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Compiler/fortolker struktur

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

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Compiler/fortolker struktur

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

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

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

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

  5. 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.

  6. Commom sub-expression b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t2 * b t6 := t5 + c d := t4 * t6 b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t5 + c d := t4 * t6

  7. Copy propagation b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t5 + c d := t4 * t6 b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t3 + c d := t4 * t6 b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t4 d := t4 * t4

  8. Dead-code elimination b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c t5 := t3 t6 := t4 d := t4 * t4 b := 4 - 2 t1 := b / 2 t2 := a * t1 t3 := t2 * b t4 := t3 + c d := t4 * t4

  9. Arithmetic transform b := 4 - 2 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

  10. 1 2a 2b 3 4 5 6 Loop optimering. 1 2 3 4 5 6

  11. Kodegenerering. Globale og static variable: Når navn indsættes i symboltabellen så SymAdr= Nextstatic; Nextstatic=+ VarSize; Lokal variable: Hvis første: NextLokal= 0; Ellers: SymAdr= NextLokal; NextLokal=+ VarSize; a= 0 b= 2 l1: ifz b goto l2 a= a + b b= b – 1 goto l1 l2: For hver linie i mellemkode: Generer koden vha informationer fra symboltabellen. Labels: Anvendelse: Kik i symboltabellen om den er defineret ellers gem i tabellen, hvor den bruges. Oprettelse: Labeladr= LC. Hvis gemte anvendelser, så sæt referencer til LabelAdr.

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