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| == The Original Code ==
| | #REDIRECT [[ist:Code Generation/Example 1]] |
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| Consider the following C function:
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| <c>
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| int main() {
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| int n = 45, i = 0, j = 1, *seg = &i;
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| while (n-- > 0) {
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| print(*seg = i + j);
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| seg = (seg == &i) ? &j : &i;
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| }
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| return 0;
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| }
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| </c>
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| == Postfix Code ==
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| <asm>
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| TEXT
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| ALIGN
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| GLOBL "main",FUNC
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| LABEL "main"
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| ENTER 16 ; n@-4, i@-8, j@-12, seg@-16
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| | |
| ;-- initialization:
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| INT 45
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| LOCA -4 ; n = 45
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| INT 0
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| LOCA -8 ; i = 0
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| INT 1
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| LOCA -12 ; j = 1
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| LOCAL -8 ; &i
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| LOCA -16 ; seg = &i
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| ;-- while cycle:
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| LABEL "while"
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| LOCV -4 ; n
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| DUP ; n (because of n--)
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| INT 1
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| SUB ; n-1
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| LOCA -4 ; n = n-1
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| INT 0
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| GT ; n > 0 (n before decrement)
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| JZ "endwhile"
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| LOCV -8 ; i
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| LOCV -12 ; j
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| ADD ; i+j
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| DUP ; same value (for assignment)
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| LOCV -16 ; seg
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| STORE ; *seg = i+j
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| CALL "print" ; we assume that "print" does not return any value
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| TRASH 4 ; trash argument (int)
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| ;-- compute trenary operator's value
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| LOCV -16 ; seg
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| LOCAL -8 ; &i
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| EQ ; seg == &i
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| JZ "false3" ; jump to "false" expression of trenary operator
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| LOCAL -12 ; &j
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| JMP "end3" ; jump to end of trenary operator
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| LABEL "false3"
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| LOCAL -8 ; &i
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| LABEL "end3"
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| DUP ; trenary operator's value (duplicated because of assignment)
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| LOCA -16 ; seg = (seg == &i) ? &j : &i
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| TRASH 4 ; trash assignment's value, since we used it as an instruction
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| JMP "while" ; restart while cycle
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| LABEL "endwhile"
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| ;-- rest of function
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| INT 0
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| POP ; return value is 0
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| LEAVE
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| RET
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| </asm>
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| [[category:Compilers]]
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| [[category:Teaching]]
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