PL Lab, DongGuk University Compiler Lecture Note, Intermediate Code Generation 컴파일러 입문 제 10 장 중간 코드 생성

Compiler Lecture Note, Intermediate Code Generation

PL Lab, DongGuk University

컴파일러 입문

제 10 장

중간 코드 생성



Contents

• Introduction

• Syntax-Directed

Translation

• Code Generation

• U-Code Translator



• Formal Specification– lexical structure : regular expression– syntactic structure : context-free grammar– the remaining phases of compilation : no such notations

but, we use a syntax-directed translation scheme which is a method associating semantic rules(or actions) with production.

• SDTS ::= cfg + semantic actions– cfg 의 production rule 에 있는 grammar symbol 을 이용하여

직접 semantic action 을 기술하는 방법 .– AST generation – Attribute grammar

Introduction



• Intermediate code generation– the phase that generates an explicit intermediate

code of the source program.– after syntax and semantic analysis. A Model for Intermediate code generation

• Our implementations:– Source program : Mini Pascal– Intermediate Representation : Abstract

Syntax Tree (AST)– Intermediate code : U-Code– Execution : U-Code Interpreter

Source Program

Scanner

Parser IntermediateRepresentation

Intermediate

Code Generation



• Implementation Model

– scanner : shift action of parser– parser : main program (LR parser)– SDT : reduce action of parser (AST generation)– ICG : Intermediate code generation by traversing

AST.※ Semantic Analysis 와 Intermediate Code Generation 을

효율적으로 처리하기 위해서 AST 의 design 은 매우 중요 .

Source Program Scanner

Parser

SDT AST ICG Ucode UcodeInterpreter

data

result



▶ Syntax-Directed Translation Scheme(SDTS)::= a production rule + semantic action(no widely-accepted

formalism)

▶ A Model of SDTS

whenever a reduction takes place, the semantic rule corresponding to the applied syntactic rule is activated.

Syntax-Directed Translation

SourceProgram

ScannerParser(Main)

get_token

token

Parsingtable

call semantic

: Semantic Actions

Result



▶ Advantages of SDT Providing a method describing semantic rules and that

description is independent of any particular implementation.

Easy to modify - new productions and semantic actions can be added without disturbing the existing ones.

▶ Disadvantages of SDT 파싱중에 error 가 일어난 경우 이제까지 행한 semantic action 이 모두

무의미해 진다 . input 에 대해 one pass 이면서 syntax-directed 하게 처리하기 때문에 어떤

경우에는 정보가 부족하여 후에 필요한 정보가 나타났을 때 backpatchingbackpatching 등 복잡하게 처리해야 한다 .

Solution Syntax-directed 한 방법으로는 의미 분석과 코드 생성시에 필요한 정보만을 구성하고 다음 단계에서 그것을 이용하여 의미 분석과 코드 생성을 한다 .



Description of Semantic Actions

▶ SDTS(Syntax-Directed Translation Scheme)::= production rules + semantic actions

▶ Description of Semantic Actions(1) Conventional PL.(2) Meta Language - Formal Semantic Language(FSL)

SemanticDescription

Preprocessor table

SDTInput Output



▶ Semantic Description using the Attributes of Grammar Symbol

::= We associate information with a programming language construct by attaching attributes to the grammar symbols representing the construct. Values for attributes are computed by "semantic rules" associated with the grammar productions.

▶ An attribute of symbol::= A value associated with a grammar symbol. Each

grammar symbol has an associated set of attributes. An attribute can represent anything we choose: a string, a number, a type, a memory location, or whatever.

ex)

Production Semantic Rules

L -> E \n print(E.val)E -> E1 + T E.val := E1.val + T.val

E -> T E.val := T.valT -> T1 * F T.val := T1.val * F.val

T -> F T.val := F.valF -> ( E ) F.val := E.valF -> digit F.val := digit.lexval



▶ Synthesized attribute::= the value of the attribute of the nonterminal on the left

side of the production is defined as a function of the grammar symbols on the right side.

ex) A XYZ A := F(X,Y,Z)

▶ Inherited attribute::= the value of the attribute of a nonterminal on the

right side of the production is defined in terms of an attribute of the nonterminal on the left.

ex) A XYZ Y.val := 2 * X.val

※ Synthesized attribute is more natural than inherited attribute for

mapping most programming language constructs into intermediate code.



