![An example: a[index]=4+2
a identifier
[ left bracket
index identifier
] right bracket
= assignment
4 number
+ plus sign
2 number
Other operations: it may enter literals into the literal
table
22
The phases of a compiler-
Scanner
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-22-320.jpg)
![• Syntax analysis/Parser:
• it determines the structure of the program
• Accepts tokens –verify the tokens with patterns that
permitted by the specific language
• The results of syntax analysis are a parse tree or a
syntax tree
• An example: a[index]=4+2;
• Parse tree
• Syntax tree ( abstract syntax tree)
23
The phases of a compiler-Parser
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-23-320.jpg)
![The semantics of a program are its “meaning”,
as opposed to its syntax, or structure, that
determines some of its running time behaviors prior
to execution.
Static semantics: declarations and type checking
Attributes: The extra pieces of information
computed by semantic analyzer
An example: a[index]=4+2
The syntax tree annotated with attributes
25
The phases of a compiler –Semantic
Analyzer
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-25-320.jpg)
![• Using intermediate code is beneficial when compilers
which translates a single source language to many
target languages are required.
• One of the popular intermediate code is three-
address code. A three-address code instruction is in
the form of x = y op z.
28
The phases of a compiler-Intermediate
Code Generation
t = 4 + 2
a[index]=t
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-28-320.jpg)
![• Replacing an inefficient sequence of instructions with a
better sequence of instructions.
• Sometimes called code improvement.
• Code optimization can be done:
• after semantic analyzing
• performed on a parse tree
• after intermediate code generation
• performed on a intermediate code
• after code generation
• performed on a target code
29
The phases of a compiler-
Code Optimizer
An example: a[index]=4+2
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-29-320.jpg)
![30
t = 4 + 2
a[index]=t
t = 6
a[index]=t
a[index]=6
The phases of a compiler-
Code Optimizer
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-30-320.jpg)
![• It takes the intermediate code or IR and generates
code for target machine
• The properties of the target machine become the
major factor:
• Using instructions and representation of data
• An example: a[index]=4+2
• Code sequence in a hypothetical assembly language
31
The phases of a compiler-
Code Generation
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-31-320.jpg)
![A possible code sequence
32
a[index]=6
MOV R0, index
MUL R0,2
MOV R1,&a
ADD R1,R0
MOV *R1,6
The phases of a compiler-
Code Generation
Mrs.D.Jena
Catherine
Bel,
AP/CSE,
VEC](https://image.slidesharecdn.com/unit1-220307091641/85/Compiler-Design-Unit-1-32-320.jpg)
Compiler Design Unit 1
- 1. UNIT 1 INTRODUCTION Mrs.D.Jena Catherine Bel, Assistant Professor, CSE, Velammal Engineering College
- 2. Overview • Translators • Need for Compiler • History • Analysis-Synthesis model of Compilation • Phases of Compiler • Bootstrapping of Compiler • Passes • Complier Construction Tools 2 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 3. Translators • Programs accepting one form of language as input and produce another form of language as output. • A few translators are listed below. • Compiler • Interpreter • Assembler • Preprocessor • Macro Processor 3 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 4. Translators Assembler Translates assembly language program into machine language Uses mnemonic codes for operation codes and data addresses. Preprocessor A translator whose source language and object language are high level language is termed as preprocessor. C Preprocessor-begins with # Macro processor A system program that replaces the macro calls in an assembly language program by the macro definition. During this, formal arguments are converted into the actual arguments. 4 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 5. Translators Compiler Translates a high level language (Source language) into a low level language (Object language) COBOL, FORTRAN to Assembly language or Machine language. Interpreter Transforms a programming language into a simplified language called intermediate code which can be directly executed. SNOBOL (String Name Oriented symBOlic Language ) to Polish notation. 5 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 6. Compilers Vs Interpreters 6 • Avoid Compilation for every Execution • Requires less time for compilation • Reporting errors in a whole • Very complex to design • Produce intermediate code directly for execution – can’t reuse • Requires large time- reducing the speed of execution • Reports error one-by-one • Easy to design Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 7. Need for Compiler Machine language: Media that directly communicate with computer Error prone Assembly Language: • Use mnemonic name for operation codes and data address • Translator assembler helps it Still it required how specific computer operates High level programming: Express algorithms in more natural notation Without knowing how specific computer works Translator compiler helps it 7 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 8. History of compilers 8 • Early computers written in Assembly language • 1950 - Machine –independent programming language were introduced - leads to the development of compilers • 1952 - first compiler was written by Grace Hopper for A-0 Programming languages • Translation is viewed as the compilation of a sequence of machine language subprograms selected from library • 1957 - first complete compiler introduced by FORTRAN team led by John Backus at IBM • 1960 – COBOL compiled on multiple architectures Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 9. History of compilers • 1962 – first self-hosting compiler – compiling its own source code by Tim Hart and Mike Levin at MIT for Lisp • 1970 – Pascal and C Compilers written in their own languages • Building self-hosting compiler creates bootstrapping problem – avoid by compiling either by a compiler in different languages or running the compiler in different languages 9 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 10. History of compilers • 1984 – GNU C Compiler by Richard Stallman • For Unix Operating system • 1987 – first release of