1. CS416 Compiler Design lec00-outline November 8, 2017

2. Course Information Instructor : Dr. Ilyas Cicekli
Office: EA504,
Phone: ,
Course Web Page:
CS416 Compiler Design

3. COMPILERS
A compiler is a program takes a program written in a source language and translates it into an equivalent program in a target language.
source program COMPILER target program
error messages
( Normally the equivalent program in
machine code – relocatable object file)
( Normally a program written in
a high-level programming language)
CS416 Compiler Design

4. Compilers
Compilers translate from a source language (typically a high level language) to a functionally equivalent target language (typically the machine code of a particular machine or a machine-independent virtual machine).
Compilers for high level programming languages are among the larger and more complex pieces of software
Original languages included Fortran and Cobol
Often multi-pass compilers (to facilitate memory reuse)
Compiler development helped in better programming language design
Early development focused on syntactic analysis and optimization
Commercially, compilers are developed by very large software groups
Current focus is on optimization and smart use of resources for modern RISC (reduced instruction set computer) architectures.

5. Why Study Compilers?
General background information for good software engineer
Increases understanding of language semantics
Seeing the machine code generated for language constructs helps understand performance issues for languages
Teaches good language design
New devices may need device-specific languages
New business fields may need domain-specific languages

6. Applications of Compiler Technology & Tools
Processing XML/other to generate documents, code, etc.
Processing domain-specific and device-specific languages.
Implementing a server that uses a protocol such as http or imap
Natural language processing, for example, spam filter, search, document comprehension, summary generation
Translating from a hardware description language to the schematic of a circuit
Automatic graph layout (graphviz, for example)
Extending an existing programming language
Program analysis and improvement tools

7. Other Applications
In addition to the development of a compiler, the techniques used in compiler design can be applicable to many problems in computer science.
Techniques used in a lexical analyzer can be used in text editors, information retrieval system, and pattern recognition programs.
Techniques used in a parser can be used in a query processing system such as SQL.
Many software having a complex front-end may need techniques used in compiler design.
A symbolic equation solver which takes an equation as input. That program should parse the given input equation.
Most of the techniques used in compiler design can be used in Natural Language Processing (NLP) systems.
CS416 Compiler Design

8. Major Parts of Compilers
There are two major parts of a compiler: Analysis and Synthesis
In analysis phase, an intermediate representation is created from the given source program.
Lexical Analyzer, Syntax Analyzer and Semantic Analyzer are the parts of this phase.
In synthesis phase, the equivalent target program is created from this intermediate representation.
Intermediate Code Generator, Code Generator, and Code Optimizer are the parts of this phase.
CS416 Compiler Design

9. Phases of A Compiler
Lexical
Analyzer
Syntax
Analyzer
Semantic
Analyzer
Intermediate
Code Generator
Code
Optimizer
Code
Generator
Source
Program
Target
Program
Each phase transforms the source program from one representation
into another representation.
They communicate with error handlers.
They communicate with the symbol table.
CS416 Compiler Design

10. Lexical Analyzer
Lexical Analyzer reads the source program character by character and returns the tokens of the source program.
A token describes a pattern of characters having same meaning in the source program. (such as identifiers, operators, keywords, numbers, delimeters and so on)
Ex: newval := oldval => tokens: newval identifier
:= assignment operator
oldval identifier
+ add operator
12 a number
Puts information about identifiers into the symbol table.
Regular expressions are used to describe tokens (lexical constructs).
A (Deterministic) Finite State Automaton can be used in the implementation of a lexical analyzer.
CS416 Compiler Design

11. Syntax Analyzer
A Syntax Analyzer creates the syntactic structure (generally a parse tree) of the given program.
A syntax analyzer is also called as a parser.
A parse tree describes a syntactic structure.
assgstmt
identifier := expression
newval expression expression
identifier number
oldval
In a parse tree, all terminals are at leaves.
All inner nodes are non-terminals in
a context free grammar.
CS416 Compiler Design

12. Syntax Analyzer (CFG)
The syntax of a language is specified by a context free grammar (CFG).
The rules in a CFG are mostly recursive.
A syntax analyzer checks whether a given program satisfies the rules implied by a CFG or not.
If it satisfies, the syntax analyzer creates a parse tree for the given program.
Ex: We use BNF (Backus Naur Form) to specify a CFG
assgstmt -> identifier := expression
expression -> identifier
expression -> number
expression -> expression + expression
CS416 Compiler Design