Implementation of SDT

▶ Designing steps Input design - language construct 에 대한 grammar

를 cfg 를 이용하여 design. Scanner, Parser 의 작성 . Semantic Specification - conventional PL.

---> SDT Translator 의 완성 - interconnection.

▶ Examples : 1. Desk Calculator 2. Conversion infix into postfix

3. Construction of AST



1. Desk Calculator(1) Input design

0. S -> E $1. E -> E + E2. E -> E * E3. E -> ( E )4. E -> num

(2) Parsing table



(3) Semantic Specification

(4) Implementation of Desk Calculator

– Parsing stack : Symbol stack + State stack + Value stack

– Value stack : holding the values of the corresponding attribute.


L -> E $ print E.valE -> E1 + E2 E.val := E1.val + E2.valE -> E1 * E2 E.val := E1.val * E2.val

E -> ( E1) E.val := E1.valE -> num E.val := num.lexval



– the code fragments do not show how variable top is managed.– lexval : token value – the code fragments are executed before a reduction takes pl

ace.

Production Code Fragment

S -> E $ print (val[top])E -> E + E val[top-2] := val[top-2] + val[top]E -> E * EE -> (E) val[top-2] := val[top-1]

E -> num val[top] := num.lexval

val[top-2] := val[top-2] * val[top]



ex) 23 * 5 + 4 $

state input symbol value parse (0 23 * 5 + 4$, , , )s3 ----> (0 3 , * 5 + 4$, num , , )

r4 ----> (0 1 , * 5 + 4$, E , 23 , 4 )s5 ----> (0 1 5 , 5 + 4$, E * , 23_ , 4 )s3 ----> (0 1 5 3 , + 4$, E * num , 23__ , 4 )r4 ----> (0 1 5 8 , + 4$, E * E , 23_5 , 4 4 )r2 ----> (0 1 , + 4$, E , 115 , 4 4 2 )s4 ----> (0 1 4 , 4$, E + , 115_ , 4 4 2 )s3 ----> (0 1 4 3 , $, E + num , 115__ , 4 4 2 )r4 ----> (0 1 4 7 , $, E + E , 115_4 , 4 4 2 4 )r1 ----> (0 1 , $, E , 119 , 4 4 2 4 1 ) ----> accept



2. Conversion infix into postfix

Production Code Fragment

E -> E + E print ‘+’

E -> E * E print ‘*’

E -> E / E print ‘/’

E -> (E)

E -> a print ‘a’

a + (a + a) * a a a a + a * +



3. Construction of AST

▶AST is a condensed form of parse tree useful for representing language constructs.

ex) a := b + 1;

ex) if a > b then x := a else x := b;

:=

a +

b 1

if

>

a b

:= :=

x a x b



▶ Functions to create the nodes of AST for expressions with binary operators. Each function returns a pointer to a newly created node.1. mktree(op,left,right) creates an operator node with label op and two

fields containing pointers to left and right.2. mknode(a) creates a terminal node for a and returns the node pointer.

▶ Semantic Specification


E -> E1 + T E.nptr := mktree(‘+’, E1.nptr, T.nptr)

E -> E1 - T E.nptr := mktree(‘-’, E1.nptr, T.nptr)

E -> T E.nptr := T.nptr

T -> (E) T.nptr := E.nptr

T -> a T.nptr := mknode(a)

– The synthesized attribute nptr for E and T keeps track of the pointers returned by the function calls.



▶ AST for a - 4 + c

+

- id

id num 4

to entry for a

to entry for c



Programming Assignment #4

• Implement a syntax-directed translator producing an AST

for MiniPascal program.

– MiniPascal Program : Perfect.pas(Text pp.427-428)

– The Output form of AST using printtree() : Text pp.428-430

scannerMini-Pascal Programs

parser

SDT AST



• AST design– Grammar form : production rule [ => node_name ] ;

Note : => node name 의 생략 시에는 부 트리를 구성하지 않음 .