GCC compiler • First portable ANSI C compiler as free software • 1992 – version 2.0 • Ability to compile C++ • 1997 – compiler EGCS was created – • to improve optimization • 2001 – version 3.0 10 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 11. History of compilers • 1995 – java compiler was introduced • Major java compilers • javac, included in JDK - open-sourced since nov 2006. • GCJ - a part of gcc which compiles C, Fortran, Pascal and other programming languages . • ECJ - the Eclipse Compiler for Java, is an open source used by the Eclipse JDT based on IBM Visual Age's Java compiler. • 11 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 12. What is a Compiler? • A compiler – translate human oriented programming language(source program) to computer oriented machine language (target program). • A source program/code is a program/code written in the source language, which is usually a high-level language. • A target program/code is a program/code written in the target language, which often is a machine language or an intermediate code. 12 compiler Source program Target program Error message Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 13. Analysis and Synthesis Model of Compilation 13 Two parts of compilation • Analysis • breaks up the source program into constituent pieces (words, phrases) • creates an intermediate representation of the source program. • Synthesis • performs code optimization, • constructs the desired target program from the intermediate representation. Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 14. Analysis and Synthesis Model of Compilation 14 In Analysis From the source program generate three- address code via tree (An intermediate representation) Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 15. Analysis and Synthesis Model of Compilation Synthesis From intermediate code –to sequence of target instructions 15 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 16. Tools that Use the Analysis- Synthesis Model • Editors (syntax highlighting) • Uses sequences of command to build the program • Analyze the program text –and put them in appropriate hierarchical structure • Pretty printers (e.g. Doxygen) • Analyze the program and print them in clearly visible format • Comments, indents 16 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 17. Tools that Use the Analysis- Synthesis Model • Static checkers (e.g. Lint and Splint) • Analyze and identify the errors without running the program • Text formatters (e.g. TeX and LaTeX) • Read input as stream of characters, tables, figures • Specify a hierarchy of boxes to be filled by some bit pattern 17 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 18. Tools that Use the Analysis- Synthesis Model • Silicon compilers (e.g. VHDL) • Input is conventional programming language • Variable represents o’s or 1’s or signal • Output is circuit • Query interpreters/compilers (Databases) • Translate Boolean and relational operators into commands that enable search in databases 18 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 19. The phases of a compiler • Six phases • Scanner • Parser • Semantic Analyzer • Intermediate Code Generator • Code Optimizer • Code generator • Three auxiliary components • Literal table • Symbol table • Error Handler 19 Compilation process divided into six sub process – Phases Take one form of representation of source program and produce output as another form Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 20. The phases of a compiler 20 Scanner Parser Semantics Analyzer Intermediate Code Generation Code Optimizer Code Generator Literal Table Symbol Table Error Handler Source code Syntax Tree Annotated Tree Intermediate code Optimized code Target code Tokens Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 21. The phases of a compiler- Scanner Lexical analysis/Scanner: it collects sequences of characters into meaningful units called tokens Regular expressions are useful notations to recognizes tokens Install class of a strings type token in symbol table and return the token identified to the parser having token type and the pointer to the symbol table 21 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 22. An example: a[index]=4+2 a identifier [ left bracket index identifier ] right bracket = assignment 4 number + plus sign 2 number Other operations: it may enter literals into the literal table 22 The phases of a compiler- Scanner Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 23. • Syntax analysis/Parser: • it determines the structure of the program • Accepts tokens –verify the tokens with patterns that permitted by the specific language • The results of syntax analysis are a parse tree or a syntax tree • An example: a[index]=4+2; • Parse tree • Syntax tree ( abstract syntax tree) 23 The phases of a compiler-Parser Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 24. The Syntax Tree 24 a index 4 2 identifier identifier number number subscript-expression additive-expression Assign-expression The phases of a compiler-Parser Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 25. The semantics of a program are its “meaning”, as opposed to its syntax, or structure, that determines some of its running time behaviors prior to execution. Static semantics: declarations and type checking Attributes: The extra pieces of information computed by semantic analyzer An example: a[index]=4+2 The syntax tree annotated with attributes 25 The phases of a compiler –Semantic Analyzer Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 26. The Annotated Syntax Tree 26 a index 4 2 identifier identifier number number subscript-expression additive-expression integer integer Assign-expression array of integer integer integer integer The phases of a compiler-Semantic Analyzer Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 27. • An intermediate code generator • takes a parse tree from the semantic analyzer • generates a program in the intermediate language. • In some compilers, a source program is translated into an intermediate code first and then the intermediate code is translated into the target language. • In other compilers, a source program is translated directly into the target language. 