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| {{TOCright}}
| | #REDIRECT [[ist:Code Generation/Exercise 12]] |
| == Problema ==
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| Considere o seguinte código C++ (assuma que ponteiros e '''int''' ocupam 32 bits e que '''double''' ocupa 64 bits).
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| <cpp>
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| static double v[] = { 1.41, 2.71, 3.14 };
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| int f(double v[], int s, double d) {
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| for (int i = 0; i < s; i++)
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| if (v[i] == d) return i;
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| return -1;
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| }
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| int main() {
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| return f(v, 3, 3.14);
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| }
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| </cpp>
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| == Código Postfix (não optimizado) ==
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| O código Postfix correspondente às funções é o seguinte (agradece-se a comunicação de questões relativas a este código).
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| No código Postfix, '''BB#''' significa "[[Optimization Topics|bloco básico]] número".
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| {{CollapsedCode|Vector "v"|
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| <asm>
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| ;; static double v[] = { 1.41, 2.72, 3.14 };
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| ;;
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| DATA
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| ALIGN
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| LABEL v ; v is a vector
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| DOUBLE 1.41
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| DOUBLE 2.72
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| DOUBLE 3.14
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| </asm>
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| }}
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| {{CollapsedCode|Função "f"|
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| <asm>
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| ;; function "f"
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| ;;
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| ;;--- BB1 --- begin ---
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| TEXT
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| ALIGN
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| GLOBAL f, FUNC
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| LABEL f
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| ENTER 4 ; i@-4, v@+8, s@+12, d@+16
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| ;; BEGIN -- for
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| INT 0
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| LOCA -4 ; int i = 0
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| ;;--- BB1 --- end ---
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| ;;--- BB2 --- begin ---
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| LABEL for_test
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| LOCAL -4 ; &i
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| LOAD ; i
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| LOCAL +12 ; &s
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| LOAD ; s
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| LT ; i < s
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| JZ for_end
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| ;;--- BB2 --- end ---
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| ;;--- BB3 --- begin ---
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| ;; BEGIN -- for body
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| LOCAL +8 ; &v
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| LOAD ; v (v is a pointer)
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| LOCAL -4 ; &i
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| LOAD ; i
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| INT 8 ; sizeof(double)
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| MUL
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| ADD ; v+1 == &v[i]
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| DLOAD ; v[i]
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| LOCAL +16 ; &d
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| DLOAD ; d
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| DCMP
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| INT 0
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| EQ ; v[i] == d
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| JZ if_end
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| ;;--- BB3 --- end ---
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| ;;--- BB4 --- begin ---
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| ;; BEGIN -- if body
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| LOCAL -4 ; &i
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| LOAD ; i
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| POP
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| LEAVE
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| RET
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| ;; end -- if body
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| ;;--- BB4 --- end ---
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| ;;--- BB5 --- begin ---
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| LABEL if_end
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| ;; END -- for body
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| LABEL for_incr
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| LOCAL -4 ; &i
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| LOAD ; i
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| DUP ; i
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| INT 1
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| ADD ; i+1
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| LOCAL -4 ; &i
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| STORE ; i = i + 1
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| TRASH 4
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| JMP for_test
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| ;; END -- for
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| ;;--- BB5 --- end ---
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| ;;--- BB6 --- begin ---
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| LABEL for_end
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| INT -1
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| POP
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| LEAVE
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| RET
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| ;;--- BB6 --- end ---
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| </asm>
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| }}
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| {{CollapsedCode|Função principal|
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| <asm>
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| ;; main function
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| ;;
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| ;;--- BB7 --- begin ---
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| TEXT
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| ALIGN
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| GLOBAL _main, FUNC
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| LABEL _main
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| START ; no local vars
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| RODATA
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| ALIGN
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| LABEL _L314
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| DOUBLE 3.14
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| TEXT
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| ADDR _L314
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| DLOAD ; 3.14
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| INT 3
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| ADDR v ; v == &v (v is a vector)
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| CALL f
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| ;;--- BB7 --- end ---
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| ;;--- BB8 --- begin ---
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| TRASH 16
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| PUSH
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| POP
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| LEAVE
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| RET
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| ;;--- BB8 --- end ---
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| </asm>
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| }}
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| == Compiling and Running ==
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| Para compilar o código Postfix directamente, pode ser utilizada a ferramenta [[pf2asm]] (assumindo uma arquitectura de 32 bits):
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| pf2asm code.pf
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| yasm -felf32 code.asm
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| Para criar o executável:
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| ld -m elf_i386 -o code code.o -L$HOME/compiladores/root/usr/lib -lrts
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| Para executar o programa:
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| ./code
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| Para aferir o resultado (retorno do programa ao shell -- zsh/bash assumidos como exemplos):
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| echo $?
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| [[category:Compiladores]]
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| [[category:Ensino]]
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