1. RIT 08/11/47Chapter 11 Chapter 1: Introduction to Compiling Dr. Winai Wichaipanitch Rajamangala Institute of Technology Klong 6 Thanyaburi Pathumthani 12110 Tel: 06-999-2974 wina@rit.ac.th http://www.en.rit.ac.th/winai

2. RIT 08/11/47Chapter 12 Purpose of Compiler  Compilers translate a program written into one language (source) into another (target) Compiler Source program Target Program Error messages Diverse & Varied

3. RIT 08/11/47Chapter 13 Introduction to Compilers  As a Discipline, Involves Multiple CS&E Areas  Programming Languages and Algorithms  Theory of Computing & Software Engineering  Computer Architecture & Operating Systems

4. RIT 08/11/47Chapter 14 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)

5. RIT 08/11/47Chapter 15 Comparison of Compiler/Interpreter CompilerInterpreter Overview Advantages Fast program execution; Exploit architecture features; Easy to debug; Flexible to modify; Machine independent; Disadvanta ges Pre-processing of program; Complexity; Execution overhead; Space overhead; interpreter Source Code Data Results compiler Source Code Data Results Object code

6. RIT 08/11/47Chapter 16 Classifications of Compilers  Compilers Viewed from Many Perspectives  However, All utilize same basic tasks to accomplish their actions Single Pass Multiple Pass Load & Go Construction Debugging Optimizing Functional

7. RIT 08/11/47Chapter 17  เรายังไม่ทราบค่าแอดเดรส ดังนั้นต้องอ่าน Source code 2 ครั้ง

8. RIT 08/11/47Chapter 18 The Model  The TWO Fundamental Parts:  We Will Discuss Both in This Class, and FOCUS on analysis. Analysis: Synthesis: Decompose Source into an intermediate representation Target program generation from representation

9. RIT 08/11/47Chapter 19 Important Notes  Today: There are many Software Tools for helping with the Analysis Part. This Wasn’t the Case in Early Days. (some) analysis is also important in:  Structure / Syntax directed editors: Force “syntactically” correct code to be entered  Pretty Printers: Standardized version for program structure (i.e., blank space, indenting, etc.)  Static Checkers: A “quick” compilation to detect rudimentary errors  Interpreters: “real” time execution of code a “line-at-a- time”

10. RIT 08/11/47Chapter 110 Important Notes  Compilation Is Not Limited to Programming Language Applications  Text Formatters  LATEX & TROFF Are Languages Whose Commands Format Text  Silicon Compilers  Textual / Graphical: Take Input and Generate Circuit Design  Database Query Processors  Database Query Languages Are Also a Programming Language  Input is compiled Into a Set of Operations for Accessing the Database

11. RIT 08/11/47Chapter 111 The Many Phases of a Compiler Source Program Lexical Analyzer 1 Syntax Analyzer 2 Semantic Analyzer 3 Intermediate Code Generator 4 Code Optimizer 5 Code Generator 6 Target Program Symbol-table Manager Error Handler 1, 2, 3 : Analysis - Our Focus 4, 5, 6 : Synthesis

12. RIT 08/11/47Chapter 112 Phases of A Modern Compiler Lexical Analyzer Syntax Analyzer Semantic Analyzer Code Optimizer Code Generation Source Program IF (a<b) THEN c=1*d; Token Sequence Syntax Tree 3-Address Code Optimized 3-Addr. Code Assembly Code IF( ID “a” < ID “b” THEN ID “c” = CONST “1” * ID “d” IF_stmt < a b cond_expr list assign_stmt c * lhs rhs 1 d GE a, b, L1 MUlT 1, d, c L1: GE a, b, L1 MOV d, c L1: loadi R1,a cmpi R1,b jge L1 loadi R1,d storei R1,c L1:

13. RIT 08/11/47Chapter 113 Language-Processing System Source Program Pre-Processor 1 Compiler 2 Assembler 3 Relocatable Machine Code 4 Loader Link/Editor 5 Executable Library, relocatable object files

14. RIT 08/11/47Chapter 114  Three Phases:  Linear / Lexical Analysis:  L-to-r Scan to Identify Tokens token: sequence of chars having a collective meaning  Hierarchical Analysis:  Grouping of Tokens Into Meaningful Collection  Semantic Analysis:  Checking to ensure Correctness of Components The Analysis Task For Compilation

15. RIT 08/11/47Chapter 115 Phase 1. Lexical Analysis Easiest Analysis - Identify tokens which are the basic building blocks For Example: All are tokens Blanks, Line breaks, etc. are scanned out Position := initial + rate * 60 ; _______ __ _____ _ ___ _ __ _

16. RIT 08/11/47Chapter 116 Phase 2. Hierarchical Analysis aka Parsing or Syntax Analysis For previous example, we would have Parse Tree: identifier expression identifier expression number expression assignment statement position := + * 60 initial rate Nodes of tree are constructed using a grammar for the language

17. RIT 08/11/47Chapter 117 What is a Grammar?  Grammar is a Set of Rules Which Govern the Interdependencies & Structure Among the Tokens statementis anassignment statement, or while statement, or if statement, or... assignment statement expression is an identifier := expression ; (expression), or expression + expression, or expression * expression, or number, or identifier, or...

