Compiler Designs and Constructions

Chapter 10: Intermediate Code Generation

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Compiler Designs and Constructions

Chapter 10: Intermediate Code Generation Objectives:

Dr. Mohsen Chitsaz


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Intermediate Language (Code)

Why Intermediate Language and not the Target Language?

Advantages of Intermediate Code:

Inter. Code

Pascal

Fortran

C

My Compiler

Back-End

---> 68000---> 8086

Front-End


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Definition:

Back-End: Intermediate ---> Machine Code

Front-End: Programming Languages ---> Intermediate


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Intermediate Code Generation

C:= A+B

What are the values of A and B?

A.PlaceB.PlaceC.Place

Translate:Gen(Temp1 ‘:=‘ A.Place ‘+’ B.Place)Gen(C.Place ‘:=‘ Temp1)


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Notation and Definition:

– id.name id in Symbol Table

– Lookup(id.name) Check Symbol Table for ‘id’ Returns Yes/No

– E.Place Name that holds the value of Expression E

– E.Code Sequence of 3 address code statements evaluating E

– NewTemp() Returns and appropriate Temp name


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Notation and Definition

– Gen() Generate Intermediate Code into an output file ( .obj)

– E.Mode Types of E (Integer, …)

– NextQuad

– GetType(ID)

Gives address of next (Gen())

– Backpatch (P,i)

– Makelist (i)– Merge (P1, P2)


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Instructions for running mICE Download the ICE.zip from

http://faculty.frostburg.edu/chitsaz/ice.htm Extract the files from ICE.zip to a directory

called mini. Check if JVM ( Java Virtual Machine) is

installed on your machine. From command prompt go to mini directory. Recompile the mini.java & mice.java files on

your machine using the commands:•javac mini.java•javac mice.java


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Instruction for running mICE

Write your test program in a file and save it in the mini directory.( eg. abc.jam )

Run the mini engine using the command:• java mini

Give the name of your test program file as the input file.

After running the mini engine,a file with .out extension is added to your directory. (eg abc.jam.out )


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Instruction for running mICE

Run the mice engine using command:

• java mice

For the input file enter the abc.jam.out file generated by mini engine.

You should see the output for the test program on the screen.


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Program Example: abc.jam

1. Sys #0,, //Blank Line2. Sys #-2,#69, //ASCII code for E3. Sys #-2,#78, //ASCII code for N4. Sys #-2,#68, //ASCII code for D5. Sys #0,, //Blank line6. Hlt ,,

Output: END


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Evaluation of Simple Expression

lefthandside ID=righthandside

righthandside expression

expression simple_expression

simple_expression term

term factor

factor ID


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lefthandside

ID

factor

term

simple_expression

expression

righthandsideID =

A=B


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factor ID• { factor.place = ID }

term factor• { term.place = factor.place }

simple_expression term• { simple_expression.place = term.place }

expression simple_expression• { expression.place = simple_expression.place }

Evaluation of A=B


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righthandside expression• { righthandside.place = expression.place }

lefthandside ID = righthandside• { GEN( NextQuad “str” righthandside.place

“,” “,” ID.place ) }

Evaluation of A=B


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factor ID• { factor.place = ID

factor.mode = GetType(ID) }

term factor• { term.place = factor.place

term.mode = factor.mode }

simple_expression term• { simple_expression.place = term.place

simple_expression.mode = term.mode }

Type checking for A=B


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expression simple_expression• {expression.place =

simple_expression.place expression.mode = simple_expression.mode }

righthandside expression• { righthandside.place = expression.place

righthandside.mode = expression.mode }



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lefthandside ID = righthandside { If (GetType(ID) == righthandside.mode )

GEN( NextQuad “str” righthandside.place “,”“,” ID.place )

else Error( NextQuad “,” Type error )

}



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factor num{ factor.place = ? num factor.mode = integer }

Evaluation of numbers


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ID

factor

term

simple_expression

expression

righthandsideID =

lefthandside

addop

+

simple_expression

ID

factor

term

Simple_expression.place term.place

A=B+C


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addop +{ addop.op = ‘add’ }

addop -{ addop.op = ‘sub’ }



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simple_expression simple_expression addop.op term

if simple_expression.mode == term.mode{simple_expression1.place = NewTemp()GEN( NextQuad addop.op simple_expression.place “,” term.place “,” simple_expression1.place )

else error( )}



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Arithmetic Operation can be:

submuldivmod


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Mixed Mode Translation: (Type)

E1 E2 E1+E2

Real Real Real

Real Int Real

Int Real Real

Int Int Int


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Method1: Using Quadruples

Assumption: Left association True=1 False=0


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Translation of Boolean Expression

Example: a < b1: IF a<b GOTO ( 4)2: t1 = 03: GOTO (5 )4: t1 = 15:

IF a<b THEN 1 ELSE 0


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Example a<b>c1 If a<b goto (4)

2 If t1=0

3 goto (5)4 t1=1

5 if t1>c goto (8)