27 The phases of a compiler-Intermediate Code Generation Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 28. • Using intermediate code is beneficial when compilers which translates a single source language to many target languages are required. • One of the popular intermediate code is three- address code. A three-address code instruction is in the form of x = y op z. 28 The phases of a compiler-Intermediate Code Generation t = 4 + 2 a[index]=t Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 29. • Replacing an inefficient sequence of instructions with a better sequence of instructions. • Sometimes called code improvement. • Code optimization can be done: • after semantic analyzing • performed on a parse tree • after intermediate code generation • performed on a intermediate code • after code generation • performed on a target code 29 The phases of a compiler- Code Optimizer An example: a[index]=4+2 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 30. 30 t = 4 + 2 a[index]=t t = 6 a[index]=t a[index]=6 The phases of a compiler- Code Optimizer Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 31. • It takes the intermediate code or IR and generates code for target machine • The properties of the target machine become the major factor: • Using instructions and representation of data • An example: a[index]=4+2 • Code sequence in a hypothetical assembly language 31 The phases of a compiler- Code Generation Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 32. A possible code sequence 32 a[index]=6 MOV R0, index MUL R0,2 MOV R1,&a ADD R1,R0 MOV *R1,6 The phases of a compiler- Code Generation Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 33. Static (or compile-time) errors must be reported by a compiler Generate meaningful error messages and resume compilation after each error Each phase of a compiler needs different kind of error handing Exception handling Generate extra code to perform suitable runtime tests to guarantee all such errors to cause an appropriate event during execution. 33 BACK Auxiliary components- Error Handling Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 34. • Identifiers are names of variables, constants, functions, data types, etc. • Store information associated with identifiers • Information associated with different types of identifiers can be different • Information associated with variables are name, type, address,size (for array), etc. • Information associated with functions are name,type of return value, parameters, address, etc. 34 Auxiliary components- Symbol Table Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 35. Auxiliary components- Symbol Table • Accessed in every phase of compilers • The scanner, parser, and semantic analyzer put names of identifiers in symbol table. • The semantic analyzer stores more information (e.g. data types) in the table. • The intermediate code generator, code optimizer and code generator use information in symbol table to generate appropriate code. • Mostly use hash table for efficiency. 35 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 36. • Store constants and strings used in program • reduce the memory size by reusing constants and strings • Can be combined with symbol table 36 Auxiliary components- Literal Table Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 37. Passes The repetitions to process the entire source program before generating code are referred as passes. Passes may or may not correspond to phases A pass often consists of several phases A compiler can be one pass, which results in efficient compilation but less efficient target code Most compilers with optimization use more than one pass One Pass for scanning and parsing One Pass for semantic analysis and source-level optimization The third Pass for code generation and target-level optimization 37 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 38. Bootstrapping 38 • Bootstrapping answers - “How the first compiler (a translator program) was compiled”. • Compiler is characterized by • it’s source language • Object language • The language in which the compiler is written. The notation CS LA refers the compiler C written in the language S to compile the language L to produce the object language A. Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 39. Bootstrapping • First Step: Write the compiler for the language L for the machine A with object language A (CA LA ) • is write a small compiler CA SA that translates a subset S of the language L into the machine language A. • This is written in the machine language of the machine A. • In the second step, write a compiler for L in the language S for which the compiler is already written. (CS LA ) • In the third step compile the compiler program written in S for L using the compiler for S. 39 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 40. Bootstrapping • Using the compiler CA LA it will be possible to write compiler for any machine. • A compiler running on one machine, producing object code for another machine is called Cross Compiler. 40 CA SA CS LA CA LA Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 41. Compiler Construction Tools • The software producing compilers on giving the specification of the source language and the target machine • Some of the compiler writing tools are compiler-compilers, compiler generators, translator writing systems. • The compiler writing tools need the following information. • Description of the lexical and syntactic structure of the source language. • Description of what output is to be generated for each source language constructs. • Description of the target machine. 41 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 42. Compiler Construction Tools The principal aids provided by the existing compiler – compilers are Scanner Generator • Transition diagram is the formal tool used for generating scanners. • The transition diagrams are constructed using the regular expressions defined to recognizing the various types of tokens. Parser Generator • The parsers are normally non-procedural and written using Context- free grammars. • The context free grammars are quite easy to specify the syntactic structure of any language • Highly reliable and easy for any correction. • 42 Mrs.D.Jena Catherine Bel, AP/CSE, VEC
- 43. Compiler Construction Tools Facilities for code generation • Code generation is done by writing high level language routines and calling them at the right time. • The selection of the routine and generating the code can be done with the help of decision tables. 43 Mrs.D.Jena Catherine Bel, AP/CSE, VEC