Code Generation/Exercise 7: Difference between revisions
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Consider the following C function: | Consider the following C function: | ||
<c> | <source lang="c"> | ||
int *traverse(int vec[], int lim) { | int *traverse(int vec[], int lim) { | ||
int *ptr = vec + lim - 1, ix = lim - 2; | int *ptr = vec + lim - 1, ix = lim - 2; | ||
| Line 12: | Line 12: | ||
return ptr; | return ptr; | ||
} | } | ||
</ | </source> | ||
== Postfix Code == | == Postfix Code == | ||
The Postfix code for the above function is as follows: | The Postfix code for the above function is as follows: | ||
{{CollapsedCode|Postfix code| | |||
<asm> | <source lang="asm"> | ||
TEXT | TEXT | ||
ALIGN | ALIGN | ||
| Line 27: | Line 27: | ||
; init prt (not assignment) | ; init prt (not assignment) | ||
LOCAL +8 | LOCAL +8 | ||
LDINT ; vec | |||
LOCAL +12 | LOCAL +12 | ||
LDINT ; lim | |||
INT 4 ; sizeof int | INT 4 ; sizeof int | ||
MUL | MUL | ||
| Line 38: | Line 38: | ||
SUB ; vec + lim - 1 | SUB ; vec + lim - 1 | ||
LOCAL -4 | LOCAL -4 | ||
STINT ; ptr = vec + lim - 1 | |||
; init ix (not assignment) | ; init ix (not assignment) | ||
LOCAL +12 | LOCAL +12 | ||
LDINT ; lim | |||
INT 2 | INT 2 | ||
SUB | SUB | ||
LOCAL -8 | LOCAL -8 | ||
STINT ; ix = lim -2 | |||
; while start: test | ; while start: test | ||
| Line 52: | Line 52: | ||
LABEL while_test | LABEL while_test | ||
LOCAL -8 | LOCAL -8 | ||
LDINT | |||
INT 0 | INT 0 | ||
GE ; ix >= 0 | GE ; ix >= 0 | ||
| Line 61: | Line 61: | ||
; ?: operator | ; ?: operator | ||
LOCAL +8 | LOCAL +8 | ||
LDINT ; vec | |||
LOCAL -8 | LOCAL -8 | ||
LDINT ; ix | |||
INT 4 ; sizeof int | INT 4 ; sizeof int | ||
MUL | MUL | ||
ADD ; vec + ix | ADD ; vec + ix | ||
LDINT ; *(vec+ix) --> vec[ix] | |||
LOCAL -4 | LOCAL -4 | ||
LDINT ; ptr | |||
LDINT ; *ptr | |||
GT | GT | ||
| Line 78: | Line 78: | ||
; ?: true part | ; ?: true part | ||
LOCAL +8 | LOCAL +8 | ||
LDINT ; vec | |||
LOCAL -8 | LOCAL -8 | ||
LDINT ; ix | |||
INT 4 ; sizeof int | INT 4 ; sizeof int | ||
MUL | MUL | ||
| Line 92: | Line 92: | ||
LOCAL -4 | LOCAL -4 | ||
LDINT ; ptr | |||
; ?: end | ; ?: end | ||
| Line 98: | Line 98: | ||
LABEL three_end | LABEL three_end | ||
DUP32 ; for assignment | |||
LOCAL -4 | LOCAL -4 | ||
STINT ; ptr = ?: ... | |||
; trash expression value (used as instruction) | ; trash expression value (used as instruction) | ||
| Line 107: | Line 107: | ||
; decrement ix | ; decrement ix | ||
LOCAL -8 | LOCAL -8 | ||
LDINT ; ix | |||
DUP32 | |||
INT 1 | INT 1 | ||
SUB | SUB | ||
LOCAL -8 | LOCAL -8 | ||
STINT ; ix = ix - 1 | |||
TRASH 4 ; (ix-- used as instruction) | TRASH 4 ; (ix-- used as instruction) | ||
| Line 124: | Line 124: | ||
; return ptr | ; return ptr | ||
LOCAL -4 | LOCAL -4 | ||
LDINT | |||
STFVAL32 | |||
LEAVE | LEAVE | ||
RET | RET | ||
</ | </source> | ||
}} | |||
== Compiling and Running == | == Compiling and Running == | ||
To compile the Postfix code directly, [[pf2asm]] can be used: | To compile the Postfix code directly, [[Compiladores/Projecto de Compiladores/Compiladores Exemplo|pf2asm]] can be used: | ||
pf2asm traverse.pf | pf2asm traverse.pf | ||
Latest revision as of 16:51, 6 May 2019
The Original Code
Consider the following C function:
int *traverse(int vec[], int lim) {
int *ptr = vec + lim - 1, ix = lim - 2;
while (ix >= 0) {
ptr = (vec[ix] > *ptr) ? vec + ix : ptr;
ix--;
}
return ptr;
}
Postfix Code
The Postfix code for the above function is as follows:
| Postfix code |
|---|
TEXT
ALIGN
GLOBL traverse, FUNC
LABEL traverse
ENTER 8 ; ptr@-4 ix@-8 vec@+8 lim@+12
; init prt (not assignment)
LOCAL +8
LDINT ; vec
LOCAL +12
LDINT ; lim
INT 4 ; sizeof int
MUL
ADD ; vec + lim
INT 1
INT 4 ; sizeof int
MUL
SUB ; vec + lim - 1
LOCAL -4
STINT ; ptr = vec + lim - 1
; init ix (not assignment)
LOCAL +12
LDINT ; lim
INT 2
SUB
LOCAL -8
STINT ; ix = lim -2
; while start: test
ALIGN
LABEL while_test
LOCAL -8
LDINT
INT 0
GE ; ix >= 0
JZ while_end
; while block
; ?: operator
LOCAL +8
LDINT ; vec
LOCAL -8
LDINT ; ix
INT 4 ; sizeof int
MUL
ADD ; vec + ix
LDINT ; *(vec+ix) --> vec[ix]
LOCAL -4
LDINT ; ptr
LDINT ; *ptr
GT
JZ three_false_part
; ?: true part
LOCAL +8
LDINT ; vec
LOCAL -8
LDINT ; ix
INT 4 ; sizeof int
MUL
ADD ; vec + ix
JMP three_end
; ?: false part
ALIGN
LABEL three_false_part
LOCAL -4
LDINT ; ptr
; ?: end
ALIGN
LABEL three_end
DUP32 ; for assignment
LOCAL -4
STINT ; ptr = ?: ...
; trash expression value (used as instruction)
TRASH 4
; decrement ix
LOCAL -8
LDINT ; ix
DUP32
INT 1
SUB
LOCAL -8
STINT ; ix = ix - 1
TRASH 4 ; (ix-- used as instruction)
; end while block
JMP while_test
; exit while cycle
ALIGN
LABEL while_end
; return ptr
LOCAL -4
LDINT
STFVAL32
LEAVE
RET
|
Compiling and Running
To compile the Postfix code directly, pf2asm can be used:
pf2asm traverse.pf yasm -felf traverse.asm