6 t2=0

7 goto (9)8 t2=1

9


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Example a<b>c 1 JLT a,b,#4

2 STO #0,,t1

3 JMP ,,#54 STO #1,,t1

5 JGT t1,C,#8

6 STO #0,,t2

7 JMP ,,#98 STO #1,,t2

9


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expression

simple_expression relop simple_expression

term

factor

id

term

factor

id

.place .op .place


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expressionsimple_expression relop simple_expression

{ expression.place = NewTemp() GEN(NextQuad relop.op simple_expression1.place

simple_expression2.place “#”NextQuad+2)GEN(NextQuad “STO” #0“,”“,” expression.place)GEN(NextQuad “JMP” “,”“,”“#”NextQuad+1)GEN(NextQuad, “STO” #1“,”“,” expression.place)

}



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relop > { relop.op = JGT }relop < { relop.op = JLT }relop >= { relop.op = JGE }relop <= { relop.op = JLE }relop <> { relop.op = JNE }relop == { relop.op = JEQ }



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factor1 not factor2

{ factor1.place = Newtemp() GEN(NextQuad “NOT” factor2.place “,”“,”factor1.place)factor1 factor2 AND factor3

factor factor OR factor{ factor1.place = NewTemp() GEN(NextQuad “AND” factor2.place “,”factor3.place “,” factor1.place) }


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Evaluation of If Statementstatement

if ( expression ) statement

simple_expression

relop

simple_expression lefthandside

ID=righthandside


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If (a == b){

c=5;d=2;a=c

}

1 JEQ a,b,#42 STO #0,,t1

3 JMP ,,#54 STO #1,,t1

5 //if (t1) goto…

6 STO #5,,c7 STO #2,,d8 STO c,,a

Evaluation of If Statement


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If (a == b){

c=5;d=2;a=c

}

1 JEQ a,b,#42 STO #0,,t1

3 JMP ,,#54 STO #1,,t1

5 JNE t1,#0,__ //jump in false

6 STO #5,,c7 STO #2,,d8 STO c,,a



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statement if (expression) statement{ Backpatch (5,9) }

statementif(expression) statement

{Backpatch(5,NextQuad()}



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If (a<b){ a=2;

b=3; if (a==c)

{ a=b;c=2;if (a>d) a=d+2

}}

Evaluation of Nested If Statement


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1 JLT a,b,#4 //a<b2 STO #0,,t1

3 JMP ,,#54 STO #1,,t1

5 JNE t1,#0,#___6 STO #2,,a7 STO #3,,b8 JEQ a,c,#11 //a==c

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exp_stack



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9 STO #0,,t2

10 JMP ,,#1211 STO #1,,t2

12 JNE t2,#0,#___13 JLT a,d,#1614 STO #0,,t3

15 JMP ,,#1716 STO #1,,t317 …..



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1 JLT a,b,#4//a<b2 STO #0,,t13 JMP ,,#54 STO #1,,t15 JNE t1,#0,#17

6 STO #2,,a7 STO #3,,b8 JEQ a,c,#11 //a==c

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exp_stack


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9 STO #0,,t2

10 JMP ,,#1211 STO #1,,t2

12 JNE t2,#0, #1713 JLT a,d,#1614 STO #0,,t3

15 JMP ,,#1716 STO #1,,t317 …..



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9 STO #0,,t210 JMP ,,#1211 STO #1,,t112 JLT a,d,#1613 JNE t2,#0,#1714 STO #0,,t315 JMP ,,#1716 STO #1,,t317 …..



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statement if(expression) statement{ BackPatch

(pop(eval_stack), NextQuad() )}



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expressionsimple_expression relop simple_expression{ expression.place = NewTemp() GEN(NextQuad relop.op simple_expression1.place

simple_expression2.place “#”NextQuad+2)GEN(NextQuad “STO” #0“,”“,” expression.place)GEN(NextQuad “JMP” “,”“,” “#”NextQuad+1)GEN(NextQuad “STO” #1“,”“,” expression.place)GEN(NextQuad “JNE” expression.place“,”#0“,”#)

}


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1. Set The Expflag to false2. In your scanner if Nexttoken()=“if”

then set Expflag to true.



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3. At the reduction of:-expressionsimple_expression-expressionsimple_expression Relop

simple_expression

If Expflag==true{push Nextquad() on Exp_stack insert a goto_ (JMP , , ___) flag=false}


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4. when reduce production:

If (exp) statement then(Backpatch with the top of Exp stack)


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while (a>b<c){

a=2;while (a==b)

a=c}

Evaluation of WHILE Statement


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1 JGT a,b,#42 STO #0,,t1

3 JMP ,,#54 STO #1,,t1

5 JLT t1,c,#8

6 STO #1,,t2

7 JMP ,,#98 STO #1,,t2

Evaluation of WHILE Statement


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9 JNE t2,#0,#_10 STO #2,,a11 JEQ a,b,#14 //while (a==b)12 STO #0,,t3

13 JMP ,,#1514 STO #1,,t3

15 JNE t3,#0,#_16 STO c,,a


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17 JMP ,,#1118 JMP ,,#1 //BackPatch(15,18)19 … //BackPatch(9,19)

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Compiler Designs and Constructions