Compiler Construction

1
Compiler Construction

• UTD CS 6353, Fall 2005

2
Compilers are Translators

• C/C
• Fortran
• Java
• PERL
• MATLAB
• Natural Lang.
• Command Lang.

• Machine code
• Virtual machine code
• Transformed code (C, Java, )
• Lower level commands
• Semantic Components

translate
3
Translation Mechanisms

• Compilation
• To translate a source program in one language
  into an executable program in another language
  and produce results while executing the new
  program
• Examples C, C, FORTRAN
• Interpretation
• To read a source program and produce the results
  while understanding that program
• Examples BASIC, LISP
• Case Study JAVA
• First, translate to java bytecode
• Second, execute by interpretation (JVM) /
  compilation (JIT)

4
Comparison of Compiler/Interpreter
Results
interpreter
Source Code
Data
5
Phases of A Modern Compiler
Source Program
IF (altb) THEN c1d
Lexical Analyzer
IF
(
ID a
lt
ID b
THEN
ID c

CONST 1

ID d
Token Sequence
a
Syntax Analyzer
cond_expr
lt
b
Syntax Tree
IF_stmt
lhs
c
list
1
assign_stmt
rhs
Semantic Analyzer

d
GE a, b, L1 MUlT 1, d, c L1
3-Address Code
Code Optimizer
GE a, b, L1 MOV d, c L1
loadi R1,a cmpi R1,b jge L1 loadi R1,d storei
R1,c L1
Optimized 3-Addr. Code
Code Generation
Assembly Code
6
Lexical and Syntax Analysis

• Lexical Analysis
• Recognize token ? smallest unit over letters
• Analyze input (strings of characters) from source
• Scan from left to right
• Report errors
• Syntax Analysis
• Group tokens into hierarchy groups

7
Semantic Analysis

• Determine the meaning using the structure
• Checks performed to ensure components fit
  together meaningfully
• Information is added
• Limited analysis to catch inconsistencies, e.g.
  type checking
• Put semantic meaning in the structure
• Produce IR (intermediate representation)
• Easier to generate machine code from IR

8
Code Optimization and Generation

• Code Optimization
• modify program representation so that program
• Run faster
• Uses less memory
• In general, reduce the resource consumed
• Code Generation produce target code
• Instruction selection
• Memory allocation
• Resource allocation registers, processors, etc.

9
Symbol Table Management

• Collect and maintain information about ids
• Attributes storage, type, scope, number,
• Used by most compiler passes
• Phases add information
• lexical, parsing, semantic
• Phases use information
• code optimization, code generation
• Debuggers use some form of symbol table

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Traditional Three-pass Compilation
Front End
Middle End
Back End
Source program
IR
IR
machine code
error

• Code 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

11
Distinction Between Phases and Passes

• Passes number of times through a program
  representation
• 1-pass, 2-pass, multi-pass compilation
• Language become more complex more passes
• Phases conceptual and sometimes physical stages
• Symbol table coordinates information between
  phases
• Phases are not completely separate
• Semantic phase may do things that syntax phase
  should do
• Interaction are possible

12
Compiler Tools

• Automatic Generator
• Lexical Analysis v lex, flex
• Syntax Analysis v yacc, bison
• Semantic Analysis
• Code Optimization
• Code Generation

13
Compilers vs. Language Design

• There is a strong mutual influence
• Hard to compile languages are hard to read
• Easy to compile languages lead to quality
  compilers, better code, smaller compiler, more
  reliable, cheaper, wider use, better
  diagnostics.
• Example dynamic typing
• seems convenient because type declaration is
  not needed
• However, such languages are
• hard to read because the type of an identifier
  is not known
• hard to compile because the compiler cannot
  make assumptions about the identifiers type.

14
Compilers vs. Computer Architecture

• Complex instructions were available when
  programming at assembly level.
• RISC architecture became popular with the advent
  of high-level languages.
• Today, the development of new instruction set
  architectures (ISA) is heavily influenced by
  available compiler technology.