18. RIT 08/11/47Chapter 118 if statement if expression then statement else statement ; id relop num=0 assign statement id:=expression id 0 assign statement id:=expression id mulop avg num/ Syntax Tree

19. RIT 08/11/47Chapter 119 Why Have We Divided Analysis in This Manner?  Lexical Analysis - Scans Input, Its Linear Actions Are Not Recursive  Identify Only Individual “words” that are the the Tokens of the Language  Recursion Is Required to Identify Structure of an Expression, As Indicated in Parse Tree  Verify that the “words” are Correctly Assembled into “sentences”

20. RIT 08/11/47Chapter 120 Phase 3. Semantic Analysis  Find More Complicated Semantic Errors and Support Code Generation  Parse Tree Is Augmented With Semantic Actions position initial rate := + * 60 Compressed Tree position initial rate := + * inttoreal 60 Conversion Action

21. RIT 08/11/47Chapter 121 Phase 3. Semantic Analysis  Most Important Activity in This Phase:  Type Checking - Legality of Operands

22. RIT 08/11/47Chapter 122 Supporting Phases/ Activities for Analysis  Symbol Table Creation / Maintenance  Contains Info (storage, type, scope, args) on Each “Meaningful” Token, Typically Identifiers  Data Structure Created / Initialized During Lexical Analysis  Utilized / Updated During Later Analysis & Synthesis

23. RIT 08/11/47Chapter 123 Symbol Table for Example

24. RIT 08/11/47Chapter 124  Detection of Different Errors Which Correspond to All Phases  What Kinds of Errors Are Found During the Analysis Phase?  What Happens When an Error Is Found? Error Handling

25. RIT 08/11/47Chapter 125 The Many Phases of a Compiler Source Program Lexical Analyzer 1 Syntax Analyzer 2 Semantic Analyzer 3 Intermediate Code Generator 4 Code Optimizer 5 Code Generator 6 Target Program Symbol-table Manager Error Handler 1, 2, 3 : Analysis - Our Focus 4, 5, 6 : Synthesis

26. RIT 08/11/47Chapter 126 The Synthesis Task For Compilation  Intermediate Code Generation  Abstract Machine Version of Code - Independent of Architecture  Easy to Produce and Do Final, Machine Dependent Code Generation  Code Optimization  Find More Efficient Ways to Execute Code  Replace Code With More Optimal Statements  2-approaches: High-level Language & “Peephole” Optimization  Final Code Generation  Generate Relocatable Machine Dependent Code

27. RIT 08/11/47Chapter 127 Reviewing the Entire Process ErrorsErrors position := initial + rate * 60 lexical analyzer syntax analyzer semantic analyzer intermediate code generator id1 := id2 + id3 * 60 := id1 id2l id3 + * 60 := id1 id2l id3 + * inttoreal 60 Symbol Table position.... initial …. rate….

28. RIT 08/11/47Chapter 128 Reviewing the Entire Process ErrorsErrors intermediate code generator code optimizer final code generator temp1 := inttoreal(60) temp2 := id3 * temp1 temp3 := id2 + temp2 id1 := temp3 temp1 := id3 * 60.0 id1 := id2 + temp1 MOVF id3, R2 MULF #60.0, R2 MOVF id2, R1 ADDF R1, R2 MOVF R1, id1 position.... initial …. rate…. Symbol Table 3 address code

29. RIT 08/11/47Chapter 129Assemblers  Assembly code: names are used for instructions, and names are used for memory addresses.  Two-pass Assembly:  First Pass: all identifiers are assigned to memory addresses (0-offset) e.g. substitute 0 for a, and 4 for b  Second Pass: produce relocatable machine code: MOV a, R1 ADD #2, R1 MOV R1, b 0001 01 00 00000000 * 0011 01 10 00000010 0010 01 00 00000100 * relocation bit

30. RIT 08/11/47Chapter 130 Loaders and Link-Editors  Loader: taking relocatable machine code, altering the addresses and placing the altered instructions into memory.  Link-editor: taking many (relocatable) machine code programs (with cross-references) and produce a single file.  Need to keep track of correspondence between variable names and corresponding addresses in each piece of code.

31. RIT 08/11/47Chapter 131 Compiler Cousins: Preprocessors Compiler Cousins: Preprocessors Provide Input to Compilers 1. Macro Processing #define in C: does text substitution before compiling #define X 3 #define Y A*B+C #define Z getchar()

32. RIT 08/11/47Chapter 132 2. File Inclusion #include in C - bring in another file before compiling defs.h ////// main.c #include “defs.h” …---…---…--- ////// …---…---…---

33. RIT 08/11/47Chapter 133 3. Rational Preprocessors  Augment “Old” Languages With Modern Constructs  Add Macros for If - Then, While, Etc.  #Define Can Make C Code More Pascal-like #define begin { #define end } #define then

34. RIT 08/11/47Chapter 134 4. Language Extensions for a Database System EQUEL - Database query language embedded in C ## Retrieve (DN=Department.Dnum) where ## Department.Dname = ‘Research’ is Preprocessed into: ingres_system(“Retr…..Research’”,____,____); a procedure call in a programming language.

35. RIT 08/11/47Chapter 135 The Grouping of Phases Front End : Analysis + Intermediate Code Generation Back End : Code Generation + Optimization vs. Number of Passes: A pass: requires r/w intermediate files Fewer passes: more efficiency. However: fewer passes require more sophisticated memory management and compiler phase interaction. Tradeoffs ……..

36. RIT 08/11/47Chapter 136 Compiler Construction Tools Parser Generators : Produce Syntax Analyzers Scanner Generators : Produce Lexical Analyzers Syntax-directed Translation Engines : Generate Intermediate Code Automatic Code Generators : Generate Actual Code Data-Flow Engines : Support Optimization

37. RIT 08/11/47Chapter 137 Tools  Tools exist to help in the development of some stages of the compiler  Lex (Flex) - lexical analysis generator  Yacc (Bison) - parser generator