A -> => node_name ;

• MiniPascal GrammarMINI_PASCAL -> 'program' IDENT ';' BLOCK '. ' =>

PROGRAM; BLOCK -> DCL COMPOUND_ST => BLOCK;DCL -> CONST_DCL VAR_DCL PROC_DCL => DCL;

Text pp. 419-421

node_name

1 2 n...



• Data Structures– A node form of AST

– NODE structure struct tokentype {

int tokennumber; /* 토큰 번호 */char * tokenvalue; /* 토큰의 값 */

}; typedef struct nodetype {

struct tokentype token; /* 토큰 종류 */enum {terminal, nonterm} noderep;/* 노드의 종류 */struct nodetype *son; /* 왼쪽 링크 */struct nodetype *brother; /* 오른쪽

링크 */} NODE;

– Nonterminal node names :enum nodename { NOTREE, PROGRAM, BLOCK, DCL, ..., ARRAY_VAL};

sontoken

tokennumber tokenvaluenoderep brother

son node

next brother node



• Shift action of parsing :– if the token is meaningful, then call buildnode. NODE *buildnode(struct tokentype token) { NODE *ptr; ptr = (NODE *) malloc (sizeof(NODE)); if (!ptr) { printf(“ build node malloc error\n”); exit(1); } ptr -> token = token; ptr -> noderep = terminal; ptr -> son = NULL; ptr -> brother = NULL; return ptr; }

• Reduce action of parsing :– if the production rule is meaningful 1. build subtree

linking brothers making a subtree

else 2. only linking brothers



• Printing the information about AST– int printnode(NODE *t, int indent) : print a node

information– int printtree(NODE *t, int indent) : print an AST

void printnode(NODE *t, int indent){ extern FILE *ast; int i;

for (i=1; i<=indent; i++) fprintf(ast," ");if (t->noderep == terminal) {

fprintf(ast," Terminal: ");fprintf(ast,"%s",t->token.value);

}if (t->noderep == nonterm) {

i = (int) (t->token.number);fprintf(ast," Nonterminal: %s", ASTname[i]);

}}

void printtree(NODE *t, int indent){ NODE * p = t;

while (p != NULL) {printnode(p, indent);if (p->noderep == nonterm) printtree(p->son,indent+5);p = p->brother;

}}



▶ A Model for ICG

Source language : Mini Pascal Intermediate Representation : Abstract Syntax

Tree(AST)Intermediate code : UcodeExecution : Ucode Interpreter

Mini-Pascal Programs scanner

parser


data

executionresult

Code Generation



▶ Three Parts of MiniPascal

• Heading part : program name• Declaration part : description of data structures• Statement part : specifying the actions

• Production rules :(MiniPascal)

MINI_PASCAL -> 'program' IDENT ';' BLOCK '.’ BLOCK -> DCL COMPOUND_ST

DCL -> CONST_DCL VAR_DCL PROC_DCL;

STATEMENT -> ASSIGNMENT_ST; -> CALL_ST;-> COMPOUND_ST; -> IF_ST; -> WHILE_ST; -> ;



▶ Code Generating Routines

The basic structure of ICG void codegen(NODE *pt)

{switch (pt->token.tokennumber) {

case PROGRAM : { … } case BLOCK : { … }

…case ARRAY_VAL : ... default: printf(" Code

generation Error");}

} /* main program */…root = parser(); /* AST generated by SDT */codegen(root);codegen(root);...



