1. COP 4620 / 5625 Programming Language Translation / Compiler Writing Fall 2003 Lecture 2, 09/04/2003
Prof. Roy Levow

2. Syntax Analysis Recursive Descent Parsing
Uses one procedure per construct
Checks production one item at a time
Verify tokens
Recursively check constructs
Easy to generate by hand

3. Parsing Routines Parse_operator() Parse_expression() (see fig. 1.13)
Parser environment & support
(see fig. 1.14)
No context handling needed

4. Code Generation Simple stack machine
PUSH n, ADD, MULT, PRINT
Generate code by recursive traversal of parse tree
(see fig. 1.18)

5. Interpretation
Directly execute code from parse tree
(see fig. 1.19)

6. Complete Compiler Structure (see fig. 1.21)
Lexical Analysis
Syntax Analysis
Context Handling
Intermediate Code Generation
IC Optimization
Symbolic Code Generation
Symbolic Code Optimization
Machine Code Generation
Executable Code Output

7. Other Issues Run-time system Short-cuts Compiler Architecture
Use assembler
Output in a compilable language (like C)
Compiler Architecture
Narrow compiler
Process small parts of program in multiple stages
Wide compiler
Complete each stage

8. Properties of a Good Compiler
Generates correct code
Conform to language specification
Handle large programs
Good compile speed
Good error reporting
Fast, small generated code

9. Other Issues
Portability
Retargetability
Optimizations

10. Grammars Based on productions Classification
Translation or replacement rules
α→β meaning α is replaced by β
Derivation: xαy => xβy
Classification
Based on limitations on form of α and β
Context free: α is a single non-terminal symbol
Regular: CF and β contains at most one non-terminal symbol

11. Context-free Grammars
Non-terminals: Language components
A, B, C
Terminals: Symbols in language
x, y, z
Strings of grammar symbols
Greek letters
Empty sequence (string): ε
Start symbol: LHS of first production, S

12. Derivations.1
A derivation is a sequence of replacements using productions
A sentential form is a string derived from the start symbol
The language defined by a grammar is the set of all sentential forms containing only terminal symbols that can be derived from the start symbol
A leftmost derivation always replaces the leftmost non-terminal

13. Derivations.2 Sample derivation (see fig. 1.26) Parse tree
Root is start symbol
NT node has RHS of production for children
See fig. 1.27

14. Extended Grammar Forms
Backus-Naur Form (BNF)
N→α | β | γ for alternatives
Extended BNF
R+ for 1 or more occurrence
R* for 0 or more occurrences
R? for 0 or 1 occurrence (optional item)
Parentheses for grouping

15. Properties of Grammars
Left-recursive production (or right-)
N → Nα (N → αN)
Nullable symbol
N *=> ε
Useless symbol never produces only terminal symbols
Ambiguous Grammar
Has two parse trees for same string

16. Closure Algorithms.1 Compute transitive closure of a relationship
If aRb & bRc, then aRc
Calling graph
Direct and Indirect (closure) calls
See figs. 1.28, 1.29

17. Closure Algorithms.2 Basic components of algorithm
Data definitions: what are information items
Initializations: where do we start
Inference rules: apply repeatedly to get closure
See fig for directed graph closure for subprogram calls
General iterative algorithm
See fig. 1.33