13. Syntax Analyzer versus Lexical Analyzer
Which constructs of a program should be recognized by the lexical analyzer, and which ones by the syntax analyzer?
Both of them do similar things; But the lexical analyzer deals with simple non-recursive constructs of the language.
The syntax analyzer deals with recursive constructs of the language.
The lexical analyzer simplifies the job of the syntax analyzer.
The lexical analyzer recognizes the smallest meaningful units (tokens) in a source program.
The syntax analyzer works on the smallest meaningful units (tokens) in a source program to recognize meaningful structures in our programming language.
CS416 Compiler Design

14. Parsing Techniques
Depending on how the parse tree is created, there are different parsing techniques.
These parsing techniques are categorized into two groups:
Top-Down Parsing,
Bottom-Up Parsing
Top-Down Parsing:
Construction of the parse tree starts at the root, and proceeds towards the leaves.
Efficient top-down parsers can be easily constructed by hand.
Recursive Predictive Parsing, Non-Recursive Predictive Parsing (LL Parsing).
Bottom-Up Parsing:
Construction of the parse tree starts at the leaves, and proceeds towards the root.
Normally efficient bottom-up parsers are created with the help of some software tools.
Bottom-up parsing is also known as shift-reduce parsing.
Operator-Precedence Parsing – simple, restrictive, easy to implement
LR Parsing – much general form of shift-reduce parsing, LR, SLR, LALR
CS416 Compiler Design

15. Semantic Analyzer
A semantic analyzer checks the source program for semantic errors and collects the type information for the code generation.
Type-checking is an important part of semantic analyzer.
Normally semantic information cannot be represented by a context-free language used in syntax analyzers.
Context-free grammars used in the syntax analysis are integrated with attributes (semantic rules)
the result is a syntax-directed translation,
Attribute grammars
Ex:
newval := oldval
The type of the identifier newval must match with type of the expression (oldval+12)
CS416 Compiler Design

16. Intermediate Code Generation
A compiler may produce an explicit intermediate codes representing the source program.
These intermediate codes are generally machine (architecture independent). But the level of intermediate codes is close to the level of machine codes.
Ex:
newval := oldval * fact + 1
id1 := id2 * id3 + 1
MULT id2,id3,temp1 Intermediates Codes (Quadraples)
ADD temp1,#1,temp2
MOV temp2,,id1
CS416 Compiler Design

17. Code Optimizer (for Intermediate Code Generator)
The code optimizer optimizes the code produced by the intermediate code generator in the terms of time and space.
Ex:
MULT id2,id3,temp1
ADD temp1,#1,id1
CS416 Compiler Design

18. Code Generator
Produces the target language in a specific architecture.
The target program is normally is a relocatable object file containing the machine codes.
Ex:
( assume that we have an architecture with instructions whose at least one of its operands is
a machine register)
MOVE id2,R1
MULT id3,R1
ADD #1,R1
MOVE R1,id1
CS416 Compiler Design

19. Compiler / Translator Design Decisions
Choose a source language
Large enough to have many interesting language features
Small enough to implement in a reasonable amount of time
Examples for us: MicroJava, Decaf, MiniJava
Choose a target language
Either a real assembly language for a machine with an assembler
Or a virtual machine language with an interpreter
Examples for us: MicroJava VM (μJVM), MIPS (a popular RISC architecture, for which there is a “SPIM” simulator)
Choose an approach for implementation:
Either use an existing scanner and parser / compiler generator
lex/flex, yacc/bison/byacc, Antlr/JavaCC/SableCC/byaccj/Coco/R.
Or implement these yourself (limits the language somewhat)

20. Example MicroJava Program
program P
final int size = 10;
class Table {
int[] pos;
int[] neg; }
Table val; {
void main()
int x, i;
{ // initialize val
val = new Table;
val.pos = new int[size];
val.neg = new int[size];
i = 0;
while (i < size) {
val.pos[i] = 0; val.neg[i] = 0; i = i + 1;
// read values
read(x);
while (x != 0) {
if (x > 0) val.pos[x] = val.pos[x] + 1;
else if (x < 0) val.neg[-x] = val.neg[-x] + 1;
main program; no separate compilation
classes (without methods)
global variables
local variables

21. Analysis of specific compilers
Programs to be discussed:
lex – Programming utility that generates a lexical analyzer
yacc – Parser generator
lcc - ANSI C compiler
Platforms:
All three programs designed for use on Unix
lcc runs under DOS and Unix

