Crafting a Compiler with C Chapter 1 Introduction Teacher : Dr' Lawrence Y' Deng contact: Lawrencema

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Crafting a Compiler with CChapter 1
IntroductionTeacher Dr. Lawrence Y.
Dengcontact Lawrence_at_mail.sju.edu.twGrading
Attendance 10, Midterm exam. 30, Homework 20,
Final exam. Team project 40

• Textbook
• Crafting a compiler with C C. N. Fischer and R.
  J. LeBlanc, Jr.1991, The Benjamin/Cummings
  Publishing Company
• Reference
• Compilers Principles, Techniques, and Tools,A.
  V. Aho, R. Sethi, J. D. Ullman, 2006 2th, Addison
  Weslay

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Outlines

• 1.1 Overview and History
• 1.2 What Do Compilers Do?
• 1.3 The Structure of a Compiler
• 1.4 The Syntax and Semantics of Programming
  Languages
• 1.5 Compiler Design and Programming Language
  Design
• 1.6 Compiler Classifications
• 1.7 Influences on Computer Design

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Overview and History

• Compilers are fundamental to modern computing.
• They act as translators, transforming
  human-oriented programming languages into
  computer-oriented machine languages.

Programming Language (Source)
Machine Language (Target)
Compiler
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Compilers are fundamental to modern computing

• Natural Language Processing
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Reference Technologies

• Finite State Machine Network
• Data Classification
• Web Content Structure/Content/Usage Mining

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Overview and History (Contd)

• The first real compiler
• FORTRAN compilers of the late 1950s, IBM
• 18 person-years to build
• Compiler technology is more broadly applicable
  and has been employed in rather unexpected areas.
• Text-formatting languages, like nroff and troff
  preprocessor packages like eqn, tbl, pic
• Silicon compiler for the creation of VLSI
  circuits
• Command languages of OS
• Query languages of Database systems
• efficient? (compared with assembly program)
• not bad, but much easier to write
• high-level languages are feasible.
• 18 man-year, ad hoc structure
• Today, we can build a simple compiler in a few
  month.
• Crafting an efficient and reliable compiler is
  still challenging.

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1.2 What Do Compilers Do?

• Compilers may be distinguished according to the
  kind of target code they generate
• Pure Machine Code
• Augmented Machine Code
• Virtual Machine Code
• JVM, P-code

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What Do Compilers Do? (Contd)

• Another way that compilers differ from one
  another is in the format of the target machine
  code they generate
• Assembly Language Format
• Relocatable Binary Format
• A linkage step is required
• Memory-Image (Load-and-Go) Format

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What Do Compilers Do? (Contd)

• Another kind of language processor, called an
  interpreter, differs from a compiler in that it
  executes programs without explicitly performing a
  translation

Output
Interpreter
Source Program Encoding
Data
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1.3 The Structure of a Compiler

• Any compiler must perform two major tasks
• Analysis of the source program
• Synthesis of a machine-language program

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The Structure of a Compiler (Contd)
Source Program
Tokens
Syntactic
Scanner
Parser
Semantic Routines
Structure
(Character Stream)
Intermediate Representation
Optimizer
Symbol and Attribute Tables
(Used by all Phases of The Compiler)
Code Generator
The structure of a Syntax-Directed Compiler
Target Machine Code
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the structure of a compiler
source program
ab20
scanner
ididintint
parser
syntax trees
semantic routine
symbol table
1. type are correct load b mul 2 add 0 sta a
optimizer
load b shL 1 sta a
code generator
oo1F 2b4A 309F
target code
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The Structure of a Compiler (Contd)

• Scanner
• The scanner begins the analysis of the source
  program by reading the input, character by
  character, and grouping characters into
  individual words and symbols (tokens)
• The tokens are encoded and then are fed to the
  parser for syntactic analysis
• For details, see the bottom of page 8.
• Scanner generators

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The Structure of a Compiler (Contd)

• Parser
• Given a formal syntax specification (typically as
  a context-free CFG grammar), the parse reads
  tokens and groups them into units as specified by
  the productions of the CFG being used.
• While parsing, the parser verifies correct
  syntax, and if a syntax error is found, it issues
  a suitable diagnostic.
• As syntactic structure is recognized, the parser
  either calls corresponding semantic routines
  directly or builds a syntax tree.

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• lt2gt Parser identify syntactic structure
• - Syntax is specified by grammars,e.g.,
• IfStmt if ( Exp ) then Stmt
• Exp
• - Parsers can be generated from grammars.

yacc or llgen
grammar
parser
- Error-repair, e.g., ")" is missing if ( a gt 3
then - Parsers may build a syntax tree or it may
call semantic routines directly.
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The Structure of a Compiler (Contd)

• Semantic Routines
• Perform two functions
• Check the static semantics of each construct
• Do the actual translation
• The heart of a compiler
• Optimizer
• The IR code generated by the semantic routines is
  analyzed and transformed into functionally
  equivalent but improved IR code.
• This phase can be very complex and slow
• Peephole optimization

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• lt3gt Semantic routines
• - Check that variables are defined, that types
  are correct, , etc. Ex.
• x x true
• - Generate IR (3-addr code), e.g.,
• ADD A, B, C
• - hand-coded
• - associated with grammar rules
• - formalized as attribute grammars (AG)

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• peephole optimization
• simple and effective
• Ex 1. STORE R1, A
• LOAD A, R1
• Ex 2. MUL R1, 1
• Ex 3. ADD R1, 0
• These innocent code can be actually generated by
  a naive compiler.

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The Structure of a Compiler (Contd)

• One-pass compiler
• No optimization is required
• To merge code generation with semantic routines
  and eliminate the use of an IR
• Compiler writing tools
• Compiler generators or compiler-compilers
• E.g. scanner and parser generators

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1.4 Compiler Design and Programming Language
Design

• An interesting aspect is how programming language
  design and compiler design influence one another.
• Programming languages that are easy to compiler
  have many advantages
• See the 2nd paragraph of page 16.

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1.5 Compiler Design and Programming Language
Design (Contd)

• Languages such as Snobol and APL are usually
  considered noncompilable
• What attributes must be found in a programming
  language to allow compilation?
• Can the scope and binding of each identifier
  reference be determined before execution begins
• Can the type of object be determined before
  execution begins?
• Can existing program text be changed or added to
  during execution?

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1.6 Compiler Classifications

• Diagnostic compilers
• Report and repair compile-time errors.
• - Add run-time checks, e.g., array subscripts.
• - should be used in real world.
• - vs. production compiler
• Optimizing compilers
• - for production use
• - 'optimal' is suspicious because
• 1. theoretically undecidable
• 2. practically infeasible
• - Perform a lot of transformations with unknown
  effects.
• Ex. place data in registers
• fast access
• slow procedure call
• Retargetable compiler
• Localize machine dependence.
• - difficult to implement
• - less efficient object code