CONSTRUCTION COMPILERS

LECTURE

Robert Plebaniak

The software platform

LINUX (it may not contain LLgen, then the installation from the page http://tack.sourceforge.net);

WINDOWS (then we can use Cygwin, this program we can found http://www.cygwin.com);

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http://tack.sourceforge.net/

LEX and YACC GENERATORS

PCYACC - commercial version http://www.abxsoft.com

MKS LEX & YACC – commercial version http://www.mkssoftware.com

Bumble-Bee Parser Generator – commercial version http://www.bumblebeesoftware.com

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Compilers

Defintion 1.Compiler is a program whose purpose is to

convert code written in a programming language (C, Ada, Java), called the source language on the equivalent code in another language, called the language of the output.

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INTERPRETER

Definition 2.Interpreter – is a program which operates as a

compiler, except that it does not generate object code, but immediately follows the instructions contained in the source code of the program.

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Stages of the compiler

The source program; Analysis; The intermediate representation; Synthesis; The resulting program;

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STAGES OF COMPILATION

Analysis – at this stage, the compiler breaks down the source program into its constituent parts and then generates the intermediate representation.

Also at this stage, we have detect errors and possible informing them about the programmer.

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LEXICAL ANALYSIS

Lexical analysis is also called scanning or line analysis. The main task of lexical analysis is a grouping of characters in the input stream in lexical symbols otherwise known as token's.

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LEXICAL ANALYSIS

Tokens are different elementary component of the source language, eg .: number, keywords, operators and identifiers, parentheses, ...

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ANALIZA LEKSYKALNA

Lexical analysis is also called scanning or line analysis. The main task of lexical analysis is a grouping of characters in the input stream in lexical symbols otherwise known as token's.

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Exampe

There is a function on C++:

int name_fun (int s){

return s+s;}

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Example

Tokens are different elementary component of the source language, eg .: number, keywords, operators and identifiers, parentheses, ...

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Example

Leksems – they are strings that form lexical symbols;

Pattern – a "recipe" for the construction token: this may be a string underscores, small, large letters and digits;

Attributes – that is the lexical value, which sometimes occur with tokens.

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EXAMPLE

))‘)’

„s”[ _a-zA-Z][ _a-zA-z0-9]*

sIDENTintintKWD_INT((‘(‘

name_fun

[ _a-zA-Z][ _a-zA-z0-9]*

name_funIDENTintintKWD_INT

ATTRIBPATTERNLEKSEM TOKEN

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EXAMPLE

„s”[_a-zA-Z][_a-zA-z0-9]*

sIDENT

„s”[ _a-zA-Z][ _a-zA-z0-9]*

sIDENT

++OP_PLUS

returnreturnKWD_RET‘{‘‘{‘‘{‘

ATRYB.PATTERNLEKSEM TOKEN

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EXAMPLE

}}‘}’;;‘;‘

ATRYB.PATTERNLEKSEM TOKEN

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PARSING

Parsing is also called the analysis of hierarchical or “synktatyczną”. The task of parsing is to investigate whether lexical units make the correct design of a given programming language (eg.: if maintained is appropriate sequence of tokens)..

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EXAMPLE

There is a function on C++:

int (int s) name_fun{ } + s ; s return

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SEMANTIC ANALYSIS

Semantic analysis has the following tasks: - Checking program (source program) in terms

of compliance with the semantic definition of the source language, in which the program is written;

- Gathering information for the generation of intermediate code;

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CODE OPTIMILIZATION

The primary purpose of optimization is to improve the efficiency of finally code. It may be carried out at all levels of the code, ie. At the source code level, intermediate and also resulting.

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EXAMPLE

And here is how the intermediate code of our example after optimization:

i:=1

s:=10*i

@loop: if i>n goto @end

cout<<s

i:=i+1

s:=s+10

goto @loop

@end:

i:=1

@loop:

if i>n goto @end

s:=10*i

cout<<s

i:=i+1

goto @loop

@end: 35

EXAMPLE

Let's create a flow chart for mathematical functions signum.

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EXAMPLE

Implementation of C ++ such a short program might look like this:

float signum (int a) {

if a<0 return -1; else if (a==0) return 0;

else return 1; }

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Example - flow graph of functions Example - flow graph of functions signumsignum

x:=a

If x<0 goto B

If x>0 goto A B: y:=-1 goto C

y=0 goto C A: y:=1 goto C

C: STOP

RUN-TIME ENVIRONMENT- rules of visibilityRules of visibility define the way in which the

compiler interprets the references in the program to non-local names. There are two possibilities:

- rules of static visibility - text analysis program (C, Ada);

- rules of dynamic visibility - during the execution of the program (snobol, Lisp, APN)

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EXAMPLELet's take a bit of code in C ++:

int k=1; main() {cout<<„the value of k is ”<<k<<endl;

{int k=30;cout<<„in the block the value of k is ”<<k<<endl;}

cout<<„again outside the block k is”<<k;} 44

EXAMPLE

And here is what appears on the screen as a result of the program:

the value of k is 1 in the blocks the value of k is 30

again outside the block k is 1

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EXAMPLEAnd here's how you can be appealed to the curtained

global names in C ++

int k=1;main(){cout<<„the value of k is ”<<k<<endl;

{int k=30;cout<<„in the block the value of k is ”<<k<<„ and the global value of k is”<<::k<<endl;}

END

END OF FIRST LECTURE