22. lex Programming Utility
General Information:
Input is stored in a file with *.l extension
File consists of three main sections
lex generates C function stored in lex.yy.c
Using lex:
Specify words to be used as tokens (Extension of regular expressions)
Run the lex utility on the source file to generate yylex( ), a C function
Declares global variables char* yytext and int yyleng

23. lex Programming Utility
Three sections of a lex input file:
/* C declarations and #includes lex definitions */
%{ #include “header.c”
int i; }% %%
/* lex patterns and actions */
{INT} {sscanf (yytext, “%d”, &i);
printf(“INTEGER\n”);}
/* C functions called by the above actions */
{ yylex(): }

24. yacc Parser Generator General Information: Using yacc:
Input is specification of a language
Output is a compiler for that language
yacc generates C function stored in y.tab.c
Public domain version available
Using yacc:
Generates a C function called yyparse()
yyparse() may include calls to yylex()
Compile this function to obtain the compiler
bison

25. yacc Parser Generator yacc source y.tab.c a.out lex.yy.c lex source
#include “lex.yy.c”
lex.yy.c
lex source
lex cc
Input source file – similar to lex input file
Declarations, Rules, Support routines
Four parts of output atom:
(Operation, Left Operand, Right Operand, Result)

26. Cross Compilation
A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is run.
Cross compiler tools are used to generate executables for embedded system or multiple platforms.
It is used to compile for a platform upon which it is not feasible to do the compiling, like microcontrollers that don't support an operating system.

27. Uses of cross compilers
The fundamental use of a cross compiler is to separate the build environment from target environment. This is useful in a number of situations:
Embedded computers where a device has extremely limited resources.
For example, a microwave oven will have an extremely small computer to read its touchpad and door sensor, provide output to a digital display and speaker, and to control the machinery for cooking food. This computer will not be powerful enough to run a compiler, a file system, or a development environment.
Since debugging and testing may also require more resources than are available on an embedded system, cross-compilation can be less involved and less prone to errors than native compilation.
CS416 Compiler Design

28. Compiling for multiple machines.
For example, a company may wish to support several different versions of an operating system or to support several different operating systems. By using a cross compiler, a single build environment can be set up to compile for each of these targets.
Compiling on a server farm. Similar to compiling for multiple machines, a complicated build that involves many compile operations can be executed across any machine that is free, regardless of its underlying hardware or the operating system version that it is running.
CS416 Compiler Design

29. GCC and cross compilation
GCC, a free software collection of compilers, can be set up to cross compile. It supports many platforms and languages.
CS416 Compiler Design

30. C4droid compiler for Android (Rs 192/-) https://play. google
C4droid is a user-friendly (but powerful) C/C++ IDE + C/C++ compiler for Android. Note that C4droid supports devices with ARM processors only (not devices with Intel x86 or MIPS processor). Basic features: - Offline compiler: create your own applications on Android device and run them even without Internet access - No root required (but C4droid can use it for your programs if you want) - Full ANSI C and ISO C99 support with TCC + uClibc - Source code editor with syntax highlighting, tabs, code completion, code formatting, file association and infinite undo/redo - Export & share your programs as APKs or native executables (for terminal apps) More features with a free GCC plugin: - Full C++ and almost complete C++11 support with GCC + Bionic libc - Native Activity, Qt, SDL and SDL2 support for GUI - The most recent version of GCC always available - Makefile support: use the same build scripts as on your PC (BusyBox is included) - Semi-automatic open-source library porting feature for enhanced programming & education
CS416 Compiler Design

31. AIDE - Android IDE - Java, C++ http://android. appstorm
AIDE is an integrated development environment (IDE) for developing real Android Apps directly on Android devices. AIDE supports the full edit-compile-run cycle: write code with the feature rich editor offering advanced features like code completion, real-time error checking, refactoring and smart code navigation, and run your App with a single click.AIDE will turn your Android tablet with keyboard into a real development box. We use the Transformer Prime running Ice Cream Sandwich to code with AIDE. AIDE will turn your Android Phone into a small development computer to browse and touch your code on the go.
AIDE supports building Apps with Java/Xml and the Android SDK as well as Apps with C/C++ and the Android NDK.
AIDE is fully compatible with Eclipse projects. You can just copy the sourcecode to your device and open the Eclipse project in AIDE to start coding. Alternatively you can keep your sourcecode on your Dropbox - AIDE integrates with Dropbox and allows to easily download from your Dropbox and sync back your changes. AIDE can also open Android Studio projects, which follow the default folder structure.
AIDE supports GIT for professional development
CS416 Compiler Design