Heading part

① Grammar

MINI_PASCAL -> 'program' IDENT ';' BLOCK '.’ => PROGRAM;

BLOCK -> DCL COMPOUND_ST => BLOCK;

② AST

PROGRAM

IDENT BLOCK

DCL COMPOUND_STMT

root



③ Code Segmentcase PROGRAM :

{/* 코드 생성에 필요한 초기화 작업 */codegen(pt->son->brother); /* BLOCK *//* 코드 생성한 후 마지막 처리 작업 */

}

• An Ucode program form :

sym(s) for global variables<name> proc

sym(s)… codes for procedureendopbgn... codes for main programendop



Declaration Part

① Grammar

DCL -> CONST_DCL VAR_DCL PROC_DCL => DCL;

VAR_DCL -> 'var' VAR_DEFS ';’ => VAR_DCL; -> ;

VAR_DEFS -> VAR_DEF; -> VAR_DEFS ';' VAR_DEF;VAR_DEF -> VAR_LIST ':' TYPE => VAR_DEF;VAR_LIST -> IDENT_LIST => VAR_LIST;TYPE -> 'integer’ => INT_TYPE; -> 'array' '[' CONSTANT '..' CONSTANT ']' 'of’ 'integer’ =>

ARRAY_TYPE;

※ Mini-Pascal 에서 선언은 상수선언 , 변수선언 , 프로시저선언으로 구성 .※ 자료형은 정수형과 정수형 배열만 있음 .



② AST

※ 변수선언은 여러 개의 변수정의로 이루어져 있으며 , 하나의 변수정의는 명칭들의 리스트와 그 명칭들이 갖는 형으로 되어 있다 .

DCL

CONST_DCL VAR_DCL

VAR_DEF

PROC_DCL

VAR_DEF VAR_DEF...

VAR_LIST TYPE_DENOTER

IDENT IDENT...



③ Code Segment

case DCL: { offset = 0; } break;case VAR_DCL : {

NODE * q = pt->son;while (q != NULL) { codegen(q);

q = q->brother; } }

break;case VAR_DEF : {

NODE *id=pt->son->son, *tp=pt->son->brother;while (id != NULL){

enter(id->token.tokenvalue, tp->token.tokennumber, offset);

offset += typesize(tp->token.tokennumber);id = id->brother;

}}

※ 함수 enter(name, type, offset) 는 symbol table 에 명칭을 삽입한다 .



Assignment Statement

① GrammarASSIGNMENT_ST -> LHS ':=' EXP =>

ASSIGN_STMT;LHS -> VARIABLE;VARIABLE -> IDENT;

-> IDENT '[' EXP ']' => INDEX;

② ASTASSIGN_STMT

IDENT <<expression>>

ASSIGN_STMT

INDEX <<expression>>

IDENT <<expression>>

Assignment Statement



③ Code Segment

case ASSIGN_STMT: {NODE *lhs = pt->son, *rhs = pt->son->brother;if (lhs->noderep == nonterm) codegen(lhs); /* array variable */if (rhs->noderep == nonterm) codegen(rhs); /* 식에 대한 코드 생성*/

else rv_emit(rhs);if ((p = lookup(lhs->token.tokenvalue)) == NULL) error();

emit1("str", p);}

– lookup() : 심 볼 테 이 블 에 서 명 칭 을 찾 아 해 당 엔 트 리 를 가 리 키 는 포인터를 반환하는 함수 . 실패할 경우 NULL 을 복귀한다 .

– rv_emit() : 매개변수가 변수인가 상수인가에 따라 lod 와 ldc 로 구분하여 출력하는 함수이다 .

– emit1() : mnemonic 이름과 하나의 operand 를 출력한다 .



Expression

① GrammarEXP -> EXP '+' TERM

=> ADD;-> EXP '-' TERM

=> SUB;-> TERM;

TERM -> TERM '*' FACTOR => MUL;

-> TERM 'div' FACTOR => DIV;

-> TERM 'mod' FACTOR=> MOD;

-> FACTOR; FACTOR-> '-' FACTOR => NEG;

-> VARIABLE; -> NUM;-> '(' EXP ')';

② AST

ASSIGN_STMT

IDENT EXP



③ Code Segment

case ADD: case SUB: case MUL: case DIV: case MOD:{

NODE *lhs = pt->son, *rhs = pt->son->brother; if (lhs->noderep == nonterm) codegen(lhs); /* 좌 피 연 산 자 의 코드생성 */

else rv_emit(lhs);if (rhs->noderep == nonterm) codegen(rhs); /* 우 피 연 산 자 의 코드생성 */

else rv_emit(rhs); switch (pt->token.tokennumber) {

case ADD: emit0("add"); break;case SUB: emit0("sub"); break;case MUL: emit0("mult"); break;case DIV: emit0("divop"); break;case MOD: emit0("modop"); break;

}}

– emit0() : mnemonic 이름만 출력한다 .



