1. Compilers Book: Crafting a Compiler with C
Author: Charles N. Fischer and Richard J. LeBlanc, Jr.
The Benjamin/Cumming Publishing Company, Inc

2. Gain Score Homework: 10% Project: 40% (Two members in a team)
Lexical analysis: 10%
Syntax analysis: 20%
Code generation: 10%
Mid Exam: 25%
Final Exam: 25%

3. Contents Introduction A Simple Compiler Scanning – Theory and Practice
Grammars and Parsing
LL(1) Parsing
LR Parsing
Semantic Processing
Symbol Tables
Run-time Storage Organization

4. Contents (Cont’d.) Code Generation and Local Code Optimization
Processing Declarations
Processing Expressions and Data Structure References
Translating Control Structure
Translating Procedures and Functions
Attribute Grammars and Multipass Translation
Code Generation and Local Code Optimization
Global Optimization
Parsing in the Real World

5. Chapter 1 Introduction

6. Contents Overview and History What Do Compilers Do?
The Structure of a Compiler
The Syntax and Semantics of Programming Languages
Compiler Design and Programming Language Design
Compiler Classifications
Influences on Computer Design

7. 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

8. Overview and History (Cont’d.)
The first real compiler
FORTRAN compilers of the late 1950s
18 person-years to build
Today, we can build a simple compiler in a few month.
Crafting an efficient and reliable compiler is still challenging.

9. Overview and History (Cont’d.)
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

10. What Do Compilers Do?
Compilers may be distinguished according to the kind of target code they generate:
Pure Machine Code
Assume there is no run-time OS support.
For systems implementation or embedded systems
Run on bare machines
Augmented Machine Code
For hardware + OS + language-specific support routines, e.g., I/O, math functions, storage allocation, and data transfer.
Virtual Machine Code
JVM, P-code
Portable
4-times slower
Code is interpreted.

11. What Do Compilers Do? (Cont’d.)
Another way that compilers differ from one another is in the format of the target machine code they generate
Assembly Language Format
Simplify compilation
Use symbolic labels rather than calculating address
Pro: good for smaller machines
Con: need an additional pass

12. What Do Compilers Do? (Cont’d.)
Relocatable Binary Format
A linkage step is required
Similar to the output of assembler
Need a linking step before execution
Good for modular compilation, cross-language references, and libraries
Memory-Image (Load-and-Go) Format
Fast
Very limited linking capabilities
Good for debugging (frequent changes)

13. What Do Compilers Do? (Cont’d.)
Another kind of language processor, called an interpreter, differs from a compiler in that it executes programs without explicitly performing a translation
Advantages and Disadvantages of an interpreter
See page 6 & 7
Interpreter
Output
Source
Program
Encoding
Data

14. What Do Compilers Do? (Cont’d.)
Advantage
Modification to program during execution
Interactive debugging
Not for every language, e.g., Basic, Pascal
Dynamic-typed languages
Variable types may change at run time, e.g., LISP.
Difficult to compile
Better diagnostics
Source code is available.
Machine independence
However, the interpreter itself must be portable.

15. What Do Compilers Do? (Cont’d.)
Disadvantage
Slower execution due to repeated examination
Dynamic (LISP): 100:1
Static (BASIC): 10:1
Substantial space overhead

16. The Structure of a Compiler
Modern compilers are syntax-directed
Compilation is driven the syntactic structure of programs; i.e., actions are associated with the structures.
Any compiler must perform two major tasks
Analysis of the source program
Synthesis of a machine-language program

17. The Structure of a Compiler (Cont’d.)
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

18. The Structure of a Compiler (Cont’d.)
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
finite automata
as programs
regular
exp for
tokens
lex or scangen

19. The Structure of a Compiler (Cont’d.)
Parser
Given a formal syntax specification (typically as a context-free grammar [CFG]), 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.
yacc or llgen
grammar
parser

20. The Structure of a Compiler (Cont’d.)
Semantic Routines
Perform two functions
Check the static semantics of each construct
Do the actual translation for generating IR
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

21. The Structure of a Compiler (Cont’d.)
One-pass compiler
No optimization is required
To merge code generation with semantic routines and eliminate the use of an IR
Retargetable compiler
Many machine description files, e.g., gcc
Match IR against target machine patterns.
Compiler writing tools
Compiler generators or compiler-compilers
Lex and Yacc
E.g., scanner and parser generators

22. 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.

23. Compiler Design and Programming Language Design (Cont’d.)
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?

24. 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
Re-targetable compiler
Localize machine dependence.
difficult to implement
less efficient object code
Integrated programming environments
integrated E-C-D