Compiler/fortolker struktur Mellem- kode Mellemk.- optimering Kode- generering Kode- optimering Lexikalsk- analyse Syntax- analyse Semantik- analyse Front end Back end

Semantik analyse Check om brug af variable svare til typereglerne for sproget. –Check procedure-kald svare til proceduren. –Check om navne bliver brug i rette sammenhæng float p1(int x) { p1= x(); x= p1(2.4,3); }

Semantik analyse Brug symboltabellen: Typisk indhold: –Navn –Adresse –Simpeltype: Funktion, char, int, float,.... –Komplextype: Pointer til symboltabellen –Hvis funktion så Returtype –Hvis funktion så Parameterliste –Brugt –Tilskrevet

Semantikanalyse: fremgangsmåde varlinelist: varline varlinelist | e varline: type varlist ”;” type: FLOAT | INT | CHAR {statement 1} varlist: IDENT ”,” varlist | IDENT {statement 2} Problem: Statement 2 afvikles før statement 1. Løsning LEX/FLEX sætter CurrentType. Statement 2 sætter typen i symboltabellen.

Eks. på Flex/Bison metode. float {CurrentType=FLOATT; return FLOATT;} int {CurrentType=INTT; return INTT;} char {CurrentType=CHART; return CHART;} [a-zA-Z][a-zA-Z0-9]* {if ((yylval.symptr= lookup_sym(yytext)) == NULL){ yylval.symptr= insert_sym(yytext); yylval.symptr->type= NULL; } return IDENTT;} varlinelist: varline varlinelist | ; varline: type varlist ”;” ; type: FLOAT {$$=FLOATT} | INT {$$=INTT} | CHAR {$$=CHART}; varlist: IDENT ”,” varlist {$1->type= CurrentType;} | IDENT {$1->type= CurrentType;};

Eks. på Flex/Bison metode. statement: ident ”=” exp {if ($1->type !=NULL){ if ($1->type || $3) error; } else error; }; exp: exp '+' exp {if ($1 != $3) error; else $$ = $1;} |.... | IDENT {$$ = $1->type;}; funktion: type IDENT ”(” parmlist ”)” funkblok {if ($2->type == NULL){ $2->type=FUNKTIONT; $2->returtype= $1; $2->parmtype= $4; } else if ($2->type != FUNKTIONT) error;};

Mellemkode. Tree-based repræsentation. Mellemkode som et parsertræ. Three-address koder: A:= b + c int main () { int a=0,b=2; while (b) { a= a+b; b--; } a= 0 b= 2 l1: ifz b goto l2 a= a + b b= b – 1 goto l1 l2:

Three-address kodeoptimering. 1.Find basic blokke. 2.Optimer hver basic blok: –Commom sub-expression –Copy propagation –Dead-code elimination –Arithmetic transform Constant folding Algebraic transform Reduction in strength –Packing af mellemvariable. 3.Loop optimering.

Basic blokke a= 0 b= 2 l1: ifz b goto l2 a= a + b b= b – 1 goto l1 l2: Blok start: Første statement Label, der hoppes til Statement efter et branch

Basic blok optimering. –Commom sub-expression Samme beregning flere gange. –Copy propagation Samme værdi i flere variable. Erstat alle med en. –Dead-code elimination Variable, der ikke bruges, slettes. –Arithmetic transform Constant folding Beregn konstanter Algebraic transform + 0, - 0, * 1 og /1 Reduction in strength Fx: 2*x -> x+x –Packing af mellemvariable Frigiv overflødig plads til mellemvariable.

Commom sub-expression b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t2 * b t6 := t5 + c d := t4 * t6 b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t5 + c d := t4 * t6

Copy propagation b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t5 + c d := t4 * t6 b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t3 + c d := t4 * t6 b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t4 d := t4 * t4

Dead-code elimination b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t4 d := t4 * t4 b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c d := t4 * t4

Arithmetic transform b := t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c d := t4 * t4 b := 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c d := t4 * t4 t1 := 1 t2 := a * t1 t3 := t2 * 2 t4 := t3 + c d := t4 * t4 t2 := a t3 := t2 * 2 t4 := t3 + c d := t4 * t4

Loop optimering b a

Kodegenerering. a= 0 b= 2 l1: ifz b goto l2 a= a + b b= b – 1 goto l1 l2: Globale og static variable: Når type og contekst kendes: så symnote->adr= Nextstatic; Nextstatic=+ type.VarSize; Lokal variable: Hvis første: NextLokal= 0; Ellers: symnote->adr= NextLokal; NextLokal=+ type.VarSize; For hver linie i mellemkode: Generer koden vha informationer fra symboltabellen. Labels: Anvendelse: Kik i symboltabellen om den er defineret ellers gem i symboltabellen, hvor den bruges. Oprettelse: symnote->adr= LC. Anvendelser: sæt referencer til symnote->adr.

HomeControler DIGIINPUT DoreOpen : 1; DIGIOUTPUT StartFan : 1; RumLight : 2; ANAINPUT _Temperature: 1,TEMP; _Humidity : 4,HUMI; _TempSetTurnButton: 3,[10.0,30.0]; ANAOUTPUT _FanVelosity: 1,[0,100]; EXPORT _Temp_Stue; TempAlarm; IMPORT _OutsideTemp; _OutsideFugt; LightB;

HomeControler SEQUENCE: Ventilation RESET= Total_stop OR Ventilation_Stop; STATE: INIT FanMotor= OFF; GO TO Ventilate WHEN LightButton; GO TO HumidityTooHigh WHEN (_Humidity > _NormalHumidity+10.0); END STATE: Ventilate FanMotor= ON; GO TO INIT WHEN DELAY(NOT light, 60.0); END STATE: HumidityTooHigh FanMotor= ON; GO TO INIT WHEN _Humidity < _NormalHumidity; GO TO Pause WHEN DELAY(HumidityTooHigh, 300.0); END STATE: Pause Start_blæser= OFF; GO TO Ventilate WHEN DELAY(Pause,300.0); GO TO INIT WHEN _Humidity < _NormalHumidity; END

HomeControler: kodegenerering SEQUENCE: Ventilation # SEK RESET= Ventilation_Stop; # LOD 13 # RES STATE: INIT # STAI 11 FanMotor= OFF; # LODF # OUT 14 GO TO Ventilate WHEN ON; # LODT # GO 15 END STATE: Ventilate # STA 15 FanMotor= ON; # LODT # OUT 14 END END # ESK

HomeControler: kodegenerering LStatement:= Ident "=" Lexp ";" (Gen OUT Ident.address) Lexp:= Lexp "OR" Lexp (Gen OR) | Lexp "AND" Lexp (Gen AND) | " NOT " Lexp (Gen NOT) | "(" Lexp ")" | Ident (Gen LOD Ident.address) | "ON" (Gen LODT) | "OFF" (Gen LODF) a= b AND (c OR NOT d); LStatement Ident = Lexp ; Lexp AND Lexp Ident( Lexp ) Lexp OR Lexp NOT Lexp Ident LOD ’d’ NOT LOD ’c’ OR LOD ’b’ AND OUT ’a’