Example)init := 10;value := init + 20 * 2;

※ 여기서 , 일련 번호는 코드 생성 순서 .※ Ucode 의 계산순서는 postorder 와 일치하므로 postorder 로 운행한다 .

ASSIGN_STMT

init 10

ASSIGN_STMT

value ADD

init MUL

20 2

②

①

③

④ ⑤

⑥

⑦

⑧



– 생성된 Ucode :

ldc 10 ①str 1 1 ; init ②lod 1 1 ; init ③ldc 20 ④ldc 2 ⑤mult ⑥add ⑦str 1 2 ; value ⑧

※ Ucode 에서 , 변수는 (base, offset) 형태로 addressing 한다 .



▶ Array variable

• In one-dimensional array,

location of i's element = Base + (i - Low) * Wwhere, Low : lower bound of array Base : start address of array

• Address of A[i] = i*W+(Base - Low * W),– 상수식 c = Base - Low * W

∴ A[i] = c + i*W

• Assume that the size of integer is 1. W = 1

Location of list[10] = ( 배열의 시작주소 ) + (10 - Low) * 1



【예】다음은 미니 파스칼에서 배열의 선언과 배열의 참조를 나타낸다 .

program bubble;const

subscript = 20;var

list : array[5..subscript] of integer;…

begin…list[10] := 3; …end.

위 프로그램에서 list[10] := 3 에 해당하는 Ucode 는 다음과 같다 .

ldc 10ldc 5subldr 1 1 /* load the address of list */addldc 3sta



• Control Statement1. conditional statement --- if, case, switch2. iteration statement --- for, while, do-while, repeat-

until3. branch statement --- goto

▶ 논리식 (Logical expression)① Grammar

CONDITION -> EXP '=' EXP => EQ;-> EXP '<>' EXP => NE;-> EXP '>' EXP => GT;-> EXP '>=' EXP => GE;-> EXP '<' EXP => LT;-> EXP '<=' EXP => LE;

Control Statement



② 관계식 a >= b + 1 에 대한 AST 와 U- 코드는 다음과 같다 .

– AST 형태 :

– Ucode :

lod a /* 1 1 */lod b /* 1 2 */loc 1addge

GE

a ADD

b 1



▶ 제어문의 코드 생성

- if-then

CONDITION 코드STATEMENT 코드

tag :

if false thengoto tag

- if-then

CONDITION 코드STATEMENT 코드

if false thengoto tag1

goto tag2

STATEMENT 코드tag1 :

tag2 :

- while-do

CONDITION 코드STATEMENT 코드 if false then

goto tag1goto tag1

tag1 :

tag2 :



① Grammar

IF_ST -> 'if' CONDITION 'then' STATEMENT => IF_STMT;

-> 'if' CONDITION 'then' STATEMENT'else' STATEMENT

=> IF_ELSE_ST;WHILE_ST -> 'while' CONDITION 'do' STATEMENT =>

WHILE_STMT;

② AST & Code SegmentIF_STMT

CONDITION STATEMENT

case IF_STMT : { char tag[5]; taggen(tag); /* label generation */ codegen(pt->son); /* CONDITION part */ emit2(“fjp”, tag); codegen(pt->son->brother); /* statement */ emit_label(tag);}

- if-then 구조



IF_ELSE_STMT

CONDITION ST1

case IF_ELSE_STMT : { char tag1[5], tag2[5]; taggen(tag1); taggen(tag2); codegen(pt->son); /* CONDITION */ emit2(“fjp”, tag1); codegen(pt->son->brother); /* true part */ emit2(“ujp”, tag2); emit_label(tag1); /* false part*/ codegen(pt->son->brother->brother); emit_label(tag2);}

- if-then-else 구조

ST2

case WHILE_STMT : { char tag1[5], tag2[5]; taggen(tag1); taggen(tag2); emit_label(tag1); codegen(pt->son); /* CONDITION 코드 생성 */ emit2(“fjp”, tag2); codegen(pt->son->brother); /* loop body */ emit2(“ujp”, tag1); emit_label(tag2);}

