create new
  challenges for the compiler by building more
  complex machines
• Compilers must hide that complexity from the
  programmer
• Success requires mastery of complex interactions

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Preparation for next class

• Review the materials for this class
• Read chapter 1 of the book

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Overview of compilers
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High-level View of a Compiler
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High-level overview of a compiler

• Implications
• Must recognize legal (and illegal) programs
• Must generate correct code
• Must manage storage of all variables (and code)
• Must agree with OS linker on format for object
  code
• Big step up from assembly languageuse higher
  level notations

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Traditional Two-pass Compiler

• Use an intermediate representation (IR)
• Front end maps legal source code into IR
• Back end maps IR into target machine code
• Admits multiple front ends multiple passes

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The Front End

• Responsibilities
• Recognize legal ( illegal) programs
• Report errors in a useful way
• Produce IR preliminary storage map
• Shape the code for the back end
• Much of front end construction can be automated

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Scanner

• Maps character stream into words
• Produces pairs (token) ltits part of speech, a
  wordgt
• x x y becomes ltid,xgt ltid,xgt ltid,ygt
• word ? lexeme, part of speech ? token type
• Typical tokens include number, identifier, , ,
  new, while, if
• Scanner eliminates white space and comments
• Speed is important

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Parser

• Recognizes context-free syntax reports errors
• Guides context-sensitive (semantic) analysis
  (type checking)
• Builds IR for source program
• Hand-coded parsers are fairly easy to build
• Most books advocate using automatic parser
  generators

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Parser

• Context-free syntax is specified with a grammar
• SheepNoise ? SheepNoise baa baa
• SheepNoise -gt nil
• This grammar defines the set of noises that a
  sheep makes under normal circumstances
• It is written in a variant of BackusNaur Form
  (BNF)

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Parser

• Formally, a grammar G (S,N,T,P)
• S is the start symbol
• N is a set of non-terminal symbols
• T is a set of terminal symbols or words
• P is a set of productions or rewrite rules
  (P N ? N ?T )

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Parser
1. goal ? expr 2. expr ? expr op term 3.
term 4. term ? number 5.
id 6. op ? 7.
-
S goal T number, id, , - N goal,
expr, term, op P 1, 2, 3, 4, 5, 6, 7
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Parser

• Context-free syntax can be put to better use
• This grammar defines simple expressions with
  addition subtraction over number and id.
• This grammar, like many, falls in a class called
  context-free grammars, abbreviated CFG.

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Parser
Production Result goal 1 expr 2
expr op term 5 expr op y 7 expr -
y 2 expr op term - y 4 expr op 2 -
y 6 expr 2 - y 3 term 2 -
y 5 x 2 - y
x 2 - y
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Parser

• A parse can be represented by a tree (parse tree
  or syntax tree)
• x 2 - y

ltid,ygt
-
1. goal ? expr 2. expr ? expr op term 3.
term 4. term ? number 5.
id 6. op ? 7. -
ltnumber,2gt

ltid,xgt
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Parser

• Compilers often use an abstract syntax tree

The AST summarizes grammatical structure, without
including detail about the derivation
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The Back End

• Responsibilities
• Translate IR into target machine code
• Choose instructions to implement each IR
  operation
• Decide which value to keep in registers
• Ensure conformance with system interfaces
• Automation has been less successful in the back
  end

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The Back End

• Instruction Selection
• Produce fast, compact code
• Take advantage of target features such as
  addressing modes
• Usually viewed as a pattern matching problem
• ad hoc methods, pattern matching, dynamic
  programming

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The Back End

• Register Allocation
• Have each value in a register when it is used
• Manage a limited set of resources
• Can change instruction choices insert LOADs
  STOREs
• Optimal allocation is NP-Complete
  (1 or k registers)
• Compilers approximate solutions to NP-Complete
  problems

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The Back End

• Instruction Scheduling
• Avoid hardware stalls and interlocks
• Use all functional units productively
• Can increase lifetime of variables
  (changing the allocation)
• Optimal scheduling is NP-Complete in nearly all
  cases
• Heuristic techniques are well developed

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Traditional Three-pass Compiler

• Code Improvement (or Optimization)
• Analyzes IR and rewrites (or transforms) IR
• Primary goal is to reduce running time of the
  compiled code
• May also improve space, power consumption,
• Must preserve meaning of the code
• Measured by values of named variables

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The Optimizer (or Middle End)

• Typical Transformations
• Discover propagate some constant value
• Move a computation to a less frequently executed
  place
• Specialize some computation based on context
• Discover a redundant computation remove it
• Remove useless or unreachable code
• Encode an idiom in some particularly efficient
  form

Modern optimizers are structured as a series of
passes
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Modern Restructuring Compiler
HL AST
HL AST
Opt Back End
Machine code
IR
IR Gen
Front End
Source Code
Restructurer

• Typical Restructuring Transformations
• Blocking for memory hierarchy and register reuse
• Vectorization
• Parallelization
• All based on dependence
• Also full and partial inlining

Errors
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Discussion

• Consider a simple web browser that takes as
  input a textual string in HTML format and
  displays the specified graphics on the screen. Is
  the display process of compilation or
  interpretation? Why?

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Next class

• Lexical analysis
• Chapter 2