WHILE_STMT

CONDITION

- while-do 구조

STATEMENT



– 예제 : if a > great then great := a;

• AST 형태 :

• 생성된 Ucode :

IF_STMT

GT ASSIGN_STMT

a great great a

lod 1 1lod 1 2gt

lod 1 1str 1 2

fjp $$1

nop$$1

; a; great; a > great

; great := a



– 예제 : while i <= 100 do begin sum := sum + i; i := i + 1

end;• AST 형태 :

WHILE_STMT

LE COMPOUND_STMT

i 100 ASSIGN_STMT ASSIGN_STMT

SUM

sum i

ADD i

i 1

ADD



• 생성된 Ucode :

$$1

lod ildc 100le

lod sumlod iaddstr sum

fjp $$2

nop

i < = 100

lod iloc 1addstr i

sum := sum + i;

i := i + 1

ujp $$1nop$$2



procedure call statement

① Grammar

CALL_ST -> IDENT OPT_ACT_PARMS => CALL_STMT;OPT_ACT_PARMS -> '(' ACTUAL_PARAMS ')’ =>

ACTUAL_PARAM; -> ;

ACTUAL_PARAMS -> EXP ;-> ACTUAL_PARAMS ',' EXP ;

② AST CALL_STMT

IDENT ACTUAL_PARAM

EXP EXP ...

Procedure



③ Code Segmentcase CALL_STMT : {

emit0("ldp");codegen(pt->son->brother); /* 실 매개 변수를 위한 코드 생성 */emit1("cal", pt->son->token.tokenvalue);

};

– 예제 : procedure swap (var x, y : integer);var …begin …end;begin /* main */ … swap( a, b ); …end.

swap proc …. … ret endop bgn … … ldp ldr a ldr b cal swap … endop

함수 호출을위한 Ucodeswap(a,b);



procedure definition

① GrammarPROC_DEF -> PROC_HEAD BLOCK ';' =>

PROC_DEF; PROC_HEAD -> 'procedure' IDENT

OPT_FORM_PARM ;OPT_FORM_PARM -> '(' FORMAL_PARAMS ')' ';’

=> FORM_PARM;

-> ';' ;

② AST

PROC_DEF

IDENT FORM_PARAM

VAR_PARAM VALUE_PARAM

BLOCK



③ Code Segment

case PROC_DEF : {block += 1;offset = 1;enter(pt->son->token.tokenvalue, PROC);emit3("proc", block, offset);codegen(pt->son->brother); /* 형식 매개 변수에 대한 코드 생성 */codegen(pt->son->brother->brother); /* Block 에 대 한 코드 생성 */emit0("ret");emit0("endop");

};



• Design and Implementation of Ucode Translator– scanner, parser, SDT, ICG

Ucode Translator

Mini-Pascal Programs scanner

parser


data

executionresult



• Execution sequence of perfect.pas

① MiniPascal program : Text pp.427-428

② The Output form of AST using printtree() : Text pp.428-430

③ Ucode that generated by code generator : Text pp.454-456

④ The execution of Ucode using Ucode Interpreter

ucodei perfect.uco

Result filename is perfect.lst

-- Assembling... -- Executing... -- Result Data

6 28 496



Programming Assignment #5

• MiniPascal 언어에 대한 Ucode Translator 를 작성하시오 . 생성된 Ucode 는 Interpreter 를 사용하여 실행하시오 .

AST ICG UcodeUcode

Interpreter

data

executionresult



• 예제 프로그램 :program perfect;const max = 500;var i, j, k, r, sum: integer;begin

i := 2;while i <= max do

begin sum := 0; k := i div 2;

j := 1; while j <= k do begin

r := i mod j;if r = 0 then sum := sum + j;j := j + 1

end; if i = sum then write(i);

i := i + 1end

end.

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PL Lab, DongGuk University Compiler Lecture Note, Intermediate Code Generation 컴파일러 입문 제 10 장 중간 코드 생성